Lengthy records of river discharge are necessary to comprehensively assess the long-term connection between synoptic climate forcings and nival-regime systems in British Columbia. A regional multi-species network of tree ring-width and ring-density chronologies was built for west central British Columbia with the intention of dendrohydrologically extending short runoff records in this area. Extended records of July-August mean discharge anomalies for the Skeena and Atnarko rivers were reconstructed back to 1660 AD. Low flow events represented during the late-1600 s, early-1700 s and late-1800 s lie beyond those experienced during the recent instrumental period for these basins. Documentation of extreme events of this magnitude necessitates consideration when planning for future water resources in this region.

Supplementary dendroclimatic reconstructions of the winter Pacific North American (PNA) pressure anomaly pattern and records of mean summer temperature and end-of-winter snow water equivalent were also constructed. These ancillary climate records provide insight into the long-term climate drivers of annual discharge dynamics within these nival basins. Correlation and wavelet analyses confirm the persistent relationship of synoptic climate regimes described by the Southern Oscillation Index, NINO 3.4, Pacific Decadal Oscillation and PNA indices on runoff in west central British Columbia. Copyright © 2012 John Wiley & Sons, Ltd.

The model presented in the complementary document entitled Reservoir Rainfall-Runoff Geomorphological Model I: Parameter application and analysis is analysed, calibrated and validated in this article. The accuracy of simulated hydrographs is analysed by means of the efficiency defined by Nash and Sutcliffe. The sensitivity of the influence of five parameters on the behaviour of the model developed is analysed. Two different calibration and validation processes of Reservoir Rainfall-Runoff Geomorphological Model are performed in Aixola watershed. Twelve events have been selected for calibrations and twenty-five for validations.

With the first calibration and validation process the model parameters are set by assigning the medians’ values of the distributions obtained by means of the optimum results. The second process is performed calibrating the most determinant parameter in the adjustment, which is the one that indicates the proportion of infiltrated water that is retained and does not flow; this is done with an empirical formulation depending on the event characteristics. Subsequently the obtained results are validated. This last process has achieved very good adjustments in both calibrated and validated events. Copyright © 2012 John Wiley & Sons, Ltd.

Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders, and HEC-RAS modeling based on LiDAR topographic data. Intra- and inter-annual gully scarp retreat rates were measured using daily time-lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration-excess runoff, soil-water seepage, river backwater, and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macro-channel up to the 100-yr RI, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2- to 5-yr RI and contributed significantly to total annual erosion. However, a majority of gully scarp retreat at all sites was driven by direct rainfall and infiltration-excess runoff, with the 24-hr rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near surface pore-water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.

The effect of the overlying water velocity on ammonium (NH₄⁺) uptake by benthic biofilms was studied in a recirculating laboratory flume (260 cm long, 29 cm wide), packed with 5 cm of silica sand arranged into bedforms. NH₄⁺ uptake was determined as the reduction in NH₄⁺ concentration in the water at average overlying water velocities of 0.8, 2, 4 and 8 cm s^-1. NH₄⁺ uptake was relatively constant under laminar flow conditions but increased when the flow regime became turbulent (>4 cm s^-1). This pattern was observed for two biofilms differing in their total biomass and in the abundance of the ammonia-oxidizing bacteria, thus indicating that NH₄⁺ uptake was strongly controlled by mass transfer processes. The near stoichiometric relationship between the rates of NH₄⁺ uptake and nitrate (NO₃^-) accumulation suggests that aerobic nitrification was the main route for NH₄⁺ uptake. Microelectrode measurements showed a sharp decline of oxygen concentrations and pH values within the biofilms, thus supporting strong nitrification activity within the surficial section of the benthic biofilms. The results of this study highlight the key role of hydrodynamic conditions in regulating NH₄⁺ uptake in the transition from laminar to turbulent flow conditions. Copyright © 2012 John Wiley & Sons, Ltd.

The main purpose of this work concerns the development and testing of an overland flow model based on the 2D fully dynamic shallow water equations. Three key aspects, fundamental to get accurate, efficient and robust computation of surface runoff at basin scale, are discussed by transferring the main findings obtained by the recent research on the topic of dam-break wave and flood propagation in the context of rainfall-runoff modeling. In particular, attention is focused on the numerical flux and bottom slope source terms computation, on a numerical treatments of friction slope terms and on an algorithm for dealing with wetting/drying fronts. The performances of the numerical model have been preliminarily evaluated using experimental or ideal tests characterized by very critical conditions for the stability of a numerical model. Then attention was focused on a real event occurred in a sub-basin of Reno river in Italy to analyze the suitability of the model in simulating real flood situations. The numerical results highlight the good performances of the model in all the simulations discussed in the paper. Copyright © 2012 John Wiley & Sons, Ltd.

In recent decades, copula functions have been applied in bivariate drought duration and severity frequency analysis. Among a number of potential copulas, Clayton has been mostly employed in drought analysis. In this research, we study the influence of the tail shape of various copula functions (i.e. Gumbel, Frank, Clayton, and Gaussian) on drought bivariate frequency analysis. The appropriateness of Clayton copula for the characterization of drought characteristics is also investigated. Drought data are extracted from standardized precipitation index (SPI) time series for four stations in Canada (La Tuque and Grande Prairie) and Iran (Anzali and Zahedan). Both duration and severity datasets are positively skewed. Different marginal distributions were first fitted to drought duration and severity data. The gamma and exponential distributions were respectively selected for drought duration and severity according to the positive skewness and Kolmogorov- Smirnov test. The results of copula modeling show that the Clayton copula function is not an appropriate choice for the employed datasets in the current study, and does not give more drought risk information than an independent model for which the duration and severity dependence is not significant. The reason is that the dependence of two variables in the upper tail of Clayton copula is very weak and similar to the independent case, while the observed data in the transformed domain of cumulative density function shows high association in the upper tail. Instead, the Frank and Gumbel copula functions show better performance than Clayton function for drought bivariate frequency analysis. Copyright © 2012 John Wiley & Sons, Ltd.

The sea level change along the Peninsular Malaysia and Sabah-Sarawak coastlines for the 21^st century is investigated along the coastal areas of Peninsular Malaysia and Sabah-Sarawak due to the expected climate change during the 21^st century. The spatial variation of the sea level change is estimated by assimilating the global mean sea level projections from the Atmosphere–ocean coupled Global Climate Model/General Circulation Model (AOGCM) simulations to the satellite altimeter observations along the subject coastlines. By means of the assimilated AOGCM projections the sea level around the Peninsular Malaysia coastline is projected to rise with a mean in the range 0.066 m to 0.141 m in 2040 and with a mean in the range 0.253 m to 0.517 m in 2100. By means of the assimilated AOGCM projections the sea level around Sabah-Sarawak coastlines is projected to rise with a mean in the range 0.115 m to 0.291 m in 2040 and with a mean in the range 0.432 m to 1.064 m in 2100. The highest sea level rise occurs at the north-east and north-west regions in Peninsular Malaysia and at north and east sectors of Sabah in Sabah-Sarawak coastline. Copyright © 2012 John Wiley & Sons, Ltd.

Identification of vegetation community growth season is critical for measuring the response of ecosystems to climate change. In this study, vegetation community growth season is measured via fixed-point monitoring of dynamic short-time processes of rock-fissure seepage in the Taihang Mountain Region (TMR). The hydro-meteorological data used in the study are obtained from tipping-bucket flow meters and automated weather stations in the region. Significant differences are noted in daily rock-fissure seepage for different growth seasons. The study shows that during growth seasons, seepage processes in the TRM study area vary with air temperature. While seepage in the region gradually decreases from 6:20 a.m. to 17:00 p.m., it increases from 18:00 p.m. to 6:00 a.m. Analysis shows a significant (R² > 0.8) negative correlation between seepage and air temperature during growth seasons. For non-growth seasons, however, seepage processes exhibit near-harmonic variations with air temperature. Also while seepage during non-growth seasons gradually increases from 2:30 a.m. to 12:30 p.m., it gradually decreases from 13:30 p.m. to 2:20 p.m. A significant (R² > 0.8) positive correlation also exists between seepage and air temperature during non-growth seasons. During seasonal crop rotations, however, significant disorders and inconsistencies occur in the seepage processes in the study area. The observed seasonal variations in daily rock-fissure seepages could lay the scientific basis for the adapting trends in crop growth seasons to climate change. Information on this process is critical for crop production and food security for the millions of people in China and beyond. Copyright © 2012 John Wiley & Sons, Ltd.

Snowmelt timing and snow water equivalent (SWE) from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) are used as inputs to the SWEHydro model to simulate spring snowmelt runoff in high-latitude, snow-dominated drainages. AMSR-E data from 2003 to 2010 are used to determine the timing of melt onset and snow saturation based on changes in brightness temperature (T_b) and diurnal amplitude variations (DAV). Pre-melt SWE data are combined with terrain information and melt rate estimates to calculate runoff. After melt onset there is a “melt transition period” with daytime melt and nocturnal refreeze. The melt transition is characterized by high T_b oscillations (high DAV). At the end of high DAV (EHD), the snowpack is melting at a higher rate. The model uses four parameters: snowmelt rate during and after melt transition (defined by T_b and DAV thresholds), and flow timing during and after melt transition. The model effectively simulates spring freshet, peak timing and magnitude, and volume (between days 50–180) in basins lacking sufficient meteorological measurements for conventional models. We compare the model response in the Pelly and Stewart Rivers, tributaries to the Yukon River, to evaluate model parameters in broadly similar basins under varying conditions. Simulated freshet timing is strongly related to snowmelt timing, and the modeled hydrograph is most sensitive to the flow timing parameter. This observationally based model has potential as a module for quantifying spring snowmelt runoff and timing in physically based models. Copyright © 2012 John Wiley & Sons, Ltd.

This article describes and formulates a model designed to simulate runoff in wet weather events, called Reservoir Rainfall-Runoff Geomorphological Model, R³GeM. In these wetlands soil saturation is the main mechanism for the generation of surface runoff. To determine the saturated areas, the model applies a relationship based on the topographic index, between watershed storage and saturated surface. Precipitation is separated into surface runoff by saturation, subsurface runoff and losses; then the flow of surface and subsurface runoff is performed. This hydrological model has five parameters and has been implemented in thirty-seven events in Aixola watershed and fifteen in Oiartzun watershed, both located on the Cantabrian coast of Spain. We analysed the influence of these five parameters in their behaviour and we have proven, noting the efficiency gains, that the proposed model is valid to simulate the rainfall-runoff process. Copyright © 2012 John Wiley & Sons, Ltd.

Multivariate statistical techniques, cluster and factor analyses were applied on the Amman/Wadi Sir groundwater chemistry, Yarmouk River basin, north Jordan. The main objective was to investigate the main processes affecting the groundwater chemical quality and its evolution. The k-means cluster analysis yields three groups with distinct ionic concentrations. Cluster 1 comprises the vast majority of the sampled wells, and the water belongs to this cluster can be classified as freshwater. Cluster 2 comprises only 2% of the sampled wells; it has the highest ionic concentration. The water of this cluster can be classified as brackish water. Cluster 3 involves 23% of the sampled wells, and it has total ionic concentration intermediate to that of clusters 1 and 2. Factor analysis yields a three-factor model, which explains 76.77% of the groundwater quality variation. Factor 1 " salinity factor" involves EC, Na⁺, Cl^-, SO₄^-2, K⁺, and Mg⁺², and reflects groundwater salinization due to overpumping. Factor 2 " hardness factor" includes Ca⁺², HCO₃^-, and the pH value, and signifies soil-water/rock interaction. Factor 3 " nitrate factor" involves only NO₃^-, and points to groundwater contamination due to human activities, mainly untreated wastewater, and crops and animals cultivation in the unconfined portion of the aquifer. Factors 1 and 3 can be described as human-induced factors, whereas factor 2 can be described as geogenic factor. Factors' scores were mapped to deduce the controlling processes on the groundwater chemistry. Stable isotope composition of ¹⁸O and ²H has revealed that the groundwater is a mixture of two water types. The radioactive isotopes tritium and ¹⁴ C were used to evaluate present day recharge to the aquifer and to estimate the groundwater age, respectively. Present day recharge to the groundwater is taking place in the unconfined portion of the aquifer as it is indicated by the measurable tritium content and low groundwater age. Copyright © 2012 John Wiley & Sons, Ltd.

Watershed models which combine hydrology and water quality are being widely utilized in integrated watershed management for the determination of best water management practices. In this study, the hydrology of the Lower Porsuk Stream Watershed in Turkey has been modeled with SWAT to determine optimal water management strategies. The calibration and validation process have been accomplished using data from two monitoring stations. The model has been run for the 1978–2009 period and while the 1998–2004 period has been used for calibration, the validation has spanned the whole period. The SWATCup calibration and uncertainity program has been utilized for this purpose. No significant differences have been detected among different iteration numbers in the calibration period. The monthly Nash-Sutcliffe and R² performance indicatiors for the upstream Esenkara station have been 0.74 and 0.88, respectively for the calibration period, and 0.87 and 0.87, respectively for the validation period. The Kıranharmanı station which is located close to the watershed outlet has shown values of 0.59 and 0.72, respectively for the calibration period, and 0.44 and 0.56, respectively for the validation period. There are uncertanities in the abstracted irrigation and groundwater quantities which have reflected in the results in the Kıranharmanı station which is more affected as it lies downstream of the irrigation areas. The effects of different irrigation practices on the flow regime have been also investigated. A scenario has been implemented in which drip irrigation wholly replaces conventional furrow and sprinkler irrigation. The scenario has shown increases in stream flows by 87 % for the whole year. The adoption of more efficient irrigation practices thus results in reducing the water stress induced by irrigation demands. With this study a modeling framework has been founded to aid water management applications in the Lower Porsuk Stream Watershed by generating scenarios for best management practices. Copyright © 2012 John Wiley & Sons, Ltd.

The aim of this paper is to improve the communication of the probabilistic flood forecasts generated by Hydrological Ensemble Prediction Systems (HEPS) by understanding perceptions of different methods of visualising probabilistic forecast information. This study focuses on inter-expert communication, and accounts for differences in visualisation requirements based on the information content necessary for individual users. The perceptions of the expert group addressed in this study are important because they are the designers and primary users of existing HEPS. Nevertheless, they have sometimes resisted the release of uncertainty information to the general public because of doubts about whether it can be successfully communicated in ways that would be readily understood to non-experts. In this paper we explore the strengths and weaknesses of existing HEPS visualisation methods and thereby formulate some wider recommendations about best practice for HEPS visualisation and communication. We suggest that specific training on probabilistic forecasting would foster use of probabilistic forecasts with a wider range of applications. The result of a case study exercise showed that there is no overarching agreement between experts on how to display probabilistic forecasts and what they consider the essential information that should accompany plots and diagrams. In this paper we propose a list of minimum properties that, if consistently displayed with probabilistic forecasts, would make the products more easily understandable. Copyright © 2012 John Wiley & Sons, Ltd.

Estimates of groundwater volumes available in semi-arid regions that rely on water balance calculations require determination of both surface to groundwater lag times and volumes from irrigation or rainfall initiated recharge. Subsurface geologic materials hydraulic properties (e.g. hydraulic conductivities, water-retention functions) necessary for unsaturated flow modeling are rarely available as are the instrumented field tests that might determine such lag times. Here we develop a simple two-parameter (specific yield, S_y and pore-size distribution index, λ), one-dimensional unsaturated flow model from simplifications of the Richards equation (using the Brooks-Corey relationships) to determine lag times from agricultural deep drainage associated with irrigation of alfalfa hay and various row crops in the Antelope Valley of California, USA. Model predicted lag times to depths of 85 m bgs were similar to that measured in a two-year ponded recharge field trial; slightly over-estimating that measured by about 15% (0.51 vs 0.44 years). Lag time estimates were most sensitive to estimated deep percolation rates and roughly equally sensitive to the model hydraulic parameters. Generally, as subsurface material textures coarsen towards larger S_y and λ values for all S_y >10%, lag times progressively increase, however, at S_y <10%, lag times decrease substantially suggesting that particular combinations of S_y and λ values that may be associated with similarly textured materials can result in prediction of different lag times for S_y ~10%. Overall, lag times of 1–3 years to a depth of 69 m bgs were estimated from deep drainage of agricultural irrigation across a variety of irrigation schedules and subsurface materials. Copyright © 2012 John Wiley & Sons, Ltd.

This paper evaluates a nonparametric technique for estimating the conditional probability distribution of a predictand given a vector of predictors. In the current application, the predictors are formed from a multi-model ensemble of simulated streamflows, such that the hydrologic uncertainties are modeled independently of any forcing uncertainties. The technique is based on Bayesian optimal linear estimation of indicator variables, and is analogous to indicator cokriging (ICK) in geostatistics. By developing linear estimators for the conditional probability that the observed variable does not exceed several thresholds, ICK provides a discrete approximation of the full conditional probability distribution. The weights of the predictors can be chosen to minimize the expected error variance at each threshold (the Brier Score) or, without loss of analytical tractability, a combination of the error variance and the expected square bias conditional upon the observation, i.e. the Type-II conditional bias (CB). The latter is referred to as Conditional Bias Penalized ICK (CBP-ICK) and is an important enhancement to ICK. Indeed, the biases in atmospheric and hydrologic predictions generally increase towards the tails of their probability distributions. The performance of CBP-ICK is evaluated for selected basins in the southeastern U.S. using a range of probabilistic verification metrics and associated confidence intervals for the sampling uncertainties. Overall, CBP-ICK produces unbiased and skillful estimates of the hydrologic uncertainties, with some sensitivity to the calibration data period at high flow thresholds. More generally, we argue that the common aim in statistical post-processing of ‘maximizing sharpness subject to reliability or Type-I CB’ should be recast to accommodate both the Type-I and Type-II conditional biases, as both are important for practical applications of hydrologic predictions. Copyright © 2012 John Wiley & Sons, Ltd.

The groundwater is the only source of drinking water in Jaisalmer district of Rajasthan, India. The study area is a part of Thar Desert. It has low and scattered population and no industries hence, the possibility of anthropogenic input of fluoride is almost negligible. Thus the enrichment of fluoride is only possible due to geochemical processes taking place in groundwater of the region. A total of 100 groundwater samples, 34 samples from Jaisalmer and 66 samples from Pokharan administrative blocks, were collected. It was observed that the concentration of fluoride ranged from 0.08 mg/l to 4.56 mg/l in groundwater of Jaisalmer and from 0.56 mg/l to 6.60 mg/l in samples of Pokharan block. The alkaline condition (average pH, 7.7 ± 0.22 and 8.01 ± 0.25 in Jaisalmer and Pokharan administrative block respectively) in the region favors fluorite dissolution. Ion-exchange, dissolution of calcite, semi-arid climate, alkaline conditions and weathering are responsible for fluoride enrichment in groundwater of the study area. Copyright © 2012 John Wiley & Sons, Ltd.

Under future climate scenarios, possible changes of drought patterns pose new challenges for water resources management. For quantifying and qualifying drought characteristics in the United Kingdom, the drought severity indices (DSI) of six catchments are investigated and modelled by two stochastic methods: autoregressive integrated moving average (ARIMA) models and the generalised linear model (GLM) approach. From the ARIMA models, autocorrelation structures are first identified for the drought index series, and the unexplained variance of the series is used to establish empirical relationships between drought and climate variables. Based on the ARIMA results, mean sea level pressure and possibly the North Atlantic Oscillation (NAO) index are found to be significant climate variables for seasonal drought forecasting. Using the GLM approach, occurrences and amounts of rainfall are simulated with conditioning on climate variables. From the GLM simulated rainfall for the 1980s and 2080s, the probabilistic characteristics of the drought severity are derived and assessed. Results indicate that the drought pattern in the 2080s is less certain than for the 1961–1990 period, based on the Shannon entropy, but that droughts are expected to be more clustered and intermittent. The 10^th and 50^th quantiles of drought are likely higher in the 2080s scenarios but there is no evidence showing the changes in the 90^th quantile extreme droughts. Copyright © 2012 John Wiley & Sons, Ltd.

Rivers and aquifers are in many cases a connected resource and as such the interactions between them need to be understood and quantified for the resource to be managed appropriately. The objective of this paper is to advance the understanding of river-aquifer interactions processes in semi-arid environments stressed by groundwater abstraction. This is done using data from a specific catchment where records of precipitation, evapotranspiration, river flow, groundwater levels, and groundwater abstraction are analysed using basic statistics, hydrograph analysis and a generic mathematical formula to determine the processes causing the spatial and temporal changes in river-aquifer interactions. This combined approach provides a novel, but simple methodology to analyse river-aquifer interactions which can be applied to catchments worldwide.

The analysis revealed that the groundwater levels have declined (~ 3 m) since the onset of groundwater abstraction. The decline is predominantly due to the abstraction rather than climatic changes (r = 0.84 for relationship between groundwater abstraction and groundwater levels; r = 0.85 for relationship between decline in groundwater levels and magnitude of seasonal drawdown). It is then demonstrated that, since the onset of abstraction, the river has changed from being gaining to losing during low-flow periods, defined as periods with flow less than 0.5, 1.0 or 1.5 GL/day (1 GL/day = 1x10⁶ m³/day). If defined as < 1.0 GL/day, low-flow periods constitute approximately 65% of the river flows. The periods where the river is losing at low-flow conditions are thus significant. Finally, a relationship between the gradient towards the river and the river flow at low-flow is demonstrated using a simple mathematical model. The results have important implications for water management as well as water ecology and quality. Copyright © 2012 John Wiley & Sons, Ltd.

Water resources assessment on climate change is crucial in water resources planning and management. This issue is becoming more urgent with climate change intensifying. In the current research of climate change impact, climate natural variability (fluctuation) has seldom been studied separately. Many studies keep attributing all changes (runoff, e.g.) to climate change, which may lead to wrong understanding of climate change impact assessment. Due to lack of long enough historical series, impacts of climate variability have been always avoided deliberately. Based on Latin Hypercube Sampling (LHS) technique, a block sampling approach was proposed for climate variability simulation in this study. The widely used time horizon (1961–1991) was defined as baseline period, and the runoff variation probability affected by climate natural variability was analyzed. Allowing for seven future climate projections in total of three GCMs (CSIRO, NCAR, MPI) and three emission scenarios (A1B, A2, B1), the impact of future climate change on water resources was estimated in terms of separating the contribution from climate natural variability. Based on the analysis of baseline period, for the future period from 2021 to 2051, the impact of climate natural variability may play a major part; while for the period from 2061 to 2091, climate change attributed to greenhouse gases may dominate the changing process. The results show that changes from climate variability possess a comparable magnitude, which highlights the importance to separate impacts of climate variability in assessing climate change, instead of attributing all changes to climate change solely. Copyright © 2012 John Wiley & Sons, Ltd.

Unlike temperate and polythermal proglacial streams, the proglacial streams in Taylor Valley (TV), Antarctica, are derived primarily from glacier surface melt with no subglacial or groundwater additions. Solute responses to flow reflect only the interaction of glacial meltwater with the valley floor surrounding the stream channel. We have investigated the major, minor, and trace element 24-h variations of two proglacial melt streams, Andersen Creek and Canada Stream, originating from the Canada Glacier in Taylor Valley (TV), Antarctica. Both streams exhibited diel mid-austral summer diurnal flow variation, with maximum flow being more than 50 times the minimum flow. Dissolved (<0.4 µm) major, minor and trace solute behaviors through diel time periods were strongly controlled by the availability of readily solubilized material on the valley floor and hyporheic-biological exchanges. Anderson Creek had generally greater solute concentrations than Canada Stream because of its greater receipt of eolian sediment. Andersen Creek also acquired greater solute concentrations in the rising limb of the hydrograph than the falling limb due to dissolution of eolian material at the surface of the stream channel coupled with minimal hyporheic biological-exchange. Conversely, Canada Stream had less available eolian sediment, but a greater hyporheic-biological exchange, which preferentially removed trace and major solutes in the rising limb and released them in the falling limb. Given the dynamic nature of discharge, eolian, and hyporheic-biological processes, solute loads in TV streams are difficult to predict. Copyright © 2012 John Wiley & Sons, Ltd.

Hydrological models are useful tools for better understanding the hydrological processes and performing the hydrological prediction. However, the reliability of the prediction depends largely on its uncertainty range. This study mainly focuses on estimating model parameter uncertainty and quantifying the simulation uncertainties caused by sole model parameters and co-effects of model parameters and model structure in a lumped conceptual water balance model called WASMOD (Water And Snow balance MODeling system). The validity of statistical hypotheses on residuals made in the model formation is tested as well, as it is the base of parameter estimation and simulation uncertainty evaluation. Bootstrap method is employed to examine the parameter uncertainty in the selected model. Yingluoxia watershed at the upper reaches of Heihe River basin in northwest of China is selected as the study area. Results show that all parameters in the model can be regarded as normally distributed based on their marginal distributions and Kolmogorov-Smirnov test, although they appear slightly skewed for two parameters. Their uncertainty ranges are different from each other. The model residuals are tested to be independent, homoscedastic and normally distributed. Based on such valid hypotheses of model residuals, simulation uncertainties caused by co-effects of model parameters and model structure can be evaluated effectively. It is found that the 95% and 99% confidence intervals (CIs) of simulated discharge cover 42.7% and 52.4% of the observations when only parameter uncertainty is considered, indicating that parameter uncertainty has a great effect on simulation uncertainty but still cannot be used to explain all the simulation uncertainty in this study. The 95% and 99% CIs become wider and the percentages of observations falling inside such CIs become larger when co-effects of parameters and model structure are considered, indicating that simultaneous consideration of both parameters and model structure uncertainties accounts sufficient contribution for model simulation uncertainty. Copyright © 2012 John Wiley & Sons, Ltd.

No study has systematically evaluated streamflow modeling between monthly and daily timescales. This study examines streamflow from seven watersheds across the United States where five different precipitation products were used as primary input into the Soil and Water Assessment Tool to generate simulated streamflow. Timescales examined include monthly, dekad (10 day), pentad (5 day), triad (3 day), and daily. The seven basins studied are the San Pedro (Arizona); Cimarron (north-central Oklahoma); mid-Nueces (south Texas); mid-Rio Grande (south Texas and northern Mexico), Yocano (northern Mississippi); Alapaha (south Georgia); and mid-St. Francis (eastern Arkansas). The precipitation products used to drive simulations include rain gauge, NWS Multisensor Precipitation Estimator, Tropical Rainfall Measurement Mission, Multi-Satellite (TRMM) Precipitation Analysis, TRMM 3B42-V6, and Climate Prediction Center Morphing Method (CMORPH). Understanding how streamflow varies at sub-monthly timescales is important because there are a host of hydrological applications such a flood forecast guidance and reservoir inflow forecasts that reside in a temporal domain between monthly and daily timescales. The major finding of this study is the quantification of a strong positive correlation between performance metrics and time step at which model performance deteriorates. Better performing simulations, with higher Nash-Sutcliffe values of 0.80 and above can support modeling at finer timescales to at least daily and perhaps beyond into the sub-daily realm. These findings are significant in that they clearly document the ability of SWAT to support modeling at sub-monthly time steps, which is beyond the capability for which SWAT was initially designed. Copyright © 2012 John Wiley & Sons, Ltd.

Meander bends in alluvial rivers morphologically evolve toward meander cutoff with narrowing intra-meander necks, and this should steepen hydraulic gradients and intensify intra-meander hyporheic flux. This research used dye tracking and head loss measurements in a 1:500 planimetrically scaled laboratory river table to quantify the spatial and temporal intensification of intra-meander flux rates at two evolution ages. The younger meander bend, M1, had a sinuosity of 2.3, a river neck width of 0.39 cm, and 0.6% river slope, and the older meander bend, M3, had a sinuosity of 5.2, a river neck width of 0.12 cm, and 0.5% river slope. Flux into and out of the meander bend was estimated along the normalized curvilinear distance s*, with the meander neck at s* = 0.1 and s* = 0.9, the meander centroid at s* = 0.37 and s* = 0.63, and the apex at s* = 0.5. Between the meander centroid and neck we documented a 60% spatial intensification for M1 and a 90% spatial intensification for M3. Between M1 and M3 we documented a 135% temporal intensification at the neck and a 100% intensification at the centroid. Our empirical spatial and temporal intensification rates involving the M1 and the M3 scenario were 1 to 3 times lower than theoretical rates derived from a river evolution model with equivalent M1 and M3 planimetry. Over estimation by the theoretical model was attributed to exaggerated head loss caused by the model neglecting groundwater contributions to river stage. Hyporheic exchange provides critical ecosystem services and its spatial and temporal variation with meander evolution should be considered in river management. Copyright © 2012 John Wiley & Sons, Ltd.

Using Lake Stechlin in northeastern Germany as an example of a small groundwater-feed lake without surface in- and outflows, we estimated the temporal scales and the variability ranges of the net groundwater contribution to the lake water budget. High-resolution water level measurements by a bottom-mounted pressure logger provided he background for the estimation of the total lake water budget. This method has demonstrated reliability for estimation of lake level variations during periods ranging from sub-diurnal to perennial. The typical amplitudes of the synoptic-to-perennial variability characterizing the groundwater climate of Lake Stechlin are estimated by comparing the two subsequent years 2006 and 2007; one of these years shows an extremely high, and the other an extremely low, annual precipitation-evaporation balance. The net groundwater flow, estimated as the difference between the total water budget and the precipitation-evaporation balance at the surface, revealed synoptic effects of lake water exfiltration into the groundwater aquifer following strong precipitation events. Perennial variations between wet and dry years superimposed seasonal oscillations. The probable origin of the latter is seasonality in the groundwater level on the watershed, although the exact amplitudes are subject to further quantification on account of seasonality in the evaporation estimation error. The results emphasize the non-stationary behavior of groundwater flow on time scales shorter than climatic ones. The analysis yielded a net quantitative relationship between groundwater flow and water balance at the lake surface: The water level changes in the lake due to evaporation and precipitation are damped to 60% due to the lake-groundwater exchange by means of intermittent in- and exfiltration events. Assuming the remaining 40% of the surface water budget may potentially result in perennial water level variability, we estimated an effect of the precipitation decrease on the lake water budget as predicted by the regional climate scenarios for the next century. Copyright © 2012 John Wiley & Sons, Ltd.

Accurate stream discharge measurements are important for many hydrological studies. In remote locations, however, it is often difficult to obtain stream flow information because of the difficulty making the discharge measurements necessary to define stage-discharge relationships (rating curves). This study investigates the feasibility of defining rating curves using a fluid mechanics-based model constrained with topographic data from airborne LiDAR scanning. The study was carried out for an 8-m wide channel in the boreal landscape of northern Sweden. LiDAR data were used to define channel geometry above a low flow water surface along the 90-m surveyed reach. The channel topography below the water surface was estimated using the simple assumption of a flat streambed. The roughness for the modeled reach was back calculated from a single measurement of discharge. The topographic and roughness information was then used to model a rating curve. To isolate the potential influence of the flat bed assumption, a “hybrid-model” rating curve was developed based on data combined from the LiDAR scan and a detailed ground survey. While this hybrid-model rating curve was in agreement with the direct measurements of discharge, the LiDAR-model rating curve was equally in agreement with the medium and high flow measurements based on confidence intervals calculated from the direct measurements. The discrepancy between the LiDAR-model rating curve and low flow measurements was likely due to reduced roughness associated with unresolved submerged bed topography. Scanning during periods of low flow can help minimize this deficiency. These results suggest that combined ground surveys and LiDAR scans or multi-frequency LiDAR scans that see “below” the water surface (bathymetric LiDAR) could be useful in generating data needed to run such a fluid mechanics-based model. This opens a realm of possibility to remotely sense and monitor stream flows in channels in remote locations. Copyright © 2012 John Wiley & Sons, Ltd.

Agricultural pollutant runoff is a major source of water contamination in California's Sacramento River watershed where 8,500 km² of agricultural land influences water quality. The Soil and Water Assessment Tool (SWAT) hydrology, sediment, nitrate and pesticide transport components were assessed for the Sacramento River watershed. To represent flood conveyance in the area, the model was improved by implementing a flood routing algorithm. Sensitivity/uncertainty analyses and multi-objective calibration were incorporated into the model application for predicting streamflow, sediment, nitrate, and pesticides (chlorpyrifos and diazinon) at multiple watershed sites from 1992–2008. Most of the observed data were within the 95% uncertainty interval, indicating that the SWAT simulations were capturing the uncertainties that existed, such as model simplification, observed data errors, and lack of agricultural management data. The monthly Nash-Sutcliffe coefficients at the watershed outlet ranged from 0.48 to 0.82, indicating that the model was able to successfully predict streamflow and agricultural pollutant transport after calibration. Predicted sediment loads were highly correlated to streamflow, while nitrate, chlorpyrifos, and diazinon were moderately correlated to streamflow. This indicates that timing of agricultural management operations plays a role in agricultural pollutant runoff. Best management practices, such as pesticide use limits during wet seasons, could improve water quality in the Sacramento River watershed. The calibrated model establishes a modeling framework for further studies of hydrology, water quality, and ecosystem protection in the study area. Copyright © 2012 John Wiley & Sons, Ltd.

The Manso Glacier (~41ºS, 72ºW), in the northern Patagonian Andes of Argentina is a regenerated glacier that, like many other glaciers in the region and elsewhere, has been showing a significant retreat. Glacial melt water feeds the Manso Superior River which, before crossing the Andes to reach a Pacific outfall, flows through the Mascardi (a deep, oligotrophic and monomictic lake) and significantly smaller Hess and Steffen lakes. Harmonic analysis of Mascardi's lake level series suggests that the ENSO signal has been strong during the 1985–1995 decade but has grown weaker during the initial decade of the 21^st century. Hydrological trend analyses applied in data recorded in the uppermost reaches, show a monthly and annual decreasing trend in the Manso Superior River discharge series and Mascardi's lake level, which are connected with both, decreasing melt water discharge and (austral) wintertime atmospheric precipitation. Downstream, the decreasing signal initially looses statistical significance and then, when flowing through Steffen Lake, reverses the lake level trend that becomes significantly positive. This suggests that, on its way to the Pacific Ocean, the Manso River receives abundant Andean snow melt water and atmospheric precipitation, which is sufficient to obliterate the negative trend recorded in the uppermost reaches. The reason for this local phenomenon is that the Manso is an antecedent river (a.k.a. superposed stream) and hence, the valley crossing the Andes allows the incursion of Pacific humidity that modifies the hydrological regime several hundred kilometers inland. Copyright © 2012 John Wiley & Sons, Ltd.

Drainage networks in agrarian landscape within floodplains constitute surface's discontinuities that are expected to affect hydrological response during floods. Drainage network recognition and quantification of water storage capacity within channels are, therefore, crucial for watershed planning and management. These evaluations require accurate spatial information for the area of interest and in most cases, when studying large catchments, broad datasets of ditches locations and descriptions are not available. In order to characterize drainage networks for large areas, the availability of high resolution topography derived by airborne laser scanner (LiDAR) represents a new and effective tool. Nowadays LiDAR DTMs covering large areas are readily available for public authorities, and there is a greater and more widespread interest in the application of such information for the development of automated methods aimed at solving geomorphological and hydrological problems. While LiDAR DTMs reliability in steep landscape has been proven by several recent studies, only few researches have been conducted to take into account the effectiveness of these data in agrarian low relief landscapes. The goal of this research is to propose a semi-automatic approach based on a LiDAR DTM to (1) detect drainage networks in agrarian/floodplain context, and (2) to estimate some of the network summary statistics (network length, width, drainage density and storage capacity). The procedure is applied in two typical alluvial-plain areas in the North East of Italy, and tested comparing automatically derived network with surveyed ones. The results underline the capability of high resolution DTMs for drainage network detection and characterization in the context of agrarian landscapes within floodplains, opening at the same time new challenges to evaluate some hydrological processes in these areas. Copyright © 2012 John Wiley & Sons, Ltd.

Natural ecosystems in the region of the lower Tarim river in northwestern China, strongly deteriorated since the 1950s due to an expanding desertification. As a result, the downstream Tarim river reaches became permanently dry land. This historical evolution in land-use change is typically the result of the anthropogenic impact on natural ecosystems. Based on a spatially distributed hydrological catchment model bi-directionally linked with a fully hydrodynamic MIKE11 river model, land-use changes characterized by historical changes in leaf area index (LAI) of vegetation as well as the evolution of irrigated surface areas, can be causally related to changes in water resources (groundwater storage and surface water resources). An increased surface area of irrigated (agricultural) land together with a majority of inefficient irrigation methods, did lead to a strong increase of water resources consumption of the farmlands located in the upper Tarim river area. Evidently, this evolution influenced available water resources downstream in the Tarim basin. As a result, farmland has been gradually relocated to the upstream regions. This has led to reduced flows from the upper Tarim stream, which subsequently accelerated the dropping of the groundwater level downstream in the basin. This study moreover demonstrates that land surface biomass changes (cumulative LAI) along the lower Tarim river are strongly related to the changes in groundwater storage. Copyright © 2012 John Wiley & Sons, Ltd.

A structure model was used to analyse solute-transport parameter estimates based on tracer breakthrough curves. In the model system groundwater flow is envisioned to be organised in a complex conduit network providing a variety of short circuits with relative small carrying capacities along different erosion levels. The discharge through the fully filled conduits is limited due to void geometries and turbulent flow; thus, a hierarchic overflow system evolves where conduits are (re-)activated or dry up depending on the flow condition.

Exemplified on the Lurbach-Tanneben karst aquifer the applicability of the model approach was tested. Information derived from multi-tracer experiments performed at different volumetric flow rates enabled to develop a structural model of the karst network, under constraint of the geomorphological and hydrological evolution of the site. Depending on the flow rate groundwater is divided into up to eight flow paths. The spatial hierarchy of flow paths controls the sequence of flow path activation. Conduits of the topmost level are strongly influenced by reversible alteration processes. Sedimentation or blocking causes an overflow of water to the next higher conduit. Flow path specific dissolutional denudation rates were estimated using the temporal development of the partial discharge. Copyright © 2012 John Wiley & Sons, Ltd.

Climate change would significantly affect many hydrologic systems, which in turn would affect the water availability, runoff, and the flow in rivers. This study evaluates the impacts of possible future climate change scenarios on the hydrology of the catchment area of the Tunga-Bhadra River, upstream of the Tungabhadra dam. The Hydrologic Engineering Center's Hydrologic Modeling System version 3.4 (HEC-HMS 3.4) is used for the hydrological modeling of the study area. Linear-regression based Statistical DownScaling Model version 4.2 (SDSM 4.2) is used to downscale the daily maximum and minimum temperature, and daily precipitation in the four subbasins of the study area. The large scale climate variables for the A2 and B2 scenarios obtained from the Hadley Centre Coupled Model, version 3 (HadCM3) are used. After model calibration and testing the downscaling procedure, the hydrological model is run for the three future periods: 2011–2040, 2041–2070 and 2071–2099. The impacts of climate change on the basin hydrology are assessed by comparing the present and future streamflow and the evapotranspiration estimates. Results of the water balance study suggest increasing precipitation and runoff and decreasing actual evapotranspiration losses over the subbasins in the study area. Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the interplay of the hydrogeological characteristics, soil properties and recent land reclamation projects on the distribution of waterlogging and salinisation within the Farafra oasis. The multi-temporal remote sensing data and field observations show that new reclaimed areas have been recently cultivated in distant areas from the old agricultural land. These new cultivations have developed widespread water logging, seepage channels and soil salinisation. Analyses of the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) showed that both old and new agricultural areas are located within same closed drainage basin. The fluvial channels of these catchments, which were developed during wet climatic pluvial have largely been obliterated by the prevailing aridity and often buried under aeolian deposits. However, the new cultivations have been developed on the fingertips of these fluvial channels, while the old fields occupy the low level playas. The soil of the new cultivated areas are mainly lithic with a high calcium carbonate content, thus limiting the downward percolation of excess irrigation water and therefore develop perched water table and seepage through the pale drainage. The automatically extract drainage networks from DEM are resembling fluvial patterns and coincide with the seepage channels slowly heading toward old cultivation. The inactive alluvial channels and landforms have to be considered when planning for new cultivation in dryland catchments to better control waterlogging and salinisation hazard. It is highly recommended that newly developed seepage-channels have to be detected and intercepted before reaching old agriculture areas. Therefore, the ‘dry-drainage’ concept can be implemented as the seepage water can be conveyed into a nearby playas reserved for evaporation. Copyright © 2012 John Wiley & Sons, Ltd.

Improved understanding of overland flow (OF) generation and its dynamics (i.e. spatial and temporal variations) is essential to understand Catchment hydrology, a prerequisite for improved water resources and soil management. In this study, our main objective was to quantify the spatial and temporal variations of OF during rainfall events and to assess its main factors of control. The research study was undertaken in an agricultural 23 ha Catchment of a communal pasture in KwaZulu-Natal (South Africa) experiencing Mediterranean climate and with variations of soil, topography and vegetation conditions. The dynamics of OF was evaluated during three rainfall seasons (2007 to 2010) by using 1 × 1 m² microplots (n = 15) located at five landscape positions. At each location a microplot was equipped with an automatic tipping bucket linked to a logger to estimate the delay between the start of the rain and the start of OF (i.e. the time to runoff initiation: TRI). Multivariate analysis was applied to the total OF and TRI data and the information on selected environmental factors (rainfall characteristics; soil type; soil clay content, Clay; proportion of the soil surface covered by vegetation, Cov; proportion of the soil surface covered by crusting, Crust; mean slope gradient, S; doil bulk density, ρ_b; soil water tension at different depths, SWT). The average OF rate over the 3-year study period varied 2.3-fold across the Catchment (from 15% footslope to 35% backslope), while the average TRI varied by a 10.6-fold factor (between 0.6 min. at bottomland and 6.4 min. at footslope). TRI temporal variations correlated the most with event duration (r = 0.8) and cumulative amount of rainfall after the onset of the rainy season (r = −0.47), while TRI spatial variations were controlled by Crust (−0.97 < r < −0.77). Ultimately, TRI spatial variations were mapped in an attempt to model OF dynamics. Copyright © 2012 John Wiley & Sons, Ltd.

Remote sensing data and digital elevation models (DEMs) were utilised to extract the catchment hydrological parameters and to delineate storage areas for the Ugandan Equatorial Lakes region. Available rainfall/discharge data are integrated with these morphometric data to construct a hydrological model which simulates the water balance of the different interconnected basins and enables the impact of potential management options to be examined. The total annual discharges of the basins are generally very low (less than 7 % of the total annual rainfall). The basin of the shallow (5 m deep) Lake Kioga makes only a minor hydrological contribution compared to the other Equatorial Lakes, because most of the overflow from Lake Victoria basin into Lake Kioga is lost by evaporation and evapotranspiration. The discharge from Lake Kioga could be significantly increased by draining the swamps through dredging and deepening certain channel reaches. Development of hydropower dams on the Equatorial Lakes will have an adverse impact on the annual water discharge downstream, including the occasional reduction of flow required for filling up to designed storage capacities, and permanently increasing the surface areas of water that is exposed to evaporation. On the basis of modeling studies, alternative sites are proposed for hydropower development and water storage schemes. Copyright © 2012 John Wiley & Sons, Ltd.

Seasonality in hydrology is closely related to regional water management and planning. There is a strong consensus that global warming will likely increase streamflow seasonality in snow-dominated regions due to decreasing snowfall and earlier snowmelt, resulting in wetter winters and drier summers. However, impacts to seasonality remain unclear in rain-dominated regions with extreme seasonality in streamflow, including South Korea. This study investigated potential changes in seasonal streamflow due to climate change and associated uncertainties based on multi-model projections. Seasonal flow changes were projected using the combination of 13 atmosphere–ocean general circulation model (AOGCM, hereafter GCM) simulations and three semi-distributed hydrologic models under three different future greenhouse gas (GHG) emission scenarios for two future periods (2020s and 2080s). Our results show that streamflow seasonality is likely to be aggravated due to increases in wet season flow (July through September) and decreases in dry season flow (October through March). In South Korea, dry season flow supports water supply and ecosystem services and wet season flow is related to flood risk. Therefore, these potential changes in streamflow seasonality could bring water management challenges to the Korean water resources system, especially decreases in water availability and increases in flood risk. Copyright © 2012 John Wiley & Sons, Ltd.

The Noah model is a land surface model of the National Centers for Environmental Prediction (NCEP). It has been widely used in regional coupled weather and climate models (i.e., Weather Research and Forecasting Model, Eta Meso-scale Model) and global coupled weather and climate models (i.e., NCEP Global Forecast System, Climate Forecast System). Therefore, its continued improvement and development are key to enhancing our weather and climate forecast ability, and water and energy flux simulation accuracy. North-American Land Data Assimilation System Phase 1 (NLDAS-1) experiments indicated that the Noah model exhibited substantial bias in latent heat flux, total runoff and land skin temperature during the warm season, and such bias can significantly affect coupled weather and climate models. This paper presents a study to improve the Noah model by adding model parameterization processes such as the inclusion of seasonal factor on Leaf Area Index (LAI) and root distribution, and selecting optimal model parameters. We compared simulated latent heat flux, mean annual runoff and land skin temperature from the Noah control and test versions with measured latent heat flux, land surface skin temperature (LST), mean annual runoff, and satellite retrieved LST. The results show that the test version significantly reduces biases in latent heat, total runoff and land skin temperature simulation. The test version has been used for the NLDAS Phase 2 (NLDAS-2) to produce 30-year water flux, energy flux, and state variable products to support the US drought monitor of National Integrated Drought Information System (NIDIS). Copyright © 2012 John Wiley & Sons, Ltd.

Quantitative assessment of surface water resources (SWRs) and evapotranspiration (ET) is essential and significant for reasonably planning and managing the water resources in the Haihe River basin which is facing severe water shortage. In this study, a distributed hydrological model of Haihe River basin was constructed using SWAT, with well considering the reservoirs and agricultural management practices for reasonable simulation. The crop parameters were independently calibrated with the observed crop data at six experimental stations. Then, sensitivity ranks of hydrological parameters were analyzed, which suggested the important parameters used for calibration. The model was successfully calibrated using the monthly observed data of discharge in around 1970–1991 and actual evapotranspiration (ET_a) in 2002–2004 for the mountainous area and Haihe plain, respectively. Meanwhile, good agreements between the simulated and statistical crop yields in 1985–2005 further verified the model's appropriateness. Finally, the calibrated model was used to assess SWRs and ET_a in time and space during 1961–2005. Results showed that the average annual natural SWRs and ET_a were about respectively 17.5 billion m³ and 542 mm, both with a slight downward trend. The spatial distribution of SWRs and ET_a were both significantly impacted by variations of precipitation and land use. Moreover, the reservoir in operation was the main factor for the noticeable decline of actual SWRs. In the Haihe plain, the ET_a with irrigation was increased by 46% compared with that under rainfed conditions. In addition, this study identified the regions with potential to improve the irrigation effects on water use. Copyright © 2012 John Wiley & Sons, Ltd.

Design flood estimation in ungauged catchments is of great importance in hydrological practice especially where there is no available data about streamflow. Except the watershed of Anseghmir who is equipped with a gauge station, all the other watersheds are ungauged catchments. The use of frequency analysis of series of rainfall and streamflow is very important for the characterization of the hydrological resources of the Upper Moulouya. The region has a semiarid climate that requires a good knowledge of the watershed's potential water to assist policymakers in forecasting extreme events, management of water resources and decision-making. The frequency analysis was used to determine the design flood of different return periods. The results obtained are used in Gradex method to estimate the hydrological variables of each sub-catchment of the Upper Moulouya. Once the hydrological study is completed a principal components analysis was made to highlight the affinities between the different sub-catchments and deduce the hydrological and hydrographical parameters that better characterize them. Copyright © 2012 John Wiley & Sons, Ltd.

Mid- to long-term runoff forecasting is important to China. Forecasting based on physical causes has become the trend of this field, and recognition of key factors is central to recent development. Here, global sensitivity analysis based on back-propagation arithmetic was used to calculate the sensitivity of up to 24 factors that affect runoff in the Nenjiang River Basin. The following five indices were found to be key factors for mid- to long-term runoff forecasting during flood season: Tibetan Plateau B, index of the strength of the East Asian trough, index of the area of the northern hemisphere polar vortex, zonal circulation index over the Eurasian continent and index of the strength of the subtropical high over the western Pacific. The hydrological climate of the study area and rainfall-runoff laws were then analyzed in conjunction with its geographical position and topographic condition. The rationality of the results can be demonstrated from the positive analysis point of view. The results of this study provide a general method for selection of mid- to long-term runoff forecasting factors based on physical causes. Copyright © 2012 John Wiley & Sons, Ltd.

The frequency and magnitude of extreme meteorological or hydrological events such as floods and droughts in China have been influenced by global climate change. The water problem due to increasing frequency and magnitude of extreme events in the humid areas has gained great attention in recent years. However, the main challenge in the evaluation of climate change impact on extreme events is that large uncertainty could exist. Therefore, this paper first aims to model possible impacts of climate change on regional extreme precipitation (indicated by 24-h design rainfall depth) at seven rainfall gauge stations in the Qiantang River Basin, East China. The LARS-WG weather generator is adopted to downscale the global projections obtained from GCMs to regional climate data at site scale. The weather generator is also checked for its performance through three approaches, namely Kolmogorov-Smirnov test, comparison of L-moment statistics and 24-h design rainfall depths. Future 24-h design rainfall depths at seven stations are estimated using Pearson Type III distribution and L-moment approach. Second, uncertainty caused by three GCMs under various greenhouse gas emission scenarios for the future periods 2020s (2011–2030), 2055s (2046–2065) and 2090s (2080–2099) is investigated. The final results show that 24-h design rainfall depth increases in most stations under the three GCMs and emission scenarios. However, there are large uncertainties involved in the estimations of 24-h design rainfall depths at seven stations due to GCM, emission scenario and other uncertainty sources. At Hangzhou Station, a relative change of −16-113% can be observed in 100y design rainfall depths. Copyright © 2012 John Wiley & Sons, Ltd.

The investigation focuses on the analysis of dissolved sulfonamides, tetracyclines, analgesics, anticonvulsants and hormones in surface water. Runoff event and baseflow samples were analyzed in two small river catchments of different landuse in Luxembourg. For most of the flood events similar pollutant loads to those transported during one day with average baseflow discharge were observed. The maximum contents during flood events and the Event Mean Concentrations are controlled by pre-event hydro-climatological conditions. For all substances under investigation maximum concentrations and Event Mean Concentrations show a decrease with raising antecedent rainfall. In addition, the inter-storm and intra-storm variability of the pollutant transport were determined. Runoff generation and corresponding transport of xenobiotic compounds show a complex pattern with many interrelated processes, taking place within bedrock, soil, anthropogenic facilities, the channel, and in different parts of the basins under investigation. Different sources of pollutants can be identified and related to particular locations in the basin. The influence of the sewer systems is obvious. In the agricultural Mess basin higher rainfall amounts lead to greater quantities of laterally inflowing soil water with higher concentrations of dissolved oxytetracycline. This originates from veterinary medicines administered to livestock and enters the environment through the application of organic fertilizers, especially by slurry that is applied to the fields. Copyright © 2012 John Wiley & Sons, Ltd.

A synthesis of groundwater ages, recharge rates and information on processes affecting groundwater quality in northern China highlights the major challenges faced for sustainable management of the region's groundwater. Direct recharge rates range from 100 s of millimetres per year in the North China Plain, to 10s of mm per year in the Loess Plateau to less than 4 mm/year in the arid northwest. Recharge rates and mechanisms to deep semi-confined and confined aquifers are poorly constrained, however based on available data these are likely to be mostly negligible. Severe groundwater level declines (0.5 to 3 m/year) have occurred throughout northern China in the last 3–4 decades, particularly in deep aquifers. Radiocarbon dating, stable isotope and noble gas data show that most intensively extracted deep groundwater is palaeowater, recharged under different climate and land-cover conditions to the present. Reservoir construction has reduced surface runoff in mountain front areas that would naturally recharge regional Quaternary aquifers in many basins. In combination with intensive irrigation practices, this has resulted in the main recharge source shifting from surface runoff and mountain-front recharge to irrigation returns. This has reduced infiltration of fresh recharge at basin margins, and rapidly increased nitrate concentrations and overall mineralisation in phreatic groundwater over wide areas (in some cases to >400 mg/L and >10 g/L, respectively). In some basins, there is evidence that poor quality shallow water has leaked into deep layers (>200 m) via preferential flow, mixing with palaeowaters stored in semi-confined aquifers. High concentrations of naturally occurring fluoride and arsenic (locally >8.5 mg/L and >4 mg/L respectively), have recently lead to abandonment of numerous supply wells in northern China, creating further pressure on stressed water resources. Increasing water demand from direct and indirect consumption poses major challenges for water management in northern China, which must consider the full water cycle. Copyright © 2012 John Wiley & Sons, Ltd.

Marine intrusion is the most serious problem facing the coastal Jorf shallow aquifer, located in south-eastern Tunisia on the Mediterranean Sea. Jorf Aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors. This work proposes a multidisciplinary investigation, involving hydro-geochemical, geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion. For this purpose, 36 water samples were conducted and analyzed. Electric conductivity, pH, Total Dissolved Solids (TDS) and major ions were measured and analyzed. Pie and Durov Diagrams, Q-mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes. Results revealed that the Na-Cl-Ca-SO₄ is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area. However, saltwater intrusion was shown to control groundwater quality essentially in coastal areas. Variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity. Kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone, implying highly saline water due to seawater intrusion. Apparent resistivity values also decrease considerably in the faulted areas, suggesting a contribution of faults to seawater intrusion. Finally, saltwater mixing ratio was computed for each sample and a refined seawater intrusion map was developed. Copyright © 2012 John Wiley & Sons, Ltd.

The correct use of the tension disc infiltrometer requires the membrane of the disc base to be completely in contact with the soil surface. To achieve this contact, a thick layer of sand is commonly placed between the soil surface and the disc base. This paper presents an alternative disc (M_DB), which, by incorporating a malleable membrane, allows direct infiltration measurements without using a contact sand layer. Infiltration curves obtained with this new design in a soil under three different tillage management treatments were compared to the corresponding curves obtained with a conventional disc (C_DB) that uses a contact sand layer. The cumulative infiltration curves measured with C_DB were analysed by the differentiated linearization (DL) method, and the corresponding curves obtained with M_DB were analysed using both the DL and the cumulative linearization (CL) models. The values of hydraulic conductivity (K₀ ) and sorptivity (S₀) estimated with C_DB were also compared to those obtained with M_DB. Finally, the cumulative infiltration curves measured with C_DB and M_DB were compared with the corresponding modelled function for the respective K₀ and S₀ values calculated with the CL and DL models. The results show that, compared to C_DB without a contact sand layer, M_DB allows complete soil surface wetting even when non-smoothed soil surfaces are used. The C_DB, which yielded average K₀ values 18% lower than those estimated with M_DB, gave the highest values of standard error for the hydraulic parameters calculated. Further, the subjective method employed in the C_DB-DL technique, which requires the first points of the differential infiltration line corresponding to the sand layer to be manually removed, introduces additional uncertainties in estimating S₀ and K₀. Comparison between the modelled and measured infiltration curves demonstrates that the DL or CL methods applied to M_DB gave excellent estimates of S₀ and K₀. Copyright © 2012 John Wiley & Sons, Ltd.

Snow temperature is a major component of many physical processes in a snowpack. Temperature and the change in temperature across a layer have a dominant impact on physical properties of snow grains as well as its hardness, strength and failure resistance. In this study, temperature and snow cover thicknesses were measured during snow season of 2007–2008 in 11 elevation classes and in 3 different sampling locations where one in an open area and two under different forest canopy covers for each class along Kartalkaya road-Bolu. Each sampling site was visited 44 times to collect data including snow depth, snow surface temperature, ground temperature, and temperature within snowpack at 20 cm intervals. Seven different models are developed to determine snowpack temperature variations under Forest Canopy Covers (FCCs) in an Open Area (OA) with different Leaf Area Index (LAI) values. All models were performed using a Multilayer Perceptron (MP) method for the Bolu-Kartalkaya area, Turkey. MP approach constitutes a standard form of neural network modeling and can modify two-layer linear perceptron methods using three and more layers. The ability of MP is to handle complex nonlinear interactions which ease the natural process of modeling. This method can overcome complex computations using neuron networks, and they can easily nonlinearly link input and output variables. The predictive errors are determined based on Mean Absolute Error (MAE) and Mean Square Error (MSE) criteria. The Nash-Sutcliffe Sufficiency Score (NSSS) showing compliance between observed and predicted values is also calculated. According to MAE, MSE and NSSS criteria, the predictive errors are within reasonable error intervals, justifying the use of the developed MP models for engineering applications. Copyright © 2012 John Wiley & Sons, Ltd.

The delicate balance between human utilization and sustaining its pristine biodiversity in the Mara River Basin (MRB) is being threatened due to expansion of agriculture, deforestation, human settlement, erosion and sedimentation, and extreme flow events. This study assessed the applicability of SWAT model for long-term rainfall-runoff simulation in MRB. The Possibilities of combining/extending gage rainfall data with satellite rainfall estimates (RFE) investigated. Monthly RFE not only overestimated but also lacked the variability of observed rainfall to substitute gage rainfall in model simulation. Uncertainties related to quality and availability of input data was addressed. Sensitivity and uncertainty analysis was reported for alternative model components and hydrologic parameters used in SWAT. Mean Sensitivity indices of SWAT parameters in MRB varied with and without observed discharge data. Manual assessment of individual parameters indicated heterogeneous response among sub-basins of MRB. SWAT was calibrated and validated with ten years of discharge data at Bomet (Nyangores River), at Mulot (Amala River) and at Mara Mines (Mara River) stations. Model performance varied from satisfactory at Mara Mines to fair at Bomet and weak at Mulot. The (Nash-Sutcliff-Efficiency, Coefficient of determination) results of calibration and validation at Mara Mines were (0.68, 0.69) and (0.43, 0.44), respectively. Two years moving time window and flow frequency analysis showed that SWAT performance in MRB heavily relied on quality and abundance of discharge data. Given the 5.5% area contribution of Amala sub-basin as well as uncertainty and scarcity of input data, SWAT has potential to simulate the rainfall runoff process in the MRB. Copyright © 2012 John Wiley & Sons, Ltd.

As the substantial component of the ecosystem respiration, soil respiration is strongly influenced by infrequent and unpredictable precipitation in arid region. In the current study we investigated the response of soil CO₂ flux to rain pulses at a saline desert in western China. Soil CO₂ flux was measured continuously during the whole growing season of 2009 at six sites. We found that there were remarkable changes in amplitude or diurnal patterns of soil CO₂ flux induced by rainfall events: from bimodal before rain to a single peak after that. Further analysis indicated there is a significant linear relationship (P < 0.001) between soil CO₂ flux and soil temperature (T_soil). However, a hysteresis between the waveform of diurnal course of CO₂ flux and T_soil was observed: with soil CO₂ flux always peaked earlier than T_soil. Furthermore, a double exponential decay function was fitted to the soil CO₂ flux after rainfall and total carbon (C) releases were estimated by numerical integration for rainfall events. The relative enhancement and total C release, in association with the rain pulses, was linearly related to the amount of precipitation. According to the size and frequency of rainfall events, the total amount of C release induced by rain pulses was computed as much as 7.88 g C·m^–2 in 2009, equivalent to 10.25% of gross primary production. These results indicated that rain pulses played a significant role in the carbon budget of this saline desert ecosystem and the size of them was a good indicator of rain-induced flux enhancement. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, by using the daily precipitation data measured at 58 meteorological stations, spatial and temporal variability of daily precipitation including zero rainfall values (called “precipitation”) and without zero rainfall values (called “rain”), as well as four precipitation extrema (P₀, P₂₀, P₅₀, and P₁₀₀ representing the daily precipitation with the magnitude smaller than 0.1 mm, bigger than 20 mm, 50 mm, and 100 mm per day, respectively), in the Yangtze River Delta (YRD) during 1958–2007 were analyzed, and the urbanization impacts were further investigated. Results indicate that: (1) differing from the downward trends in 1958–1985, daily precipitation and rain in 1986–2007 show slowly downward trends in the mid YRD, but show upward trends in the northern and southern YRD; (2) spatial and temporal variability of the rain is more complex than daily precipitation. Both of them become smaller, but show more obvious fluctuations in 1986–2007; (3) urbanizations cause not only the urban rainfall island problem but also more obvious fluctuations of rain intensity in the mid YRD, reflecting more uncertainty of daily precipitation variability; (4) urbanizations have little impacts on the variability of P₀ and P₁₀₀ but cause notable increases of P₂₀ and P₅₀; and (5) the spatial variability of daily precipitation and precipitation extrema in 1958–1985 clearly shows a breakpoint at 30°20′N latitude, but the breakpoint disappears afterwards due to the urbanization impacts. Copyright © 2012 John Wiley & Sons, Ltd.

Mediterranean aquifers are frequently subject to the joint effect of intensive exploitation and low recharge values. Besides, groundwater is the only available water resource in many Mediterranean regions. Groundwater recharge studies are therefore necessary to underpin water management practices. This manuscript presents a methodology to estimate groundwater recharge in a small limestone aquifer of SE Spain. The HYDROBAL model is used to calculate daily soil water balances based on hydrological and soil data, as well as on vegetation cover. Deep drainage model outputs are converted into water table variations by means of a lumped model add-on. The adjustment between observed and calculated water-table levels is in the order of r² = 0.87. This correlation coefficient suggests that HYDROBAL is a useful tool to estimate groundwater recharge in the region. In addition, differences in groundwater recharge rates are observed for dry, average and wet years. Estimated recharge rates range between 0 and 18% of the mean annual rainfall, which corresponds to a net recharge of 0 to 59 mm year^-1. Recharge rates increase proportionally with precipitation (r² = 0.90). Copyright © 2012 John Wiley & Sons, Ltd.

Urban expansion and the scarcity of water supplies in arid and semi-arid regions have increased the importance of urban runoff to localized water resources. However, urban catchment responses to precipitation are poorly understood in semi-arid regions where intense rainfall often results in large runoff events during the short summer monsoon season. To evaluate how urban runoff quantity and quality respond to rainfall magnitude and timing, we collected stream stage data and runoff samples throughout the 2007 and 2008 summer monsoons from 4 ephemeral drainages in Tucson, Arizona. Antecedent rainfall explained 20 – 30% of discharge (mm) and runoff ratio in the least impervious (22%) catchment, but was not statistically related to hydrologic responses at more impervious sites. Regression models indicated that rainfall depth, imperviousness, and their combined effect control discharge and runoff ratios (p < 0.01, r² = 0.91 and 0.75, respectively). In contrast, runoff quality did not vary with imperviousness or catchment size. Rainfall depth and duration, time since antecedent rainfall, and event and cumulative discharge controlled runoff hydrochemistry and resulted in five specific solute response patterns: 1) strong event and seasonal solute mobilization (solute flush), 2) event chemostasis, strong seasonal flush, 3) event chemostasis, weak seasonal flush, 4) event and seasonal chemostasis and 5) late seasonal flush. Our results indicate that hydrologic responses of semi-arid catchments are controlled by rainfall partitioning at the event scale, while wetting magnitude, frequency and timing alter solute stores readily available for transport and control temporal runoff quality. Copyright © 2012 John Wiley & Sons, Ltd.

Vegetation has a major influence on the water and energy balance of the earth's surface. In the last century, human activities have modified land use, inducing a consequent change in albedo and potential evapotranspiration (PET). Linear vegetation structures (hedgerows, shelterbelts, open woodland, etc.) were particularly abundant, but have declined considerably over the past several decades. In this context, it is important to quantify their effect on water and energy balance both on a global scale (climate change and weather prediction) and on a local scale (soil column, hillslope, and watershed). The main objective of this study was to quantify the effect of hedgerows on the water cycle by evaluating spatial and temporal variations of water-balance components of a hillslope crossed by a hedgerow. Water-flow simulation was performed using Hydrus-2D to emphasize the importance of transpiration in the water balance and to evaluate water extraction from groundwater. Model validation was performed by comparing simulated and observed soil matric potentials and groundwater levels. Hedgerow transpiration was calculated from sap-flow measurements of four trees. Water-balance components calculated with a 1-D water-balance equation were compared to simulations. Simulation runs with and without tree-root uptake underlined the effect of hedgerow transpiration, increasing capillary rise and decreasing drainage. Results demonstrated that spatial and temporal variability of water-balance components was related to hedgerow presence as well as to the meteorological context. The relations between transpiration, groundwater proximity, and soil-water availability determined the way in which water-balance components were affected. Increased capillary rise and decreased drainage near hedges were related to the high transpiration of trees identified in this study. Transpiration reached twice the PET when groundwater level and precipitation amounts were high. Water-balance analysis showed that transpiration was a substantial component, representing 40% of total water output. These results may offer support for improving hydrological models by including the impact of land use and land cover on hydrological processes. Copyright © 2012 John Wiley & Sons, Ltd.

In a deciduous larch forest in eastern Siberia, the mean and standard deviation of the total evapotranspiration (E) during May–September (Day of Year (DOY) = 121–274) for 2003–2006 were 181.5 mm and 26.4 mm, respectively. The interannual variation (IAV) in the total E was caused by the IAV in E for the canopy-foliated period (DOY = 164–253), not by the IAV in the dates of leaf expansion and leaf fall. For the years with higher total E, E in the canopy-foliated period was consistently higher, which corresponded to the higher soil water content in these years. Copyright © 2012 John Wiley & Sons, Ltd.

Winter climatic conditions can influence the timing and magnitude of water and nitrate (NO₃-N) export from seasonally snow-covered catchments. Specifically, mid-winter rain-on-snow (ROS) events are a major source of NO₃-N export to forested streams, but the impact of these events on other nutrients is not known. Climate projections for Ontario suggest that climate warming will be most pronounced during the winter months, which could result in more mid-winter rain events and consequent changes in nutrient delivery to streams. The objective of this study was to examine the impact of winter climate variability on the timing of NO₃-N export relative to water and other nutrients at six head-water catchments in south-central Ontario that have long-term water quality and hydrology records (1980–2002). The catchments represent a wide range of physiographic characteristics and stream chemistry, yet the timing of nitrate export from all catchments was coherent. In warmer winters with more ROS events, the bulk of NO₃-N export relative to the export of water shifted earlier in the year from spring (i.e. the main period of snow melt) to winter. Rain-on-snow events did not cause similar temporal shifts in the export of other nutrients, including dissolved organic carbon (DOC), total phosphorus (TP) and calcium (Ca). Instead, their export was synchronous with the bulk of water export. Future shifts to earlier export of NO₃-N relative to water and other nutrients may impact aquatic productivity and cause more frequent episodic acidification of surface waters. Copyright © 2011 John Wiley & Sons, Ltd.

The deformation of the solid matrix affects the fluid pore pressure and flow by altering the pore volume. Such interaction in turn affects the storage of groundwater in the void space. Obviously, this subject is of interest in groundwater hydrology. This paper describes an investigation of the effect of aquifer heterogeneity on the variability of the fluid pressure head and solid's volume strain, where the assumption of a constant vertical total stress leads to a relatively simple relationship between changes in solid's volume strain and fluid pressure head. To solve the problem analytically, focus is placed on the one-dimensional models. It is found from our closed-form solutions that the variance and correlation length of the log hydraulic conductivity are important in increasing the variability of pressure head and solid's volume strain. It is hoped that our findings will provide a basic framework for understanding and quantifying field-scale volume strain processes and be useful in stimulating further research in this area. Copyright © 2011 John Wiley & Sons, Ltd.

The study published by García-Santos and Bruijnzeel (2011) (referred hereafter as GB2011) aims to characterize the water dynamics of a cloud forest in the Garajonay National Park (La Gomera) from measurements taken in a plot located in the upper part of a selected watershed within the Park. Reported magnitudes of hydrological variables and conclusions based on them are in disagreement with those of numerous studies carried out previously at the same site. Large data dispersion and inapplicability of some of the hypothesis assumed are shown to invalidate most of the results. Copyright © 2011 John Wiley & Sons, Ltd.

A key aspect of large river basins partially neglected in large-scale hydrological models is river hydrodynamics. Large-scale hydrologic models normally simulate river hydrodynamics using simplified models that do not represent aspects such as backwater effects and flood inundation, key factors for some of the largest rivers of the world, such as the Amazon. In a previous paper, we have described a large scale hydrodynamic approach resultant from an improvement of the MGB-IPH hydrological model. It uses full Saint Venant equations, a simple storage model for flood inundation and GIS based algorithms to extract model parameters from DEMs. In the present paper, we evaluate this model in the Solimões River basin. Discharge results were validated using 18 stream gauges showing that the model is accurate. It represents the large delay and attenuation of flood waves in the Solimões basin, while simplified models represented here by Muskingum Cunge provide hydrographs wrongly noisy and in advance. Validation against 35 stream gauges shows that the model is able to simulate observed water levels with accuracy, representing their amplitude of variation and timing. The model performs better in large rivers and errors concentrate in small rivers possibly due to uncertainty in river geometry. The validation of flood extent results using remote sensing estimates also shows that the model accuracy is comparable to other flood inundation modelling studies. Results show that (i) river-floodplain water exchange and storage, and (ii) backwater effects play an important role for the Amazon River basin hydrodynamics. Copyright © 2011 John Wiley & Sons, Ltd.

The use of data-driven modelling techniques to deliver improved suspended sediment rating curves has received considerable interest in recent years. Studies indicate an increased level of performance over traditional approaches when such techniques are adopted. However, closer scrutiny reveals that, unlike their traditional counterparts, data-driven solutions commonly include lagged sediment data as model inputs and this seriously limits their operational application. In this paper we argue the need for a greater degree of operational reasoning underpinning data-driven rating curve solutions and demonstrate how incorrect conclusions about the performance of a data-driven modelling technique can be reached when the model solution is based upon operationally-invalid input combinations. We exemplify the problem through the re-analysis and augmentation of a recent and typical published study which uses gene expression programming to model the rating curve. We compare and contrast the previously-published, solutions, whose inputs negate their operational application, with a range of newly developed and directly comparable traditional and data-driven solutions which do have operational value. Results clearly demonstrate that the performance benefits of the published gene expression programming solutions are dependent on the inclusion of operationally-limiting, lagged data inputs. Indeed, when operationally-inapplicable input combinations are discounted from the models, and the analysis is repeated, gene expression programming fails to perform as well as many simpler, more standard multiple linear regression, piecewise linear regression and neural network counterparts. The potential for overstatement of the benefits of the data-driven paradigm in rating curve studies is thus highlighted. Copyright © 2011 John Wiley & Sons, Ltd.

This study aims to investigate the changing properties of drought events in Weihe River basin, China, by modeling the multivariate joint distribution of drought duration, severity and peak using trivariate Gaussian and Student t copulas. Monthly precipitations of Xi'an gauge are used to illustrate the meta-elliptical copula-based methodology for a single-station application. Gaussian and Student t copulas are found to produce a better fit comparing with other six symmetrical and asymmetrical Archimedean copulas, and, checked by the goodness-of-fit tests based on a modified bootstrap version of Rosenblatt's transformation, both of them are acceptable to model the multivariate joint distribution of drought variables. Gaussian copula, the best-fitting, is employed to construct the dependence structures of positively associated drought variables so as to obtain the multivariate joint and conditional probabilities of droughts. A Kendall's return period (KDP) introduced by Salvadori and De Michele (2010) is then adopted to assess the multivariate recurrent properties of drought events, and its spatial distributions indicate that prolonged droughts are likely to break out with rather short recurrence intervals in the whole region while drought status in the southeast seems to be severer than the northwest. The study is of some merits in terms of multivariate drought modeling using a preferable copula-based method, the results of which could serve as a reference for regional drought defense and water resources management. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents the development of a probabilistic multi-model ensemble (PME) of statistically downscaled future projections of precipitation of a watershed in New Zealand. Climate change research based on the point estimates of a single model is considered less reliable for decision making and multiple realizations of a single model or outputs from multiple models are often preferred for such purposes. Similarly a probabilistic approach is preferable over deterministic point estimates. In the area of statistical downscaling, no single technique is considered a universal solution. This is due to the fact that each of these techniques has some weaknesses, owing to its basic working principles. Moreover, watershed scale precipitation downscaling is quite challenging and is more prone to uncertainty issues than downscaling of other climatological variables. So multi-model statistical downscaling studies based on a probabilistic approach are required. In the current paper, results from the three well reputed statistical downscaling methods are used to develop a Bayesian weighted multi-model ensemble. The three members of the downscaling ensemble of this study belong to the following three broad categories of statistical downscaling methods ;(1) multiple linear regression; (2) multiple non-linear regression; and (3) stochastic weather generator. The results obtained in this study show that the new strategy adopted here is promising because of many advantages it offers e.g. it combines the outputs of multiple statistical downscaling methods, provides probabilistic downscaled climate change projections and enables the quantification of uncertainty in these projections. This will encourage any future attempts for combining the results of multiple statistical downscaling methods. Copyright © 2011 John Wiley & Sons, Ltd.

Better parameterization of hydrological model can lead to improved streamflow prediction. This is particularly important for seasonal streamflow forecasting using hydrological modeling. Considering the possible effects of hydrologic non-stationarity, this paper examined 10 parameterization schemes at twelve catchments, located in three different climatic zones in east Australia. These schemes are grouped into four categories based on the period where the data are used for model calibration, i.e., calibration using: 1) data from a fixed period in the historical records, 2) different lengths of historical records prior to prediction year, 3) data from different climatic analogue years in the past, 4) data from individual month. Parameterization schemes were evaluated according to model efficiency in both calibration and verification period. The results show that the calibration skill changes with different historic periods where data are used at all catchments. Comparison of model performance between calibration schemes indicates that it is worth calibrating the model using data from each individual month for purpose of seasonal streamflow forecasting. For the catchments in winter-dominant rainfall region of southeast Australia, more significant shift in rainfall-runoff relationships in different periods was found. For those catchments, model calibration using 20 years of data prior to the prediction year leads to more consistent performance. Copyright © 2011 John Wiley & Sons, Ltd.

Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are a widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages, and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well-developed biological soil crusts than in physical or poorly-developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared to the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils. Copyright © 2011 John Wiley & Sons, Ltd.

A nonlinear function approach for the normalized complementary relationship evaporation model that is different from the methodology maintaining the symmetric complementary relationship with appropriate definitions of potential and wet environment evaporation is proposed and verified. This approach employs the definitions used in the advection-aridity model, wherein the potential is estimated using the Penman equation. Normalized by Penman potential evaporation, the complementary relationship model is expressed as a function describing the relationship between the evaporation ratio (the ratio of the actual to the Penman potential evaporation) and the proportion of the radiation term in Penman potential evaporation. The new nonlinear function proposed in the current study is approximately equivalent to the advection-aridity and the modified Granger models under conditions that are neither too wet nor too dry, but is more reasonable under arid and wet conditions. The new nonlinear function model performs well in estimating actual evaporation, as verified by the observed data from four sites under different land covers. Copyright © 2011 John Wiley & Sons, Ltd.

The rise in stream stage during high flow events (floods) can induce losing stream conditions even along stream reaches that are gaining during baseflow conditions. The aquifer response to flood events can impact the geochemical composition of both near-stream groundwater and post-event streamflow, but the amount and persistence of recharged floodwater may differ as a function of local hydrogeologic forcings. As a result, this study focuses on how vertical flood recharge varies under different hydrogeologic forcings and the significance that recharge processes can have on groundwater and streamflow composition after floods.

River and shallow groundwater samples were collected along three reaches of the Upper San Pedro River (Arizona, USA) before, during and after the 2009 and 2010 summer monsoon seasons. Tracer data from these samples indicates that subsurface floodwater propagation and residence times are strongly controlled by the direction and magnitude of the dominant stream-aquifer gradient. A reach that is typically strongly gaining shows minimal floodwater retention shortly after large events, whereas the moderately gaining and losing reaches can retain recharged floodwater from smaller events for longer time periods. The moderately gaining reach likely returned flood recharge to the river as flow declined. These results indicate that reach-scale differences in hydrogeologic forcing can control (1) the amount of local flood recharge during events, and (2) the duration of it's subsurface retention and possible return to the stream during low-flow periods. Our observations also suggest that the presence of floodwater in year-round baseflow is not due to long-term storage beneath the streambed along predominantly gaining reaches, so three alternate mechanisms are suggested: (1) repeated flooding that drives lateral redistribution of previously recharged floodwater, (2) vertical recharge on the floodplain during overbank flow events, and (3) temporal variability in the stream-aquifer gradient due to seasonally varying water demands of riparian vegetation. Copyright © 2011 John Wiley & Sons, Ltd.

The goal of the presented research is the derivation of flood hazard maps, using Monte Carlo simulation of flood propagation at an urban site in the UK, specifically an urban area of the city of Glasgow. A hydrodynamic model describing the propagation of flood waves, based on the De Saint Venant equations in two dimensional form capable of accounting for the topographic complexity of the area (preferential outflow paths, buildings, manholes, etc.) and for the characteristics of prevailing imperviousness typical of the urban areas has been used to derive the hydrodynamic characteristics of flood events (i.e, water depths and flow velocities). The knowledge of the water depth distribution and of the current velocities derived from the propagation model along with the knowledge of the topographic characteristics of the urban area from digital map data allowed for the production of hazard maps based on properly defined hazard indexes. These indexes are evaluated in a probabilistic framework to overcome the classical problem of single deterministic prediction of flood extent for the design event and to introduce the concept of the likelihood of flooding at a given point as the sum of data uncertainty, model structural error and parameterization uncertainty. Copyright © 2011 John Wiley & Sons, Ltd.

In this study, the characteristic of multiple Glacial Lake Outburst Floods (GLOFs) in the Pho Chu River basin in Bhutanese Himalayas is evaluated to help assess the potential impact. Thorthormi Cho (TC) and Lugge Cho (LC) in the east branch and two unnamed lakes labeled A and B in the west branch of Pho Chu are chosen for the study. Numerical models were employed to simulate different involved processes. The results show that the peak sediment discharge in the east branch of the Pho Chu River by the TC dam breach reached about 5000 m³/s (during the first GLOF) at 4 km while by the LC dam breach is about 600 m³/s (second GLOF) at 6 km. However, the highest peak hydrographs (sediment and water mixture) calculated during first and second GLOF are about 10000 m³/s at the 18 km section and about 23000 m³/s at the 10 km section respectively. In the west branch of Pho Chu, erosion and depositions are the frequent intermittent local processes during the first GLOF event from Lake A. Since the first event stabilized the irregular river bed profile, there is not much sediment discharge developed during the second GLOF from Lake B. At the 17 km section of the west branch, the peak hydrograph reached about 9000 m³/s during the first event against the peak of about 800 m³/s during the second event. The results suggest that even if multiple dam breaches occur simultaneously, GLOF surges pass through the main river channel at different time with very different flood characteristics. The differences in travel time and flood characteristics mostly depend on the distributions of bed-slope and potential erosion depth along the reach. Further, the amount of sediment accumulated in and transported by each surge is reliant on the temporal geomorphologic setting of the river and therefore the impact of the previous GLOF on riverbed profile and potential erosion depth. The robustness in peak GLOF hydrographs is associated with sediment flow dynamics. As a consequence, serious inundation of Punakha, Lobeysa and the major portion of Wangdue Phodrang is anticipated. Copyright © 2011 John Wiley & Sons, Ltd.

Due to its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consists of long-term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use Zhang et al.’s iterative pre-whitening method, which aims to separate positive autocorrelation from trend present in time series.

Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during NDJ. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post-1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly due to increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared to nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2011 John Wiley & Sons, Ltd.

Heavy rainfall events during the fall season are causing extended damages in Mediterranean catchments. A peaks-over-threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in fall over six catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux (FHUM) from the Mediterranean Sea. Reanalysis data are used to compute the daily FHUM during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, whereas daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are considered to compute FHUM in future climate with the emission scenario A1B and hence to evaluate the effect of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties in climate projections. By comparison to the reference period 1960–1990, all models project an amplification of the mean seasonal FHUM from the Mediterranean Sea for the projection period 2070–2099, on average by +22%. This increase in FHUM leads to an increase in the number of heavy rainfall events, from an average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited effects on the magnitude of extreme events, with only a 5% increase in the median of the 100-year quantiles. Copyright © 2011 John Wiley & Sons, Ltd.

This study examines the variability of in-pool temperatures in Imnavait Creek, a beaded arctic stream consisting of small pools connected by shallow chutes, for the purpose of predicting potential impacts of climate variations on the system. To better understand heat fate and transport through this system, the dominant heat sources and sinks creating and influencing thermal stratification within even the smallest and shallowest pools must be quantified. To do this, temperature data were collected vertically within the pool water column and surrounding bed sediments during stratified conditions. These temperature and other supporting data (e.g. instream flow, weather data, and bathymetry) were used to formulate and develop an instream temperature model that captures the site-specific processes occurring within the pools during summer low flow conditions. The model includes advective, air–water interface, and bed conduction fluxes, simplified vertical exchange between stratified pool layers, and attenuation of shortwave radiation within the water column. We present the model formulation, data collection methods used in support of model development and population, and the resulting model calibration and validation for one of the study pools. We also provide information regarding dominant heat sources and sinks and residence times of different layers within the stratified pool. We found that the dominant heat sources vary between stratified layers and that increases in thaw depths surrounding these pools due to possible climate changes can shift stratification, mixing, and instream storage dynamics, thereby influencing the fate and transport of heat and other constituents of interest (e.g. nutrients). Copyright © 2011 John Wiley & Sons, Ltd.

The Gurbantonggut Desert, China, is an ideal site for study of sublimation from the snowpack because there are sparse vegetation and simple topography, and the wind speed is not large enough to blow snow into the atmosphere from the snowpack. Daily sublimation was measured by manual snow lysimeters at 8:00, and an automatic weather station was deployed at the top of a stout longitudinal dune chain at the southeastern edge of the desert. It is shown that on a daily scale, there was an extremely significant no-intercept linear relationship between the measured sublimation and that calculated by the bulk aerodynamic method, although the former was only 83.8% of the latter. It is also demonstrated that −10°C and 2 m/s were the thresholds where the sublimation varied with the air temperature and the wind speed. When these two thresholds were exceeded, the sublimation accelerated. However, the air temperature and the wind speed at 2 m above the ground averaged −17.2°C and 1.3 m/s, respectively, and the percentages of the time when the air temperature was below −10 °C and the wind speed was below 2 m/s were 76.9% and 85.1%, respectively. As a result, the rate of sublimation was quite low most of the time, and the thin snowpack remained in a quasi-static state until the melt stage started. Copyright © 2011 John Wiley & Sons, Ltd.

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km²) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub-páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C-horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.

Coastal rivers represent a significant pathway for the delivery of natural and anthropogenic sediment-associated chemical constituents to the Atlantic, Pacific and Gulf of Mexico coasts of the conterminous USA. This study entails an accounting segment using published average annual suspended sediment fluxes with published sediment-associated chemical constituent concentrations for (1) baseline, (2) land-use distributions, (3) population density, and (4) worldwide means to estimate concentrations/annual fluxes for trace/major elements and total phosphorus, total organic and inorganic carbon, total nitrogen, and sulphur, for 131 coastal river basins. In addition, it entails a sampling and subsequent chemical analysis segment that provides a level of ‘ground truth’ for the calculated values, as well as generating baselines for sediment-associated concentrations/fluxes against which future changes can be evaluated.

Currently, between 260 and 270 Mt of suspended sediment are discharged annually from the conterminous USA; about 69% is discharged from Gulf rivers (n = 36), about 24% from Pacific rivers (n = 42), and about 7% from Atlantic rivers (n = 54). Elevated sediment-associated chemical concentrations relative to baseline levels occur in the reverse order of sediment discharges: Atlantic rivers (49%) > Pacific rivers (40%) > Gulf rivers (23%). Elevated trace element concentrations (e.g. Cu, Hg, Pb, Zn) frequently occur in association with present/former industrial areas and/or urban centres, particularly along the northeast Atlantic coast. Elevated carbon and nutrient concentrations occur along both the Atlantic and Gulf coasts but are dominated by rivers in the urban northeast and by southeastern and Gulf coast (Florida) ‘blackwater’ streams. Elevated Ca, Mg, K, and Na distributions tend to reflect local petrology, whereas elevated Ti, S, Fe, and Al concentrations are ubiquitous, possibly because they have substantial natural as well as anthropogenic sources. Almost all the elevated sediment-associated chemical concentrations found in conterminous US coastal rivers are lower than worldwide averages. Copyright © 2011 John Wiley & Sons, Ltd.

Although the identification of the moisture sources of a region is of prominent importance to characterize precipitation, the origin and amount of moisture towards the Indian Subcontinent and its relationship with the occurrence of precipitation are still not completely understood.

In this article, the origin of the atmospheric water arriving to the Western and Southern India during a period of 5 years (1 January 2000–31 December 2004) is investigated by using a Lagrangian diagnosis method. This methodology computes budgets of evaporation minus precipitation by calculating changes in the specific humidity of thousands of air particles aimed to the study area following the observed winds. During the summer monsoon, the main supply of moisture is the Somali Jet, which crosses the equator by the West Indian Ocean. The recycling process is the main water vapour source in winter. Two additional moisture sources located over northwestern India and the Bay of Bengal are identified.

A 30% increase in the moisture flux from the Indian Ocean has been related to the occurrence of strong precipitation in the area, and at the end of the monsoon, the recycling became a significant contribution to the last part of the wet season of Western and Southern India. Copyright © 2012 John Wiley & Sons, Ltd.

Short-term Quantitative Precipitation Forecasts (QPFs) can be achieved from numerical weather prediction (NWP) models or radar nowcasting, that is the extrapolation of the precipitation at a future time from consecutive radar scans. Hybrid forecasts obtained by merging rainfall forecasts from radar nowcasting and NWP models are potentially more skilful than either radar nowcasts or NWP rainfall forecasts alone. This paper provides an assessment of deterministic and probabilistic high-resolution QPFs achieved by implementing the Short-term Ensemble Prediction System developed by the UK Met Office. Both radar nowcasts and hybrid forecasts have been performed. The results show that the performance of both deterministic nowcasts and deterministic hybrid forecasts decreases with increasing rainfall intensity and spatial resolution. The results also show that the blending with the NWP forecasts improves the performance of the forecasting system. Probabilistic hybrid forecasts have been obtained through the modelling of a stochastic noise component to produce a number of equally likely ensemble members, and the comparative assessment of deterministic and probabilistic hybrid forecasts shows that the probabilistic forecasting system is characterised by a higher discrimination accuracy than the deterministic one. Copyright © 2011 John Wiley & Sons, Ltd.

Dominant flow pathways (DFPs) in mesoscale watersheds are poorly characterized and understood. Here, we make use of a conservative tracer (Gran alkalinity) and detailed information about climatic conditions and physical properties to examine how temporally and spatially variable factors interact to determine DFPs in 12 catchments draining areas from 3.4 to 1829.5 km² (Cairngorms, Scotland). After end-member mixing was applied to discriminate between near surface and deep groundwater flow pathways, variation partitioning, canonical redundancy analyses and regression models were used to resolve: (i) What is the temporal variability of DFPs in each catchment?; (ii) How do DFPs change across spatial scales and what factors control the differences in hydrological responses?; and (iii) Can a conceptual model be developed to explain the spatiotemporal variability of DFPs as a function of climatic, topographic and soil characteristics? Overall, catchment characteristics were only useful to explain the temporal variability of DFPs but not their spatial variation across scale. The temporal variability of DFPs was influenced most by prevailing hydroclimatic conditions and secondarily soil drainability. The predictability of active DFPs was better in catchments with soils supporting fast runoff generation on the basis of factors such as the cumulative precipitation from the seven previous days, mean daily air temperature and the fractional area covered by Rankers. The best regression model R² was 0.54, thus suggesting that the catchments’ internal complexity was not fully captured by the factors included in the analysis. Nevertheless, this study highlights the utility of combining tracer studies with digital landscape analysis and multivariate statistical techniques to gain insights into the temporal (climatic) and spatial (topographic and pedologic) controls on DFPs. Copyright © 2011 John Wiley & Sons, Ltd.

Seasonal streamflow forecasts based on climate information can guide water managers toward superior reservoir operations, leading to improved water resources management efficiency. Uncertainty, however, is always present in seasonal streamflow forecasts, affecting the forecast value. Thus, a forecast should not be considered complete without a description of its uncertainty, which is critical for climate risk and water resources management. This study investigates the uncertainties of a seasonal streamflow forecast system for Northeastern Brazil based on climate precipitation forecasts and hydrologic modeling. These two sources of uncertainty are treated independently and then compared in order to guide future investments in the forecast system. Sea surface temperature is considered to be the primary source of uncertainty for the seasonal precipitation forecasts, based upon a 10-member climate model ensemble. Parameter uncertainty is considered to be the only source of uncertainty for the hydrologic model. Estimation of parameter uncertainty is estimated by the Shuffled Complex Evolution Metropolis algorithm, which employs a Markov Chain Monte Carlo scheme to provide the posterior distribution of the parameters and form uncertainty bounds on streamflow forecasts. Results indicate that uncertainties associated with the climate forecast are much larger than those from parameter estimation in the hydrologic model. Although model structure has not been considered in the evaluation of hydrologic uncertainties, this study indicates that future efforts to address the predominant source of uncertainty should focus on the climate prediction models. Copyright © 2011 John Wiley & Sons, Ltd.

This article explores the relations between network properties and the effect from moving rainstorms in terms of the peak response and time to centroid of hydrographs. A simple conceptual rectangular catchment is introduced with different configurations of drainage network simulated by the Gibbs stochastic model. The efficiency of the urban pipe networks varies widely compared with natural river networks; hence, the Gibbs model can be an appropriate approach to represent the network properties in urban drainage system. Simple cases of rainstorms moving with upstream and downstream directions and different speeds are considered to investigate the effect of rainstorm movement on urban drainage network runoff hydrographs. The results indicate that the effect of the direction and speed of the rainstorm movement varies significantly depending on the network properties. The relationship between storm speed and direction and the change in the peak runoff is dependent on the network configuration and network efficiency. In contrast to previous studies, this study indicates that the speed and direction of the rainfall movement that produces the maximum peak discharge changes depending on the network configuration. Copyright © 2011 John Wiley & Sons, Ltd.

This study focuses on the prediction of event-based runoff coefficients (an important descriptor of flood events) for nested catchments up to an area of 50 km² in the Eastern Ore Mountains. The four main objectives of the study are (i) the prediction of runoff coefficients with the statistical method of generalized linear models, (ii) the comparison of the results of the linear models with estimates of a distributed conceptual model, (iii) the comparison of the dynamics of observed soil moisture and simulated saturation deficit of the hydrological model and (iv) the analysis of the relationship between runoff coefficient and observed and simulated wetness.

Different predictor variables were selected to describe the runoff coefficient and were differentiated into variables describing the catchment's antecedent wetness and meteorological forcing. The best statistical model was estimated in a stepwise approach on the basis of hierarchical partitioning, an exhaustive search algorithm and model validation with jackknifing. We then applied the rainfall runoff model WaSiM ETH to predict the runoff processes for the two larger catchments. Locally measured small-scale soil moisture (acquired at a scale of four to five magnitudes smaller than the catchment) was identified as one of the key predictor variables for the estimation of the runoff coefficient with the general linear model. It was found that the relationship betweenobserved and simulated (using WaSiM ETH) wetness is strongly hysteretic. The runoff coefficients derived from the rainfall runoff simulations systematically underestimate the observed values. Copyright © 2012 John Wiley & Sons, Ltd.

Water content and movement in soil profile and hydrogen isotope composition (δD) of soil water, rainwater, and groundwater were examined in a subalpine dark coniferous forest in the Wolong National Nature Reserve in Sichuan, China, following rainfall events in 2003–2004. Light rainfall increased water content in the litter and at soil depth of 0–80 cm, but the increased soil water was lost in several days. Heavy rainfall increased soil water content up to 85% at depths of 0–40 cm. Following the light rainfall in early spring, the δD of water from the litter, humus, illuvial, and material layers decreased first and then gradually reached the pre-rainfall level. In summer, light rainfall reached the litter humus, and illuvial layer, but did not hit the material layer. Heavy rainfall affected δD of water in all layers. The δD of soil interflow slightly fluctuated with rainfall events. The δD of shallow groundwater did not differ significantly among all rainfall events. Light rainfall altered the shape of δD profile curve of water in the upper layer of soil, whereas heavy rainfall greatly affected the shape of δD profile curve of water in all soil layers. Following the heavy rainfall, preferential flow initially occurred through macropores, decayed plant roots, and rocks at different depths of soil profile. With continuing rainfall, the litter and surface soil were nearly saturated or fully saturated, and infiltration became homogeneous and plug-like. Forest soil water, particularly in deeper soil profile, was slightly affected by rainfall and, thus, can be a source of water supply for regional needs, particularly during dry seasons. Copyright © 2011 John Wiley & Sons, Ltd.

Sublimation is a critical component of the snow cover mass balance. Although sublimation can be directly measured using eddy covariance (EC), such measurements are relatively uncommon in complex mountainous environments. The EC measurements of surface snowpack sublimation from three consecutive winter seasons (2004, 2005 and 2006) at a wind-exposed and wind-sheltered site were analysed to characterise sublimation in mountainous terrain. During the 2006 snow season, snow surface and near-surface air temperature, humidity and wind were also measured, permitting the calculation of sublimation rates and a comparison with EC measurements. This comparison showed that measured and simulated sublimation was very similar at the exposed site but less so at the sheltered site. Wind speeds at the exposed site were nearly four times than that at the sheltered site, and the exposed site yielded measured sublimation that was two times the magnitude of that at the sheltered site. The time variation of measured sublimation showed diurnal increases in the early afternoon and increased rates overall as the snow season progressed. Measured mean daily sublimation rates were 0.39 and 0.15 mm day⁻¹ at the exposed and sheltered sites, respectively. At the exposed site, measured sublimation accounted for 16% and 41% of the maximum snow accumulation in 2006 and 2005, respectively. At the sheltered site, measured seasonal sublimation was approximately 4% in 2004 and 2006 and 8% in 2005 of the maximum snow water equivalent. Simulated sublimation was only available for 2006 and suggested smaller but comparable percentages to the sublimation estimated from observations. At the exposed site, a total of 42 mm sublimated for the snow season, which constituted 12% of the maximum accumulation. At the sheltered site, 17 mm (2.2% of maximum accumulation) was sublimated over the snow season. Copyright © 2011 John Wiley & Sons, Ltd.

The governing equations of coupled density-driven flow and solute transport problems in porous media, with velocity-dependent dispersion coefficient, are strongly nonlinear and must be solved numerically. This contribution presents a network model, based on the network simulation method, capable of simulating the transient solution to this kind of problem efficiently and with a relatively low computational time. The mathematical model is formulated using the stream function and concentration variables. Simulation of the network model is carried out in the standard electric circuit simulation code, Pspice. The present model is first applied to simulate the original benchmark Henry problem, and the solution is compared with those obtained by other authors. A study of the grid size is also carried out. In addition, the modified version of Simpson and Clement of the Henry problem, as well as the groundwater flow in the closed desert basin of Pilot Valley, is studied using the proposed model. Copyright © 2011 John Wiley & Sons, Ltd.

Estimation of snow cover characteristics (snow grain size, snow contamination, snow depth and liquid water content) from satellite data are important components for many hydrological models used for the water resource management. This research aimed to use Landsat ETM+ (Enhanced Thematic Mapper Plus) data to estimate the snow pack characteristics in northern Pakistan. The Normalized Difference Snow Index (NDSI), Snow Contamination Index (SCI) and Snow Grain Size Index (SGI) are applied to estimate the snow cover characteristics in northern Pakistan for the first time. Qualitative maps are generated to show the snow cover distribution, snow contamination concentration and snow grain size distribution over snow cover area. Our results show that NDSI, SCI and SGI can be effectively used to identify snow area, contaminated snow and ageing snow. Furthermore, the results of the current study indicate that in the HKH region 99.8% of the snow is least contaminated whereas 94.50% of the area has fine snow grain size. As no such attempt in the past has been made in northern Pakistan, it is envisaged that the results of this study will be helpful in planning remote sensing data for the water resource management and in characterizing the snow cover for the climate change applications in the region. Copyright © 2011 John Wiley & Sons, Ltd.

Artificially enhancing recharge rate into groundwater aquifer at specially designed facilities is an attractive option for increasing the storage capacity of potable water in arid and semi-arid region such as Damascus basin (Syria). Two dug wells (I and II) for water injection and 24 wells for water extraction are available in Mazraha station for artificial recharge experiment. Chemical and stable isotopes (δ²H and δ¹⁸O) were used to evaluate artificial recharge efficiency. 400 to 500*10³ m³ of spring water were injected annually into the ambient shallow groundwater in Mazraha station, which is used later for drinking purpose. Ambient groundwater and injected spring water are calcium bicarbonate type with EC about 880 ± 60 μS/cm and 300 ± 50 μS/cm, respectively. The injected water is under saturated versus calcite and the ambient groundwater is over saturated, while the recovered water is near equilibrium. It was observed that the injection process formed a chemical dilution plume that improves the groundwater quality. Results demonstrate that the hydraulic conductivity of the aquifer is estimated around 6.8*10⁻⁴ m/s. The effective diameter of artificial recharge is limited to about 250 m from the injection wells. Mixing rate of 30% is required in order to reduce nitrate concentration below 50 mg/l which is considered the maximum concentration limit for potable water. Deuterium and oxygen-18 relationship demonstrates that mixing line between injected water and ambient groundwater has a slope of 6.1. Oxygen-18 and Cl⁻ plot indicates that groundwater salinity origin is from mixing process, and no dissolution and evaporation were observed. These results demonstrate the efficiency of the artificial recharge experiments to restore groundwater storage capacity and to improve the water quality. Copyright © 2011 John Wiley & Sons, Ltd.

The performance of temperature-index melt models is particularly affected by the choice of near-surface lapse rate used to determine the sum of positive daily temperatures at different elevations, and by the choice of factor used to relate this sum to the rate of melting. Data from the Langjökull ice cap are used in this study to quantify the influence of lapse-rate and degree-day factor variation on temperature-index melt simulations. The lapse rate was significantly lower during summer than in spring or autumn, as a result of diabatic cooling, reducing boundary-layer sensitivity to free-air temperature change. The summer lapse rate was also significantly lower than the saturated adiabatic lapse rate. A sensitivity of approximately 600 mm water equivalent (w.e.) cumulative June–August melt per 0.1 °C 100 m^–1 change in lapse rate was found across a 500-m altitude range. The sensitivity to a 1-mm w.e. °C^–1 day^–1 change in degree-day factors varied more: from approximately 500 mm w.e. cumulative summer melt at low elevation to approximately 200 mm w.e. at high elevation, reflecting the decline in melt rates associated with the greater persistence of snow with increasing altitude. The determination of a degree-day factor for snow is complicated by the densification of the ageing snowpack, but the application of a parameterization for near-surface density on the basis of albedo helped account for the development of snow water equivalence. Lapse rate was parameterized as a function of standardized anomalies in 750 hPa reanalysis temperature and significantly improved the simulation of cumulative summer melt compared with models applying the saturated adiabatic lapse rate. Copyright © 2012 John Wiley & Sons, Ltd.

Digital elevation models of the surface and bed of Midtdalsbreen, Norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden. A distributed degree-day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer, which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions. In addition, 78 dye-tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons. Comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady-state water pressures beneath the glacier are ~70% of ice overburden. Analysis of the dye return curves, together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad, low channels (average width/height ratio ≈ 75). The smaller drainage network on the west consists of a hydraulically inefficient distributed system, dominated by channels that are exceptionally broad and very low (average width/height ratio ≈ 350). The even smaller central drainage network also consists of a hydraulically inefficient distributed system, dominated by channels that are very broad and exceptionally low (average width/height ratio ≈ 450). The channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system. Copyright © 2011 John Wiley & Sons, Ltd.

Recognizing the spatial heterogeneity of hydraulic parameters, many researchers have studied the solute transport by both groundwater and channel flow in a stochastic framework. One of the methodologies used to up-scale the stochastic solute transport equation, from a point-location scale to a grid scale, is the cumulant expansion method combined with the calculus for the time-ordered exponential and the calculus for the Lie operator. When the point-location scale transport equation is scaled up to the grid scale, using the cumulant expansion method, a new dispersion coefficient emerges in the dispersive term of the solute transport equation in addition to the molecular dispersion coefficient. This velocity driven dispersion is called ‘macrodispersion’. The macrodispersion coefficient is the integral function of the time-ordered covariance of the random velocity field. The integral is calculated over a Lagrangian trajectory of the flow. The Lagrangian trajectory depends on the following: (i) the spatial origin of the particle; (ii) the time when the macrodispersion is calculated; and (iii) the mean velocity field along the trajectory itself. The Lagrangian trajectory is a recursive function of time because the location of the particle along the trajectory at a particular time depends on the location of the particle at the previous time. This recursive functional form of the Lagrangian trajectory makes the calculation of the macrodispersion coefficient difficult. Especially for the unsteady, spatially non-stationary, non-uniform flow field, the macrodispersion coefficient is a highly complex expression and, so far, calculated using numerical methods in the discrete domains. Here, an analytical method was introduced to calculate the macrodispersion coefficient in the discrete domain for the unsteady and steady, spatially non-stationary flow cases accurately and efficiently. This study can fill the gap between the theory of the ensemble averaged solute transport model and its numerical implementations. Copyright © 2011 John Wiley & Sons, Ltd.

Generally, the statistical downscaling approaches work less perfectly in reproducing precipitation than temperatures, particularly for the extreme precipitation. This article aimed to testify the capability in downscaling the extreme temperature, evaporation, and precipitation in South China using the statistical downscaling method. Meanwhile, the linkages between the underlying driving forces and the incompetent skills in downscaling precipitation extremes over South China need to be extensively addressed. Toward this end, a statistical downscaling model (SDSM) was built up to construct future scenarios of extreme daily temperature, pan evaporation, and precipitation. The model was thereafter applied to project climate extremes in the Dongjiang River basin in the 21st century from the HadCM3 (Hadley Centre Coupled Model version 3) model under A2 and B2 emission scenarios. The results showed that: (1) The SDSM generally performed fairly well in reproducing the extreme temperature. For the extreme precipitation, the performance of the model was less satisfactory than temperature and evaporation. (2) Both A2 and B2 scenarios projected increases in temperature extremes in all seasons; however, the projections of change in precipitation and evaporation extremes were not consistent with temperature extremes. (3) Skills of SDSM to reproduce the extreme precipitation were very limited. This was partly due to the high randomicity and nonlinearity dominated in extreme precipitation process over the Dongjiang River basin. In pre-flood seasons (April to June), the mixing of the dry and cold air originated from northern China and the moist warm air releases excessive rainstorms to this basin, while in post-flood seasons (July to October), the intensive rainstorms are triggered by the tropical system dominated in South China. These unique characteristics collectively account for the incompetent skills of SDSM in reproducing precipitation extremes in South China. Copyright © 2011 John Wiley & Sons, Ltd.

The southern coastal plain of Laizhou Bay, which is the area most seriously affected by salt water intrusion in north China, is a large alluvial depression, which represents one of the most important hydrogeological units in the coastal region of northern China. Chlorofluorocarbons (CFCs, including CFC-11, CFC-12 and CFC-113) and tritium were used together for dating groundwater up to 50 years old in the study area. There are two cones of depression, caused by intensive over-exploitation of fresh groundwater in the south and brine water in the north. The assigned CFC apparent ages for shallow groundwater range from 8 a to >50 a. A binary mixing model based on CFC-113 and CFC-12 concentrations in groundwater was used to estimate fractions of young and pre-modern water in shallow aquifers and to identify groundwater mixing processes during saltwater intrusion. Discordance between concentrations of different CFC compounds indicate that shallow groundwater around the Changyi cone of depression is vulnerable to contamination. Pumping activities, CFC contamination, mixing and/or a large unsaturated zone thickness (e.g. >20 m) may be reasons for some groundwater containing CFCs without tritium. Saline intrusion mainly occurs because of large head gradients between fresh groundwater in the south and saline water bodies in the north, forming a wedge of saline water below/within fresh aquifer layers. Both CFC and tritium dates indicate that the majority of the saline water is from >50 a, with little or no modern seawater component. Based on the distribution of CFC apparent ages, tritium contents plus chemical and physical data, a conceptual model of groundwater flow along the investigated Changyi-Xiaying transect has been developed to describe the hydrogeological processes. Three regimes are identified from south to north: (i) fresh groundwater zone, with a mixing fraction of 0.80–0.65 ‘young’ water calculated with the CFC binary mixing model (groundwater ages <34 a) and 1.9–7.8TU of tritium; (ii) mixing zone characterized by a mixing fraction of 0.05–0.65 young groundwater (ages of 23–44 a), accompanied by local vertical recharge and upward leakage of older groundwater; and (iii) salt water zone, mostly comprising waters with ages beyond the dating range of both CFCs and tritium. Some shallow groundwater in the north of the Changyi groundwater depression belongs to the >50a water group (iii), indicating slow velocity of groundwater circulation and possible drawing in of saline or deep groundwater that is tracer-free. Copyright © 2012 John Wiley & Sons, Ltd.

The suitability of the physically based model SHETRAN for simulating sediment generation and delivery with a high degree of spatial (20 m) and temporal (sub-hourly) resolution was assessed through application of the model to a 167-km² catchment leading to an estuary in New Zealand. By subdividing the catchment and conducting calculations on a computer cluster for a 6-month hydrology initialisation period, it was possible to simulate a large rainfall event and its antecedent conditions in 24 h of computation time. The model was calibrated satisfactorily to catchment outlet flow and sediment flux for a large rainfall event in two subcatchments (~2 km²). Validation for a separate subcatchment was successful for flow (Nash–Sutcliff efficiency of 0.84) with a factor 2.1 over-prediction for sediment load. Validation for sediment at full catchment scale using parameters from the subcatchment scale was good for flow but poor for sediment, with gross under-estimation of the dominant stream sources of sediment. After recalibration at catchment scale, validation for a separate event gave good results for flow (Nash–Sutcliff efficiency of 0.93) and sediment load within a factor of two of measurements. An exploratory spatially explicit landslide model was added to SHETRAN, but it was not possible to test this fully because no landslides were observed in the study period. Application to climate change highlighted the non-linear response to extreme rainfall. However, full exploration of land use and climate change and the evaluation of uncertainty were severely constrained by computational limitations. Subdivision of the catchment with separate stream routing is suggested as a way forward to overcome these limitations. Copyright © 2011 John Wiley & Sons, Ltd.

There are various factors governing the spatial and temporal variability of soil water storage including soil properties, topography and vegetation. Some factors act locally, whereas others act nonlocally, which means that a factor measured at one location has effect on soil water storage at another location. The objective of this study was to examine the effects of local and nonlocal controls of soil water storage in a hummocky landscape using cyclical correlation analysis. Soil water storage, soil properties and terrain indices were measured along a 128-point transect of 576 m long from the semiarid, hummocky, prairie pothole region of North America. There are large coefficients of determination (r²) between soil water storage and sand content (r² = 0.32–0.53), organic carbon content (r² = 0.22–0.56), depth to carbonate layer (r² = 0.13–0.63), wetness index (r² = 0.25–0.45) and other variables at the measurement scale at different times, indicating strong local effects from these variables. The correlation coefficients were also calculated by physically shifting the spatial series of soil water storage with respect to that of controlling factors. The shifting improves the correlation between the spatial series, and the length of shifting indicated the difference in the response of soil water to its controlling factors. For example, the value of r² increased more than eightfold (r² = 0.47–0.64) after shifting the spatial series of soil water storage by 54 m, almost equal to the average length of existing slope, compared with the very weak correlation (r² = 0.02–0.08) at the measurement scale. This indicated the nonlocal effect from the relative elevation. The identification of nonlocal effects from factors improves the prediction of soil water storage. Copyright © 2011 John Wiley & Sons, Ltd.

Processes of soil erosion and sediment transport are strongly influenced by land use changes so the modelling of land use changes is important with respect to the simulation of soil degradation and its on-site and off-site consequences. The reliability of simulation results from erosion models is circumscribed by considerable spatial variation in many parameters. However, most of the currently widely used erosion models at the mesoscale are semidistributed, which leads to difficulties in incorporating a high degree of spatial information, especially land use information, so that the effects of land use changes on soil erosion have hitherto not been investigated in detail using these models. In this article, a grid-based distributed erosion and sediment transport model is introduced, which simulates the spatial pattern of erosion and deposition rates and sediment transport processes in river channels. In this model, land use affects soil erosion through altering soil loss and influencing sediment delivery. Simulated soil erosion for events recorded in 1989 and 1996 in the Lushi basin in China was analyzed by comparing it with historical land use maps. The results indicated that even relatively minor land use changes had a significant effect on regional soil erosion rates and sediment transport to rivers. The average erosion rate increased from 1989 to 1996, after the transformation of forest to farmland. The results of the study suggest that the proposed soil erosion model can be applied in similar river basins. Copyright © 2011 John Wiley & Sons, Ltd.

Reducing or stabilizing the stream temperature of ChiChiaWan Creek is a crucial work for Formosan Landlocked Salmon because ChiChiaWan Creek is the only one habitat for this endangered species. Planting trees in the riparian zone would be one of the alternatives. The purpose of this study was to evaluate the effects of several planting strategies on daily maximum stream temperature along the river. The results showed the effective vegetative shading angles should be more than 50° along ChiChiaWan Creek to reduce the direct solar radiation heating effectively. Upstream planting with 70° vegetative shading angle could be the most effective way among all the scenarios. However, this planting strategy could not improve the worst situations in summer because of the large solar elevation angles. The upstream planting in ChiChiaWan Creek was strongly recommended because the canopies could be easier to extend to totally cover the narrow width of river producing the most effective shades. Practicing the upstream planting with 90° vegetative shading angle can increase more than 1 km long suitable habitats for the endangered Salmon in summer. Alternatively, the west-side planting scenario was the second effective way for temperature reduction. Our result provided a useful suggestion for the authorities in charge of saving the Formosan Landlocked Salmon, particularly under the stress of global warming. Copyright © 2011 John Wiley & Sons, Ltd.

This paper proposes a new orientation to address the problem of hydrological model calibration in ungauged basin. Satellite radar altimetric observations of river water level at basin outlet are used to calibrate the model, as a surrogate of streamflow data. To shift the calibration objective, the hydrological model is coupled with a hydraulic model describing the relation between streamflow and water stage. The methodology is illustrated by a case study in the Upper Mississippi Basin using TOPEX/Poseidon (T/P) satellite data. The generalized likelihood uncertainty estimation (GLUE) is employed for model calibration and uncertainty analysis. We found that even without any streamflow information for regulating model behavior, the calibrated hydrological model can make fairly reasonable streamflow estimation. In order to illustrate the degree of additional uncertainty associated with shifting calibration objective and identifying its sources, the posterior distributions of hydrological parameters derived from calibration based on T/P data, streamflow data and T/P data with fixed hydraulic parameters are compared. The results show that the main source is the model parameter uncertainty. And the contribution of remote sensing data uncertainty is minor. Furthermore, the influence of removing high error satellite observations on streamflow estimation is also examined. Under the precondition of sufficient temporal coverage of calibration data, such data screening can eliminate some unrealistic parameter sets from the behavioral group. The study contributes to improve streamflow estimation in ungauged basin and evaluate the value of remote sensing in hydrological modeling. Copyright © 2011 John Wiley & Sons, Ltd.

The study of runoff is a crucial issue because it is closely related to flooding, water quality and erosion. In cultivated catchments, agricultural ditch drainage networks are known to influence runoff. As anthropogenic elements, agricultural ditch drainage networks can therefore be altered to better manage surface runoff in cultivated catchments. However, the relationship between the spatial configuration, i.e. the density and the topology, of agricultural ditch drainage networks and surface runoff in cultivated catchments is not understood. We studied this relationship by using a random network simulator that was coupled to a distributed hydrological model. The simulations explored a large variety of spatial configurations corresponding to a thousand stochastic agricultural ditch drainage networks on a 6.4 km² Mediterranean cultivated catchment. Next, several distributed hydrological functions were used to compute water flow paths and runoff for each simulation. The results showed that (i) denser networks increased the drained volume and the peak discharge and decreased hillslopes runoff, (ii) greater network density did not affect the surface runoff any further above a given network density, (iii) the correlation between network density and runoff was weaker for small subcatchments (< 2 km²) where the variability in the drained area that resulted from changes in agricultural ditch drainage networks increased the variability of runoff and (iv) the actual agricultural ditch drainage network appeared to be well optimized for managing runoff as compared with the simulated networks. Finally, our results highlighted the role of agricultural ditch drainage networks in intercepting and decreasing overland flow on hillslopes and increasing runoff in drainage networks. Copyright © 2011 John Wiley & Sons, Ltd.

The stable isotope analysis of all major rain events from Moinabad (MB), Rajendranagar (RN) and Osmanasagar (OS) reservoir, three closely placed locations in Hyderabad, India, were carried out during the 2005 to 2008 period. The OS station recorded the highest amount of rainfall with an average value of 1000 mm, whereas the MB station recorded the lowest average rainfall of 790 mm. The stable isotope (δ¹⁸O) values of the precipitation samples during these period varied from −11.43‰ to −0.03‰ for the MB station, −8.21‰ to 0.54‰ for the RN station and −11.47‰ to 0.72‰ for the OS station. The d-excess of precipitation at the three stations also showed considerable variations and revealed that the precipitation in the region undergoes significant modification through secondary evaporation during its fall. The possible causes for these observed spatial and temporal variations in amount and the isotopic composition of precipitation in a small geographical area within the city were studied. The observed variations may be attributed to the regional scale differences in water budget induced by rapid urbanisation activities in the city coupled with the differences in secondary effects undergone by the falling drops. This study elucidating changes in precipitation patterns in the city and its possible causes may largely help in its water balance calculation. Copyright © 2011 John Wiley & Sons, Ltd.