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Keywords:

  • climate changes;
  • precipitation regimes;
  • extreme rainfall;
  • trend test;
  • water vapour flux;
  • atmospheric circulation

Abstract

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

In this study, we comprehensively analysed daily precipitation time series of 590 rain stations in China covering 1960–2005. Ten indices were defined to evaluate changing patterns of precipitation regimes and trend detection was performed using Mann–Kendall trend test and linear regressive technique. For the sake of better understanding of underlying causes behind changing properties of precipitation regimes, we also investigated spatial and temporal variations of atmospheric circulation of water vapour flux. The results revealed different changing properties of precipitation events across China. Generally, wet tendency was identified in the south China and dry tendency in north China. Besides, slight wet tendency could be found in northwest China. In addition, increasing precipitation intensity could be observed mainly in the lower Yangtze River basin and the Pearl River basin. Remarkable seasonal shifts of wet/dry conditions were also detected in China: wet tendency in winter and dry tendency in summer. Furthermore, this study revealed good agreement between spatial distribution of precipitation regimes and water vapour flux, showing tremendous influences of water vapour flux on the precipitation changes across China. Regions east to 100°E were dominated by increasing water vapour flux in winter. Weaker East Asian Summer Monsoon was the main cause responsible for decreasing northward propagation of water vapour flux, causing different wet (dry) tendency in south (north) China. This study can provide theoretical evidence for effective water resource management and sound arrangement of agriculture activities on river basin scale under the changing environment across China. Copyright © 2010 Royal Meteorological Society


1. Introduction

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

Tremendous importance has been attached to the study of climatological variables, such as air temperature, precipitation amount, sea level, atmospheric pressure and so on (Piervitali et al., 1997). It is particularly the case for the study of the precipitation variations (Brunetti et al., 2000; Osborn et al., 2000; Kunkel, 2003; Ramos and Martínez-Casasnovas, 2006; Fatichi and Caporali, 2009) which can be well justified by the fact that the temporal and spatial variability of precipitation has always affected human societies all over the world. Study of changes in precipitation regimes is believed to be the first step to understand impacts of climate changes on water resource availability (Jiang et al., 2007). Rogers (1994) stressed the necessity to understand changes in means, variances and persistence of the precipitation regimes with the aim to improve the accuracy of plans for future water demand. The tremendous importance of water for human societies and nature underscores the necessity of understanding how a changing climate could affect regional water supplies (Xu and Singh, 2004; Xu et al., 2006). Thus, a good understanding of magnitude and frequency of precipitation events, especially extreme precipitation events, is essential for effective water resource management and flood control (e.g. Durrans and Kirby, 2004).

Different changing properties of precipitation regimes have been detected for different regions over the world implying diverse regional responses of precipitation variations to global climate changes. Karl and Knight (1998) showed increasing trends in 1-day and multiday heavy precipitation events with heavy 24-h precipitation totals in the United States and other countries. Significant decreasing trends in extreme rainfall events have been found in Western Australia (Haylock and Nicholls, 2000). However, some researchers have found an increasing trend in extreme precipitation events in the United States (Kunkel, 2003). Other scholars reported no trend in extreme rainfall events in Canada (Zhang et al., 2001). As for the studies of precipitation regimes in China, numerous reports can be found in the literatures. Becker et al. (2006) found significant changing trends in monthly precipitation totals in the Yangtze River basin. Wang and Zhou (2005) studied trends in annual and seasonal mean precipitation totals and extreme precipitation events in China during 1961–2001 using linear regression method showing increasing annual mean precipitation in southwestern, northwestern and eastern China and decreasing annual mean precipitation in central, northern and northeastern China. Chen et al. (1991) indicated that the majority of China was characterized by decreasing precipitation, especially northern and northwest China. Zhai et al. (1999) reported no significant trend in the annual precipitation over China between 1951 and 1995. Wang et al. (2004) showed an increasing precipitation during the second half of the 20th century in the West China. Ren et al. (2000) demonstrated an increasing summer precipitation over the middle and the lower Yangtze River and a decreasing trend over the Yellow River basin, but almost no change in the high-latitude areas. Zhai et al. (2005) investigated the trends in annual and seasonal total precipitation and in extreme daily precipitation for the year, summer and winter half years. Zhang et al. (2009c) thoroughly analysed annual, winter and summer precipitation records during 1951–2005 of 160 stations in China using the rotated empirical orthogonal function, Mann–Kendall (MK) trend test and Continuous Wavelet Transform method, addressing changing properties of precipitation regimes in different parts of the China and discussed implications of these changes with respect to river basin scale water resource management. Zhang et al. (2008b, 2009a) investigated precipitation extremes in the Yangtze River basin and Pearl River basin and linked these changes to atmospheric circulation demonstrating that decreasing northward propagation of water vapour flux should be the major cause for increasing precipitation maxima in the lower reaches of these river basins. Besides, study of drought/wetness episodes in the Pearl River basin (Zhang et al., 2009b) indicated seasonal shifts of humidity conditions, i.e. summer is being dryer and winter being wetter. This finding means too much for scientific management of water resources and agriculture activities in the Pearl River basin. Table I displays the major studies for the precipitation changes in China.

Table I. Summary for the major studies concerning the precipitation changes in China
Study regionPrecipitation indicesTime scales of precipitation changesReferences
Yangtze RiverMonthly precipitationSeasonal scaleBecker et al., 2006
Whole ChinaAnnual precipitationAnnual scaleChen et al., 1991
Yangtze RiverMonthly precipitationSeasonal scaleJiang et al., 2007
Whole ChinaAnnual precipitationDecadal scaleWang et al., 2004
Whole ChinaAnnual and seasonal precipitationAnnual and seasonal scaleWang and Zhou, 2005
Whole ChinaSeasonal 1-day maximum, annual mean precipitation intensityAnnual scaleZhai et al., 1999
Whole ChinaAnnual and seasonal total precipitationAnnual and seasonal scaleZhai et al., 2005
Yangtze RiverAnnual/seasonal maximum precipitationAnnual and seasonal scaleZhang et al., 2009d
Whole ChinaMonthly precipitationSeasonal scaleZhang et al., 2009a
Pearl RiverAnnual precipitation and summer or winter precipitation totalsAnnual and seasonal scaleZhang et al., 2009b

Our previous studies (Zhang et al., 2008b, 2009a, 2009b, 2009c) indicated remarkable differences in changing properties of precipitation regimes over China. Increasing temperature has the potential to alter the changes of atmospheric circulation of water vapour flux in both space and time. Furthermore, good relations between precipitation changes and atmospheric circulation are observed in the Yangtze River basin and the Pearl River basin (Zhang et al., 2009a, 2009c). Thus, increasing temperature can cause alterations of spatial and temporal distribution of precipitation regimes by influencing the atmospheric circulation, and this will exert tremendous impacts on water resource management at river basin scale and on agricultural activities over China (Chavas et al., 2009). In addition, the societal infrastructure is becoming more sensitive to weather and climate extremes, which would be exacerbated by climate change (Easterling et al., 2000). Therefore, in this case, we investigate changing properties of the average regime and the extreme behaviour of the rainfall processes over China and try to link these changing properties to atmospheric circulation with the aim to address causes behind precipitation changes. Based on the fact that precipitation changes are always in close relation with availability and variability of water resources, we divided the entire territory of China into ten parts based on the range of ten river basins (Figure 1). The objectives of this study are (1) to clarify changing properties of precipitation regimes in China in terms of average and extreme behaviour; (2) to explore precipitation concentration by analysing fraction of annual and seasonal total precipitation due to events exceeding the 75th or falling below the 25th percentile; (3) to understand causes behind changing properties of precipitation regimes in China by analysing variations of water vapour flux in both time and space. This study will provide an entire picture of average and extreme behaviours of precipitation in China and underlying atmospheric circulation background.

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Figure 1. Meteorological stations considered in this study and the ten drainage basins. The solid dots denote the rain stations. Numbers denote the ten drainage basins: 1, Songhuajiang River; 2, Liaohe River; 3, Haihe River; 4, Yellow River; 5, Huaihe River; 6, Yangtze River; 7, SE rivers (rivers in the southeast China); 8, Pearl River; 9, southwest rivers (rivers in the southwest China); 10, northwest rivers (rivers in the northwest China)

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2. Data and methodology

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

Daily precipitation data of 590 rain stations during 1960–2005 were collected in this study, which were provided by the National Climate Center of China Meteorological Administration. The spatial distribution of rain stations over China is shown in Figure 1. The missing data of 1 or 2 days are replaced by the average precipitation values of the neighbouring days. If consecutive days have missing data, the missing values are replaced with long-term averages of the same days. We assumed that this gap-filling method will have no influence on the long-term temporal trend. Furthermore, the data consistency was checked by the double-mass method and the result showed that all the data series used in the study are consistent (Zhang et al., 2009d).

The precipitation indices are used in other studies (Tebaldi et al., 2006; Fatichi and Caporali, 2009). Based on the previous studies, in this article, precipitation indices are defined as (1) total annual precipitation (TAP); (2) total precipitation in summer (JJA) denoted as TSP; (3) total precipitation in winter (DJF) denoted as TWP; (4) number of wet days with precipitation > 1 mm on annual basis (NWa) and seasonal basis (NWs for summer and NWw for winter); (5) annual and seasonal changes in precipitation intensity defined as mean daily precipitation of wet days in summer (PIs), winter (PIw) and on annual basis (PIa); (6) number of days (with respect to wet days with daily precipitation > 1 mm) with daily precipitation exceeding 75th (ND75) and falling below 25th percentiles (ND25) on seasonal (NDs75, NDs25 for summer; NDw75, NDw25 for winter) and annual basis (NDa75, NDa25); (7) total precipitation of ND75 and ND25 denoted by T75 and T25, respectively (Ts75, Ts25 for summer; Tw75, Tw25 for winter and Ta75, Ta25 for annual); (8) precipitation intensity defined as T75/ND75 and T25/ND25 denoted by PI75 and PI25, respectively (PIs75, PIs25 for summer; PIw75, PIw25 for winter and PIa75, PIa25 for annual); (9) fraction of annual and seasonal total precipitation due to events exceeding 75th percentile and falling below 25th percentile. These events are denoted as F75 and F25, respectively. Fs75 and Fs25 denote fraction of TSP due to events exceeding 75th percentile and falling below 25th percentile. Following the same definition rules, Fw75 and Fw25 for winter and Fa75 and Fa25 for annual. For the sake of clear presentation, we summarize all the precipitation indices and their meanings in Table II.

Table II. Indices of precipitation regimes considered in this study
SeasonsAbbreviationDefinitions
AnnualTAPSum of precipitation of all wet days of a year. Wet day in this study is defined as the rainy day with precipitation > 1 mm
 NwaSum of the days with precipitation of > 1 mm
 PIaMean daily precipitation of wet days with precipitation of > 1 mm
 NDa75Number of days with daily precipitation exceeding 75th percentile on the annual basis
 Fa75This index is defined as the ratio of the total precipitation of days with precipitation exceeding 75th percentile to the TAP amount
 PIa75This index is defined as the mean daily precipitation of days with precipitation of > 75th percentile
 NDa25Number of days with daily precipitation falling below 25th percentile on annual basis
 Fa25This index is defined as the ratio of the total precipitation of days with precipitation falling below 25th percentile to the TAP amount
 PIa25This index is defined as the mean daily precipitation of days with precipitation of < 25th percentile
SummerTSPSum of precipitation of all wet days in summer
 NWsSum of the days with precipitation of > 1 mm in summer
 PIsMean daily precipitation of wet days in summer
 FsThis index is defined as the ratio of the total precipitation of wet days in summer to the TAP amount
 NDs75Number of days with daily precipitation exceeding 75th percentile in summer
 Fs75This index is defined as the ratio of the total precipitation of days with precipitation exceeding 75th percentile to the total precipitation amount in summer
 PIs75This index is defined as the mean daily precipitation of days with precipitation of > 75th percentile in summer
 NDs25Number of days with daily precipitation falling below 25th percentile in summer
 Fs25This index is defined as the ratio of the total precipitation of days with precipitation falling below 25th percentile to the total precipitation amount in summer
 PIs25This index is defined as the mean daily precipitation of days with precipitation of < 25th percentile
WinterTWPSum of precipitation of all wet days in winter
 NWwSum of the days with precipitation of > 1 mm in winter
 PIwMean daily precipitation of wet days in winter
 FwThis index is defined as the ratio of the total precipitation of wet days in winter to the TAP amount
 NDw75Number of days with daily precipitation exceeding 75th percentile in winter
 Fw75This index is defined as the ratio of the total precipitation of days with precipitation exceeding 75th percentile to the total precipitation amount in winter
 PIw75This index is defined as the mean daily precipitation of days with precipitation of > 75th percentile in winter
 NDw25Number of days with daily precipitation falling below 25th percentile in winter
 Fw25This index is defined as the ratio of the total precipitation of days with precipitation falling below 25th percentile to the total precipitation amount in winter
 PIw25This index is defined as the mean daily precipitation of days with precipitation of < 25th percentile in winter

For further understanding of the atmospheric circulation patterns behind the spatial and temporal patterns of precipitation regimes, the moisture and related transport features of the whole ps layer (surface pressure) − 300 hPa will be explored based on the NCAR/NCEP reanalysis data (Zhang et al., 2008a; 2008b) from 1960 to 2005. In the actual atmosphere, the moisture is very low over 300 hPa, so p = 300 hPa will be used in the calculation. The zonal moisture transport flux (QU), meridional moisture transport flux (QV) and whole layer moisture budget (QT) at regional boundaries were calculated based on the following equations (Miao et al., 2005; Zhang et al., 2008b):

  • equation image

where u and v are the zonal and meridional components of the wind field, respectively, q is the specific humidity, ps is surface pressure, p is atmospheric top pressure, g is acceleration of the gravity, QW, QE, QS, QN are the West, East, South and North regional boundaries, respectively, and φ1, φ2, λ1, λ2 are the latitude and longitude according to the regional boundaries (Miao et al., 2005).

In this study, simple linear regressive technique and the MK are used to detect the trends and associated significance in the precipitation regimes. The rank-based MK method (Mann, 1945; Kendall, 1975) is a nonparametric method and is commonly used to assess the significance of monotonic trends in hydro-meteorological series (Alan et al., 2003; Yue and Pilon, 2004; Gao et al., 2007; Zhang et al., 2008a). MK technique is highly recommended for general use by the World Meteorological Organization (Mitchell et al., 1966). The significance level used in this study is 0.05.

3. Results

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

3.1. Changes in annual precipitation regimes

In this study, we comprehensively investigate changes in precipitation regimes over China and try to relate these changing properties in both time and space to atmospheric circulation on seasonal and annual basis. Figure 2(a) shows increasing TAP in the lower Pearl River and the Yangtze River basins. Upper Yangtze River and southwest rivers were also characterized by increasing TAP. Larger magnitude increase of TAP could be observed mainly in the east parts of the Yangtze River and the Pearl River basins when compared to other regions of China. In addition, Figure 2(a) also illustrates slight increasing TAP in the river basins of northwest China. Decreasing TAP can be observed in the middle part of the Yangtze River basin, a majority of Yellow River basin, northeast part of Huaihe River, Songhuajiang River, Liaohe River and Haihe River (Figure 2(a)). In summary, large magnitude of increase in TAP can be found mainly in the east part of the Pearl River, the Yangtze River and also in the southwest rivers and the west parts of the Yangtze River basin. Figure 2(b) shows increasing wet days (with precipitation > 1 mm) on annual basis (NWa) in northwest China. Significant increase in NWa can be found in north parts of the northwest China. However, regions of China east to 100°E were dominated by decreasing NWa. Precipitation intensity on annual basis is defined as mean daily precipitation of wet days (PIa). Figure 2(c) illustrates increasing PIa in the east parts of the Yangtze River basin, majority parts of the Pearl River basin and west parts of the Huaihe River. North parts of the northwest China are also characterized by increasing PIa. Stations characterized by significant increase in PIa distributed sporadically in the east parts of the Yangtze River basin, southeast and north parts of the northwest China. Visual comparison between Figure 2(a)–(c) indicates that the increasing PIa in the east parts of the Yangtze River and in the Pearl River was the result of increasing TAP and decreasing NWa.

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Figure 2. Spatial and temporal distribution of (a) annual total precipitation; (b) wet days with precipitation > 1 mm and (c) precipitation intensity defined as mean daily precipitation of wet days across China. Dashed contours show decreasing trends and thick dashed contours show significant decreasing trends. Shaded areas show significant trends

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We define the precipitation concentration by the number of days with precipitation exceeding 75th and falling below 25th percentiles and associated total precipitation and precipitation intensity, i.e. NDa75, NDa25, PIa75, PIa25, Fa75 and Fa25 as displayed in Table II. It can be seen from Figure 3(a) that increasing NDa75 was detected mainly in the northwest China in addition to parts of the west and east Yangtze River basin. Stations characterized by significant increase in NDa75 distributed sporadically in the west part of the Yangtze River basin and north parts of the northwest China (Figure 3(a)). Regions of China east to 100°E were dominated by decreasing NDa75. Figure 3(b) shows that most places of China were characterized by decreasing PIa75. Stations characterized by increasing PIa75 distributed mainly in the middle and east parts of the Yangtze River basin. Similar spatial patterns of Fa75 can be observed in Figure 3(c) when compared to those of PIa75 in Figure 3(b). Increasing Fa75 was found mainly in the east parts of the Yangtze River basin, north part of northwest China and some regions in the Pearl River basin. Majority of places of China were dominated by decreasing Fa75. Therefore, increasing precipitation concentration represented by increasing Fa75 mainly occurred in the lower Yangtze River basin and some areas of the Pearl River basin. Figure 4 illustrates spatial distribution of precipitation regimes defined by 25th percentile. Remarkable differences could be identified in Figure 4 in terms of spatial patterns of precipitation regimes by 25th percentile when compared to those shown in Figure 3. Increasing NDa25 was found mainly in the Yellow River basin, south parts of the Haihe River and middle parts of the Yangtze River, showing dry-towards tendency in these regions (Figure 4(a)). Significant decrease in NDa25 and increase in PIa25 were found mainly in the northwest China tending to imply wet-towards tendency in northwest China (Figure 4(b)). Figure 4(c) shows that the entire China was characterized by decreasing Fa25, showing decreasing precipitation concentration represented by Fa25.

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Figure 3. Spatial and temporal distribution of changes of precipitation of > 75th percentile. (A) Days with precipitation of > 75th percentile; (b) precipitation intensity defined by daily mean precipitation of days with precipitation of > 75th percentile and (c) ratio of total precipitation of > 75th percentile to the annual total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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Figure 4. Spatial and temporal distribution of changes of precipitation of < 25th percentile. (a) Days with precipitation of < 25th percentile; (b) precipitation intensity defined by daily mean precipitation of days with precipitation of < 25th percentile and (c) ratio of total precipitation of < 25th percentile to the annual total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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3.2. Changes in precipitation regimes in summer

China is climatically controlled by East Asian Monsoon system. Precipitation mainly occurs in summer; therefore, summer is always the flooding season in most parts of China. In this section, we study the changing properties of precipitation regimes in summer. In this season, increasing TSP prevailed over China (Figure 5(a)). Similar to TAP, larger magnitude increase of TSP was observed in the middle and lower reaches of the Yangtze River basin, in the southwest part of the Yangtze River basin (Figure 5(a)) and also in the Pearl River basin. Slight increase of TSP could also be found in northwest China. However, decreasing TSP had the controlling position in the Yellow River basin, the northeast parts of the Huaihe River, the Songhuajiang River and the Liaohe River. Therefore, increase of TSP mainly occurred in southeast China. The increase in magnitude of TSP in northwest China and other regions of China were much smaller when compared to that in southeast China. NWs was decreasing in a majority of regions in China (Figure 5(b)). Increasing NWs could be observed mainly in the east part of the Yangtze River basin and in the west corner of the northwest China. Significant decrease in NWs marked by thick dashed lines could be found in east parts of the Liaohe River and Haihe River. Figure 5(c) shows that the regions characterized by increasing PIs distributed in a scattered way across China. Generally, middle, east and southwest parts of the Yangtze River basin were featured by increasing and even significant increase in PIs. Areas characterized by increasing PIs distributed sporadically in the northwest China. Still, it can be found from Figure 5(c) that decreasing PIs prevailed over China. Figure 5(d) shows increasing Fs in middle and lower Yangtze River basin, in the south part of the Yellow River basin and in the west corner of northwest China. Most places of China were characterized by decreasing Fs showing decreasing fraction of summer precipitation in the TAP.

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Figure 5. Changes of summer precipitation regimes in space and time. (a) Summer total precipitation; (b) wet days with precipitation of > 1 mm; (c) precipitation intensity defined as mean daily precipitation of wet summer days and (d) ratio of summer total precipitation to annual total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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As for changes in NDs75 (Figure 6(a)), increasing NDs75 was observed mainly in the lower Yangtze River basin and west parts of the northwest China. Stations characterized by significant increase in NDs75 distributed sporadically in the lower Yangtze River basin and in the northwest China. Decreasing NDs75 still dominated the entire territory of China. Fewer regions were characterized by increasing PIs75 when compared to those featured by NDs75 (Figure 6(a) and (b)). Figure 6(b) shows that no fixed spatial patterns could be identified for the changes in PIs75. Decreasing PIs75 still prevailed across China. When it comes to the variations of Fs75 shown in Figure 6(c), increasing Fs75 could be identified mainly in the middle and east parts of the Yangtze River basin. Besides, north, east and east parts of the northwest China and some regions in the Pearl River basin were also featured by increasing Fs75. Even so, decreasing Fs75 occurred in most regions of China (Figure 6(c)).

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Figure 6. Changes of precipitation regimes defined as 75th percentile in summer in space and time. (a) Wet days with precipitation of > 75th percentile; (b) precipitation intensity of days with precipitation of > 75th percentile and (c) ratio of total precipitation of > 75th percentile to summer total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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Figure 7 shows spatial distribution of changes in precipitation regimes defined by the 25th percentile. It can be found in Figure 7(a) that increasing NDs25 mainly occurred in north China, such as east parts of Songhuajiang River, Liaohe River and Haihe River. In addition, some regions in the upper Yangtze River and upper Pearl River were also characterized by increasing NDs25. Decreasing NDs25 was found in middle and west China. Significant decrease in NDs25 was observed in the southwest part of the northwest China (Figure 7(a)). Figure 7(b) demonstrates that significant decrease in PIs25 occurred mainly in north China. Only a couple of stations were characterized by significant increase in PIs25 and these stations mainly distributed in northwest China. Also, China was dominated by decreasing PIs25 though most stations showed no significant decrease in PIs25. Similarly, China was dominated by decreasing Fs25. Very few stations showed increasing Fs25.

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Figure 7. Changes of precipitation regimes defined as 25th percentile in summer in space and time. (a) Wet days with precipitation of < 25th percentile; (b) precipitation intensity of days with precipitation of < 25th percentile and (c) ratio of total precipitation of < 25th percentile to summer total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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3.3. Changes in precipitation regimes in winter

Figure 8 illustrates spatial distribution of changes in precipitation regimes in winter. Similar to the changes in summer precipitation regimes in terms of total seasonal precipitation amount, larger magnitude of increase of TWP was found mainly in the lower Yangtze River basin and in the Pearl River basin. Besides, what is different from changing patterns of TSP (Figure 5(a)) is increasing TWP prevailed over China. Fewer regions were characterized by decreasing TWP. Regions dominated by decreasing TSP were characterized by increasing TWP, such as Songhuajiang River, Liaohe River and Haihe River. Therefore, from the standpoint of total seasonal precipitation, China tended to be wetter in winter; comparatively, China came to be dryer in summer. Similarly, when compared to changes in NWs (Figure 5(b)), more areas were characterized by increasing NWw (Figure 8(b)). Specifically, increasing NWw could be identified in the Songhuajiang River, the upper Yellow River basin, the upper Yangtze River basin, the lower Yangtze River basin and the majority of northwest China. Significant increase in NWw could be observed mainly in the upper Yangtze River basin, the lower Yangtze River basin, the north part of northwest China and the majority of the Songhuajiang River. Comparison between Figures 5(b) and 8(b) indicates that larger extent of areas and more stations showed increasing NWw when compared to NWs. This result also supports the viewpoint that winter in China came to be wetter and summer tended to be dryer. As for PIw, decreasing PIw could be identified mainly in the lower Yangtze River basin and in the Pearl River basin. In addition, increasing PIw could also be observed in the upper Yangtze River basin and the upper Yellow River basin. North parts of the northwest China and the Songhuajiang River were also dominated by increasing and even significant increase in PIw. Figure 8(d) shows spatial patterns of Fw over China. Increasing Fw indicated increasing precipitation in winter or more seasonal shifts of precipitation in winter when compared to other seasons. It can be seen from Figure 8(d) that increasing Fw was identified mainly in the lower and the upper Yangtze River basin, the upper Pearl River basin, the Yellow River, the Songhuajiang River and parts of the northwest China. Decreasing Fw was found in the Liaohe River, the Haihe River and the middle Yangtze River basin.

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Figure 8. Changes of winter precipitation regimes in space and time. (a) Winter total precipitation; (b) wet days with precipitation of > 1 mm; (c) precipitation intensity defined as mean daily precipitation of wet winter days and (d) ratio of winter total precipitation to annual total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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Figure 9 shows changes in precipitation regimes defined by the 75th percentile. Increasing NDw75 was detected mainly in the lower Yangtze River basin, east parts of Huaihe River and also in the Pearl River basin (Figure 9(a)). Besides, increasing NDw75 could also be found in the north part of the northwest China. The majority of China was characterized by decreasing NDw75, though the decreasing trends were not significant at > 95% confidence level. Figure 9(b) shows increasing Fw75 in southeast China, such as the lower Yangtze River basin, the SE rivers and the Pearl River basin. The rest of the regions of China were dominated by decreasing Fw75. This result indicates increasing winter precipitation fraction relative to the TAP, implying wet-towards tendency in these regions in winter. Changes in precipitation regimes defined by the 25th percentile are illustrated in Figure 10. Remarkable changing properties of precipitation regimes were identified in Figure 10 that NWw25 and Fw25 were decreasing across the entire territory of China. Regions dominated by significant decrease in NWw25 and Fw25 scattered sporadically over China without discernable spatial patterns. As for changes in PIw25 (Figure 10(b)), increasing PIw25 could be identified in northwest China, parts of upper Yellow River basin and upper Yangtze River basin. Besides, east parts of the Songhuajiang River were characterized by increasing PIw25. The majority of China was featured by decreasing PIw25 though the decreasing trends are not significant at > 95% confidence level.

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Figure 9. Changes of precipitation regimes defined as 75th percentile in winter in space and time. (a) Wet days with precipitation of > 75th percentile; (b) ratio of total precipitation of > 75th percentile to winter total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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Figure 10. Changes of precipitation regimes defined as 25th percentile in winter in space and time. (a) Wet days with precipitation of < 25th percentile; (b) precipitation intensity of days with precipitation of < 25th percentile and (c) ratio of total precipitation of < 25th percentile to winter total precipitation. Solid contours denote increasing trend and dashed contours show decreasing trends. Shaded areas show significant trends

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3.4. Large-scale atmospheric circulation

The currently increasing temperature leads to alterations of atmospheric water budget as a result of the high sensitivity of the saturation vapour pressure in air to temperature. Thus, perturbations in the global water cycle are expected to accompany the climate warming (Allen et al., 2002). Precipitation efficiency is the fraction of the average horizontal water vapour flux in a region that falls as precipitation. Precipitation is overwhelmingly subject to moisture transportation and propagation and deep convection (Heideman and Fritsch, 1988). Previous studies demonstrated good relations between precipitation changes, hydrological processes and moisture budget or water vapour propagation (Zhang et al., 2009d, 2008a). In this study, to better understand the changes in the precipitation regimes in space and time, we analyse the spatial and temporal variations of water vapour flux over China with the aim to explore the underlying causes of precipitation changes. This will help to shed light on the mechanisms behind the precipitation changes and benefit effective water resource management on river basin scale under the changing climate, particularly under the well-evidenced global warming. Figure 11 shows trends of water vapour flux in latitudinal direction. The upper panel shows trends of water vapour flux in space and time for summer. It can be seen from Figure 11 that regions north to the Yangtze River basin were characterized by decreasing water vapour flux. Parts of the northwest China were also featured by decreasing water vapour flux. North corner and southeast parts of the northwest China were dominated by increasing water vapour flux. In addition, it can be clearly observed from the upper panel of Figure 11 that there was a belt dominated by increasing water vapour flux which extended westwards from the lower Yangtze River basin to the upper Yangtze River basin and till the south part of northwest China. Parts of the Pearl River basin were dominated by decreasing water vapour flux. In winter (middle panel of Figure 11), however, the majority of regions in China was characterized by increasing water vapour flux. Larger magnitude of increase of water vapour flux could be found in the Pearl River basin and the lower Yangtze River basin and also in the northeast China. Besides, increasing water vapour flux could also be identified in the north part of the northwest China. Decreasing water vapour flux could be found only in the middle and south part of the northwest China. As for the annual trends of water vapour flux (the lower panel of Figure 11), regions north to the Yangtze River basin were controlled by decreasing water vapour flux. Increasing water vapour flux was observed mainly in the regions south to the Yangtze River basin, including the Yangtze River basin itself. North corner of the northwest China was characterized by increasing water vapour and decreasing water vapour flux was found in the middle and the west part of the northwest China.

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Figure 11. Linear trends of water vapour flux (unit: kg/m·s) in latitudinal direction for summer (upper panel), winter (middle panel) and annual (lower panel)

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Figure 12 demonstrates spatial patterns of trends of water vapour flux propagating in longitudinal direction. Upper panel shows changes of water vapour flux in summer. The remarkable features of trends of water vapour flux in summer were decreasing water vapour flux in the east China. Middle parts of the northwest China were characterized by decreasing water vapour flux. Increasing water vapour flux could be found in the southwest China (upper panel of Figure 12). Middle panel of Figure 12 shows distinctly different properties of water vapour flux trends. Generally, regions east to 100°E were largely controlled by increasing water vapour flux. Furthermore, larger magnitude of increase in water vapour flux could be found in the lower Yangtze River basin and in the Pearl River basin. In addition, northwest China was also characterized by increasing water vapour flux, except middle parts of the northwest China. Lower panel of Figure 12 shows similar spatial patterns of trends of annual water vapour flux changes when compared to those in summer (upper panel of Figure 12). Decreasing water vapour flux dominated the east China. Increasing water vapour flux occurred in northwest China except middle parts of the northwest China (lower panel of Figure 12). Generally, propagation of the water vapour flux along the east China was decreasing and this should be attributed to weakening strength of East Asian Summer Monsoon. This point will be discussed in more detail in the next section.

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Figure 12. Linear trends of water vapour flux (unit: kg/m·s) in longitudinal direction for summer (upper panel), winter (middle panel) and annual (lower panel)

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4. Discussions

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

Spatial and temporal distribution of precipitation changes exerts considerable impacts on water resource management on river basin scale and also on the agricultural activities. Particularly, the currently well-evidenced global warming characterized by increasing temperature has the potential to alter the distribution of water vapour flux and moisture budget at regional and global scale. And just because of this reason, the regional patterns of the surface hydro-climatological changes tend to be more complicated when compared to changes in temperature series. Even so, under the influences of altered spatial distribution of atmospheric circulation, distribution of precipitation regimes in time and space will also be driven to shift annually and seasonally and the direct consequences of altered precipitation changes are the decreasing and/or increasing runoff at regional or global scale (Milly et al., 2005), which posed new challenges for the water resource management. China is climatically characterized by various climate zones, from arid, semi-arid, semi-humid, to humid climates. Different intensity of human activities and various underlying surface properties can be identified within the entire territory of China. Therefore, different regional or local responses of precipitation regimes to global climate changes could be expected. Our previous studies indicated weaker East Asian Summer Monsoon during 1975–2005 when compared to 1961–1974 (Zhang et al., 2008a). The spatial distribution patterns of the geopotential height in the Eurasia and west Pacific Ocean do not benefit the northward propagation of the water vapour flux. Decreasing transportation of water vapour flux in the longitudinal direction in the east China further corroborates this viewpoint. Increasing water vapour flux could be identified in northwest China except in the middle parts of the northwest China. Propagation of water vapour flux in latitudinal direction was decreasing in regions north to the Yangtze River basin. Increasing water vapour flux in latitudinal direction could be observed mainly in south China. This kind of spatial pattern of water vapour flux decided the spatial changes in precipitation regimes. Precipitation in north China was decreasing and was increasing in south China, showing tremendous influences of propagation of water vapour flux on changes in precipitation regimes in time and space. In addition, visual comparison of the aforementioned figures showed good agreement in the spatial distribution of precipitation regimes and that of trends in water vapour flux. What deserves attention is the generally increasing precipitation regimes defined by thresholds or total annual and seasonal precipitation across the entire territory of China in winter. However, the precipitation changes in summer present adverse changing properties. This phenomenon manifested wetting tendency of winter and drying trend of summer. We also found that the Pearl River basin tended to be wetter in winter and dryer in summer. Wet tendency of the Pearl River basin was reflected by increasing number of wet winters across the Pearl River basin and this could be attributed to increasing moisture content and moisture budget in winter (Zhang et al., 2009b). Now, based on the results of this study, we can say that the wet tendency dominated the majority of the territory of China. In addition, study on the precipitation regimes defined by the 75th and 25th percentiles indicated increasing precipitation concentration in the lower and the upper Yangtze River and also in the Pearl River basin, the northwest China. Based on the aforementioned, we can say that, under the influences of global warming, the winter came to be wetter and the summer dryer. In addition, north China (regions north to the Yangtze River basin) came to be controlled by dry tendency; wet tendency dominates the south China, i.e. regions south to the Yangtze River basin, including the Yangtze River basin itself. The northwest China was also in wet tendency which is due to increasing propagation of water vapour flux in longitudinal direction.

5. Conclusions

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

In this study, we systematically analyse changing properties of average regime and the extreme behaviour of the precipitation process over China. Precipitation concentration defined as the ratio of total precipitation of the 75th and 25th percentiles to the annual and seasonal total precipitation is also studied in terms of its changes in space and time. To better understand causes and mechanisms behind these changing characteristics of precipitation regimes, atmospheric circulation of water vapour flux based on NCAR/NCEP reanalysis dataset is also analysed. We obtain some interesting and important conclusions based on the aforementioned analyses.

  • 1.
    Increasing precipitation mainly occurred in the middle and lower Yangtze River basin and in the Pearl River basin. Slight increase of precipitation could also be observed in the northwest China. On the contrary, north China (regions north to the Yangtze River basin) was dominated by decreasing precipitation regimes. Precipitation concentration and precipitation intensity was increasing in the lower Yangtze River basin and also in the north and south parts of the northwest China. No fixed spatial patterns could be found for changes in precipitation regimes. Stations characterized by significant trends usually distributed sporadically across China showing inhomogeneous distribution of precipitation changes.
  • 2.
    Remarkable seasonal shift of precipitation changes could be detected in China. Generally, winter came to be wetter and summer tended to be dryer. It was particularly the case for the northeast China, the upper and the lower Yangtze River, the Pearl River basin and the northwest China. Slight wet tendency could also be found in the Yellow River which was reflected by increasing ratio of winter total precipitation to the annual total precipitation. These altered precipitation changes pose new challenges for the water resource management and sound arrangement of agricultural activities on river basin scale under the changing environment. Timely and effective policy making should be carried out accordingly based on changing precipitation scenarios and altered humid conditions in different parts of China.
  • 3.
    Spatial patterns of changes in precipitation regimes matched well with the trends of water vapour flux over China. With respect to the water vapour flux in latitudinal direction, in summer, the Yangtze River basin was controlled by a belt characterized by increasing water vapour flux. On annual basis, the Yangtze River basin and the Pearl River basin were both characterized by increasing water vapour flux. Decreasing water vapour flux in north China led to decreasing precipitation. In the northwest China, the regions dominated by increasing precipitation regimes were controlled by increasing water vapour flux showing tremendous influences of water vapour flux propagation on changes of precipitation in time and space. Decreasing water vapour flux in longitudinal direction dominated in the east China could be attributed to weakening East Asian Summer Monsoon (Zhang et al., 2009c). Weaker East Asian Summer Monsoon in recent decades did benefit northward propagation of water vapour flux and had potential to cause increasing moisture content and moisture budget in the regions south to the Yangtze River basin. Furthermore, altered atmospheric moisture, temperature fields and shifts in strength of Asian monsoon could have driven across the board shifts in the precipitation intensity and precipitation regimes in the south and northwest China.

Acknowledgements

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References

This work was financially supported by the ‘985 Project’ (Grant No. 37000-3171315), the Program for Outstanding Young Teachers of the Sun Yat-sen University (Grant No.: 2009-37000-1132381), the Key National Natural Science Foundation of China (Grant No.: 50839005), the Scientific Project of Xinjiang (Grant No.: 200931105), the Program of Introducing Talents of Discipline to Universities—the 111 Project of Hohai University, and by the KLME (Grant No. KLME0801). Thanks should be owed to the National Climate Centre of China for providing meteorological data. Cordial gratitude should be extended to the professional comments and advices from the two anonymous reviewers and the editor, Prof. Dr Glenn McGregor, which greatly improved the quality of this article.

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  2. Abstract
  3. 1. Introduction
  4. 2. Data and methodology
  5. 3. Results
  6. 4. Discussions
  7. 5. Conclusions
  8. Acknowledgements
  9. References
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