Continental scale modelling of in-stream river water quality: a report on methodology, test runs, and scenario application

Abstract

To address the continental and large-scale aspects of water quality assessments, new modelling approaches are required. This paper describes the development of a continental-scale model of river water quality – WorldQual. Simple equations, consistent with the availability of data on the continental-scale, are used to simulate the response of biochemical oxygen demand (BOD₅) and total dissolved solids (TDS) to anthropogenic loadings and flow dilution. A methodology is developed that is appropriate for scenario analysis on the continental and global scale. Average monthly river water quality is modelled on a 5 arcmin grid covering all Europe. Loadings are derived from assumptions about water use, return flows and other variables. The model WorldQual is tested against measured longitudinal gradients and time series data at specific river locations. The model performance on European scale shows that a good fit can be reached when using concentration classifications as a measure: For BOD₅, 51% of the simulated data is in the same quality class as the measurements and 30% differ only by one water-quality class; for TDS, the respective values are 35% and 41%. WorldQual was applied to investigate the impact of climate change on resulting changes of in-stream concentrations. The results for Europe show that future climate changes only have a small impact on European in-stream concentration levels of BOD₅, except for the Eastern part and the Black Sea region. This effect is stronger for the IPCM4-A2 scenario than for the MIMR-A2 scenario. Copyright © 2012 John Wiley & Sons, Ltd.