Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 12 3 2008 10.5194/hess-12-797-2008 http://www.hydrol-earth-syst-sci.net/12/797/2008/ http://www.hydrol-earth-syst-sci.net/12/797/2008/hess-12-797-2008.html http://www.hydrol-earth-syst-sci.net/12/797/2008/hess-12-797-2008.pdf 797 810 2008-05-23 Importance of stream temperature to climate change impact on water quality A. Ducharne Laboratoire Sisyphe, CNRS/Université Pierre et Marie Curie, Paris, France The sensitivity of some aspects of water quality to climate change was assessed in the Seine River (France) with the biogeochemical model RIVERSTRAHLER, which describes the transformations and fluxes of C, N, P and Si between the main microbiological populations, the water column and the sediment, along the entire river network. Point and diffuse sources are prescribed, stream temperature undergoes a sinusoidal annual cycle constrained by observations, and runoff is calculated by a physically-based land surface model. The reference simulation, using meteorological forcing of 1986–1990 and point sources of 1991, compares very well with observations. The climate change simulated by a general circulation model under the SRES emission scenario A2 was used to simulate the related changes in runoff and stream temperature. To this end, a statistical analysis was undertaken of the relationships between the water and air temperatures in the Seine watershed over 1993–1999, using 88 points that correctly sampled the variability of the tributaries. Most of stream temperature variance was explained by the lagged moving average of air temperature, with parameters that depended on Strahler stream order. As an interesting simplification, stream temperature changes could be approximated by air temperature changes. 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