Impact of a climate change on the Rhone river catchment hydrology

[1] Within the framework of the Global Energy and Water Cycle Experiment (GEWEX)/ Rhone project, a system has been built to estimate the hydrological budget of the Rhone, one of the major European rivers (with a 86,500 km(2) surface area for the French part of the catchment). The methodology is based on three models, one for each component of the hydrometeorological system: The atmospheric parameter analysis, the snow cover, the surface water and energy budget, and the underground water transfer and discharge estimation. This tool has been validated for 14 years (from 1981 to 1994) by comparing the daily river flows simulated by the models with measurements from 145 gauging stations. In this study, the results of the ARPEGE-Climat general circulation model (GCM) have been used to estimate the climate of the Rhone catchment in 60 years. The perturbation of the air temperature and precipitation amount has been used to modify the actual set of meteorological parameters in order to simulate the hydrological budget of the Rhone river. Vegetation and soil structure are supposed to be identical to current values, which is a strong hypothesis. The river discharge and soil water resources under the climatic scenario are compared with the results of the actual simulation. Strong contrasts in the hydrological response of the catchment are noticeable, depending on the location of the subcatchments and the amount of precipitation. Snow cover is the most sensitive hydrological component to the air temperature increase, and the high mountainous river regimes are strongly modified. When considering the soil water content, it appears that the northern part of the domain stays quite wet, whereas drying is enhanced in the south. The uncertainties in the results are estimated by analyzing the model sensitivity to different simple climatic scenarios. In particular, the analysis brings into light the impact of the downscaling of the GCM results.