Impact of a climate change on the hydrology of the French Rhône river

In the frame of the GEWEX/Rhône project, a global system has been built to estimate the hydrological budget of the Rhône, one of the major European river (with a 86500 km2 catchment). The methodology is based on 4 models, one for each component of the hydro-meteorological system : SAFRAN for the atmospheric parameters analysis, Crocus for the snow cover, ISBA for the surface water and energy budget and MODCOU for the underground transfers and the discharge estimation. This tool has been validated for 14 years (from 1981 to 1994) by comparing the daily flows simulated by the models with measurements of 145 gauge stations. In a second part, the results of the GCM ARPEGE-Climat have been used to estimate the climate of the Rhône 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 Rhône river. Vegetation and soil structure are supposed to be identical, which is a strong hypothesis. The river discharges and soil water resources under the climatic scenario are compared with the results of the actual simulation. Strong contrast in the hydrological response of the catchment are noticeable, depending of the location of the sub-catchments and the evolution of the amount of precipitation. Snow cover is the most sensitive component to the elevation of the air temperature, whereas dryness becomes important in the south of the domain. A particular attention is paid to the incertitude of the results, due to the hypothesis made in the models and our imperfect knowledge of future climate at regional scale.