Simulation of the water budget and the river flows of the Rhone basin from 1981 to 1994

As a first step toward the simulation of the continental water cycle at a regional scale, the Rhone basin simulation has been done from 1981 to 1994 using a soil–vegetation–atmosphere transfer model coupled with a hydrological model. A first study with a 8 km resolution and a 5 min time step was already done for one year (1987/1988) by Habets et al., 1999b (Habets F., Etchevers P., Golaz C., Leblois E., Ledoux E., Martin E., Noilhan J. and Ottlé C. (1999): Simulation of the water budget and the river flows of the Rhône basin. J. of Geophysical Research, 104, n° D24, 31145–31172.) Because of the strong snow component of the basin, a detailled multi-layer snow model has been added to the original modelling system. This analysis covers a longer time period in order to examine the interannual variability of climatic conditions and streamflows. The observed atmospheric forcing has been interpolated in time and space with a system especially adapted to the Alps mountains. Although only a limited calibration using observed discharges was done, the model results compare fairly well with the daily observed discharges at 145 gauging stations located on the largest rivers of the catchment. Poor results are obtained for some of the smaller catchments (smaller than 1000 km2), possibly because of inacurracies in the interpolated atmospheric forcing at small spatial scales. The evolution of the simulated snow pack is in good agreement with the daily observed snow depths at 24 high altitude stations located between 1500 and 3000 m in the Alps. The surface water budget shows large spatial variations due both to vegetation and climatic conditions. The interannual variability of the groundwater table is strongly related to the variability of precipitation with positive storage of water for wet years.