The regional climate model CHRM is used in a nested mode with horizontal resolutions of 56 km and 14 km. The boundary conditions are taken from the original (CTRL) and modified (WARM) ECMWF reanalysis. The distributed runoff model (WaSiM) is used at a horizontal resolution of 1 km for the whole Rhine basin (gauge Cologne), covering more than 140'000 square-kilometers. The coupling of the models is provided by a downscaling of the climate model fields (precipitaion, temperature, radiation, humidity, and wind) to the resolution of the distributed runoff model. The simulations cover the five winter seasons 1989/90 till 1993/94, each from November until January.
A detailed validation of the control simulation shows a good correspondance of the precipitation fields from the regional climate model with measured fields regarding the distribution of precipitation at the scale of the Rhine basin. Systematic errors are visible at the scale of single subcatchements, in the altitudinal distribution and in the frequency distribution of precipitation. These errors only marginally affect the runoff simulations, which show good correspondance with runoff observations.
The presentation includes results from the scenario simulations for the whole basin as well as for Alpine and lowland subcatchements. The change in the runoff statistics is being analyzed and discussed with respect to the changes in snowfall and to the fequency distribution of precipitation.