The hydrological role of snow and glaciers in alpine river basins and their distributed modeling

A temperature index approach including incoming solar radiation was used as a sub-model in the gridded hydrological catchment model WaSiM-ETH to simulate the melt rate of glacierized areas. Melt water and rainfall are transformed into glacier discharge by using linear reservoir approaches. The complex WaSiM model was applied to three Swiss high-alpine river catchments with different portions of glacierized areas to simulate the discharges of the whole catchments. Gridded data sets of elevation, soil type, and land-use were used including meteorological input data from the network of MeteoSwiss. These data were spatially and temporally interpolated and modified according to exposition, slope and topographic shading. Continuous discharge simulations for the catchment areas were performed in a spatial resolution of 100 m and a temporal resolution of 1 h for the period 1981-2000 and compared with hourly discharge observations measured at the catchment outlets. To improve the calculation of glacier runoff, a seasonal varying radiation factor has been implemented in the glacier melt equation. The pronounced diurnal and seasonal fluctuations in discharge, which are typical of partly glacierized catchment areas, were simulated in a good agreement with the observed values. For the investigated catchments mean annual values of precipitation, evapotranspiration, snowmelt, runoff, and components of glacier runoff are discussed and compared in their altitudinal dependence. Further, the temporal and the spatial distribution of snowmelt and runoff generation in these glacierized catchment areas are discussed.