Simulation of snowmelt runoff in lowland and lower Alpine regions of Switzerland

This study investigates the influence of snowmelt model structure on the overall performance of runoff modelling in various-sized basins, where the snow cover is typically short-lived and rather thin. The per¬ formance of the following snowmelt models is compared: temperature-index method (Bergstrom, 1976) ; temperature and wind-index method; combination method (Anderson, 1973); extended combination method (using also water vapour pressure as an input variable) energy balance method. The performance is assessed by comparing linear scale plots of measu¬ red and simulated discharge and by applying the numerical efficiency criterion according to Nash and Sutcliffe (1970). For a given catchment, melt rates as calculated by the various snowmelt models are used as input to one and the same runoff model. In the small-scale Rietholzbach basin (3.18 km2), meteorological data as used in this study are measured at a point having a temporal resolu¬ tion of one hour and are considered representative for the whole basin. Over the 300 days of simulation an increase of snowmelt model perfor¬ mance by about 4 % can be demonstrated when moving from the tempera¬ ture-index to any other method. During advection-melt conditions the energy balance method yields the best results, whereas during radiationmelt conditions index methods are sufficient. The combination method seems to be the most suitable approach for operational purposes. In the four Thur basins varying from 79 km2 to 1696 km2, standard climatological data are used (temporal resolution of 12 hours), which are distributed on the basis of an optimal interpolation method into various sub-basins and elevation belts. Discharge is simulated on a daily time