Evaluation of snow-surface energy balance models in alpine terrain

Abstract

The increasing complexity of snow-cover models demands high-quality forcing data. In complex alpine terrain, both short and long wave incoming radiation components are expected to be influenced by small-scale topographic effects, i.e. shading and multiple scattering as well as long-wave irradiance from the surroundings. Not only should the latter be included in distributed energy balance models, but, because of their increasing resolution, also in meteorological models of the next generation. The energy balance at the snow-cover surface is calculated by means of different distributed energy balance models over a region of a few square kilometres, the spatial resolution being 25 m. The models include topographical effects on the radiation components of the energy balance. The region of interest is located in the Eastern Swiss Alps, around study sites of the Swiss Federal Institute for Snow and Avalanche Research SLF, Davos. The primary forcing data are taken from automatic weather stations located within the study area. To assess performance and differences of the models, two approaches are taken. First, model outputs are compared to measurements of both incoming radiation and snow surface temperature measured at automatic weather stations located on either level or inclined terrain within the region. Second, the models are used to calculate snowmelt at the beginning of the ablation period. The results are compared with changes of the snow water equivalent as measured in various spots of the modelled region, including all aspects on one elevation range. In view of the above comparison, the necessity to include small-scale topographic influences on the energy balance at the snow-cover surface as well as to consider snow surface properties and internal processes within the snow cover will be discussed. The possible implications for hydrological and meteorological models of the next generation will be addressed too.