Performance of Complex Snow Cover Descriptions in a Distributed Hydrological Model System and Simulation of Future Snow Cover and Discharge Characteristics: A Case Study for the High Alpine Terrain of the Berchtesgaden Alps

Abstract

The water balance in high Alpine regions in its full complexity is so far insufficiently understood. Large altitudinal gradients, a strong variability of meteorological variables in time and space, complex hydrogeological settings, and heterogeneous snow cover dynamics result in high uncertainties in the quantification of the water flux and storage terms. In this study, the deterministic model system WaSiM-ETH was complemented with physically based formulations to describe high Alpine specific snow processes. To enhance the reproduction of snow deposition and ablation processes, the new system calculates the energy balance of the snow cover considering the terrain-dependent radiation fluxes, as well as lateral snow transport processes induced by wind and gravitation. Test site for the study is the Berchtesgaden National Park (Bavarian Alps, Germany) which is characterized by extreme topography and climate conditions. The performance of the enhanced model system is analyzed and validated via measurements of the snow water equivalent and snow depths, satellite-based remote sensing data, and runoff gauge data. The model has proven to work stable in reproducing seasonal snow cover development over a wide range of elevations. It was able to reproduce the general spatial patterns and most of the fine scale details of snow coverage. With increasing snow model complexity, model efficiency (Nash-Sutcliffe coefficient) for simulated runoff increases from 0.57 to 0.68 in a high Alpine headwater catchment and from 0.62 to 0.64 in total. To assess possible impacts of a changing climate on the regional hydrology, the optimized model system was forced with dynamically downscaled climate simulations. Model results are compared between the control period 1971 - 2000 and the scenario period 2021 - 2050. The projected future precipitation characteristics are the main driver for the consequent changes in the regional hydrology. Mean snow cover duration decreases significantly (-19 d/year), whereas the absolute changes in seasonal snowmelt and runoff amounts are projected to remain relatively small