Operational use of a snowpack model for the avalanche warning service in Switzerland : model development and first experiences

Abstract

The national Swiss avalanche warning service must provide high quality avalanche danger forecasts with an increasing spatial resolution. For this purpose, forecasters require objective tools to judge local and regional avalanche danger. One important prerequisite for such objective methods is to characterize the snowpack status and to assess the snowpack - atmosphere interaction with a high spatial and temporal resolution. A snowpack model can provide this information if it is able to simulate the crucial physical processes such as snowpack settlement, formation of surface hoar and finally weak layer evolution. This contribution presents a one-dimensional model based on finite element numerics which is directly coupled to the measurements of the new automatic weather and snow stations which operate at typical avalanche starting zone altitudes between 2000 and 3000 m ASL in the Swiss Alps. A simple prototype of the model is already in operational use and calculates snowpack parameters for over 40 locations with weather and snow stations. First results from the model are encouraging. Important parameters such as new snow heights, temperature profiles and density profiles can reliably be calculated. Major research work is devoted towards an improvement of the metamorphism scheme, which is currently based on the French model CROCUS. Especially the addition of new parameters such as grain bond size and coordination number should establish a link to thermal and mechanical properties. The final goal will be a description of weak layer development and an assessment of the mechanical stability of a layer. In addition, the coupling of the model to the Swiss weather forecast model and a description of wind erosion and accumulation is in preparation.