Combining snow drift and SNOWPACK models to estimate snow loading in avalanche slopes

Snow drift is one of the major factors influencing avalanche activity in high Alpine terrain. This concerns catastrophic avalanches as well as regularly occurring touristic avalanches. When discussing the role of snow drift in avalanche formation, four physically connected processes have to be taken into account: the windfield over steep topography, the preferential deposition of snow during snowfall events, the possible redistribution of already deposited snow, and the different developments of the snow cover at sites of ablation and accumulation. This paper presents an integrated model approach for the estimation of snow loading in steep avalanche slopes. The assessment includes an atmospheric model analysis of the high resolution wind field over topography, a novel formulation of wind transport in saltation and suspension that allows one to treat preferential deposition and redistribution, and a distributed model assessment of the snow cover characteristics. The snow cover model is important to judge the erodability of the deposited snow and yields information on the status of the snowpack on the slope that is crucial for a final estimation of slope stability. Results are presented for a drift period in January 1999. A comparison with measurements shows good agreement. Over steep Alpine terrain (up to 50 deg), the model is able to simulate snow distribution and snow cover status with a reasonable computational effort. A discussion is given of future development toward an operational assessment of snow drift for the purpose of avalanche warning. The model is the first available tool to study the atmosphere-snow-vegetation interaction and the distribution of snow water equivalent in steep Alpine terrain.