Statistical probability predetermination of avalanche runout altitudes using a combination of deterministic model and well documented data base

Studying snow avalanches using a statistical approach raises several issues. First, even in the heavy populated areas in the Alps, there are few relevant data on avalanche motion or extension. Second, most of the field data are related to the point of the furthest reach in the avalanche path (run-out distance or altitude). As data of this kind are tightly dependent on the avalanche path profile, it is a priori not permissible to extrapolate the cumulative distribution function fitted to these data without severe restrictions or further assumptions, Here, in order to overcome this issue, we propose a novel methodology. First, using an avalanche-dynamics numerical model, we fit the model parameters (two friction coefficients and the volume of snow involved in the avalanches) to the field data. Then, as these parameters are random variables, we adjust appropriate statistical distributions. The third step involves simulating a large number of (fictive) avalanches using a Monte Carlo approach. In this way. the cumulative distribution function of the run-out distance can be computed on a much broader range than initially with the historic data.