Temporal Trend and Spatial Distribution of Avalanche Activity during the Last 50 Years in Switzerland

Abstract

Avalanche observations are an important factor for operational avalanche warning and the main parameter to carry out an objective verification of the avalanche bulletin in retrospect. For the first time, a 50-year long series of avalanche activity data of 84 Swiss avalanche observation stations is analysed and discussed. After careful data preparation a regional avalanche activity index (RAAI) for seven snow-climatological regions of Switzerland was developed. Using different statist- ical descriptors, we were unable to detect a long-term change in avalanche activity, which stands in contrast to a significant increase of winter precipitation. The comparison of the RAAI with a compre- hensive database for destructive avalanches (DADB) resulted in a low correlation. This shows clearly the difficulties involved in determining a good measure for specifying the true avalanche activity. Depending on the degree of the avalanche activity DADB and avalanche observations represent the avalanche activity differently and overlap. Suggestions are given for the improvement of the ongoing avalanche observation programme in order to achieve an overall consistent and reliable data set in future.