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

Avalanche observations are an important factor foroperational avalanche warningand the main parameter to carry out an objectiveverification of the avalanche bulletinin retrospect. For the first time, a 50-year longseries of avalanche activity data of 84Swiss avalanche observation stations is analysed anddiscussed. After careful datapreparation a regional avalanche activity index (RAAI)for seven snow-climatologicalregions of Switzerland was developed. Using differentstatistical descriptors, we wereunable to detect a long-term change in avalancheactivity, which stands in contrast toa significant increase of winter precipitation.The comparison of the RAAI with acomprehensive database for destructive avalanches(DADB) resulted in a low correlation.This shows clearly the difficulties involved indetermining a good measure for specifyingthe true avalanche activity. Depending on thedegree of the avalanche activity DADB andavalanche observations represent the avalancheactivity differently and overlap. Suggestionsare given for the improvement of the ongoingavalanche observation programme in order toachieve an overall consistent and reliabledata set in future.