Development and validation using ground truth of a method to identify potential release areas of snow avalanches based on watershed delineation

Abstract

Abstract. Snow avalanches are a prevalent threat in mountain territories. Large-scale mapping of avalanche prone terrain is a prerequisite for land-use planning where historical information about past events is lacunar. To this aim, the most common approach is the identification of Potential Release Areas (PRAs) followed by numerical avalanche simulations. Existing methods for identifying PRAs rely on terrain analysis. Despite their efficiency, they suffer from i) a lack of systematic validation on the basis of adapted metrics and past observations over large areas and ii) a limited ability to distinguish PRAs corresponding to individual avalanche paths. The latter may preclude performing numerical simulations corresponding to individual avalanche events, questioning the realism of resulting hazard assessments. In this paper, a method that well identifies individual snow avalanche PRAs based on terrain parameters and watershed delineation is developed, and confusion matrices and accuracy scores computed both in terms of PRA numbers and areas are proposed to test and evaluate it. Confrontation to an extensive cadastre of past avalanche limits from different massifs of the French Alps used as ground truth leads to high accuracy rates, between 89.8 % and 93.5 % in numbers and 96.2 % and 97.1 % in areas. This shows the applicability of the method to the French Alps context. A sensitivity study is performed, highlighting the most important steps to reach high accuracy in PRA detection, among which the strong role of watershed delineation to identify the right number of individual PRAs. Outlooks for further progresses are discussed. Notably, the proposed data and evaluation framework could be used for additional developments of the method, and to benchmark existing and/or new PRA detection methods.