Development and evaluation 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 insufficient. 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 evaluation 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 accurately identifies individual snow avalanche PRAs based on terrain parameters and watershed delineation is developed, and confusion matrices and different scores are proposed to evaluate it. Comparison to an extensive cadastre of past avalanche limits from different massifs of the French Alps used as ground truth leads to true positive rates (recall) between 80 % and 87 % in PRA numbers and between 92.4 % and 94 % in PRA areas, which shows the applicability of the method to the French Alps context. A parametric study is performed, highlighting the overall robustness of the approach and the most important steps/choices to maximize PRA detection, among which the important role of watershed delineation to identify the right number of individual PRAs is highlighted. These results may contribute to better understanding avalanche hazard in the French Alps. Wider outcomes include an in-depth investigation of the issue of evaluating automated PRA detection methods and a large data set that could be used for additional developments, and to benchmark existing and/or new PRA detection methods.

Snow and avalanche climates in the French Alps using avalanche problem frequencies

“…In the 23 French Alpine regions, we performed snow cover simulations at 1800, 2100, 2400, 2700 and 3000 m, and not exceeding the summit elevation of each region. For the analysis of avalanche problem types, we used the simulation at the elevation which is closest to the median elevation of the release areas in each region (Duvillier and others, 2023). In all regions the selected elevation lay in the interquartile range of the release area elevations, which represents half of the release areas, except for the Chartreuse region, where half of the release areas actually lie between 1544 and 1748 m (1st and 3rd quartile) and we had to use the simulations at 1800 m. Hence, when comparing different regions, our simulations may be less representative of the conditions in the Chartreuse region, as actual release areas are slightly lower.…”

Mapping and characteristics of avalanches on mountain glaciers with Sentinel-1

“…1). Slope has been identified as one of the main controls for avalanche release (Voellmy, 1955), and numerous algorithms use this as a primary criterion to classify avalanche-prone slopes, along with secondary criteria such as terrain curvature, roughness or the presence of vegetation (Maggioni and Gruber, 2003;Bühler et al, 2018;Duvillier et al, 2023). Avalanche deposits are thus expected to occur only for slopes lower than 35°, which is generally the criteria taken for the automated detection of avalanche deposits in remote sensing images (Leinss et al, 2020;Eckerstorfer et al, 2019).…”