Combined change detection analysis of the impacts resulting from heavy rainfall events in mountainous areas

Heavy Rainfall Events (HREs) are expected to increase their frequency and intensity under the relentless global warming. Mountain areas are particularly vulnerable to such events, as they are already undergoing profound transformations driven by cryosphere degradation. Glaciers retreat and permafrost degradation leave loose debris which can be entrained by flowing water. A systematic assessment of the effects of HREs in mountain environments is of utmost importance to detect patterns and trends, but also to target efforts for in-depth field investigations. Among the several satellite-based approaches available, in this work we test a combined change detection analysis (over land and water) for evaluating the severity of impacts of HREs at the catchment scale. The defined workflow relies on freely available data and tools to maximize its transferability to different contexts and needs. It is based on simple processing steps to limit computational times and to ensure its usage in the post-emergency phases of HREs. This method is applied to two regional-scale HREs that affected the Western Alps in 2024. A variable rate of 59–65% of the catchments severely affected based on our methodology include documented instability events. The combination of land and water change detection increases recall and reduces omission errors of 6–11% when compared to more traditional land change detection alone. This method may allow the detection of affected areas not identified by field/aerial surveys. This work represents an initial step for developing a workflow specifically tailored to manage natural hazards in mountain areas.