Adaptation and implementation of the HOTSED framework for assessing seasonal scenarios and short-term weather extremes in a high-altitude watershed of the Eastern Alps

We present the first preliminary adaptation and implementation of the HOTSED framework in a high-altitude watershed of the Eastern Italian Alps chosen as pilot area. HOTSED was applied to assess the spatio-temporal variability of sediment source hotspots driven by rainfall-induced surface runoff across different climatic conditions and rainfall intensities. We analyzed four seasonal scenarios and four daily scenarios, including an ordinary event and three extreme events with different return periods (10-year, 30-year, and 50-year). A pre-existing polygon-based geomorphological map was used to spatially define sediment sources across the study area. The geomorphic potential of each sediment source was estimated through a qualitative scoring of map attributes, supported by semi-quantitative, spatially distributed indices, including slope, permafrost distribution, and a proxy for frost-cracking incidence on the bedrock. Structural sediment connectivity was estimated using a geomorphometric index based on a Digital Terrain Model. For each scenario, a proxy for sediment transport potential was computed using a rainfall-calibrated index, applying a 0 °C ground surface temperature threshold to exclude snow-covered areas. All components were then integrated through a raster-based equation, yielding the HOTSED model. Results show that hotspots become more widespread and geomorphologically active during warmer and wetter seasons, particularly in summer and autumn, due to a combination of higher cumulative rainfall, intensified thermo-mechanical weathering, and increased topographic-altitudinal control on water flows. The model successfully identified hotspot toposequences with a high potential to trigger hazardous cascade processes. The analysis shows that even moderate rainfall extremes (e.g., 10-year return period events) can significantly amplify hazard patterns. This highlights the importance of identifying and monitoring geomorphic responses and, hence, managing appropriately cascading systems in Alpine watersheds under changing climatic conditions.