From sediment source hotspots to toposequence-based cascade systems: Modelling potential hazard response under seasonal and extreme rainfall scenarios in Alpine catchments.

Keywords: Integrated model; Sediment dynamics; Sediment connectivity; Scenario analysis; Extreme events; HOTSED.

 

This study presents the preliminary results from the adaptation and implementation of the HOTSED framework (La Licata et al., 2025) in two high-altitude catchments in the Eastern Alps. The HOTSED model assesses the spatial distribution of sediment source hotspots and highlights the sediment transfer pathways driven by water runoff. Here, we adapted HOTSED to analyze how sediment sources and sediment patterns vary seasonally and between daily extreme rainfall events. We analyzed four seasonal scenarios as well as four daily scenarios including extreme events with different return periods (i.e. daily, 10-year, 30-year, and 50-year events). A polygon-based geomorphological map was used to spatially distribute sediment sources and sinks across the catchments. The potential contribution of each geomorphological unit as a sediment source was evaluated through a qualitative scoring system based on database attributes, complemented by numerical semi-quantitative indices of variables like slope, permafrost distribution, and a proxy of frost-cracking-induced slope instability. A geomorphometric connectivity index was used to calculate structural sediment connectivity. For each scenario, the potential for sediment transport was assessed using a sediment transport index calibrated to rainfall intensity, excluding snowfall-driven contributions using a 0°C ground surface temperature threshold to mask snow-covered areas. Finally, all components were integrated using a raster-based approach yielding the HOTSED model. Results show pronounced seasonal variability in hotspot distribution across the two catchments, where the strongest contrasts between winter and summer-autumn are driven by differences in rainfall-snowfall spatial patterns and intensity. Extreme rainfall scenarios led to significant increases in hotspot distribution and extent, with the most pronounced variance occurring between the standard and 10-year event scenarios. This suggests that more frequent extremes, expected to become even less rare under climate change, may have a greater overall impact than rarer high-intensity events. In addition, the model highlights sequences of connected landforms, classified with different degrees of hazard potential, which may represent the most interesting locations for the occurrence of cascading events. These findings offer critical insights for sediment-related risk management in Alpine catchments under ongoing climatic changes.

 

Acknowledgement

We express our gratitude to Anuschka Buter for providing the geomorphological map dataset used in this study.

References

La Licata, M., Bosino, A., Sadeghi S.H., De Amicis, M., Mandarino, A., Terret, A. & Maerker, M. (2025). HOTSED: A new integrated model for assessing potential hotspots of sediment sources and related sediment dynamics at watershed scale. Int. Soil Water Conserv. Res., 13(1), 80-101. DOI: 10.1016/j.iswcr.2024.06.002.