WATER EROSION AND OVERLAND FLOW GENERATION IN ALPINE HILLSLOPES: FROM THE DETECTION OF LAND COVER AND GEOMORPHIC CHANGES TO THE TRACER CHARACTERIZATION OF WATER SOURCES

This PhD thesis addresses a range of hydrological and erosional processes in a steep mountainous catchment of the eastern Italian Alps, where frequent avalanches and extreme hydrometeorological events pose significant environmental challenges. Despite these pressures, such catchments remain largely overlooked by policymakers and researchers compared to intensively used agricultural areas. This thesis aims to investigate water erosion and overland flow generation on Alpine hillslopes by combining land use and land cover (LULC) and geomorphic change detection with a tracer-based characterization of water sources. The first specific objective (Chapter 2) is the investigation of the effects of avalanches and the Vaia storm on land cover changes and erosion susceptibility in the upper Cordevole catchment, in the eastern Italian Alps. This large-scale investigation combined high-resolution spatial data (e.g., temporal LULC change and vegetation index) with geographic information systems and multi-criteria decision analysis to predict and map spatio-temporal erosion susceptibility in the catchment. The second specific objective (Chapter 3) focuses on the factors (i.e., rainfall characteristics and temperature) influencing geomorphic changes and sediment yield in a steep experimental hillslope at risk of erosion, which is in the upper Cordevole catchment. This section deeply investigates the combined role of surface temperature (an aspect often overlooked in previous research and less understood) and rainfall intensity on sediment dynamics. We applied advanced geospatial techniques, particularly high-resolution multitemporal Unmanned Aerial Vehicle (UAV) data for geomorphological change detection. These observations were complemented by ground-based hillslope erosion monitoring, providing a comprehensive understanding of erosion processes in a mountainous catchment. The third and final specific objective (Chapter 4) focuses on the characterization of the typical tracer signatures of overland flow (OVF) originating from the experimental eroded hillslope and compares with other water sources in the catchment. We examined the isotopic composition (δ2H and δ18O) and the electrical conductivity of different water sources (stream water, spring water, shallow groundwater, and OVF from experimental hillslope and riparian zones) in the catchment to improve our understanding of the origin of OVF. In conclusion, land and water resources management practices in Alpine areas should pay particular attention to the monitoring of soil erosion following natural hazards and aim for the restoration of Alpine grasslands on hillslopes at risk of erosion.