Optimising the identification of river sediment supply areas and their connectivity in the mountainous river basins of central Italy

Climate change is increasingly exposing Mediterranean regions to extreme weather events with severe geomorphic impacts, such as flash floods, debris flows, and rapid landslides. Understanding the processes that supply sediment to catchment areas is crucial, given the strong upstream–downstream connectivity typical of mountainous regions. This can exacerbate vulnerabilities, cause localised flooding, and pose significant hazards. This study presents a semi-quantitative GIS-based procedure for optimising the identification of sediment supply areas and their structural connectivity in mountainous catchments of central Italy. The method combines three morphometric indices - the Stream Power Index (SPI),Index of Connectivity (IC), and Stream Length-Gradient (SL) index - derived from a detailed geomorphological characterisation of the study area. The methodology is designed to delineate sediment-source areas and assess their degree of connectivity with the drainage network. It incorporates a linear morpho-hydraulic component, based on SL index and longitudinal profile analyses, which supports the interpretation of channel energy conditions and sediment transfer dynamics. Finally, a synoptic raster map is generated to visually and spatially highlight the most critical values of the three indices. The approach was tested in the mountain portion of the Burano River basin (Northern Apennines), severely affected by the15 September 2022 flood. The analysis revealed strong correspondence between high-connectivity areas and zones of post-event instability, indicating effective identification of both sediment sources and preferential transport corridors. Validation was performed through multi-source comparison, integrating Normalised Difference Vegetation Index(NDVI) analysis, UAV photogrammetry, and detailed traditional field surveys, thereby confirming the robustness of the results. The proposed approach is time- and cost-efficient and provides reliable insight into sediment transfer along slopes and river channels within a simplified and operational framework.