Debris-flows in Northern Apennines and climate change: recent events analysis and reconstructions at different temporal scales

This thesis investigates debris flow processes in the Northern Apennines, Italy, through a multidisciplinary, multi-scalar and novel approach that integrates geomorphological mapping, dendrogeomorphology, sedimentological analysis, climatological data, GIS-based geomorphometry, susceptibility and numerical modeling. Debris flows represent one of the most hazardous geomorphic processes in this mountain range. By combining traditional methods with advanced quantitative techniques, this work provides both localized reconstructions of past events and regional-scale insights into debris flow dynamics. At the local scale, a detailed geomorphological survey supported by a high-resolution digital elevation model (5 m) allowed systematically mapping the existing landforms in the study site: i.e. glacial, cryogenic, and slope-related landforms, and to particularly emphasize debris flow channels. GIS-derived morphometric indices, including slope angle, Topographic Wetness Index (TWI), Terrain Ruggedness Index (TRI), and elevation, that were extracted along channel profiles and analyzed in relation to channel length classes. This analysis revealed anomalous morphometric patterns in debris flow channels, indicating distinctive topographic anomalies compared to non-affected debris flow channels. Dendrogeomorphological analyses extended the temporal resolution, reconstructing debris flow activity over the past six decades. Growth disturbances in tree rings, combined with soil infiltration studies, precipitation data, and orthophoto interpretation, enabled the identification and classification of major, intermediate, and minor debris flow events. The events of 1972 and 1987 were particularly significant, disturbing up to 54% of trees, causing widespread tree damage and substantial geomorphic change, while intermediate events in 1996, 2003, and 2013 with 20-30% of disturbed trees produced more localized impacts. Minor events were characterized by less than 20% of disturbed trees, indicating limited geomorphic impact and localized disturbance. It is noteworthy that the multidisciplinary analysis revealed that not all high-intensity rainfall events corresponded to debris flows, highlighting the importance of other parameters such as soil temperature and saturation that influence slope stability by affecting infiltration and runoff dynamics. Sedimentological analysis of debris flow features such as levee and lobe deposits showed sorting patterns and different slope geometries, indicating differential energy dissipation during transport and deposition. The 1987 debris flow event, identified as the last major event in the study area, was reconstructed using the RAMMS-DF numerical model. Calibration based on field evidence, mapped deposit extents, and channel morphology showed good agreement with simulated runout, demonstrating the potential of physically based models to reproduce debris flow dynamics in steep Apennine catchments. At the regional scale, a database of approximately 500 documented debris flows was analyzed to evaluate catchments characteristics by using Melton Ruggedness Index (MRI), Hypsometric Integral (HI), average slope, and channel gradient indices together with the hydro-geomorphological Stream Power Index (SPI) to analyze DFs drainage basins in the Northern Apennines. This broader analysis distinguished zones where debris flow susceptibility is high across the Apennine chain. By integrating local reconstructions with regional analyses, this thesis develops a robust framework for understanding debris flow initiation, propagation, and deposition. The findings provide critical insights into hazard assessment, offering methodological advances that combine geomorphological mapping, tree ring evidence, and modeling. Ultimately, this research contributes to improving predictive capability and informing risk mitigation strategies in mountain environments increasingly threatened by hydroclimatic extremes.