Multi-disciplinary reconstruction of debris flow events and dynamics in the Northern Apennines, Italy: A multi-scale approach linking ground evidence with climatic triggers

A multidisciplinary approach is used to reconstruct debris flow (DF) events and extent through time in a remote (data scarce) site located in the Northern Apennines, Italy. Field-based techniques such as geomorphological mapping of the area, dendrogeomorphological dating and the characterization of soils and water infiltration processes were integrated with the analysis of precipitation triggers and temperatures to reconstruct the sequence of DF events over the last 70 years. Major DF events detected by comparing the dendrochronological evidence and climatic data, occurred in 1972 and 1987 disturbing up to 54 % of the sampled trees, whereas intermediate events occurred in the years 1996, 2003 and 2013 with 20–30 % of disturbed trees. Minor events were characterized by less than 20 % of disturbed trees, indicating limited geomorphic impact and localized disturbance. Historical orthophotos analysis directly confirmed most of the events in chronology as well as their spatial patterns. The analysis of the site-specific hourly precipitation records highlighted that not all high rainfall events resulted in DFs occurrence. Such chronologies are valuable because DF inventories often lack non-damaging events. A database of approximately 500 DFs occurred in the region of the Northern Apennines was analyzed using composite susceptibility index (CSI) and lithology to provide broader context. Results highlight three main situations in the investigated region: i) areas of intense precipitation and corresponding DF-prone catchments and observed DFs, along the Northern Apennine ridge in East and West sectors; ii) areas of intense precipitation events over non-DF-prone catchments and without observed DF in the far-West sector; iii) areas along the mountain ridge where DFs are observed despite the absence of intense precipitation in the central sector. By integrating a multi-disciplinary approach to analyze the DFs, this study advances understanding of DF dynamics and provides a framework for improved hazard assessment in mountain environments.