The May 2023 Rainstorm-Induced Landslides in the Emilia-Romagna Region (Northern Italy): Considerations from UAV Investigations Under Emergency Conditions

Rainstorm-induced landslides are a widespread geomorphological hazard that can lead to major emergencies, causing severe damage to life and property. Due to the extent of the areas usually affected by these phenomena (up to thousands of km2) and/or their typical high areal density, in the early stages of the emergency it can be useful to reconstruct a comprehensive, albeit preliminary, overview of the landslides. With this aim, in this work we provide an outline of the landslides that occurred in the eastern part of the Emilia-Romagna region (northern Italy) after two severe rainstorms in May 2023. By combining information collected during the emergency through direct field inspections and UAV (unmanned aerial vehicle) surveys with preliminary analyses of historical rainfall/landslide data, we inferred the main characteristics of the landslides (e.g., movement type, involved materials, triggering mechanisms) and the relation with antecedent landslide phenomena, rainfall exceptionality, and anthropogenic activities. The latter were found to have likely contributed to landslides triggering by increasing water discharge and, in turn, infiltration and runoff erosion (i.e., inadequate drainage devices) and steepening slope gradients (e.g., road cuts). The vastness of the territory hit by the May 2023 landslides and their exceptional areal density can be explained not only with the extreme rainfall intensity (>500 years at several rainfall stations), but also with the widespread occurrence of slope materials which are very sensitive to sudden changes in hydraulic conditions. The high landslide susceptibility of the area is confirmed by the fact that many of the May 2023 landslides occurred at or close to previously identified and mapped landslide sites.