Debris flows in northeastern Italy: data collection and approaches for a preliminary debris-flow characterization at the regional scale

Debris flows are a widespread natural hazard in mountain catchments causing major damage when they intersect transport vulnerable elements at risk, including transport routes and urban areas. Climate change is expected to lead to an increase in the frequency and magnitude of those phenomena. It is thus fundamental to extend the collection of primary data on debris-flows occurrence and volume in order to evaluate the variations of debris-flow frequency and magnitude with time and, at the same time, provide new tools for the assessment of areas affected by debris flows and their spatial characterization. This work presents the results of the analysis of date of occurrence and volume of a large dataset of debris-flows collected in the eastern Italian Alps. The occurrence, in the last forty years, of some high-magnitude debris flows characterized by the largest unit volumes of the dataset might be associated with current climate changes. In order to deal with the observed increase in this processes in mountain environments, a simple and fast semi-automated procedure is proposed for the regional-scale identification of debris-flow prone channels and alluvial fans. The main aim is to develop a low data-demanding method for a preliminary mapping of potentially debris-flow affected areas to enable priority ranking of channels and alluvial fans at risk by debris flows. This approach has been validated by means of field checks and through its extensive application in the eastern Italian Alps.