On the criteria to create a susceptibility map to debris flow at a regional scale using Flow-R

Studies on susceptibility to debris flows at regional scale (100-1000 square kilometers) are very important for the protection and management of mountain areas. To reach this objective, routing models, mainly based on land topography, can be used because they can predict susceptible areas rapidly and necessitate few input data. In this research, Flow-R model is implemented to create the susceptibility map to debris flow of the Vizze Valley (BZ, North-Eastern Italy; 134 square kilometers). The analysis considers the model application at local scale for three sub-catchments and then it explores the model upscaling at the regional scale by verifying two methods to generate the source areas of debris-flow initiation. Using data of an extreme event occurred in the Vizze Valley (4 August 2012) and historical information, the modelling verification highlights that the propagation parameters are relatively simple to set in order to obtain correct runout distances. Furthermore, a double DTM filtering - using a threshold for the upslope contributing area (0.1 km2) and a threshold for the terrain-slope angle (15°) - provides a satisfactory prediction of source areas and susceptibility map within the geological conditions of the Vizze Valley.