Innovative debris flow event warning system based on short-term forecasting and phenomenology
Debris flows are rapid, gravity-induced mass movements consisting of water-sediments mixture that route along channels incised on mountain slopes. In the Alps, the main factors triggering these phenomena are extreme rainfall events that cause abundant runoff which entrain large quantity of debris forming solid-liquid surges that route downstream destroying or damaging each obstacle (houses, works) they meet, causing also death of people. The increase of extreme rainfalls likely due to the climate change, increased the frequency of these phenomena. The mostly short duration of the rainfalls triggering debris flows (10-30 minutes), the short times (5-15 minutes) of their downstream routing forbids the use of standard rainfall forecasting for their predictability as for flash floods and landslides. Moreover, early-warning systems based on sensors detect the debris flow transit and allow only short alert times. The project's aim is to provide an early-warning system that increases the alert time. The proposed system is based on a models cascade: nowcasting, hydrological and triggering models. Nowcasting anticipates rainfall pattern (1-3h) that is transformed into runoff by the hydrological model. The triggering model estimates the sediments volume that the runoff can entrain, and compares it with a critical threshold. If this is exceeded the alert is launched. This new system will be tested by monitoring stations in sites frequently subject to debris flows in all the regions.