Physically-Based Models for Estimating Rainfall Triggering Debris Flows in Campania (Southern Italy)

The societal risk related to rainfall-triggered rapid debris flows is commonly managed in urbanized areas by means of early warning systems based on monitoring of hydrological parameters (such as rainfall or soil moisture) and analysis of thresholds values. This paper deals with physically-based modelling of ash-fall pyroclastic soil coverings involved in debris flows along mountain slopes nearby the Somma-Vesuvius volcano (Campania, southern Italy), which represent one of the major geohazards of Italy. The methods adopted combine deterministic approaches at the site-specific and distributed scales to estimate Intensity-Duration rainfall thresholds triggering debris flows. The first approach is based on the reconstruction of detailed physical models of ash-fall pyroclastic soil coverings in representative source areas of debris flows and on the related hydrological and slope stability modelling. The second is focused on a regional distribution model of ash-fall pyroclastic soils over mountain slopes surrounding the Somma-Vesuvius volcano, which takes into account total thicknesses of pyroclastic coverings and variable stratigraphic settings. For both, effects of different initial antecedent hydrological conditions, associated with summer and winter, are considered.