Geomorphological approach to flash flood hazard and vulnerability evaluation in torrential basin-fan systems in Campania (South Italy)

A flash flood is a very quick increase in the discharge of a stream, generally caused by short duration and high intensity rainfalls. This phenomenon is very frequent in Europe and in Italy too, where generally occurs in small catchments with short response time, causing many damages in the outlet zones. In historical times, numerous flash flood events occurred in Campania Region (Southern Italy), with an increase in frequency in the last decades, associated with the present trend of climate change. 
This note summarizes the results of the last ten years studies on the flood events occurred in the torrential basin-fan systems of the Campania region, aiming to contribute to the assessment of the hazard and risk condition. In these watersheds flash flood events resulted in a series of phenomena, passing from debris flow to debris flood and water flood, which produced serious damage to urban centers and cultivated areas. Unfortunately, these catchments are often not monitored and the lack of information on rainfall and flow data makes more difficult to apply hydrological and hydraulic models to evaluate hazard and risk. Hence, in these settings, geomorphological study and post-event field campaign have been useful to identify the flooding prone areas and the magnitude of the occurred events. The latter has been achieved by the estimate of the maximum water heights of the flow, of the thickness of eroded and/or deposited material and of the relative particle size of the deposits and finally of the volumes. The acquisition of remotely sensed images by means of UAV (drones) enhanced the field surveys to obtain these data. More in detail, the integration of morphometric analysis in GIS, with field and remotely sensed data permitted to draw several thematic maps, that together with the identification of the damage states have been exploited to produce empirical vulnerability curves for these events. 
Collecting such data represents a fundamental issue for calibrating hydraulic flow models for the hazard evaluation, while the development of vulnerability tools can be adopted to assess the risk and define the best mitigation strategies.