Improving flash flood risk assessment using a simple approach for extreme rainfall scaling and storms transposition

A simple approach based on rainfall scaling and storms transposition of occurred events is presented to identify areas where design discharges underestimate the flash flood risk. The methodology considers the spatial distribution of the observed storms over a specific zone and the areal reduction factors to scale the observed hyetographs for different river basins extensions. Hyetographs of past observed events are used as input of a hydrological model in a set of river basins located in Northern Tuscany (Italy). The results show how peak discharges of short-duration events are usually greater than the design floods of the small river basins with an area generally less than 30 km2.