G. Boni, P. La Barbera & F. Siccardi (Environmental Montoring Research Centre, University of Genova, Cadorna, 17100 Savona, Italy)

The region along the Mediterranean Sea includes steep orographic relief all along the coastline: small catchments drain this thin strip of territory. In the northern Mediterranean regions the floodplains of these rivers are densely urbanised. By this reason coastal urban settlements are exposed to high risk of flood: the main challenge is to mitigate the impact of floods on people and economic activities. In the developing southern regions the coast is not yet densely urbanised, but the challenge is that to avoid the errors done in the policy of the urban development of the northern regions. To start a correct policy of mitigation of the risk of flooding and to avoid urbanisation of areas higly exposed to this risk, an homogeneous definition of the criteria for the evaluation of the flood frequency is needed. The recent results obtained in the study of the characteristics of the Mediterranean storms allow some innovation in the methods for flood frequency evaluation. The new method is presented, which includes the possibility to directly obtain the expression for the areal reduction factor. The method allows to get the mean areal rainfall as a function of easily observed meteorological and geomorphologic parameters. The application of the method provides the peak flow discharge for a population of catchements in a region, for a given return period, provided that the region is sensibly meteorologically and geomorphologically homogeneous.