The role of the high resolution weather forecast in estimating the run-offusing a simple hydrological model

Recent and repeated episodes of severe weather in Italy have stressed the need to have a suffi ciently accurate forecast
to give adequate warning to the involved areas. The impact of the precipitation, however, is also a function of the
characteristics of the hydrological basin. From this point of view, a rather startling example is the disaster which
hit the Campania region on 5th May, 1998 in which a moderate precipitation (about 100 mm in 24 h) produced
a huge landslide which killed or injured several tens of people and produced serious damage to the area. Such
localized events require among other things the use of a high resolution weather forecast. In this paper, a forecast
of the Campania event using a limited area model at 3 km grid resolution is presented. The forecast rainfall at
several grid resolution is used to initialize a simple hydrological model to estimate the run-off. The numerical
experiments suggest that high resolution may be a key factor in predicting the run-off.