Analysis of widespread rainfall spatial distribution by a parameterized numerical model

The aim of this work is to discuss a parameterized numerical model suitable for investigating, on the meso-local scale, widespread rainfall patterns over hilly terrain, in the absence of convective processes. In this model and for the area under investigation, the rainfall rate, as measured at soil surface in a zone which is not affected by contributions due to orographic slope, is adjusted as precipitation rate at Z=2000 m; in the region of the atmosphere beneath this level the orographic effects are then computed, disregarding the large scale vertical velocity. Finally, two model applications to rainfalls over an area within the basin of the Upper Tiber Valley are presented. The comparison of theoretical and experimental rainfall rates, with differences between mean values less than 10%, indicates a good reliability of the model; however, this must be confirmed utilizing a larger number of cases and a more complex orographic structure.