Multifractal Dynamic Rainfall Processes in Italy

 Historical daily rainfall events, measured at different Italian stations, are found to follow fractal relationships within specific time ranges. It is found that the fractal dimension D describes the strength of the clustering of daily rainfall events in a more realistic way than the commonly used number of daily rainfall events: the more isolated the clusters, the smaller the value of D. The large dependence of D and of the specific scaling region on the threshold intensity is an indication of a more complex property of the rainfall called multifractality: a large-scale rain-field is successively broken into smaller and smaller eddies, each receiving an amount of the total field specified by a multiplicative parameter. Circumstantial evidence indicates, moreover, that the significant secular decreases of D over the Mediterranean area can be reasonably related to the simultaneous coherent decrease of zonal atmospheric circulation.