Estimation of annual rainfall erosivity in Calabria through regional frequency analysis

First a brief critical review of the main methods used in estimating rain aggressiveness is proposed, followed by original formulations and methods that aim to: (I) estimate the aggressiveness of the single rainstorm, by means of a new formula, adequate to the climate of southern Italy; (II) accurately assess, the at site mean annual erosivity, R, through the analysis of more than 45000 rainfall erosive events having 5-minutes time detail; (III) estimate the rainfall erosivity, R, based on regressive analysis with easily available rainfall characteristics; (IV) characterize R in terms of probability, even in sites without data, by regional frequency analysis. In this last regard, the observations of a variable of interest, collected within a homogeneous region, have been used in order to estimate the probability distribution of the variable. The analysed variable is the modified Fournier index, FF, that is well correlated with mean annual erosivity R. For estimating FF, data are available in a large number of rain gauges and for long observation periods. As a result of the analysis, 4 homogeneous regions for FF and consequently for R, have been obtained. In these regions, it will be possible to obtain an estimate, for different return times, of the rainfall erosivity, even in sites where rainfall observations are unavailable.