Regional Frequency Analysis of extreme rainfall events, Tuscany (Italy)

The probability distribution TCEV - Two Component Extreme Value is used in the frame of the procedure for the parameters estimation based on a three levels hierarchical approach. The methodology deal with the delineation of homogeneous regions, the identification of a robust regional frequency distribution and the assessment of the scale factor or the index rainfall. A four regions subdivision, coincident with four subregions, which takes into account the orography, the geomorphological and climatic peculiarities of the region, has been adopted. For each region the daily rainfall growth curve has been estimated. The growth curves for the hourly duration have been estimated when the daily rainfall growth curve is not able to describe the sample cumulate frequency distribution. In order to define the index rainfall for each homogenous region and each duration, a multivariate model that combines the Mean Annual Precipitation, the elevation, the aspect and the sample mean of the annual maxima time series of the gauge sites has been used.