Rainfall extreme values analysis: a multivariate approach

In the framework of regional frequency analysis of short duration rainfall annual maxima, aim of this work is to find expressions able to model the scale factor of the non dimensional regional probability distribution for ungauged sites, i.e. the index rainfall. Considering the Tuscany region divided in three zones and subzones, the first and second level of a hierarchical regionalization procedure is carried out using the Two Component Extreme Value (TCEV) distribution, and the growth factor is calculated. On the time series, characterized by a low spatial correlation, a local extreme value analysis based on the Generalized Extreme Value (GEV) distribution is also achieved. Assuming the local rainfall extreme estimation, at the gauge site, equal to the estimated regional extreme, the index rainfall at the gauge site can be considered given by the ratio of the estimated GEV and the growth factor. A multivariate analysis is proposed to model the relationship among the spatial variability of index rainfall and territory characteristics.