Rainfall regionalization techniques

Regionalization techniques have been developed to estimate design rainfall in ungauged sites and to support ordinary data-based frequency analysis of areal rainfall or in presence of short records. Regional techniques use principles of data augmentation based on hydrologic similarity, trying to overcome limitations due to low rain gauge density or to any other data inadequacy, which hamper the estimation of high return period quantiles. This chapter intends to summarize the state of the art of regionalization techniques applied to rainfall data, starting from the identification of today’s problems in data availability, and then highlighting the differences between traditional and more innovative approaches aimed to provide intensity – duration – frequency rainfall curves everywhere in a large area. In line with the frequent changes observed in station density over large areas, the chapter deals with the advantages of interpolation methods over the homogeneous region paradigm, addressing the valorization of the local information deriving from short or intermittent records. With the overall aim of providing a guide to regional model building based on updated datasets, considerations on applicability and evolution of the models are finally made on the methods currently adopted in the practice, based also on a case study in North-Western Italy.