Agregação do Coeficiente de Abatimento Espacial à Relação Intensidade-Duração-Freqüência das Precipitações Sobre a Região Metropolitana de Belo Horizonte

Abstract

The so-called “indirect methods” for flood discharge estimation generally presuppose previous knowledge of the areally-averaged precipitation for a given duration over the drainage area concerned. It is a frequent practice among engineers to take point precipitation, from onsite IDF curves, as uniformly distributed over the area in question. However, it is known that precipitation does not fall uniformly over a given area and does vary with its relief and shape, as well as with storm duration and intensity, among other factors. This paper summarizes the studies for estimating the areal-reduction factors (ARF) to be applied to the storms over the Metropolitan Region of Belo Horizonte, in southeastern Brazil. The methodology used is based on the spatial correlation coefficient between point precipitation depths, on the characteristics of the rainfall events, and on the area itself. The resulting ARF estimates, which are variable not only according to area but also according to storm duration and associated return period, could then be incorporated to the existing IDF relationship of the study area. This paper also shows comparisons with other studies, some results verification for observed short-duration storms and a brief discussion on linking some spatial characteristics of rainfall fields to storm type and duration. Key-words: areal reduction factor; intensity-duration-frequency relations.