The aim of this work was to determine the dependable rainfall using different levels of probability in Dourados, Mato Grosso do Sul State, Brazil. This study was conducted for intervals of 10, 15 and 30 days, based on daily data of rainfall for 17 years. Series were adjusted to a mixed distribution and a non-parametric test Kolmogorov-Smirnov was used . The parameters of gama distribution were estimated by the method maximum likelihood. Data were adjusted to all periods. Based on the accumulated mixed distribution were generated values of rainfall for periods return of 2, 3, 4, 5, 10, 12 and 17 years. Results allow irrigation personal to adopt criterions values of rainfall for designing irrigation projects near Dourados-MS. The average rainfall should not be used because it may result in under estimation of the rainfall.
irrigation; design; precipitation
