With the objective of studying the effect of the size of different historic series of climatic data in the volume of water, in the Gorutuba Irrigation District, a computer model and three historic series with different sizes were considered. For each one, the volume of water was simulated and was compared with the volume of water measured in the year of 1996. The results showed that using a historical series of 1984-1994, the volumes of water were lower 16.2% per month than based on 1984-98, and 53.8% per month with regard to estimated on data of 1996, and that the number of years of historic series may have strong influence on the estimation of the irrigation water volume.
dependable precipitation; evapotranspiration; irrigation demand; irrigation district
