Water balance in Cubatão-Sul river catchment, Santa Catarina, Brazil

Abstract

The objective of the present study was to evaluate the water balance in the Cubatão-Sul river catchment (403.83 km2), Santa Catarina State, Brazil, which is very important for irrigated horticulture and drinking-water supply to the Great Florianópolis Region. The daily data obtained from the Poço Fundo hydrometeorological station and São José Meteorological station during the period between 1977 and 1994 were used for the analysis. A lumped and storage model HYCYMODEL was used for both water balance and evapotranspiration analyses and five additional methods were used for the evapotranspiration analysis. The results from the HYCYMODEL showed that the total discharge and the evapotranspiration in the catchment are approximately 62% and 44% of the annual rainfall (1563 mm), respectively. The total discharge consists on the direct runoff of 26% and the base flow of 74%. The actual evapotranspiration estimated with the water budget method was practically equal to that obtained with the HYCYMODEL. And the values of the ratio of the annual actual evapotranspiration to the annual potential evapotranspiration are 0.39, 0.58, 0.65 and 0.69 for Hamon method, modified Penman method, Blaney and Criddle method and Thornthwaite method, respectively. The increasing rate of the discharge over rainfall is larger than that of the evapotranspiration. When the annual rainfall is more than 930 mm, the discharge is always larger than the evapotranspiration.