Currently, there is an urgent need to manage and rationalize the use of water resources worldwide, especially in areas subject to periodic droughts such as the semiarid Northeast of Brazil. One of the first steps of the great task of managing water resources is on the estimate of the supply of water within the basin. To do so, it is necessary to study the interactions between climate, land use and physiographic. Given the importance of proper management of water resources, the aim of this study is to examine the impacts of space-time variability of rainfall, soil depth and plant cover on the production of water from the reservoir basin Epitácio Pessoa, located in semiarid state of Paraiba - Brazil. A program called TOPAZ was used to obtain the physical characteristics of the basin, based on data from digital terrain elevation. The Landsat TM-5 was used to estimate the vegetation cover. Among several scenarios, the fifth was the best represented the overland flow in the reservoir basin Epitácio Pessoa. In general, the model responded well to the space-time variability of rain. Approximately 12% of rainfall was turned into the confluence Epitácio Pessoa. The coefficients of determination and Nash were on average 0.89 and 92% respectively. The results showed that there were changes in the pattern of runoff upstream of the dam. These changes are resulting in delayed and reduced runoff tributary to Epitácio Pessoa, due to the construction of new reservoirs upstream of it.