The process changes are arising mainly due to the land cover/use variability, but, mainly due to the decreasing in the rainfall rates during 1995-2008 when compared with the first period analysed, which in turn decreased the streamflow and sediments during the wet seasons and reduced the base flow during the dry seasons.

Water scarcity and sediment yield scarcity are major environmental problems in the Brazilian semi-arid region that influence the quantity and quality of water used for water supply. Thus, the aim of the paper was to analyse the water balance and the sediment yield in the Epitácio Pessoa Dam river basin using the Soil and Water Assessment Tool model. Rainfall, streamflow, air temperature, air humidity data from 1970 to 1993, a soil type map, a land cover map, and a digital elevation model were used in this study. The model was calibrated and validated by comparing simulated mean monthly streamflow with observed long-term mean monthly streamflow for the Poço de Pedras and Caraúbas streamflow gauges after sediment yield values were estimated. The Soil and Water Assessment Tool model results indicated good performance by the model during the calibration, with an observed mean streamflow of 6.86 m 3 /s and a simulated streamflow of 5.68 m 3 /s for Poço de Pedras and 9.33 m 3 /s for Caraúbas. The mean sediment yield was 3.91 ton/ha/month. The results of the water balance analysis indicate a high rate of evapotranspiration in the basin (68% evapotranspiration), and 7% of the rainfall was converted to streamflow (5% streamflow and 2% base flow). Therefore, this study found that Soil and Water Assessment Tool could be effectively used for assessing the water balance components and sediment yield of the Epitácio Pessoa Dam river basin, Paraíba State, Brazil.