The purpose of this article is to simulate how future climate scenarios will affect evapotranspiration, surface runoff and drainage in an agricultural area. The area's behaviour is represented by a lysimeter consisting of an undisturbed soil core with volume 1 m3, sited in the basin of the Concordia River near the town of Lontras in the southern Brazilian State of Santa Catarina. The simulation used the SWAP (Soil-Water-Atmosphere-Plant) model, calibrated and verified with data on rainfall, temperature, relative humidity, wind speed and direction, radiation and soil water content over a 34-month period. Hydrological processes characterizing the basin soils were determined from present climate as baseline, and from series generated for maximum and minimum scenarios of carbon emissions (scenarios A2 and B2, respectively). Simulations were made for conditions of bare soil and for maize cultivation. Results showed that for these two conditions A2 and B2 give annual mean rainfall depths, evapotranspiration and interception of the same order of magnitude as in the baseline period. Depths of surface runoff were greater than baseline for both scenarios and for both cultivation conditions. For bare soil, the increases were about 118 and 268% for B2 and A2, respectively. These differences were generated from frequency distributions of maximum daily rainfalls in scenarios A2 and B2 that were greater than those for baseline. However, drainage flow was lower for the two soil conditions, and for the two scenarios A2 and B2, relative to baseline conditions.