In the present study, an ArcSWAT model was utilized to simulate the hydrological responses due to land use and climatic changes in the Omo-Gibe river basin, Ethiopia. The performance of the model was evaluated through sensitivity, uncertainty analysis, calibration and validation. The most sensitive parameters were identified which are governing on surface runoff generation processes in the selected basin. The calibration and validation of the model was done using SWAT-2005. Also, the sensitivity and uncertainty analysis was performed using the SUFI-2 and SWAT-CUP algorithm. The model results revealed that a good performance during the calibration (R 2 = 72.4%, NSE = 62.6% and D = 14.37%) and validation (R 2 = 68.1%, NSE = 68% and D = 4.57%). SUFI-2 algorithm gave good results in minimizing the differences between observed and simulated flow in the Great Gibe sub-basin. The studies show that there is an overall increasing trend in future annual temperature and significant variation of monthly and seasonal precipitation from the base period 1985-2005. Also, the annual potential evapotranspiration shown increasing trend for future climate change scenarios. Similarly, the surface water decreases in terms of mean monthly discharge in the dry season and increases in the wet season. The percentage change in future seasonal and annual hydrological variables was shown increasing trends. Therefore, this study found that SWAT can be effectively used for assessing the water balance components of a river basin in Omo-Gibe basin, Ethiopia.

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