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Changes in rainfall, temperature and streamflow (stf) will be one of the most critical factors determining the overall impact of climate change (CC). Thus, in this study we evaluated rainfall(rf), temperature, and stf pattern under changing climate in the Abelti-Watershed (a sub-watershed of upper Omo Gibe basin), Ethiopia. The Representative Concentration Pathway (RCP) scenarios of Hadley Global Environment Model 2-Earth System (HadGEM2-ES) under Coordinated Regional Climate Downscaling Experiment (CORDEX)-Africa database selected for the near (2011-2040), med (2041-2070), and end (2071-2100) periods. Hydrologic Engineering Centers-Hydrologic Modelling System (HEC-HMS) model applied for stf projection. XL-STAT conducts average annual and seasonal rf, minimum and maximum temperature (tmin&tmax), and stf trend tests. Mean seasonal and annual rf and stf variation evaluation taken using the coefficient of variation (CV). Finally, the impact of CC analysis is taken based on the baseline period. The results revealed that the climate model projection is successful for given weather stations. HEC-HMS model showed a satisfactory performance during calibration (R2=0.82) and validation (R2=0.78). The MK trend of tmin&tmax show significantly increasing; whereas rf and stf show insignificantly decreasing except under RCP8.5. The rf and stf CV analysis indicated less, moderate, and high in the study area. And the future long year average annual rf increased by -3.6%, -1.9% and -7.7%; temperature +1.15%, +2.2% and +4.2%; and stf -2.9%, -0.05% and -8.5% under RCP2.6, RCP4.5 and RCP8.5 respectively. Thus, the decrement in rf and the increment in temperature lead to more evapotranspiration and affect the stf negatively. In conclusion, stf in the Abelti-watershed could significantly decline with adverse consequences for water supplies, agriculture, and ecosystem health for the future. Therefore, this study may contribute to the planning and implementation of sustainable resources development and management strategies and help to mitigate the consequences of CC.

This study assessed the impact of climate change (cc) on the water balance of the Lake Hawassa catchment. The CMhyd (Climate model data for hydrologic modeling) model was used to correct biases of the Representative Concentration Pathways (RCP) scenarios for 2050’s (2041–2070) and 2080’s (2071–2100). The impact of cc on water balance components was analyzed by Soil and Water Assessment Tool (SWAT) model and its very good performance during the calibrate and validate periods, respectively are coefficient of determination (R²) 0.61 and 0.88 and Nash-Sutcliffe efficiency (NSE) 0.81 and 0.85. Projected precipitation (ppt) decreased by 11.4% and 8% in RCP4.5 and 20.67% and 15% in RCP8.5 respectively in 2050s and 2080s. The projected minimum and maximum temperature (Tmin&Tmax) is increased by 26.2% and 15.6% under RCP4.5 and increased by 45.8% and 29.5% under RCP8.5 respectively. The future water balance of Lake Hawassa catchment under RCP4.5 and RCP8.5 by the end of 2100; ppt decreased by 12% and 27%, surface runoff increased by 10% and decreased by 16%, lateral discharge decreased by 39% and 50%, water yield decreased by 27% and 46%, evapotranspiration (ET) increased by 23% and 21% and potential evapotranspiration (PET) increased by 77% and 75.3% respectively. The increment in temperature and the decrement in ppt resulted increment in PET largely because the water holding capacity of air is increased. Moreover, the climatic variations and human influence the water balance of the study has affected. Therefore, constantly monitored and updated sustainable water resources management is needed in the area.