Streamflow Modeling Under the Impact of Climate Change. (Case Study of Dabus River Sub-Basin, Ethiopia)

Currently the impact of climate change affects many water resources projects that result in pattern change of annual runoff, reservoirs pool level change, increasing of irrigation demand due to increasing temperature and evaporation and etc., and thus it is important to assess its impact on streamflow. This study mainly forecast streamflow of Dabus river Sub Basin. The future climate variables which were downscaled by Climate Limited area Model (CLM) at the basin level for A1B emission scenario was used for future flow simulation. For streamflow generation HEC-HMS model was used by using the bias corrected precipitation and Evapotranspiration which was estimated by FAO Penman-Monteith. After the flow was forecasted, the performance of the model was assessed via calibration at Dabus near Asosa, Sechi near Mendi and Aleltu at Nedjo using Relative Volume Error (D), coefficient of determination (R 2 ) and Nash-Sutcliffe Efficiency (NSE) performance coefficients. Then the model was validated using the parameters optimized during model calibration. The trend of Dabus streamflow forecasted at its outlet to main basin river (Abbay River) was assessed. The projected mean annual maximum temperature increases from the baseline period by 0.43 0 C, 1.3 0 C and 2.5 0 C for short-term, midterm and long-term respectively whereas minimum temperature increases by 0.47 0 C, 1.53 0 C and 2.83 0 C. Generally the projected future maximum and minimum temperature shows an increasing trend whereas precipitation shows variation (does not reveal clearly increasing or decreasing) for earlier century and decreasing trend in mid and late century. The evapotranspiration shows an increasing trend. The HEC-HMS model shows a good performance at Dabus near Asosa which resulted D=0.0066, R 2 =0.90 and NSE=0.89 during calibration and D=4.9285, R 2 =0.84 and NSE=0.82 during validation. The streamflow of Dabus River Basin shows an average annual increase of 2.83% for short-term forecast (2011-2040) and decrease of 2.83% and 4.56% for mid-term forecast (2041-2070) and long-term forecast (2071-2100) respectively.