Modeling the impact of changing in climatic variables on streamflow of Borkena River catchment, Awash Basin, Ethiopia

Poor land management coupled with increasing climate extremes is affecting the livelihoods of Ethiopian communities. So, evaluating the possible impact of climate change on water resource is essential for planning a sustainable water use system. As a result, this study aimed to investigate the impact of climatic variable changes on streamflow in the Borkena River Catchment, Awash Basin, Ethiopia, using projected climate data of canESM2 (Canadian Earth System Model of second generation) global climate model. Future scenario, analysis was performed for the 2020s, 2050s and 2080s for the Representative Concentration Pathway of RCP4.5 and RCP8.5. Impact assessment of climatic variable changes on streamflow was done by HBV Light hydrological models. The model was calibrated using a semi-automated method and the performance was measured by the coefficient of determination (R-2), Nash-Sutcliffe efficiency (NSE) and mean difference. The performance of HBV Light hydrological model during the calibration and validation period showed a satisfactory agreement between observed and simulated flow with R-2, NSE and mean difference. The value of R-2, NSE and mean differences was 0.84, 0.82 and 0 for calibration and 0.83, 0.78 and 8.23 for validation periods, respectively. The downscaled precipitation and temperature result reveals decrease and increase value in all future three-time horizon for both RCP8.5 and RCP4.5 scenarios in an annual basis respectively. This condition was expected to result decreased in mean annual streamflow of Borkena River in the future three-time horizon with the value of -16.81%,-17.25% and -18.28% for RCP8.5 scenario and -6.88%, -9.89% and -10.66% for RCP4.5 scenario in the 2020s, 2050s and 2080s, respectively. Inoculation future climate variation has a significant impact on the surface water potential of the catchment. So, for sustainable development of the River catchment in water use the streamflow of the catchment should be harvested.