Modeling Climate Change Impact on the Hydrology of Keleta Watershed in the Awash River Basin, Ethiopia

Regional and local hydrological regimes are significantly vulnerable to global climate change which threaten water resources and food security of nations. This study investigates the likely impact of climate change on hydrological processes of the Keleta watershed in the Awash River Basin, Ethiopia. Delta statistical downscaling methods were used to downscale 20 global circulation models (GCMs) and 2 representative concentration pathways (RCPs) (RCP 4.5 and RCP 8.5) over the study periods of 2050s and 2080s. The Soil and Water Assessment Tool (SWAT) model was used to simulate hydrological processes. The model was calibrated and validated using monthly observed streamflow data for the baseline year (1985). It performed well with a Nash-Sutcliffe efficiency (NSE) ≥ 0.74, ratio of the root mean square error to the standard deviation of measured data (RSR) ≤ 0.51, and percent bias (PBIAS) ≤ 15.3. The results show that RCP 4.5 predicts an average precipitation increase of 15.2 and 17.2% for mid- and end-of-century data, respectively. Similarly, RCP 8.5 predicts an average precipitation increase of 19.9 and 34.4% for mid- and end-of-century data, respectively. Mid-century minimum and maximum temperature increases range from 1.8 to 1.6 °C (RCP 4.5) to 2.6 to 2.1 °C (RCP 8.5), respectively, while end-of-century increases vary from 2.4 to 2.0 °C (RCP 4.5) and 4.6 to 3.7 °C (RCP 8.5), respectively. This leads to an average increase in runoff by 70%. The increased rainfall, warmer temperature, and significant increment in the hydrologic components, and particularly the excess runoff and associated extreme peak flow over the coming decades, are likely to put a tremendous pressure on the hydrological system of the watershed. This calls for sustainable and effective adaptive measures for future water resource management.