Predicting Climate Change Impacts on Stream flow of Mille Watershed, Lower Awash River Basin, Ethiopia

Climate change manifests itself primarily through changes in average temperature and precipitation, affecting overall flow magnitude. This study evaluated the impact of climate change on the stream flow of the Mille watershed, which is situated in the northeast part of Ethiopia. Different materials and Soil and Water Assessment Tools were used to arrive at the stated objectives. Downscaled future climate projections of precipitation and temperature were developed from the Hadley Global Environment Model 2-Earth System (HADGEM2- ES) under two radiative forcing scenarios (RCP4.5 and RCP8.5). These climate scenarios were bias-corrected for each selected station and areal rainfall over the catchment was determined. This study used the period 1976-2005 as the baseline period, while 2041-2070 (2050’s) and 2071-2100 (2080’s) as the middle-future and the far-future respectively. The current average daily temperatures vary little throughout the year: The mean monthly minimum and maximum temperature of the station ranges from 7.93°C to 11.2°C and 23.91°C to 24.13°C respectively. As temperature is projected the climate would become warmer for both scenarios in the future. The future projection of climate variables showed an increase in minimum temperature by 1.4oC and 1.3oC for RCP4.5 and 1.5oC and 1.8oC for RCP8.5 in 2050’s and 2080’s respectively. The current rainfall distribution of the catchment is bimodal with a very short rainy season in March to April and the main rains from July to September As Rainfall is projected the climate would become drier under RCP8.5, which showed a decrease in Rainfall by 8.05% and 8.73%, while under RCP4.5 Rainfall decrease by 3.87% in the 2050s but it becomes rise by 4.64% in 2080’s. The Soil and Water Assessment Tool (SWAT) model was calibrated and validated for streamflow simulation The result showed a change in stream flow by -6.37% and 5.8% for RCP4.5, -13.9%, and -26.3% for RCP8.5 in the 2050s and 2080 respectively. The results of this study are expected to arouse serious concern about water resource availability in the Mille watershed under the continuously warming climate. Therefore, there is a need to minimize the sensitivity to climate change by making stringent climate policies. Keywords: Climate Change, Representative Concentration Pathways, Hydrology, Soil and Water Assessment Tool, Mille