Modeling blue and green water resources availability at the basin and sub-basin level under changing climate in the Weyb River basin in Ethiopia

Abstract

The Weyb River basin, water from which is utilized for diverse water resources schemes, is one of the important rivers of Ethiopia. However, increase in temperature and change in both magnitude and its spatiotemporal distribution of rainfall under changing climate are adversely affecting the freshwater resources availability. This study aims to model the blue and green water resources availability under changing climate within Weyb River basin in Ethiopia at both basin and sub-basin level using ArcSWAT hydrologic model. All water balance components including blue water flow (sum of the water yield and the deep aquifer recharge), green water flow (actual evapotranspiration), and green water storage (soil water) at both entire basin and sub-basin level were examined. Results reveal that mean annual blue water flow, green water flow, and green water storage exhibit a rise in the entire basin and in all the sub-basins under representative concentration pathway (RCP)8.5/4.5/2.6 scenarios. The mean annual blue and green water flow increases by 28% and 30% under RCP8.5, 20% and 29.89% under RCP4.5, and 17% and 28.65% under RCP2.6 scenarios respectively, while the mean annual green water storage rises by 13.87%, 13.62%, and 13.60% under RCP8.5, RCP4.5, and RCP2.6 scenarios respectively in the entire basin. The sub-basin level analysis reveals that spatial variations of blue and green water resources availability in all the six sub-basins are very high as compared to that of the entire basin analysis under all RCP scenarios. This study provided significant insights into freshwater availability on a sub-basin level under future changing climate and it is paramount important to develop climate change adaptation and mitigation strategies at sub-basin level for optimum planning and management of freshwater availability within the Weyb River basin in upcoming period.