Climate change impacts on water resources in the Upper Blue Nile (Abay) River Basin, Ethiopia

摘要

This study assesses the impact of climate change on water resources in the Upper Blue Nile (Abay) River Basin using a regional climate model (RCM), COSMO Climate Limited-area Model (CCLM), coupled with a hydrological model, Soil and Water Assessment Tool (SWAT). The SWAT model was calibrated and validated using measured streamflow data from four gauging stations. Climate change projections showed increases in mean annual temperature and decrease in precipitation in most parts of the Basin. Such changes are expected to affect the hydrologic regime of the Basin; these were assessed by running the SWAT model with the past (1981-2010) and future (2010-2039, 2040-2069 and 2070-2099) climate scenarios. The results show an increase of potential evapotranspiration (PET) by up to 27% by the end of the 21st century under RCP8.5 compared to the baseline period. Surface runoff is projected to increase by up to 14%. However, the increase in surface runoff could not increase the total water yield of the Basin. Instead, the total water yield of the Basin is estimated to decrease by -1.7 to -6.5% and -10.7 to -22.7%, for simulations forced by RCP4.5 and RCP8.5 scenarios, respectively. By the end of the 21st century, the contribution of baseflow to the total water yield of the Basin is also projected to decline to 11.4% from 41.3% during the baseline period. The decrease in baseflow partly explains the decline in the total water yield of the Basin. Such changes in the hydrologic balance will have significant implications for water management in the Basin.