ASSESSING THE IMPACTS OF CLIMATE CHANGE ON STREAMFLOW UNDER CMIP6 CLIMATE PROJECTION IN THE UPPER OMO GIBE RIVER BASIN, ETHIOPIA

Abstract

Climate Change is projected to have an impact on future streamflow in various watersheds. This study examined the impacts of climate change on streamflow in the Upper Omo River Basin using a Soil and Water Analysis Tool (SWAT). Projected climate variables (precipitation and temperature) ensemble of 5 Global Circulation Models (GCMs) were obtained from the World Climate Research Programme (WCRP), downscaled by the SDSM4.2 model and applied under the Shared Socioeconomic concentration pathways (SSP2-4.5) and (SSP5-8.5) scenarios. The downscaled SSPs data cannot be directly used to the hydrological model (SWAT) to simulate flow so, Distribution Mapping bias correction method was selected for this study. SWAT was calibrated and validated before it was used for simulation purpose. The performance measures R2 and NSE for calibration (2000-2013) and validation (2014-2019) were 0.79 and 0.71 and 0.86 and 0.85 respectively. Mann Kendall (MK) trend testing was used to determine if a change is statistically significant and to detect trends in temperature and precipitation. According to RCP4.5 and RCP8.5, the emission scenarios predicted significant increasing temperature, but significant decreasing precipitation. Streamflow was simulated for two consecutive periods from 2020 to 2045 and from 2046 to 2071 for both scenarios and compared with the base period from 2000 to 2019 to explore the impact of climate change on Streamflow. The results indicated that the basin is likely to experience increased temperatures and altered precipitation patterns, whereas overall annual flow was projected to be significantly decreasing under SSP2-4.5 and SSP5- 8.5 emission scenarios in the mid and near future. These changes are likely to have major implications for water resources management in the region, particularly for agriculture, hydropower generation, and ecosystem services. The findings suggest the need for adaptive measures to address these impacts, including improved water management strategies and increased investment in climate-resilient infrastructure.