ASSESSMENT OF CLIMATE CHANGE IMPACT ON SURFACE WATER RESOURCE IN WOSHA WATERSHED, RIFT VALLEY LAKES BASIN, ETHIOPIA

Abstract

Climate change (CC) and Land Use/Land Cover (LULC) changes present significant threats to global water resources and socio-economic systems. This study aimed to evaluate the impact of climate change and LULC changes on the availability of surface water resources in the Wosha watershed, located in the Rift Valley Lakes Basin (RVLB) of Ethiopia. The available water resources were assessed using the Soil and Water Assessment Tool (SWAT), a semi-distributed, physically-based hydrological model. Calibration and validation of computed stream flow were conducted using SWAT-CUP with the SUFI-2 algorithm. Bias-corrected data from three climate models output from Coupled Model Intercomparison Project Phase 6 (CMIP6) models such as CANESM5, MIROC6, and NESM3 were used to assess baseline (1985-2014), mid-term (2041- 2070), and long-term (2071-2100) periods under the Shared Socioeconomic Pathways (SSP2 4.5 and SSP5 8.5) climate scenarios. The SWAT model's performance was robust, achieving R² values of 0.88 and NSE values of 0.75 during calibration, and R² values of 0.83 and NSE values of 0.72 during validation for monthly simulations. The projections indicate that both rainfall and temperature will increase under SSP2 4.5 and SSP5 8.5 scenarios in the mid-term period, with a temperature rise of 1.2°C expected under SSP5 8.5. Precipitation is also expected to increase by 1% to 10% in the long term for both scenarios. Therefore, the primary objective of this study was to assess the impact of climate and LULC changes on the availability of surface water resources in the Wosha watershed. The results underscore the importance of understanding surface water availability and mitigating the impact of climate change to ensure future water resources for the region.