Climate change impact on water resources availability in the kiltie watershed, Lake Tana sub-basin, Ethiopia

Climate change's influence on water resource availability in watersheds must be evaluated to ensure food and water security. Using an ensemble of two global climate models (MIROC and MPI) and one regional climate model (RCA4), the impact of climate change on the availability of water in the Kiltie watershed was evaluated under the RCP4.5 and RCP8.5 scenarios for the year 2040s and 2070s. The flow was simulated using the HBV hydrological model, which needs fewer data and is typically employed in data-scarce settings. The model calibration and validation result, show RVE (relative volume error) of −1.27% and 6.93%, and NSE of 0.63 and 0.64 respectively. Seasonal Water Supply in the Future Under the RCP4.5 Scenario for the 2040s increased between 1.1 mm and 33.2 mm showing maximum incremental in August and a decrease in a range from 0.23 mm to 6.89 mm with a maximum decrease in September. While in the 2070s, water availability increases between 7.2 mm and 56.9 mm, with the largest increases occurring in October and the smallest reductions occurring in July by 9 mm. Future water availability increases under the RCP8.5 scenario during the 2040s period between 4.1 mm and 38.8 mm, with the highest increase occurring in August, and falls between 9.8 mm and 31.2 mm, with the maximum declines occurring in the spring seasons. Water availability in the 2070s, according to the RCP8.5 scenario, increases between 2.7 mm and 42.4 mm with the highest increments in August, and it decreases between 1.8 mm and 80.3 mm with maximum decreases in June. According to this study, climate change would make it easier to access water during the rainy season, necessitating the construction of water storage facilities so that surplus water can be used for dry farming. A watershed-level integrated water resource management strategy should be created quickly as future water supply will decline during the dry seasons.