The combined effects of LULC changes and climate change on hydrological processes of Gilgel Gibe catchment, southwest Ethiopia

The Gilgel Gibe catchment in southwest Ethiopia is undergoing rapid changes in land use, land cover (LULC), and climate, that have significant effect on its hydrological processes. The study uses LULC change scenarios (2021, 2039, and 2057) and climate change scenarios RCPs 4.5, and 8.5 to simulate the hydrological response of the catchment from 1991 to 2099. Land use and land cover (LULC) in the 2039 and 2057 scenarios are expected to increase surface runoff by 2.02% and 4.09%, respectively. The groundwater flow is projected to decrease by 0.63%, 0.32%, and 0.09% under the 2021, 2039, and 2057 time horizons, respectively. The results showed that the water yield increased by 2.62%, 2.71%, and 3.23% for the 2021, 2039, and 2057 scenarios, respectively, due to the expansion of agricultural land and the reduction of forest cover. With the RCP8.5 scenario forecasting the largest declines in surface runoff, groundwater flow, and water yield by 2057. The combined effect of LULC change and climate change was additive, resulting in increased surface runoff and water yield, but decreased groundwater flow in 2039 and 2057 under the RCP8.5 scenario. These results provide useful information on vulnerability of Gilgel Gibe catchment to LULC and climate change.