Evaluating the potential of Nature-based solutions to mitigate land use and climate change impacts on the hydrology of the Gefersa and Legedadi watersheds in Ethiopia

Surface water supply source of Addis Ababa, the capital city of Ethiopia, relies primarily on the small reservoirs in Gefersa and Legedadi water supply systems located upstream of Little and Big Akaki rivers. Thus, Gefersa and Legedadi are the study watersheds of this research. This study evaluates the impacts of land use and climate changes on surface water availability and the benefits of nature-based solutions (NbS) to enhance the water supply and the life of the dams in the Gefersa and Legedadi small watersheds that supply water to Addis Ababa city, Ethiopia. Several land use and climate change scenarios have been developed and integrated into baseline hydrological model to assess their impact on water balance components and sediment yield. Extreme climate change scenarios were developed using the combination of the 5th, 50th and 95th percentiles of future precipitation and temperature changes. The results of the land use change analysis revealed a shift between 2012, 2022 and 2042, with a significant expansion of urban settlements and a decline in forestland and vegetation cover. Under climate change scenario, the simulations project that drier seasons become drier and wet seasons become wetter. Overall, this study highlights the potential benefits of NbS in enhancing water availability, particularly during the dry season, promoting dry season farming and increasing the water supply to meet the water demand. The approach followed in this study can be adapted to other watersheds with access to more recent and good quality datasets for future research. [Display omitted] •Land use changes pose a significant challenge to the availability of surface water supply for Addis Ababa, Ethiopia.•The land use change analysis revealed an expansion in urban areas and a decline in forestland and vegetation cover.•The model simulation results with land use change highlighted potential increases in surface runoff and sediment yield.•Climate change scenarios model simulations projected that drier seasons become drier and that wet seasons become wetter.•Implementing NbS reduces soil erosion, enhances GW recharge, supports dry-season farming, and water supply sustainability.