Hydrological impacts of climate change in gauged sub-watersheds of Lake Tana sub-basin (Gilgel Abay, Gumara, Megech, and Ribb) watersheds, Upper Blue Nile Basin, Ethiopia

Climate change has been increasing in influencing the water resources of the whole world as a result of increasing carbon emissions. Hence, evaluating the impacts of climate change on the hydrology of gauged watersheds of Lake Tana sub-basin where the socio-economic activities of the surrounding community highly depend on this basin is the prime task of the researchers. For this study, HBV hydrological model was used to simulate future climate change impacts on hydrology. For Gilgel Abay, Gumara, Megech, and Ribb, the model exhibited NS values of 0.803, 0.79, 0.68, and 0.797 during calibration and 0.82, 0.8, 0.801, and 0.82 during validation, respectively. For Gilgel Abay, Gumara, Megech, and Ribb, model results RVE of − 0.72%, 3.7%, 8.9%, and − 0.68% are during calibration and 8.76%, − 1.5%, − 5.89%, and 8.5% during validations, respectively. Climate change impacts on the hydrology of the Gilgel Abay, Gumara, Megech, and Ribb watersheds were assessed using projections from two ensembles GCMs (MPI and MIROC) for one RCM (RCA4) under RCP 4.5 and RCP 8.5 for the 2040-s and 2070-s time domains. Even though the expected number of changes differed among watersheds, GCMs, and RCPs, increasing runoffs in the dry season and lowering runoffs in the wet season are detected in both periods, owing primarily to changes in projected precipitation. Even if future flow improves in the dry seasons, which might provide water for agriculture, a decrease in flow during the wet seasons would diminish Lake Tana storage during the summer, which would be used for the Tana Belles Hydropower project, potentially affecting Tana Belles Hydropower water demand and Lake Navigation depth. These changes will harm the country's economic well-being, necessitating successful adaptation measures to lessen susceptibility. The study revealed that climate change will influence the hydrology of the basin; hence, the government and concerned bodies have to be planned and implement future water resources management and adoption activities in the Lake Tana sub-basins.