Investigation of the impact of climate change on hydrological responses using the CMIP6 model for Upper Omo Gibe Basin, Ethiopia

Abstract Evaluating the impact of climate change on the hydrological processes is critical for effective and sustainable water resources management. Robust Coupled Model Intercomparsion Project Phase 6 (CMIP6) based evaluations of climate driven hydrological shifts remain critically underexplored regionally. This study examines the potential impacts of projected climate scenarios on the hydrology of Upper Omo Gibe Basin using the Soil and Water Assessment Tool (SWAT), driven by the CMIP6 climate model under Shared Socioeconomic Pathway (SSP245) and (SSP585) scenarios. Essential hydrological components are investigated for both the near future (2031–2065) and long future (2066–2100) periods. The historical mean annual precipitation (1499.18 mm) is projected to increase under all scenarios, with increments in +12.1% (SSP245 near future), +21.4% (SSP245 long future), +24.4% (SSP585 near future), and +46% (SSP585). The largest monthly decrease is observed in March, whereas November and the Autumn season show the largest increases under SSP585. Temperature projections show the most significant warming in the long-term SSP585 scenario, attaining +3.9 °C in July and August. Annual streamflow is expected to increase across all scenarios, especially during Autumn and Winter. Surface runoff indicates an initial decrease (−33.9% under SSP245 near future) followed by subsequent increases, with the maximum rise occurring in October under SSP585, whereas the highest decrease is recorded in February under SSP245. Water yield rises significantly, reaching up to +78.2%, except for Autumn under SSP245, which declines by 7.8%. Lateral flow, evapotranspiration, and groundwater recharge show an overall increase, with the highest increments during Winter and Autumn under SSP585. Seasonal variability remains significant, with significant rises in Autumn and declines in Summer under SSP245 scenarios. Projected streamflow and runoff increases may strain Gibe cascade hydropower dam, these results indicate the importance of regularly updating reservoir operating rules, flood control strategies, and risk assessments under changing climate conditions.