Hydrological response to climate change in an Ethiopian Rift Valley basin: A multi-model ensemble analysis

The Hamessa watershed, located in the Ethiopian Rift Valley, is highly sensitive to climate variability and relies heavily on rainfall for water resources activities. Climate change alters the hydrological cycle and the frequency and intensity of extreme events, affecting seasonal water availability, drought occurrence, and groundwater recharge. This study assesses the influence of climate change on hydrological responses by employing a multi-model ensemble of five regional climate models under RCP4.5 and RCP8.5 scenarios, in conjunction with the SWAT hydrological model. REMO2015 demonstrated the best performance, while RACMO22T and RCA4 showed relatively poor performances. The ensemble mean provides a smoothed and intermediate representation, while inter-model variability is used to assess uncertainty. The SWAT model showed excellent performance during calibration and validation (R² = 0.85/0.80, NSE = 0.80/0.75, PBIAS = −0.1/−0.2). Results indicate a consistent increase in potential evapotranspiration and actual evapotranspiration under both scenarios, with greater increases under RCP8.5. Precipitation projections exhibit substantial inter-model variability. Water yield and groundwater recharge are anticipated to diminish, notwithstanding fluctuations in surface runoff responses, signifying heightened water stress. Reduction in groundwater contribution suggests heightened vulnerability of dry-season water availability. These findings provide a mechanistic understanding of hydrological changes beyond net streamflow trends and highlight the importance of incorporating climate model uncertainty into water resource planning and adaptation strategies. • Multi-Model Ensemble climate data analys is to handle uncertainty analysis in the future precipitation and temperature. • Causal Chain Analysis (CCA) identifying effects of rising temperature and change precipitation patterns. • Climate models project a significant increase in both potential and actual evapotranspiration, driven by rising temperatures, which accelerates water loss. • Hamessa watershed shifts to a more arid hydrological regime due to reduced surface runoff and groundwater recharge.