Evaluation of CMIP6 Model Performance and Future Climate Projections over the Genale Dawa River Basin, Ethiopia

The Genale Dawa River Basin (GDRB) in southeastern Ethiopia is highly vulnerable to climate variability. Yet, limited research has assessed how well the latest CMIP6 climate models simulate key variables in this complex, data-scarce region, posing challenges for effective climate risk assessment and adaptation planning. This study evaluates the performance of 12 CMIP6 Global Climate Models (GCMs) in simulating historical precipitation, maximum temperature (Tmax), and minimum temperature (Tmin) over the GDRB for the baseline period 1985–2014. Future projections are also assessed for 2021–2050 and 2051–2080 under two emission scenarios: SSP2-4.5 and SSP5-8.5. Observational data from ENACTS and 60 ground-based stations were used to validate model outputs, which were re-gridded to 0.5° × 0.5° and bias-corrected using quantile mapping. Model performance was assessed using Mean Bias Error (MBE), Root Mean Square Error (RMSE), Pearson correlation, Taylor Skill Score (TSS), and visual diagnostics. The multi-model ensemble (MME) outperformed individual GCMs, with TSS values of 0.80 for precipitation, 0.98 for Tmax, and 0.99 for Tmin. Individually, CNRM-CM6-1 was best for precipitation, GFDL-CM4 and NorESM2-MM for Tmax, and FGOALS-g3 and MRI-ESM2-0 for Tmin. While seasonal patterns were well captured historically, Tmin was consistently overestimated. Future projections indicate steady warming, with Tmin rising more rapidly than Tmax. Under SSP5-8.5 by mid-century, Tmax is projected to increase by 1.8°C (6.7%) and Tmin by 1.8°C (15.0%). Precipitation may increase by 11.1% (5.4 mm), though seasonal shifts are notable, including a > 60% March decline and > 120% November increase. These findings emphasize the need for localized climate projections to support resilient development planning.