Abstract
Kibwezi watershed is highly susceptible to climate variability due to a mix of natural and anthropogenic stressors. This study assessed projected changes in rainfall and temperature using Regional Climate Models (RCMs) under RCP 4.5 and RCP 8.5 scenarios. RCM datasets were bias-corrected using the CMhyd tool, with CHIRPS and ERA5 serving as observational references. Seasonal and annual projections were analyzed for the short-term (2010–2039), mid-term (2040–2069), and long-term (2070–2100) 21st century relative to a historical baseline (1971–2005). Model evaluation indicated strong performance, with rainfall metrics of R² = 0.92, NSE = 0.64, PBIAS = -21.0%, and RMSE = 42.6 mm; and temperature metrics of R² = 0.92, NSE = 0.82, PBIAS = 0.90%, and RMSE = 0.56 °C. Rainfall is projected to increase by 24.5%-28.4% under RCP 4.5 and 21.5%-75.0% under RCP 8.5sceanrio across the three future periods. Seasonal shifts include increased rainfall during January-February and October-December, and decreases during March-May and June-August. Maximum temperatures are expected to rise by 0.6-1.5 °C (RCP 4.5) and 1.2-4.2 °C (RCP 8.5), while minimum temperatures will increase by 0.6-1.28 °C (RCP 4.5) and 0.68-2.40 °C (RCP 8.5). Spatially, the entire watershed is projected to experience warming and wetter conditions, with the eastern, central, and northern regions seeing the greatest rainfall increases and northern areas showing the highest temperature rise. These trends underscore the urgent need for climate-resilient watershed management strategies in the face of escalating climate risks.
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