Evaluation of past and future trends of temperature and rainfall under CMIP6 scenarios in the Ayehu watershed, Upper Blue Nile Basin, Ethiopia

ABSTRACT Understanding past and future climate trends is essential for effective adaptation strategies. This study examines past and future climate trends using CMIP6 scenarios in the Ayehu watershed of northwestern Ethiopia. The study utilized CMIP6 rainfall and temperature data under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios for the near-term (2030–2060) and long-term (2070–2100) periods. The IPSL-CM6A-LR model for temperature and the MPI-ESM-1-2-LR model for rainfall were selected based on performance. Statistical methods, including the Mann-Kendall test and Sen's slope estimator, were used to identify trends and estimate the magnitude of changes. Results revealed a statistically non-significant decrease in annual rainfall by 1.53 mm/year, with significant declines in Belg rainfall (2.78 mm/year) and increases in Kiremt rainfall (7.84 mm/year). Historical temperature trends showed statistically significant warming in both the Kiremt and Bega seasons, with increases in maximum temperatures. Projections indicate declining annual rainfall under SSP1-2.6, SSP2-4.5, and SSP3-7.0 but an increase under SSP5-8.5. Both minimum and maximum temperatures will rise across all scenarios, with the highest increases under SSP5-8.5. These climatic shifts may intensify extreme weather events, posing risks to agriculture and water resources. Thus, urgent adaptation strategies are needed to mitigate potential impacts and enhance climate resilience.