Historical and future trends in rainfall and temperature in the North Gojjam Sub-Basin of the Upper Blue Nile Basin in Ethiopia

Climate variability and long-term changes in rainfall and temperature have important implications for water availability and rain-fed agriculture in the Ethiopian Highlands. This study assessed historical (1986–2022) and projected (2041–2100) trends and changes in rainfall, maximum temperature (Tmax), and minimum temperature (Tmin) in the North Gojjam Sub-Basin of the Upper Blue Nile Basin, Ethiopia. Daily observations from six meteorological stations were used to characterize historical climate conditions and basin-average temporal trends, while CHIRPS v2 gridded rainfall data were used to examine the spatial distribution of historical rainfall trends. Future projections were derived from three CMIP6 models (CNRM-CM6-1, EC-Earth3, and HadGEM3-GC31-LL f3) under SSP2-4.5 and SSP5-8.5 for the mid-century (2041–2070) and late-century (2071–2100) periods. Model simulations were bias-corrected using monthly linear scaling based on the 1995–2014 reference period, and trends were evaluated using the Modified Mann-Kendall test and Sen’s slope estimator. Historical rainfall showed significant increasing trends during Belg and Kiremt and annually, whereas the Bega trend was not significant. Tmax showed an overall increasing tendency, with a statistically significant trend only during Beljg, while Tmin increased significantly across all seasons and annually. Future rainfall exhibited strong scenario- and period-dependent variability. Relative to the 1986–2022 reference period, mean annual rainfall under SSP2-4.5 decreased by 11.2% in the mid-century and 7.8% in the late century, whereas SSP5-8.5 resulted in changes of + 0.4% and + 14.6%, respectively. Thus, positive trends detected within some future periods do not necessarily indicate increases relative to the historical mean. Both Tmax and Tmin showed significant warming trends under the two scenarios, with stronger warming under SSP5-8.5 and during the late-century period. The projected changes may increase climate-related pressures on rain-fed production of cereals, pulses, and oilseed crops, including maize, teff, wheat, barley, and finger millet, through changes in rainfall reliability, soil-moisture availability, and crop water requirements. The findings highlight the need for flexible planting strategies, climate-resilient crop varieties, and improved soil and water conservation and water-management practices. Further integration of climate projections with crop and hydrological models is recommended to quantify future impacts on agricultural production and water resources.