Rainfall, air temperature, and reference evapotranspiration variability and trend and their implication for agroforestry development in the Lake Tana sub-basin of Ethiopia

This study investigated the variability and trends of precipitation (P), air temperature, and reference evapotranspiration (ET ₀ ) in the Lake Tana sub-basin of Ethiopia from 1980 to 2023, assessing their implications for water resources, agriculture, and forestry development. The Lake Tana sub-basin, a crucial ecological and socio-economic zone within the Upper Blue Nile Basin, is increasingly vulnerable to climate change impacts. Using long-term monthly climate data from five sources, including MSWX-Past, MERRA-2, ERA-5, CRUTS4.06, and TerraClimate, spatiotemporal climate variability and trends were analyzed. The Penman-Monteith (FAO56) method was employed to estimate ET ₀ , and statistical techniques, including the trend of linear regression, CV, and standardized precipitation anomaly, were used to assess trends and variability. Results indicate significant increasing trends in annual and Kiremt (June-September) rainfall, while Belg (February-May) and Bega (October-January) seasons showed non-significant decreasing trends. Air temperatures exhibited significantly increasing trends, with the highest monthly temperatures in March. ET ₀ values were higher in the northern part of the sub-basin and during the Belg season. Rainfall variability was low for annual and Kiremt seasons but moderate to high for Belg and Bega, indicating higher unpredictability during drier seasons. The study also examined the climatic water balance which exhibited increasing seasonal and annual trends. Increased rainfall variability and rising temperature and annual & seasonal ET ₀ pose challenges for sustainable resource management. Enhanced climate monitoring, integrated water management, and climate-resilient practices are crucial for sustainable forestry and mitigating climate change impacts in the Lake Tana sub-basin