Comparative analysis of empirical evapotranspiration models across Northern Ethiopia's Climatic Zones

Accurate estimation of reference evapotranspiration (ETo) is essential for irrigation scheduling, water resources management, and climate adaptation. This study evaluated the performance of twelve empirical ETo models at Bahir Dar, Gondar, Debre Tabor, Debre Markos, Kombolcha, Mekelle and Adigrat meteorological stations representing diverse climatic and topographic conditions in northern Ethiopia. The assessed models included temperature-based, radiation-based, and mass-transfer methods. ETo estimates were compared against the FAO 56 Penman-Monteith method. The results revealed substantial spatial variability in model performance, reflecting the climatic heterogeneity of the region. The temperature-based Enku model consistently outperformed other methods at five stations, achieving IoA values of up to 0.87, NSE values exceeding 0.70, and NRMSE as low as 12.61%, particularly in humid and sub-humid highland environments. In contrast, the radiation-based Abtew model provided the most accurate estimates in the arid Mekele station (IoA = 0.87, NRMSE = 19.59%), highlighting the dominant influence of solar radiation under water-limited conditions. The Priestley-Taylor, Turc, and Makkink models generally exhibited lower accuracy and larger biases across most stations. The findings demonstrate that no single empirical model is universally applicable across northern Ethiopia and emphasize the importance of climate-specific model selection, local calibration, and validation.