Bikila, Gebeyehu Ashemi2026-09-252026-09-252026-09-162784-0379https://repository.iuls.ro/handle/20.500.12811/7034Reference evapotranspiration (ETO) is a fundamental component of irrigation scheduling, estimation of crop water requirements, and sustainable water-resource management, particularly in semi-arid regions where water resources are limited. This study evaluated the performance of four empirical ETO estimation methods (Blaney–Criddle, Hargreaves, Radiation, and Modified Penman) against the FAO-56 Penman–Monteith method in the Ziway area of the Central Rift Valley, Ethiopia. Long-term meteorological data (1990–2023), including air temperature, relative humidity, sunshine duration, wind speed, and rainfall, were obtained from the Ziway Meteorological Station. The FAO-56 Penman–Monteith method implemented in CROPWAT 8.0 served as the benchmark, and model performance was evaluated using root mean square error (RMSE), mean absolute error (MAE), mean bias error (MBE), coefficient of determination (R2), Nash–Sutcliffe efficiency (NSE), Willmott’s index of agreement (d), mean absolute percentage error (MAPE), and normalised root mean square error (NRMSE). Monthly ETO estimated by the benchmark method ranged from 2.87 to 5.00 mm day–1. Among the evaluated methods, the Modified Penman method produced the lowest prediction errors, whereas the Hargreaves method exhibited the strongest correlation with the benchmark. Comparison of rainfall and ETO showed that atmospheric evaporative demand exceeded precipitation during most months of the year, particularly during the dry and pre-rainy seasons, indicating the need for supplementary irrigation. Because independent evapotranspiration measurements, such as lysimeter or eddy-covariance observations, were unavailable, the results should be interpreted as agreement with the FAO-56 Penman–Monteith benchmark rather than as absolute model accuracy. These findings provide useful guidance for selecting appropriate ETO estimation methods under data-limited conditions in the semi-arid regions of Ethiopia.EnglishAttribution 4.0 International (CC BY 4.0)http://creativecommons.org/licenses/by/4.0atmospheric water deficitEthiopiaFAO-56 Penman–MonteithHargreavesirrigation managementModified Penmanreference evapotranspirationZiwayArticle2784-0360https://doi.org/10.46909/alse-592215