Reference evapotranspiration (ETo) must be precisely predicted in order to manage water supplies. For water-smart irrigation in arid areas, ETo is essential. An alternative to FAO-56 with less data is provided by mass-transfer models. However, their empirical nature demands careful calibration and local testing. For the Nile Delta, pursuing such studies could yield new, practical ETo estimators that enhance irrigation efficiency. The FAO-56 method was used as the reference standard to evaluate the performance of four mass transfer-based. Daily meteorological data were collected for 40 consecutive years (1985 to 2024) to ensure statistical robustness. Performance of studied models were analyzed by scatter plot and regression analysis and evaluated by the coefficient of determination (R2), root mean square error (RMSE), mean bias error (MBE) and mean absolute error (MAE).
Penman showed better agreement with FAO-56 (1.46 mm day⁻¹ RMSE; 1.26 mm MAE; 1.03 mm MBE). Its regression slope was 1.03 (close to unity) and R² 0.86, showing both slight proportional bias and good correlation with the standard. The resulting 3 % average overestimation shows that Penman can be employed as an excellent proxy for FAO-56 with negligible adjustments, allowing precise irrigation scheduling and avoiding water loss. WMO and Mahringer are moderately acceptable alternatives but show significant overestimation, particularly at high ETo. Dalton, while sometimes precise, displays extreme bias and inconsistency (ETo values are more than doubled relative to FAO-56 PM). Such high bias would encourage excessive irrigation, potentially wasting as much as 80 % more water than is required, rendering it unsuitable without local calibration.
Keywords: Irrigation management; climate change; evapotranspiration; FAO-56
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