Determination of Wheat Evapotranspiration using the Earth Engine Evapotranspiration Flux (EEFLUX)

Abstract

In this study an automated Earth Engine Evapotranspiration Flux (EEFlux) was used to produce actual evapotranspiration (ETa) estimates for rabi wheat, compared against the FAO-56 approach using ground-measured weather data. Eight cloud-free Landsat images from the 2020-2021 rabi season were processed in METRIC-EEFlux, producing ETa values ranging from 0.95 mm to 4.07 mm, with an average of 2.41 mm. Conversely, the FAO-56 method estimated ETa values between 0.64 mm and 4.80 mm, averaging 2.58 mm. Cumulative ETa for wheat was 290 mm (EEFlux) and 336 mm (FAO-56). The comparison showed moderate agreement (IA = 0.67), with EEFlux underestimating by 13.69% relative to FAO-56. EEFlux-ETa had an RMSE of 0.93 mm/day and NRMSE of 0.33. The findings suggest that EEFlux can achieve more accurate ET estimates with frequent satellite imagery, improved weather data, and automated ETrF adjustments, necessitating further validation across multiple years to confirm its general applicability.