Comparison of actual evapotranspiration by the google earth engine evapotranspiration flux (EEFlux) to the METRIC model using remote sensing data and in-situ climate observations

Actual evapotranspiration (ETa) is essential data in developing water budgets and calculating irrigation water requirements in large-scale irrigation schemes. Nowadays, remote sensing (RS)-based surface energy balance models help us estimate ETa with high resolution when compared to direct methods that focus only on a single point in a field. This study aimed both at estimating ETa by Mapping EvapoTranspiration at high Resolution with Internal Calibration (METRIC) and Google Earth Engine Evapotranspiration Flux (EEFlux) platform and comparing reference evapotranspiration based on the Penman-Monteith equation (ETo) with ETa by the METRIC and EEFlux in a sub-catchment (A=9495 ha) under irrigation, located in the Lower Seyhan Plain (LSP), Turkiye in the 2020 hydrological year. For this purpose, 16 Landsat 7 and Landsat 8 images, local climatic data acquired from two meteorological stations in the catchment, and CFSv2 gridded global data were used. Results showed a good agreement between ETa-EEFlux with ETa-METRIC. Moreover, a strong correlation was found between ETo and ETa-METRIC (r=0.93 and slope close to 1 and RMSE value of 0.74 mm day-1) if compared to the relationship between ETo with ETa-EEFlux. The results show the potential of applying the METRIC model and EEFlux for mapping ETa over a large-scale irrigation scheme.