Estimation of Actual Evapotranspiration at Local Scale Using the SSEBop Model

Accurate estimation of the actual evapotranspiration (ETa) and analysis of its spatiotemporal variations is crucial for irrigation water management, particularly at local and daily scales. The Operational Simplified Surface Energy Balance (SSEBop) model is among the most efficient and practical single-source surface energy balance models based on remote sensing data. Nevertheless, limited studies are made to assess the performance of this model in Iran. In this study, a modified version of SSEBop (based on the use of local weather data, automatic calculation of daily reference evapotranspiration, and variable surface albedo) was introduced and its performance was examined over a 14-ha alfalfa farmland in East Isfahan. To this end, the model was calibrated and both the intermediate model outputs (e.g., surface temperature and albedo) and the estimated actual daily evapotranspirations were validated against the in-situ ETas obtained from a scintillometer and an adjacent automatic weather station. The results showed an acceptable performance (RMSE= 0.8 mm.day-1, r= 0.81) of the modified and locally calibrated SSEBop model for estimating daily ETa throughout the growth season. However, during and after harvesting, when the crop biomass was low (NDVI<0.4), the model failed. This study reveals the promising application of the SSEBop for operational irrigation management practices