Remotely Sensed and Empirical Reference Evapotranspiration Models to Derive Crop Coefficients for Pistachios in the Central Basin of Iran

The main objective of this study is to estimate the actual evapotranspiration rate and determine the water requirement of pistachio crops in the central plateau of Iran using satellite remote sensing products. In order to achieve this main goal, 12 images from the Operational Earth Imager (OLI) of the Landsat 8 satellite for the water year 2018–2019 were downloaded from NASA's Land Processes Distributed Active Archive Center. The daily data of the five variables, namely maximum temperature, minimum temperature, wind speed, relative humidity, and sunshine hours of Taft station, were also obtained from the Iran Meteorological Organization as the closest meteorological station to the study area after preparing images and collecting data. First, the actual evapotranspiration rate of the pistachio product was estimated on a monthly scale for every 12 months of the study using two surface energy balance (SEBAL) and Surface Energy Balance Index (SEBS). Evapotranspiration potential was also acquired in a station scale applying 12 experimental methods. In a comparative study, the results revealed that the evapotranspiration values achieved from the four experimental models H–S, B–C, Trabert, and Rn-Based, have the highest correlation and the lowest error value with the values estimated from the two SEBAL and SEBS models. Finally, the water requirement of the pistachio crop during its growth period was estimated separately using two models, namely SEBAL and SEBS, and confirmed the experimental models.