The aim of this research was to investigate actual evapotrairation of pistachio trees through the Surface Energy Balance Algorithm for Land (SEBAL) and to modify this algorithm by selecting and replacing the most appropriate method for determination of Land Surface Temperature (LST), across about 43’000 hectare of pistachio orahards in Yazd province, central Iran. In the reprentative orchards, paratemetrs of soil moisture, irrigation depth, oil salinity, and drainage water salinity were measured, as well. In addition, a time series of Landsat 8 satellite imagery (including 54 images) were acquired and used to find the most suitable method for accurate estimation of LST in the studied region. This method then inserted into the LST module of SEBAL algorithm, to modify it, partially. Then the daily and seasonal maps of evapotrairation were prepared by the modified SEBAL. Also their evaluations were performed by the ground observations. The results showed that the Split Window (SW) method has higher accuracies compared with other LST methods and effectively could be used for LST determination procedure of SEBAL algorithm. It was found that the error of modified SEBAL is less than 0.5 mm.day -1 , indicating adequacy of the modification procedure used in this research. KeyWords: Evapotrairation, Landsat 8, Leaching Fraction, Pistachio, Salinity, SEBAL.
