Abstract <p>Humans have always met their need for water by digging wells and using surface sources. With the passage of time and the rapid growth of the urban population and more attention to public health, legislation for the use of water, the creation of water resources and its transfer to human settlements seem to be necessary issues that can only be solved with the help of experienced specialists. Accurate estimation of evaporation and transpiration is of special importance in water management in the agricultural sector. In this study, the accuracy of Sebal’s algorithm was investigated in estimating annual evapotranspiration by considering the statistical period from 1999 to 2022 and selecting images, cold and warm pixel ends, and the type of evapotranspiration interpolation for days without images. In this study, suitable images were used with the method of automatic selection of hot and cold pixels, which can estimate evaporation at the basin level with the Sebal algorithm. In order to verify the validity of Sebal’s algorithm, it is better to use the measured data of evaporation, so the recorded temperature and evaporation of the meteorological station in each region corresponding to each image and the novel period of 1999–2022 were used. In order to ensure the accuracy of this work, SWAT hydrological model was used to evaluate the accuracy. This model was used in the period of 2002 to 2014 as a calibration to extract discharge and evaporation of the area in selected stations and it was also used in the direction of verification in the period of 2015 to 2018, and the results showed that the evaporation obtained from the Sebal algorithm in the scale, the large time (annual), and spatial scale of the basin will be closer to the SWAT model than the monthly time scale, which is caused by the uncertainty of both the SWAT model and the Sebal algorithm, or the inappropriate selection of hot and cold pixels in the Sebal algorithm.</p>