Calibration of SEBAL Surface Energy Balance Algorithm in Determining Evapotranspiration of Plains Affected by Flood Spreading (Qaracherian-Zanjan Province)

Evapotranspiration is one of the most important elements of the hydrological cycle. Estimation of evapotranspiration is imperative for effective forest, irrigation, rangeland and water resources management as well as to increase yields and for better crop management. The aim of this study is to calibrate the SEBAL algorithm in estimating evapotranspiration in the Sohrin-Qaracheryan plain, which is affected by flood spreading. In this study, Landsat 8 satellite images were used in 2020-2021 to obtain the coefficients of the relevant bands. Then, the net radiation flux on the earth’s surface and the earth’s heat flux is obtained using incoming-outgoing radiation fluxes from albedo, surface emissivity, land surface temperature, and plant indicators. Next, the sensible heat flux is calculated by determining the hot and cold pixels. Finally, evapotranspiration maps are plotted. Based on the results of this research evapotranspiration obtained from soil water balance model and SEBAL algorithm were estimated as 24115 and 19642 m3, respectively. Also, the calibration of the results obtained from the SEBAL algorithm with reference evapotranspiration was done using R2 and RMSE statistical indices, and were calculated the values of these two indices as 0.64 and 2.15, respectively.