Evaluation and comparison of the SEBAL and METRIC algorithms in the estimation of evapotranspiration: A case study, Malayer County

Estimation of evapotranspiration as one of the affective factors in the management of water resources is essential. There are different methods for estimating evapotranspiration. In this study، the feasibility of using two remotely-sensed-based models of SEBAL and METRIC، and their differences with each other in the Malayer County using MODIS images of 2013 were investigated. Using these models، the surface fluxes are calculated for each image pixels and actual evapotranspiration was estimated as a residual in the energy balance equation. According to the existing formula and differences between the two models in the calculation of atmospheric transparency coefficient and the soil heat flux، in both algorithms، the energy fluxes were calculated in both models and the results showed the Sebal algorithm with average daily evapotranspiration of 6. 83 mm in comparison with the metric algorithm with 7. 21 mm per day، about 5. 26 percent has estimated to be less the daily actual evapotranspiration in the Malayer county. The main reason for this difference is using different equations to calculate the coefficient of atmospheric transparency and soil heat flux، which majority of these differences is because of the large variation in soil heat flux values calculated by the method of extraction. Moreover، based on the obtained results، both actual evapotranspiration models can be adapted to estimate the actual evapotranspiration in regarding to the distribution of vegetation and topographical conditions of the county.