Evaluation of Different Models for Estimating Reference Evapotranspiration (ETo) in Aleshtar Plain

Accurate estimation of reference evapotranspiration (ETo) in each region is necessary due to its significant contribution to water resources management and proper irrigation planning.  Since direct (ETo) measurement methods are time consuming and costly, therefore, in many cases, experimental and mathematical models are used for this purpose. These models, however, can’t be used unless they are validated and verified using lysimetric data. A various methods can be used to estimate evapotranspiration; but the performance of these equations are varied from one climatic condition to another. Therefore, in the present study, lysimetric data have been used to evaluate 15 ETo estimation models in Aleshtar region. The data required in different (ETo) estimation models were collected from Aleshtar synoptic station. According to the statistical evaluation results, the Jensen- Haise (RMSE = 1.14) and Turk (RMSE = 1.42) models from the radiation group and the Hargreaves–Samani (HS) model (RMSE = 1.72) from the temperature group were found to be the most accurate ETo estimation models in the study area. On the other hand, Meyer (RMSE = 4.78) and WMO (RMSE = 4.73) models from mass transfer group were found to be the least accurate ETo estimation models, respectively. Finally, taking into account the significance of the FAO Penman-Monteith model in evapotranspiration calculations, comparing lysimetric data with the values estimated ​​by this model showed that the FAO-Penman-Monteith model ​​(RMSE = 5.83 and R2= 0.10) has the least accurate to estimate ETo in the region.