Ability of Gene Expression Programming Model to Estimate Reference Evapotranspiration with Minimal Meteorological Data

amount of reference evapotranspiration using meteorological data, the period of 30-year of Ahvaz meteorological station was used. The reference method for calculating evapotranspiration was the Penman-Monteith method. In this research, four scenarios with different combinations of model input parameters were examined. Finally, the results showed that the best combination of input parameters for the gene expression programming model included parameters of minimum temperature, maximum temperature, relative humidity and sunshine hours. For these input parameters, R2, MAE, and RMSE statistics in the training phase are 0.964, 0.421 mm/d, and 0.507 mm/d, respectively, and in the test phase, they are 0.965, 0.419 mm/d, and 0.506 mm/d, respectively. was obtained Rainfall was the only parameter that showed the least effect on the rate of evaporation and transpiration, so that the increase of this parameter to the input parameters of the model caused a slight change (less than one percent) in the values of the evaluation indices. It seems that the reason for this is the low amount of rainfall in this area, so that in most months, the amount of rainfall is very small. Finally, the results of this research showed that the gene expression programming model can be used as a suitable tool with good accuracy for estimating reference evaporation and transpiration.