Comparison of Regression tree, artificial neural network and Hargrives-Samani in estimation of reference evapotranspiration in semi region

The purpose of this study was to evaluate three models of artificial neural networks (ANN)، regression trees (M5) and Hargrives-Samani (HG) in estimation of reference evapotranspiration. for this purpose was used climate information of Sistan va Baloochestan، Kerman، Yazd and Khorasan Jonoobi from 1998 to 2008. in addition to effect of wind (U) on evapotranspiration (ET0)، estimation of ET0 was done based on wind change in tree groups including U3. 67 m/s. the results showed that optimum result of each tree methods was in U1 group. The amount of RMSE and R2 in ANN were 1. 41 mm/day and 0. 84 respectively، in MS were 1. 46 mm/day and 0. 83 and in HG were 2. 02 mm/day and 0. 69. These results showed that both ANN and MS methods are better than HG model. Besides، the run of MS to ANN is easy.