Provide a Adjusted Coefficient to improve the accuracy of the Hargreaves method in the estimation of reference evapotranspiration

Evapotranspiration is one of the most important components of the hydrological cycle, which has an important role in water resource management. In the present study, the accuracy of the Hargreaves method for estimating evapotranspiration with the help of Adjusted coefficient K was investigated using artificial neural network model and M5 decision tree model. The weather data used in this study during the period of 2013-2004 from Farakhshahr station and Shahrekord airport in Chaharmahal and Bakhtiari province included minimum temperature, maximum temperature and relative humidity with cold and arid climate. Data were divided into 75% for training and validation and 25% for testing. The results show that neural network and decision tree model have good correlation modeling. Before using the Adjusted coefficient for Farkhshahr station, the root mean square of the Hargreaves strain was RMSE = 0.90 according to the Penman-Monteith-FAO method, which after applying the Adjusted coefficient using the neural network to RMSE = 0.69 and using The Adjusted coefficient for the decision tree was RMSE = 0 72. In general, the results showed that the Hargreaves model improved after using the Adjusted coefficient. Neutbay showed that the performance of the artificial neural network is more accurate, but the tree model offers linear, easier, and more intelligible relationships.