Calibration and Evaluation of Seven Radiation-Based Reference Crop Evapotranspiration Methods at Urmia Lake Basin

The aim of this study is to compare and calibrate seven different radiation-based reference crop evapotranspiration () estimation methods in monthly time scale at Urmia Lake basin. The selected methods were Doorenbos-Pruitt (DP)، Priestly-Taylor (PT)، Makkink (M)، Jensen-Haise (JH)، Turk (T)، Abtew (A) and McGuinness-Bordne (MB). For this purpose the information of ten synoptic weather stations in the period 1986-2010 wشس used. Results of the mentioned methods were compared with the outputs of the FAO-56 Penman-Monteith (PM56) method. Calibration of the methods were performed for every station and month in the mentioned time period. Performances of the methods were evaluated using the R2، RMSE، MBE، MAE and RE statistics. Results indicated that before calibration، larger biases were shown with the selected methods comparing to the PM56. Calibration of the methods considerably improved their accuracy. The DP method was recognized as the best method after calibration for the studied watershed and R2 value of this method was 0. 982. In the mentioned method (after calibration) the median values of the RMSE، MBE، MAE and RE were equal to 7. 89، -0. 62، 6. 03 and -3. 40 mm per month، respectively. The Priestly-Taylor method was selected as the second best Method. Models of M، JH، T، A and MB were ordered as the third- till seventh-rank، respectively.