علوم و مهندسی آبیاری (Sep 2014)
Comparison of Four Temperature Based Reference Crop Evapotranspiration Estimation Method at Urmia Lake Basin
Abstract
The aim of this study is to compare and calibrate of four different temperature based estimation methods in monthly time scale at Urmia Lake basin. The selected methods were Hargreaves (HG), Thornthwaite (TW), Blaney- Criddle (BC) and Linacre (Lin). For this purpose the information of weather parameters in the period 1986-2010 were used. Results of mentioned methods compared with the output of the FAO Penman- Monteith (PM56). Methods calibrated using the two distinct approaches. At first state only one calibration coefficient estimated along every year. At second state calibration coefficients estimated for each station and every month in a year. Performance of methods evaluated using the , RMSE, MBE and MAE statistics. The effectiveness of method’s calibration evaluated using the. Results showed that before calibration larger biases existed for selected methods comparing PM56. Calibration of methods considerably improved their performances. Results indicated that calibration of methods in the case of second state was very effective comparing the first state. The HG method was recognized as a best method either before or after calibration (in the first state) at the Urmia lake watershed. Linacre and Blaney- Criddle methods selected as the best methods following the Linacre method (after calibration at first state). Thornthwaite method had large error and therefore was not suitable method for estimation of at the study area. The Linacre method was known as the best method of estimation at Urmia Lake basin after calibration (at second state). HG, BC and TW were in the second to fourth rank orders, respectively.
