Comparative analysis of reference evapotranspiration estimation methods using temperature data

Accurate estimation of reference evapotranspiration (ETo) is the basis of irrigation water management. When weather data is lacking or only temperature data is available, ETo has to be estimated with limited weather data. An attempt was made to estimate daily ETo by using temperature-based and radiation-based methods, i.e., Penman-Monteith temperature method (PMT), corrected PMT method (PMT-cor), HG equation, modified HG (HG-M1, HG-M2), Thornthwaite equation and Irmak equation, corrected Irmak equation (Irmak-cor), McGuinness Bordne equation (M-B). These equations were evaluated against the PM model in Xinxiang. When using the PMT method to estimate ETo, the adjustment of Tmin for estimating Tdew was adopted, when using the Irmak equation, the multiple linear regression was adopted to modify this equation. Results showed that the performance of PMT, PMT-cor, HG, Irmak and Irmak-cor methods were similar, which got the best ETo estimation with coefficient of regression (b) and determination (R2) around 1.0, relative error RE0.95, five models fitted the standard of good model. Cross-comparison of the five good models showed that Irmak-cor equation was the best method which had the highest accuracy in all models with b=1.00, R2=0.98, RMSE=0.17 mm/d, RE=7%, d=1.00; secondly, the Irmak equation, with b=1.03, R2=0.95, RMSE=0.31 mm/d, RE=12%, d=0.99. The precision of five models was in turn as Irmak-cor, Irmak, PMT-cor, PMT and HG equation. When considering the precision of the formula, the Irmak-cor equation was the best-suited equation for estimating ETo among the methods, but it was likely more appropriate to use HG equation, due to it was easy to compute and no requirements of temperature adjustment. ©, 2015, Chinese Society of Agricultural Machinery. All right reserved.