Hargreaves ET0 Equation Regression Correction and Parameter Spatialization for Mainland China

HighlightsCorrelation coefficient between ET0 calculated by the PM and the HE, = 0.9 at 95% stations.Simple spline interpolation method more applicable than kriging interpolation for ET0 in mainland China.Linear regression correction model for the HE suggested by the FAO was further validated in large scale.Abstract. Reference crop evapotranspiration (ET0) is an important parameter employed in irrigation engineering. The Hargreaves ET0 equation (HE) is a simplified calculation method recommended by the Food and Agriculture Organization (FAO) of the United Nations and is used to determine ET0. However, the HE is empirical, and thus, the FAO suggests that linear regression correction be conducted when applying the HE in new areas. To discuss the validity of applying the HE linear regression correction model combined with spatial interpolation methods to the Chinese mainland, this study used meteorological data released by the China National Meteorological Data Service Center and considered the ET0-PM calculated by the Penman-Monteith equation to be the true value. With respect to conducting a linear regression correction with the HE, a regression analysis of the multi-year average of mean monthly daily ET0-PM and ET0-HE calculated by the HE showed that the values were significantly correlated, and correlation coefficients and R2 of 95% of stations exceeded 0.9 and 0.8, respectively. This indicates that the HE linear regression correction model recommended by the FAO is applicable for use in mainland China. The accuracy of ET0-HE corrected by the linear regression correction coefficient combined with simple tension spline interpolation was the optimal and stable at validation stations, whereas the accuracy of ET0-HE corrected by the linear regression correction coefficient combined with simple ordinary kriging interpolation contrasts with the accuracy from existing studies. This study can be used as a reference in large-scale correction research using ET0-HE, and it lays the foundation for research and development relating to spatiotemporal ET0 data products. Keywords: Coefficient modification, Linear regression model, Reference crop evapotranspiration, Spatial interpolation.