Abstract:Solar radiation (Rs) is a necessary input variable for Penman-Monteith (PM) formula recommended by FAO to calculate reference crop evapotranspiration (ET0-PM). The influence analysis of solar radiation (Rs-c) from Angstrom equation and its parameters on ET0-c calculation based on PM was taken as the objective in nine agricultural regions of China. Using monthly valid average solar radiation (Rs-o) (from dataset of monthly values of radiation data from Chinese Surface Stations) and relative sunshine duration data (from dataset of monthly values of climate data from Chinese Surface Stations) at 112 stations during Jan.1957—Mar.2017, through comparative analysis and correlation analysis, the spatiotemporal differences between Rs-c and Rs-o were mainly explored. Then the spatiotemporal differences between ET0-c and ET0-o were obtained by input Rs-c and Rs-o to PM respectively, and it was also analyzed for illustrating the applicability of Rs-c to ET0-PM calculation in different regions of China. The result showed that Rs-c and Rs-o in the nine agricultural regions had significant and unstable spatial and temporal differences. There may be a large error when Rs-c directly replaced Rs-o to participate in the calculation of ET0-PM. However, the analysis of the spatiotemporal difference of ET0-c and ET0-o showed that whether in the entire continent, or the agricultural regions, ET0-c and ET0-o were characterized by a significant and relatively stable linear correlation, the R2 was more than 067 and the error of mean ET0-c was only 006~026mm/d. Considering Chinas agricultural region types, dealing with the “spring drought” in the northern area of irrigation demand, the application can be directly to get ET0-PM by Rs-c, but for the “summer drought” period nationally, ET0-c was slants bigger than ET0-o, and the corresponding correction model was necessary in the application of high precision of watersaving agriculture.
