where Rs is the solar or shortwave radiation (MJ m−2 d−1), n is the actual duration of sunshine (h), N is the maximum possible duration of sunshine or daylight hours (h), ( is thus the relative sunshine duration), Ra is the extraterrestrial radiation (MJ m−2 d−1), as and bs are the Angstrom coefficients. We calibrate the Angstrom coefficient using the observation of n and Rs from 51 stations widespread the whole China. Meanwhile, Ra and N are computed based on date and latitude according to the equations provided by the FAO P-M method. Overall, the high R2 values (see Table S3) between observed and estimated Rs indicate that the Angstrom model is suitable for daily global radiation estimation in China. For stations with no observation of solar radiation but sunshine duration, as and bS are estimated by Kringing interpolation method.