Reconstruction of daily global radiation for past years for use in agricultural models

A method of estimation of daily global radiation based on standard meteorological observations is presented. Global radiation may be calculated with one-dimensional regression equations, either with or without conditions (constraints). Daily duration of sunshine, mean cloudiness or temperature range can be used as predictors in either case. In general to select the proper equations with conditions, humidity was chosen as a master variable. Formulation and validation of the regression equations is done on the basis of data from 42 German radiation stations. The annual root mean square error (RMSE) between values calculated for individual days with the estimation method developed, and measured data, was about 1.6 MJ m⁻² day⁻¹ using sunshine duration as the predictor and 3.0 MJ m⁻² day⁻¹ using both temperature range and relative humidity as predictors.

This estimation method has been used for reconstruction of daily global radiation for about 400 German meteorological stations for years, and for stations without observations of global radiation. Reconstructed data will be used in agricultural and hydrological models.