Evaluation and Regional Calibration of Solar Radiation Prediction Models in Southern Spain

Solar radiation (Rs) is a very important variable in agricultural meteorology, but it is measured at a very limited number of weather stations. In addition, Rs data are usually low quality because of to sensor failure or lack of calibration. Rs can be predicted from other meteorological measurements (e.g., air temperature), but the accuracy of these methods needs to be tested. In this work, the mechanistic model of Hargreaves-Samani, three modified versions of this model, a modified Bristow-Campbell equation, and the Mahmood-Hubbard model were evaluated at 56 sites in the Andalusian region in southern Spain. All of these methods use the daily temperature range of the air (ΔT=Tmax-Tmin) to estimate Rs. The estimated values of Rs were compared with measurements of Rs to check their suitability. The accuracy of the methods was primarily affected by the magnitude of ΔT, with larger ΔT resulting in a greater accuracy. Finally, the parameter of the Hargreaves-Samani equation (Kr) was adjusted to regional conditions using ΔT, improving the estimations of incoming solar radiation for a wide ΔT range.