Evaluation of Incoming Solar Radiation Parameter Derived from Empirical and Satellite Models

Evapotranspiration is one of the most important processes in water and radiative transfer in hydrological cycle, and the required energy for this process is provided by solar radiation. Therefore, the accuracy of evapotranspiration estimation is strongly depends on the accuracy of solar radiation estimation. This study was conducted to evaluate the different surface solar radiation models such as empirical models (Angstrom and Hargreaves-Samani), physically-based models (NCEP and GLDAS) and a satellite observation model (CM-SAF). The results showed that the calibrated Angstrom model with R2=0.9 and SEE=2.58 was the most efficient model. However, the accuracy of this model is strongly depends on the calibration procedure and the existence of sunshine data. The GLDAS model with R2= 0.87 and SEE=3.5 was the second most efficient model after calibrated Angstrom model. The GLDAS model, in spite of 10.2% overestimation of surface solar radiation, can be the most efficient model in areas with the lack of meteorological data.