Evaluation of Solar Radiation Estimation Models in Estimating Reference Evapotranspiration

Document Type : Research Paper



Solar radiation is an essential factor in irrigation scheduling, hydrological cycle, crop growth simulation models and estimation of reference evapotranspiration. The aim of the present research was to investigate the accuracy of solar radiation estimation models and their effects on reference evapotranspiration. For this purpose, the meteorological data of 4 synoptic stations including Urmia, Takab, Salmas and Mahabad in West of Urmia lake catchment in daily scale were used. Solar radiation was estimated using seven models including, Hargreaves-Samani, Allen, Self-Calibrating, Samani, Annandale, Bristow-Campbell and Angstrom–Prescott. Then, the obtained values were used in FAO- Penman-Monteith equation to estimate the reference evapotranspiration. In order to evaluate the models' accuracy, the statistical indicators including root mean square error, mean bias error and determination coefficient were used. The evaluation results of the models showed that the Angstrom – Prescott model had the best performance, and the Samani method was the weakest method in the studied stations. The average values of the root mean square error for the Angstrom–Prescott and Samani methods in the studied region were obtained 0.48 and 1.43 mm/day, respectively.