Validation and calibration of solar radiation equations for estimating daily reference evapotranspiration at cool semi-arid and arid locations

Abstract

In this work, the applicability of 12 solar radiation (RS) estimation models and their impacts on daily reference evapotranspiration (ETo) estimates using the Penman‐Monteith FAO-56 (PMF-56) method were tested under cool arid and semi-arid conditions in Iran. The results indicated that the average increase in accuracy of the ETo estimates by the calibrated RS models, quantified by the decrease in RMSE, was 2.8% and 6.4% for semi-arid and arid climates, respectively. Mean daily deviations in the estimated ETo by the calibrated RS equations in semi-arid climates varied from −0.283 mm/d-1 for the Glover‐McCulloch model to 0.080 mm/d for the El-Sebaii model, with an average of −0.109 mm/d-1, and in arid climates, they ranged from −0.522 mm/d-1 for the Samani model to 0.668 mm/d for the El-Sebaii model, with an average of 0.125 mm/d-1.