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 (R-S) 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 R-S 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 R-S 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). [GRAPHICS]