Evaluation of pan coefficient equations for estimating reference crop evapotranspiration in the arid region

Abstract

Reference evapotranspiration (ET₀) can be estimated on basis of pan evaporation data (E_pan), whose measurements have the advantage of low cost, simplicity of the measuring equipment, simple data interpretation and application as well as suitability for locations with limited availability of meteorological data. E_pan values were converted to ET₀ using the pan evaporation coefficient (K_pan). In this study, seven common K_pan equations were evaluated for prediction of ET₀ in the growing season (April to October) in arid region of Iran. The Cuenca approach was best suited compared to the standard FAO Penman–Monteith method (FAO-56 PM).

Keywords:

• pan coefficient
• reference evapotranspiration
• FAO Penman–Monteith
• arid environment

Acknowledgements

The authors wish to express a gratitude to the Islamic Republic of Iran Meteorological Organization (IRIMO) for access to the weather station data. Authors are also grateful to editor and two anonymous reviewers and Mr. Namvar, a professor at the Islamic Azad University of Kashan, for their comments.