Evaluation of Reference Crop Evapotranspiration Equations in Various Climates

Evapotranspiration is one of the most important elements for quantifying available water since it generally constitutes the largest component of the terrestrial water cycle. This study evaluated four models (Makkink, Turc, Priestley–Taylor and Hargreaves) commonly used to estimate monthly reference crop evapotranspiration (ET<Subscript>o</Subscript>) values. The main aim of this study was to determine the model used to estimate ET<Subscript>o</Subscript> with small data requirements and high accuracy for twelve synoptic stations in four climates of Iran. The results showed that the Turc model was the best suited model in estimating ET<Subscript>o</Subscript> for cold humid and arid climates. The Hargreaves model turned out to be the most precise model under warm humid and semi-arid climatic conditions. In contrast, the Makkink model presented the poorest estimates in all of the climates exception for cold humid environment. In cold humid climate, the Hargreaves model was the least accurate model in estimating ET<Subscript>o</Subscript>. In general, the results obtained from this study revealed very clearly that the Makkink and Priestley–Taylor models estimated ET<Subscript>o</Subscript> values less accurately than Turc and Hargreaves models for the all climates. Copyright Springer Science+Business Media B.V. 2010