Evaluation of 13 Empirical Reference Potential Evapotranspiration Equations on the Island of Crete in Southern Greece
Publication: Journal of Irrigation and Drainage Engineering
Volume 137, Issue 4
Abstract
Knowledge of reference potential evapotranspiration () conditions is important for a number of vegetation- and hydrological-related applications. Direct estimations of are difficult and require sophisticated instrumentation. The Food and Agriculture Organization (FAO), therefore, proposed a method for the estimation of using only meteorological data. This equation has been widely accepted as the standard method for the estimation of because of its good fit with measured values. Nevertheless, it requires several meteorological variables (e.g., wind speed), which are rarely available. Where such data are not available, its application is hampered. To overcome this problem, a number of simpler, empirical equations requiring only a fraction of the meteorological input variables required by the FAO have been developed. Before using these equations, it is important to evaluate their performance and choose the equation that will have the lowest possible bias in the estimation of . Using daily meteorological observations obtained from seven meteorological stations on the island of Crete (southern Greece), the performance of 13 empirical equations (radiation- and temperature-based) for the estimation of has been evaluated against the estimations of using the FAO equation. Performance was evaluated on a daily and a monthly basis, and five different measures of goodness of fit were used. The results showed that when the use of the FAO equation is not possible because of the unavailability of data, some empirical methods can serve as appropriate alternatives. The radiation-based equations generally performed better than those that included only temperature-related input variables. The equations proposed by Hansen and Turc were the most useful because they had an average monthly absolute error ranging from 5.7 to 17.7 mm and 5.5 to 19.2 mm, respectively.
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Acknowledgments
The authors would like to thank Dr. David Butler-Manning for proofreading the manuscript. We thank also the Hellenic National Weather Service for providing us the climate data of Crete. To this end we would also like to thank the two anonymous reviewers and the editor of the Journal of Irrigation and Drainage Engineering—ASCE for their valuable comments which significantly contributed to the improvement of this publication.
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Published In
Journal of Irrigation and Drainage Engineering
Volume 137 • Issue 4 • April 2011
Pages: 211 - 222
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© 2011 American Society of Civil Engineers.
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Received: Jan 24, 2010
Accepted: Aug 3, 2010
Published online: Aug 20, 2010
Published in print: Apr 1, 2011
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