Evapotranspiration adjustment factors in Florida

David A. Chin, Ruochen Li

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Actual evapotranspiration (ET) is commonly estimated at daily time intervals as the product of a crop coefficient and a reference-crop evapotranspiration (ET 0) that is calculated by using a daily time step. When subdaily time steps are used, crop coefficients must be multiplied by adjustment factors to account for the discrepancy between ET 0 calculated by using daily and subdaily time steps. These adjustment factors depend on the method used to calculate ET 0. By using the ASCE and FAO-56 Penman-Monteith methods with data from several meteorological stations in Florida, the ASCE equation is shown to be preferable for all locations and seasons because it requires the least adjustment to the crop coefficient when 15-min and 1-h time steps are used. The required adjustment factors depend on location and season, are greatest in the summer, and are approximately the same for 15-min and 1-h time steps. A comparative evaluation between daily ET 0 and values of potential evapotranspiration (PET) provided by three public databases shows that PET estimates should generally not be used as substitutes for ET 0, because the relationship between PET and ET 0 varies significantly with location and season. For all locations and seasons considered in this study, daily ET 0 agrees most closely with the PET given by the Florida Automated Weather Network.

Original languageEnglish (US)
Pages (from-to)403-411
Number of pages9
JournalJournal of Irrigation and Drainage Engineering
Issue number7
StatePublished - Jul 5 2011


  • Coefficients
  • Crops
  • Evapotranspiration
  • Florida

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Water Science and Technology
  • Civil and Structural Engineering


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