Current frameworks for reference ET and crop coefficient calculation

Richard G. Allen, Ayse Kilic, Clarence W. Robison

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations


This article describes current and likely near-term future frameworks for calculating evapotranspiration. These include structures for estimating crop coefficients (Kc) primarily centered on the FAO-56 dual Kcapproach, with example applications. Emphasis is placed on estimation of parameters and special cases to be considered. Newer, and often preferred, bases for establishing Kcbcurves include thermal units and vegetation indices. Also described and discussed are the application of reference ET calculations using hourly vs. 24-hour timesteps, the use of and conditioning of gridded weather data sets, and the likelihood of movement toward multi-layer and multi-source resistance models for ET estimation. Complementing this is satellite-based determination of ET using both vegetation indices and surface energy balance.

Original languageEnglish (US)
Title of host publication6th Decennial National Irrigation Symposium
PublisherAmerican Society of Agricultural and Biological Engineers
ISBN (Electronic)9781713839743
StatePublished - 2020
Externally publishedYes
Event6th Decennial National Irrigation Symposium 2020 - San Antonio, United States
Duration: Nov 30 2020Dec 4 2020

Publication series

Name6th Decennial National Irrigation Symposium


Conference6th Decennial National Irrigation Symposium 2020
Country/TerritoryUnited States
CitySan Antonio


  • Consumptive use
  • Dual crop coefficient
  • Evapotranspiration
  • FAO-56
  • Gridded weather data
  • Irrigation water requirements
  • Remote sensing

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Soil Science


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