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Modification of FAO Penman-Monteith equation for minor components of energy
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Iwa Publishing
The conventional Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith (P-M) equation requires knowledge of the available energy to estimate reference evapotranspiration (ETo); however, it is common to ignore the minor energy components (MECs). This study was conducted to determine the effect of not including the MECs in the FAO P-M equation. Fifteen-min micrometeorological records of four sites (covered with corn, soybeans, and prairie) in central Iowa, USA, during the years 2007-2012 were investigated. The major/ minor components of the energy equation were either measured or estimated by in-situ eddy covariance instruments. It was discovered that, on average, the MECs accounted for at least 13% of daily net radiation, leading to 27% decrease in daily ETo. Therefore, an equation is introduced to estimate MECs as a function of net radiation, air temperature, and Monin-Obukhov length; and another equation is regressed to roughly estimate daily MECs as a function of net radiation and day of the year. The findings in this study suggest a fundamental modification of FAO P-M formula by considering the inclusion of MECs in the energy term.
crop coefficient methodFAO Penman-Monteithminor energy componentsreference evapotranspiration
Varmaghani, Arman、Eichinger, William E.、Prueger, John H.
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Univ Iowa, IIHR Hydrosci & Engn, 100 C Maxwell Stanley Hydraul Lab, Iowa City, IA 52242 USA
NETL
NSTL
Iwa Publishing
