The given Penman-Monteith method is an energy balance method. The key equation shows Rn - G - λET - H = 0 . Whereas there is no method given to calculate H, and I could not find its explanation.
The energy balance equation is equal to:
RN= H+LE+G
Also the value H is equal to:
Dear Waqar: I send you the method that we use to calculate H. It is an article that we published with some colleagues. I send you the article and an excel spreadsheet to calculate the aerodynamic resistance. There are simpler approximations to estimating H, but it is a long conversation. Any questions you have we can talk about.
Hi Waqar,
It is difficult or confusing to estimate H from the FAO PM method, since that method estimates ET from a grass reference surface. If you are desiring H from some other surface, then you need to begin with a measurement or estimate of ET from that other surface.
In the case of ETo, yes, one can estimate H very simply by inverting the energy balance: H = Rn - G - ETo. However, again, This will be the H expected from the grassed reference surface. H from other surfaces will be different.
Rick Allen, Univ. Idaho
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