A Resistance Model to Predict Evapotranspiration and Its Application to a Sugar Beet Field1
- K. W. Brown and
- Norman J. Rosenberg2
A method is needed to extrapolate the detailed micrometeorological and lysimetric determinations of evapo-transpiration and its dependence on the microclimate and crop factors to fields where such detailed measurements are not made. The dependence of latent heat flux (LE) from a crop on crop resistance (rc), air resistance (ra), air temperature (Ta), water vapor pressure (ea), and net radiation minus soil heat flux (Rn-S) was evaluated means of an electrical resistance analogue of the transfer process (referred here as the model) and by means an energy balance equation. The difficulties inherent in the application of the model to both the single leaf and the crop are discussed.
The major difficulty in applying the resistance model to a field crop may be that the sinks and sources of latent and sensible heat flux may not be identical within the crop. Hourly LE predicted by the model and determined by the energy balance generally agreed within 5%. Daily totals of LE, evaluated by the two methods, agreed well on all occasions. Despite the objections to use of this model for a crop, it mimicked the behavior of the irrigated sugar beet crop used here. As more detailed data on experimental fields becomes available, the model may prove useful in extrapolation to extensive vegetated areas. It may also be usefully incorporated into larger models of total hydrologic systems in which evapotranspiration is an important component.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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