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This article in AJ

  1. Vol. 68 No. 4, p. 607-611
    Received: July 7, 1975

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An Evaluation of a Resistance Form of the Energy Balance to Estimate Evapotranspiration1

  1. J. L. Heilman and
  2. E. T. Kanemasu2



Evapotranspiration (ET) models that use the air-diffusion resistance to momentum (rD) have been unsatisfactory under certain conditions. A field study was conducted in soybean [Glycine max (L.) ‘Williams’] and sorghum [Sorghum bicolor (L.) ‘Pioneer 846’] to evaluate an ET model that uses the diffusion resistance to heat transport (rH) in the energy-balance equation and to assess the effect of replacing the resistance for heat with that for momentum.

Resistances were determined using wind speed and temperature profiles. Model estimates of latent-heat flux (LE) were compared with lysimetric measurements of LE. When using rH, model estimates of LE were within 4% and 15% of lysimetric measurements for soybean and sorghum, respectively. When using rD, estimates of LE for soybean were 25% greater, but for sorghum only 10% greater than when using rH. Results indicated that the resistance form of the energy balance can be useful for estimating ET if the proper resistance is used. Significant errors may occur if the momentum resistance is used in the model instead of the resistance for heat.

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