Advection Modification of the Priestley and Taylor Evapotranspiration Formula¹

Abstract

The empirical formula of Priestly and Taylor (1972) relating the evapotranspiration from a well‐watered surface to the net radiation and a function of the air temperature is modified to include a saturation deficit term to account for high local advection. The model is tested on two seasons of daily evapotranspiration measurements over irrigated potatoes (Solarium tuberosum L.), resulting in good agreement and a substantial improvement over the unmodified formula. Alfalfa (Medicago saliva L.) measurements are also represented well by the model, but no better than by the Priestley‐Taylor formula calibrated during a period of high advection.

Estimation of the diurnal variation of potential evaporation from a wet bare soil surface

“…Many studies have found that ~ is approximately equal to 1.26 for a variety of wet surfaces (e.g. Davies and Allen, 1973;Jury and Tanner, 1975;Rouse, 1976, 1977;Doorenbos and Pruitt, 1977). The formulation has proven to be useful for humid sites with minimal advection (De Bruin and Holtslag, 1982;Stagnitti et al, 1989).…”

Simulation of the soil water balance of an undeveloped prairie in west-central Florida

“…The quantity (S+J)/S is temperature dependent, and it varies from 1.85 at 10°C to 1.30 at 30°C. Some experimental evidence indicates that a is approximately 1.26 for short, actively growing, wellwatered crops (Davies and Alien, 1973;Jury and Tanner, 1975) and open water (DeBruin and Keijman, 1979). The similarity between a reported for short, actively growing vegetation and a reported for open water indicates such vegetation can be indistinguishable from fully wet surfaces in terms of supplying water to meet evaporative demand.…”

Two-Source Energy Balance Model to Calculate E, T, and ET: Comparison of Priestley-Taylor and Penman-Monteith Formulations and Two Time Scaling Methods

“…The use of equation 1 is supported by numerous TSEB studies that reported good agreement between measured and calculated daytime or 24 h latent heat flux or ET (e.g., Kustas and Norman, 1999;Li et al, 2005;Anderson et al, 2005;French et al, 2007;Agam et al, 2010;Colaizzi et al, 2012a;Kustas et al, 2012;Anderson et al, 2012). However, a number of studies have reported improved estimates of latent heat flux or ET when α PT is variable and calculated as a locally calibrated empirical function of vapor pressure deficit (e.g., Jury and Tanner, 1975;Steiner et al, 1991;Agam et al, 2010) or when α PT is increased to larger values such as ~2.0 when vapor pressure deficit exceeds approximately 4 kPa (relative humidity below ~30%) (e.g., Kustas and Norman, 1999), which would increase LE CI and mimic the vapor pressure deficit (i.e., aerodynamic) term in the Penman-Monteith model.…”

“…However, E and T were consistently over-and underestimated, respectively, by up to 4 mm d -1 compared with measurements using microlysimeters and sap flow gauges. This could not be mitigated by specifying α PT as a locally calibrated empirical function of VPD (Jury and Tanner, 1975;Steiner et al, 1991;Agam et al, 2010) or increasing the value of α PT (Kustas and Norman, 1999) (data not shown). Steiner et al (1991) derived the empirical relation α PT = 1.0 + 0.26 × VPD for the Bushland study location by following the method of Jury and Tanner (1975).…”

“…This could not be mitigated by specifying α PT as a locally calibrated empirical function of VPD (Jury and Tanner, 1975;Steiner et al, 1991;Agam et al, 2010) or increasing the value of α PT (Kustas and Norman, 1999) (data not shown). Steiner et al (1991) derived the empirical relation α PT = 1.0 + 0.26 × VPD for the Bushland study location by following the method of Jury and Tanner (1975). This resulted in agreement between calculated and measured ET using their version of the Priestley-Taylor equation that was nearly as good as the Penman-Monteith equation for full-cover, fully irrigated grain sorghum, where ET was measured by the same large weighing lysimeter used in the present study.…”