Priestley-Taylor Model Research Articles

Reliable estimation of evapotranspiration on agricultural fields predicted by the Priestley–Taylor model using soil moisture data from ground and remote sensing observations compared with the Common Land Model

Evapotranspiration (ET) is a crucial factor in understanding the hydrological cycle and is essential to many applications in hydrology, ecology and water resources management. However, reliable ET measurements and predictions for a range of temporal and spatial scales are difficult. This study focused on the comparison of ET estimates using a relatively simple model, the Priestley–Taylor (P-T) approach, and the physically based Common Land Model (CLM) using ground and remotely sensed soil moisture data as input. The results from both models were compared directly with hourly eddy covariance measurements at two agricultural field sites during the Soil Moisture–Atmosphere Coupling Experiment (SMACEX) in the corn soybean production region in the Upper Midwest, USA. The P-T model showed a significant overestimation of the potential ET compared to the measurements, with a root mean square error (RMSE) between 115 and 130 W m–2. Actual ET was better predicted by the CLM, with the RMSE ranging between 50 and 75 W m–2. However, actual ET from the P-T model constrained with a soil moisture dependency parameterization showed improved results when compared to the measurements, with a significantly reduced bias and RMSE values between 60 and 65 W m–2. This study suggests that even with a simple semi-empirical ET model, similar performance in estimating actual ET for agricultural crops compared to more complex land surface–atmosphere models (i.e. the CLM) can be achieved when constrained with the soil moisture function. This suggests that remote sensing soil moisture estimates from the Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) and others such as the Soil Moisture and Ocean Salinity (SMOS) mission may be effective alternatives under certain environmental conditions for estimating actual ET of agricultural crops using a fairly simple algorithm.

Evaluation of Reference Crop Evapotranspiration Equations in Various Climates

Evapotranspiration is one of the most important elements for quantifying available water since it generally constitutes the largest component of the terrestrial water cycle. This study evaluated four models (Makkink, Turc, Priestley–Taylor and Hargreaves) commonly used to estimate monthly reference crop evapotranspiration (ETo) values. The main aim of this study was to determine the model used to estimate ETo with small data requirements and high accuracy for twelve synoptic stations in four climates of Iran. The results showed that the Turc model was the best suited model in estimating ETo for cold humid and arid climates. The Hargreaves model turned out to be the most precise model under warm humid and semi-arid climatic conditions. In contrast, the Makkink model presented the poorest estimates in all of the climates exception for cold humid environment. In cold humid climate, the Hargreaves model was the least accurate model in estimating ETo. In general, the results obtained from this study revealed very clearly that the Makkink and Priestley–Taylor models estimated ETo values less accurately than Turc and Hargreaves models for the all climates.

Transport of Tritium Contamination to the Atmosphere in an Arid Environment

Soil–plant–atmosphere interactions strongly influence water movement in desert unsaturated zones, but little is known about how such interactions affect atmospheric release of subsurface water‐borne contaminants. This 2‐yr study, performed at the U.S. Geological Survey's Amargosa Desert Research Site in southern Nevada, quantified the magnitude and spatiotemporal variability of tritium (3H) transport from the shallow unsaturated zone to the atmosphere adjacent to a low‐level radioactive waste (LLRW) facility. Tritium fluxes were calculated as the product of 3H concentrations in water vapor and respective evaporation and transpiration water‐vapor fluxes. Quarterly measured 3H concentrations in soil water vapor and in leaf water of the dominant creosote‐bush [Larrea tridentata (DC.) Coville] were spatially extrapolated and temporally interpolated to develop daily maps of contamination across the 0.76‐km2 study area. Maximum plant and root‐zone soil concentrations (4200 and 8700 Bq L−1, respectively) were measured 25 m from the LLRW facility boundary. Continuous evaporation was estimated using a Priestley–Taylor model and transpiration was computed as the difference between measured eddy‐covariance evapotranspiration and estimated evaporation. The mean evaporation/transpiration ratio was 3:1. Tritium released from the study area ranged from 0.12 to 12 μg d−1 and totaled 1.5 mg (8.2 × 1010 Bq) over 2 yr. Tritium flux variability was driven spatially by proximity to 3H source areas and temporally by changes in 3H concentrations and in the partitioning between evaporation and transpiration. Evapotranspiration removed and limited penetration of precipitation beneath native vegetation and fostered upward movement and release of 3H from below the root zone.

Estimation of banana (Musa sp.) plant transpiration using a standard 20 cm pan in a greenhouse

An experiment was carried out in a naturally ventilated greenhouse to study the relationship between banana (Musa sp.) plant transpiration (Tr) measured with load cells, reference crop evapotranspiration (ETo) calculated with five widely used models (i.e. the Priestley-Taylor, FAO radiation, Hargreaves, FAO Penman and FAO Penman-Monteith models) and pan evaporation (Epan) measured with a standard Chinese 20 cm pan. Microclimatic conditions were measured inside the greenhouse. Results show that vapor pressure deficit and air temperature had good linear correlations to banana Tr with R2 of 0.67 and 0.62, respectively. Among the five models tested, banana Tr and ETo calculated with the FAO-Penman model yielded the highest determination coefficient (R2 = 0.67), followed by the FAO-PM model (R2=0.63), the FAO radiation model (R2=0.52), the Hargreaves model (R2=0.49) and the Priestley-Taylor model (R2=0.47). Banana transpiration Tr vs. Epan yielded an R2 of 0.83, which is higher than the five models tested. In conclusion, the 20 cm pan can be useful for estimating banana Tr in greenhouses.

Water Balance of a Stock-Watering Pond in the Flint Hills of Kansas

Small ponds are often the main source of drinking water for grazing livestock. The hydrology of these ponds must be understood so impoundments can be located, designed, and managed to avoid water shortages during dry weather. A study was conducted to measure the water balance of a stock-watering pond in the Flint Hills region of east-central Kansas from June 2005 to October 2006. The 0.35-ha pond supplied water to 250-kg yearling steers in a 65-ha pasture of native tallgrass prairie. Evaporation, depth change, and cattle consumption were measured continuously using meteorological sensors, depth recorders, and water meters. Seepage, transpiration, and inflow were measured periodically or modeled. Evaporation was also predicted from weather data using forms of the Penman and Priestley-Taylor models. Evaporation accounted for 64% of the total water loss annually, while seepage, cattle consumption, and transpiration accounted for 31%, 3%, and 2%, respectively. The greatest water loss was observed in July, with total monthly losses over 358 mm and peak daily losses sometimes exceeding 18 mm ? d 21 . Cattle consumption averaged 30 L ? day 21 ? animal 21 with peak usage of 46 L ? day 21 ? animal 21 . On average, the Priestley-Taylor and Penman evaporation models estimated monthly evaporation to 3% and 5%, respectively. Thus, evaporation, the main form of loss, can be predicted with simple models using data from weather station networks. Inflows from runoff proved difficult to predict and were highly dependent on antecedent soil water content. Results showed that losses from ponds can be measured or predicted with reasonable accuracy. These data could be incorporated into catchment-scale hydrology models to provide site-specific designs for stock-watering ponds and livestock-watering strategies.

Global estimates of the land–atmosphere water flux based on monthly AVHRR and ISLSCP-II data, validated at 16 FLUXNET sites

Numerous models of evapotranspiration have been published that range in data-driven complexity, but global estimates require a model that does not depend on intensive field measurements. The Priestley–Taylor model is relatively simple, and has proven to be remarkably accurate and theoretically robust for estimates of potential evapotranspiration. Building on recent advances in ecophysiological theory that allow detection of multiple stresses on plant function using biophysical remote sensing metrics, we developed a bio-meteorological approach for translating Priestley–Taylor estimates of potential evapotranspiration into rates of actual evapotranspiration. Five model inputs are required: net radiation ( R n), normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), maximum air temperature ( T max), and water vapor pressure (ea). Our model requires no calibration, tuning or spin-ups. The model is tested and validated against eddy covariance measurements (FLUXNET) from a wide range of climates and plant functional types—grassland, crop, and deciduous broadleaf, evergreen broadleaf, and evergreen needleleaf forests. The model-to-measurement r 2 was 0.90 (RMS = 16 mm/month or 28%) for all 16 FLUXNET sites across 2 years (most recent data release). Global estimates of evapotranspiration at a temporal resolution of monthly and a spatial resolution of 1° during the years 1986–1993 were determined using globally consistent datasets from the International Satellite Land-Surface Climatology Project, Initiative II (ISLSCP-II) and the Advanced Very High Resolution Spectroradiometer (AVHRR). Our model resulted in improved prediction of evapotranspiration across water-limited sites, and showed spatial and temporal differences in evapotranspiration globally, regionally and latitudinally.

Effect of spatial variation on areal evapotranspiration simulation in Haibei, Tibet plateau, China

Quantification of areal evapotranspiration from remote sensing data requires the determination of surface energy balance components with support of field observations. Much attention should be given to spatial resolution sensitivity to the physics of surface heterogeneity. Using the Priestley–Taylor model, we generated evapotranspiration maps at several spatial resolutions for a heterogeneous area at Haibei, and validated the evapotranspiration maps with the flux tower data. The results suggested that the mean values for all evapotranspiration maps were quite similar but their standard deviations decreased with the coarsening of spatial resolution. When the resolution transcended about 480 m, the standard deviations drastically decreased, indicating a loss of spatial structure information of the original resolution evapotranspiration map. The absolute values of relative errors of the points for evapotranspiration maps showed a fluctuant trend as spatial resolution of input parameter data layers coarsening, and the absolute value of relative errors reached minimum when pixel size of map matched up to measuring scale of eddy covariance system. Finally, based on the analyses of the semi‐variogram of the original resolution evapotranspiration map and the shapes of spatial autocorrelation indices of Moran and Geary for evapotranspiration maps at different resolutions, an appropriate resolution was suggested for the areal evapotranspiration simulation in this study area.

Seasonal and interannual variability in evapotranspiration of native tallgrass prairie and cultivated wheat ecosystems

Year-round measurements of evapotranspiration (ET) were made, using the eddy covariance technique, in tallgrass prairie and winter wheat ecosystems in north-central Oklahoma during 1996–2000. Seasonal and interannual variability in water vapor flux was examined in terms of relevant controlling variables. During the growing season, the daily ET was 3.5–5.0 mm day −1 for the prairie and 2.5–7.0 mm day −1 for wheat. Annual ET ranged 640–810 mm for the prairie, and 710–750 mm for wheat. “Non-growing” season ET was about 25% of the annual ET in the prairie (during November–April) and about 50% of the annual ET in wheat (during July–February). Differences in ET between the two ecosystems and the corresponding interannual variability were related mostly to the effects of soil moisture stress and variations in green foliage area, while the weather parameters had a smaller impact. The ET model of Priestley and Taylor (1972) [Priestley, C.H.B., Taylor, R.J., 1972. On the assessment of surface heat flux and evaporation using large-scale parameters. Mon. Weather Rev. 100, pp. 81–92.] was modified to incorporate the effects of soil moisture and foliage area, and tested against field measurement. The modification improved the prediction of ET significantly as compared to the original model. On average, the overestimation of the actual ET by the original model reduced from 47 to 9% at the prairie site, and from 20 to 4% at the wheat site. Improved performance of the modified Priestley–Taylor model over a wide range of environmental conditions makes it potentially a practical tool for predicting ET in grasslands and agricultural systems.

Comparison of seven models for estimation of evapotranspiration and groundwater recharge using lysimeter measurement data in Germany

AbstractThis study evaluates seven evapotranspiration models and their performance in water balance studies by using lysimeter measurement data at the Mönchengladbach hydrological and meteorological station in Germany. Of the seven evapotranspiration models evaluated, three models calculate actual evapotranspiration directly using the complementary relationship approach, i.e. the CRAE model of Morton, the advection–aridity (AA) model of Brutsaert and Stricker, and the GG model of Granger and Gray, and four models calculate first potential evapotranspiration and then actual evapotranspiration by considering the soil moisture condition. Two of the four potential evapotranspiration models belong to the temperature‐based category, i.e. the Thornthwaite model and the Hargreaves model, and the other two belong to the radiation‐based category, i.e. the Makkink model and the Priestley–Taylor model. The evapotranspiration calculated by the above seven models, together with precipitation, is used in the water balance model to calculate other water balance components. The results show that, for the calculation of actual evapotranspiration, the GG model and the Makkink model performed better than the other models; for the calculation of groundwater recharge using the water balance approach, the GG model and the AA models performed better; for the simulation of soil moisture content using the water balance approach, four models (GG, Thornthwaite, Makkink and Priestley–Taylor) out of the seven give equally good results. It can be concluded that the lysimeter‐measured water balance components, i.e. actual evapotranspiration, groundwater recharge, soil moisture, etc., can be predicted by the GG model and the Makkink model with good accuracy. Copyright © 2005 John Wiley & Sons, Ltd.

Comparison of Simpler Radiation-Based ET Models with Penman Monteith model for Humid Region

The three relatively simpler radiation-based models: Ture, Jensen-Haise and Priestley-Taylor were used to estimate reference evapotranspiration (ET0> at different humid locations of Assam, India. The Penman-Monteith model was selected as the standard for evaluating the performance of the other three radiation-based models. The averaged monthly meteorological data were used for estimating the ETo' Good correlation was found between ETo values estimated by each of the three radiation-based models. The least and the highest values of RMSE varied between 0.16 (Gohpur) and 0.82 (Dhubri) for Priestley-Taylor model; 0.95 (Dhubri) and 1.68 (Silicorie) for Ture model; and 1.89 (Dhubri) and 2.97 (Silicorie) for lensen-Haise model. The study revealed that among all the three radiation-based models, the Priestley-Taylor model yielded average estimate of ET0 closest to the Penman-Monteith model.

Evapotranspiration models compared on a Sierra Nevada forest ecosystem

Evapotranspiration, a major component in terrestrial water balance and net primary productivity models, is difficult to measure and predict. This study compared five models of potential evapotranspiration (PET) applied to a ponderosa pine forest ecosystem at an AmeriFlux site in Northern California. The AmeriFlux sites are research forests across the United States, Canada, Brazil, and Costa Rica with instruments on towers that measure carbon, water, and energy fluxes into and out of the ecosystems. The evapotranspiration models ranged from simple temperature and solar radiation-driven equations to physically-based combination approaches and included reference surface and surface cover-dependent algorithms. For each evapotranspiration model, results were compared against mean daily latent heat from half-hourly measurements recorded on a tower above the forest canopy. All models calculate potential evapotranspiration (assuming well-watered soils at field capacity), rather than actual evapotranspiration (based on soil moisture limitations), and thus overpredicted values from the dry summer seasons of 1997 and 1998. A soil moisture function was integrated to estimate actual evapotranspiration, resulting in improved accuracy in model simulations. A modified Priestley–Taylor model performed well given its relative simplicity.

Modelling actual, reference and equilibrium evaporation from a temperate wet grassland

AbstractActual and reference evaporation from a wet grassland in Southeast England was studied over the spring and summer of 1999 (March to September) through changes in surface wetness. The Penman–Monteith (using resistance values for reference grass surface), equilibrium evaporation and Priestley–Taylor models were compared with output from the Bowen ratio energy balance (BREB) method. On field visits, inundation of the grazing marsh was mapped and surface soil moisture monitored in a regular grid using a capacitance probe. During the study period, the extent of flooding fell from approximately 10% to 0% and the surface soil moisture declined from over 38% to 15%. Daily averaged Bowen ratios displayed large variation but were below unity, indicating that latent energy flux was the dominant energy sink. The Penman–Monteith and equilibrium evaporation models underestimated during periods of surface inundation and overestimated when no surface water was present. Computed values of the Priestley–Taylor parameter α showed daily variability, but α was predictable with surface wetness such an average value of α = 1·25 characterized periods of inundation, and an average values of α = 0·80 represented periods of no surface water. The performance of the models in computing actual evaporation was compared with the BREB using the root‐mean‐square error and index of agreement. The optimal model was the Priestley–Taylor model. Copyright © 2004 John Wiley & Sons, Ltd.

GOES surface insolation to estimate wetlands evapotranspiration

Incoming solar radiation derived from GOES-8 satellite observations, in combination with local meteorological measurements, were used to model evapotranspiration from a wetland. The wetland experiment was conducted in the Paynes Prairie Preserve, North Central Florida during a growing season characterized by significant convective activity. The satellite solar radiation measurements generally agreed with pyranometer data gathered at the site. The satellite net radiation estimates were in good agreement with the 30-min averages of measured net radiometer data. Satellite derived net radiation estimates were used in the Penman–Monteith and Priestley–Taylor models to calculate evapotranspiration. The calculated instantaneous evaporative fluxes were in good agreement with 30-min average ground-based eddy correlation system measurements. The daily averages of modeled evapotranspiration were in very good agreement ( r 2=0.90) with reference eddy flux measurements.

EVAPOTRANSPIRATION FROM A BULRUSH‐DOMINATED WETLAND IN THE KLAMATH BASIN, OREGON1

ABSTRACT: Growing‐season evapotranspiration and surface energy and water balances were investigated for an extensive, bulrush‐dominated wetland in the Upper Klamath National Wildlife Refuge of south‐central Oregon, a semi‐arid region with competing demands for scarce water resources. Turbulent fluxes of sensible and latent heat were measured by eddy covariance for 1.2 to 1.9 days during each of four site visits during late‐May to mid‐October 1997. Mean daytime latent heat flux and the Bowen ratio ranged from 148 to 178 W m−2 and from 0.38 to 0.51, respectively, during late May, mid‐July, and late August site visits. By mid‐October, when the plant canopy had senesced, daytime latent heat flux and the Bowen ratio averaged 46 W m−2 and 2.8, respectively. An hourly Penman‐Monteith (PM) model that was fitted to the surface‐flux data provided values for the surface resistance to water‐vapor diffusion that ranged from 78 s m−1 during late August to 206 s m−1 during mid‐October. Similarly, a Priestley‐Taylor (PT) model provided values for the PT multiplier (a) that ranged from 0.96 during late August to 0.37 during mid‐October. The PM and PT models predicted evapotranspiration totals of 560 and 480 mm, respectively, for May 28 to October 12, 1997.

A comparison of approaches for evapotranspiration estimation

Flux (sensible heat, ground heat and net radiation) and meteorological data measured from the Lucky Hills and Kendall subwatersheds during the winter period (41 days) were used to obtain the daily actual evapotranspiration and to compare the daily evapotranspiration estimated from energy blance approach (Penman-model), radiation approach (Priestley-Taylor model), mass transfer approach (adjusted Dalton model), single source approach (adjusted Penman-Monteins model), and temperature approach (Thornthwaite model). The numericals and graphical tests were performed to compare the measured and estimated evapotranspiration. For the numerical tests, root mean square error (RMSE) and mean absolute error (MAE) were applied. For graphical tests, time series plots were used. The study results indicate that Penman-Monteith single source approach does not provide the satisfactory estimation of actual evapotranspiration. For the Lucky Hills subwatershed, the RMSE of adjusted Penman-Monteith model is 2.031, and the MAE is 1.645. For the Kendall subwatershed, the root mean square error of adjusted Penman-Monteith model is 2.132, and the mean absolute error is 1.851. Adjusted Dalton model gives the better estimation of evapotranspiration compared with adjusted Penman-Monteith model for the Kendall subwatershed (RMSE=1.984; MAE=1.744). The evapotranspiraton rate estimated from Penman potential ET model (energy balance approach) is much higher than those estimated from other potential ET models such as Priestley-Taylor model and Thornthwaite model. The evapotranspiraton rate estimated from Thornthwaite potential evapotranspiration model is even much lower than actual evapotranspiration.

Application of Revised Priestley-Taylor Model for Soil Moisture Prediction in a Maize Field under Drought Condition

Based on measurement in a maize field during 1994 and 1995, the modified Priestley-Taylor model presented by Nakayama et al. (1993) was tested for predicting soil moisture in the field under drought conditions. It was found that the correction factor in the model was strongly influenced by soil hydraulic property. For a wide region soil moisture prediction, to remove difference of soil hydraulic property, the modifying term in the model should use soil water potential instead of soil moisture content. Under drought conditions, for a maize field, the main soil water depletion was not in the shallow root zone, but extended to a deeper soil layer. In that condition for the deeper root crops, when this modified model is applied, the root zone should be regarded as a thicker soil layer.

Comparison of Evapotransiration Variation among Different Vegetative Canopies Using ‘Decoupling’ Theory

The decoupling theory presented by Jarvis and McNaughton (1986) was used in the comparison of the evapotranspiration characteristics of forest, corn and alfalfa canopies. The average values of the decoupling factor Ωc were 0.53, 0.74 and 0.88 in the forest, corn and alfalfa, respectively, which was in the opposite order for the aerodynamic roughness of the canopies. Ωc varied largely with the change of the canopy resistance. The Ωc indicated the variability of the ratio of the evapotranspiration to the available energy (lE/A). When Ωc<0.8, the reliability of the evapotranspiration models based on the available energy (e. g. Priestley-Taylor model) should decrease.

Evaporation from a Small Lake in the Continental Arctic using Multiple Methods

Daily evaporation from a small lake in the continental Low Arctic of Canada was examined using three independent experimental methods and a simplified combination model. Mean daily lake evaporation (± variability between methods) was estimated to be 3.2+0.3−0.3 mm d−1 and 2.5+0.6−0.3 mmd−1 over fifty-day periods during two consecutive summers. Based on these results and additional class-A pan data, total thaw-season evaporation estimates of 220 mm to 320 mm were obtained, equivalent to 70% to 100% of annual precipitation. These values are 15 to 70% higher than predicted by standard evaporation maps of Canada. Our results indicate that the Priestley-Taylor model provides a good approximation of the Bowen ratio energy balance model in this setting. As expected, estimates based on mass balance are highly sensitive to uncertainty in measurement of lake inflow and outflow.

PLANTMOD 2.1, exploring the physiology of plant communities

Based on ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) remote sensing data, bare soil evaporation was estimated with the Penman-Monteith model, the Priestley-Taylor model, and the aerodynamics model. Evaporation estimated by each of the three models was compared with actual evaporation, and error sources of the three models were analyzed. The mean absolute relative error was 9% for the Penman-Monteith model, 14% for the Priestley-Taylor model, and 32% for the aerodynamics model; the Penman-Monteith model was the best of these three models for estimating bare soil evaporation. The error source of the Penman-Monteith model is the neglect of the advection estimation. The error source of the Priestley-Taylor model is the simplification of the component of aerodynamics as 0.72 times the net radiation. The error source of the aerodynamics model is the difference of vapor pressure and neglect of the radiometric component. The spatial distribution of bare soil evaporation is evident, and its main factors are soil water content and elevation.

A Comparison of a Hierarchy of Models for Determining Energy Balance Components over Vegetation Canopies

Several methods for estimating surface energy balance components over a vegetated surface are compared. These include Penman-Monteith, Deardorff, and multilayer canopy (CANWHT) models for evaporation. Measurements taken during the 1991 DOE-sponsored Boardman Area Regional Flux Experiment over a Well-irrigated, closed wheat canopy are used in the comparison. The relative performance of each model is then evaluated. It is found that the Penman-Monteith approach using a simple parameterization for stomatal conductance performs best for evaporation flux. The Deardorff model is found to have the best relative performance for sensible heat, while the CANWHT model gives the best results for net radiation and soil heat flux. The Priestley-Taylor model for evaporation and a resistance-analog equation for sensible heat flux are also tested.