Lysimetric Calibration of the Bowen Ratio-Energy Balance Method for Evapotranspiration Estimation in the Central Great Plains

Blaine L. Blad Conservation and Survey Division and Dept. of Horticulture and Forestry, University of Nebraska, Lincoln 68503

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Norman J. Rosenberg Conservation and Survey Division and Dept. of Horticulture and Forestry, University of Nebraska, Lincoln 68503

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Abstract

Most reports show good agreement between evapotranspiration (ET) rates estimated by the Bowen Ratio-Energy Balance (BREB) method and rates measured with lysimeters, although underestimation by the BREB model has occasionally been reported. This study was conducted to evaluate the performance of the BREB technique in the climatic conditions characteristic of the central Great Plains, a region where a significant proportion of the energy consumed by evapotranspiration is supplied from advected sensible heat.

Agreement between the BREB method and lysimetric measurements of ET is good during non-advective periods but during advective periods the BREB model underestimates ET by about 20%. Data collected in this study suggest that the difference is due primarily to an inequality of the exchange coefficients for beat (Kh) and water vapor (Kw). In the development of the BREB method these coefficients are assumed to be identical but our results indicate that the ratio Kh/Kw is greater than 1 for the stable conditions associated with the downward transport of sensible heat.

Abstract

Most reports show good agreement between evapotranspiration (ET) rates estimated by the Bowen Ratio-Energy Balance (BREB) method and rates measured with lysimeters, although underestimation by the BREB model has occasionally been reported. This study was conducted to evaluate the performance of the BREB technique in the climatic conditions characteristic of the central Great Plains, a region where a significant proportion of the energy consumed by evapotranspiration is supplied from advected sensible heat.

Agreement between the BREB method and lysimetric measurements of ET is good during non-advective periods but during advective periods the BREB model underestimates ET by about 20%. Data collected in this study suggest that the difference is due primarily to an inequality of the exchange coefficients for beat (Kh) and water vapor (Kw). In the development of the BREB method these coefficients are assumed to be identical but our results indicate that the ratio Kh/Kw is greater than 1 for the stable conditions associated with the downward transport of sensible heat.

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