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United States Department of Agriculture

Agricultural Research Service

Research Project: USING REMOTE SENSING & MODELING FOR EVALUATING HYDROLOGIC FLUXES, STATES, & CONSTITUENT TRANSPORT PROCESSES WITHIN AGRICULTURAL LANDSCAPES Title: Partitioning evapotranspiration using an eddy covariance-based technique: Improved assessment of soil moisture and land-atmosphere exchange dynamics

Authors
item Scanlon, T -
item Kustas, William

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2012
Publication Date: September 24, 2012
Citation: Scanlon, T.M., Kustas, W.P. 2012. Partitioning evapotranspiration using an eddy covariance-based technique: Improved assessment of soil moisture and land-atmosphere exchange dynamics. Vadose Zone Journal. 11:3.

Interpretive Summary: The capability to partition evapotranspiration (ET) measurements into two components, namely direct evaporation (E) from soil, leaf, and litter surfaces and transpiration (T) via plants is critical in better understanding plant water use efficiency for water and crop management and conservation. A recently-developed partitioning technique was employed using high frequency measurements of water vapor and carbon dioxide collected by an eddy covariance flux tower system in a corn field near Beltsville, MD for a full growing season. Results showed an increase in the T/ET ratio from ~5% during the early portion of the growing season to ~70-80% by the time the corn crop reached maturity. This was consistent with observed dynamics of the soil moisture profile, which indicated that water was removed from deeper soil layers as the growing season progressed. The partitioned estimates of T are shown to be essential for the appropriate calculation of canopy conductance, a key variable in many land surface and crop growth and yield models. Insight gained through flux partitioning using this technique with eddy covariance systems, which are deployed in networks worldwide, has the potential to significantly improve the structure and parameterization of hydrological and crop models for many agro-ecosystems, ultimately improving irrigation and water management decision support systems and crop stress and yield predictions.

Technical Abstract: The capability to partition evapotranspiration (ET) measurements into two components, namely direct evaporation (E) from soil, leaf, and litter surfaces and transpiration (T) via plants is critical toward better defining hydrological processes along the soil-plant-atmosphere continuum. Such information also has practical applications ranging from water resource management to climate modeling. A recently-developed partitioning technique was employed using high frequency measurements of water vapor and carbon dioxide collected by an eddy covariance flux system, which was deployed over a corn field near Beltsville, MD for a full growing season. The partitioning technique is based on flux-variance similarity theory and has the benefit of relying on routinely-collected eddy covariance measurements, with no additional instrumentation required. Results showed an increase in the T/ET ratio from ~5% during the early portion of the growing season to ~70-80% by the time the corn crop reached maturity. This was consistent with observed dynamics of the soil moisture profile, which indicated that water was removed from deeper soil layers as the growing season progressed. The partitioned estimates of T are shown to be essential for the appropriate calculation of canopy conductance, a key variable in land surface models. Finally, the transient impact of rainfall events were examined, in which the relative partitioning indicated a suppression of T and an enhancement of E for up to several days following rainfall. Insight gained through flux partitioning has the potential to significantly improve the structure and parameterization of land surface hydrological models.

Last Modified: 11/24/2014
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