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 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 (Zea mays L.) 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 useful 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 suppression of T and enhancement of E were observed for up to several days following rainfall. Insight gained through the partitioning of ET fluxes has the potential to significantly improve the structure and parameterization of land surface hydrological models.

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