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  • Daily underlying water use efficiency for AmeriFlux sites

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    ZhouPUB275.pdf (5.090Mb)
    Author(s)
    Zhou, Sha
    Yu, Bofu
    Huang, Yuefei
    Wang, Guangqian
    Griffith University Author(s)
    Yu, Bofu
    Year published
    2015
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    Abstract
    Water use efficiency (WUE) is a crucial parameter to describe the interrelationship between gross primary production (GPP) and evapotranspiration (ET). Incorporating the nonlinear effect of vapor pressure deficit (VPD), underlying WUE (uWUE = GPP · VPD0.5/ET) is better than inherent WUE (IWUE = GPP · VPD/ET) at the half-hourly time scale. However, appropriateness of uWUE has not yet been evaluated at the daily time scale. To determine whether uWUE is better than IWUE, daily data for seven vegetation types from 34 AmeriFlux sites were used to validate uWUE at the daily time scale. First, daily mean VPD was shown to be a good ...
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    Water use efficiency (WUE) is a crucial parameter to describe the interrelationship between gross primary production (GPP) and evapotranspiration (ET). Incorporating the nonlinear effect of vapor pressure deficit (VPD), underlying WUE (uWUE = GPP · VPD0.5/ET) is better than inherent WUE (IWUE = GPP · VPD/ET) at the half-hourly time scale. However, appropriateness of uWUE has not yet been evaluated at the daily time scale. To determine whether uWUE is better than IWUE, daily data for seven vegetation types from 34 AmeriFlux sites were used to validate uWUE at the daily time scale. First, daily mean VPD was shown to be a good substitute for the effective VPD that was required to preserve daily GPP totals. Second, an optimal exponent, k*, corresponding to the best linear relationship between GPP · VPDk* and ET, was about 0.55 both at half-hourly and daily time scales. Third, correlation coefficient between GPP · VPDk and ET showed that uWUE (k = 0.5 and r = 0.85) was a better approximation of the optimal WUE (k = k* and r = 0.86) than IWUE (k = 1 and r = 0.81) at the daily scale. Finally, when yearly uWUE was used to predict daily GPP from daily ET and mean VPD, uWUE worked considerably better than IWUE. Comparing observed and predicted daily GPP, the average correlation coefficient and Nash-Sutcliffe coefficient of efficiency were 0.81 and 0.59, respectively, using yearly uWUE, and only 0.59 and −0.83 using yearly IWUE. As a nearly optimal WUE, uWUE consistently outperformed IWUE and could be used to evaluate the effects of global warming and elevated atmosphere CO2 on carbon assimilation and evapotranspiration.
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    Journal Title
    Journal of Geophysical Research: Biogeosciences
    Volume
    120
    Issue
    5
    DOI
    https://doi.org/10.1002/2015JG002947
    Copyright Statement
    © 2015. The Authors.This is an open access article under theterms of the Creative CommonsAttribution-NonCommercial-NoDerivsLicense, which permits use and distri-bution in any medium, provided theoriginal work is properly cited, the use isnon-commercial and no modi?cationsor adaptations are made.
    Subject
    Physical Geography and Environmental Geoscience not elsewhere classified
    Geophysics
    Publication URI
    http://hdl.handle.net/10072/100902
    Collection
    • Journal articles

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