Evapotranspiration partitioning for three agro-ecosystems with contrasting moisture conditions: a comparison of an isotope method and a two-source model calculation

Wei, Zhongwang; Lee, Xuhui; Wen, Xuefa; Xiao, Wei

doi:10.1016/j.agrformet.2018.01.019

Cited by 82 publications

(70 citation statements)

References 89 publications

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“…Also central to many E and T partitioning approaches is the notion that T/ET intermittently approaches 1 (Berkelhammer et al, 2016;Nelson et al, 2018;Zhou et al, 2016), as suggested by some modeling analyses (Wei et al, 2018). This assumption was critiqued by Perez-Priego et al (2018), who demonstrated that T/ET was rarely greater than 0.8 in a Mediterranean ecosystem, even during dry periods when surface soil moisture was less than 0.2 m 3 m -3 , and that E scaled with time -0.5 5 following (Brutsaert, 2014) [see also Boese et al (2018)].…”

Section: Does T/et Approach Unity?mentioning

confidence: 99%

Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities

Stoy¹,

El‐Madany²,

Fisher³

et al. 2019

Preprint

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Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. Our ability to partition evapotranspiration (ET) into E and T is limited at the ecosystem scale, which renders the validation of satellite data and land surface models incomplete. Here, we review current progress in partitioning E and T, and provide a prospectus for how to improve theory and observations going forward. Recent advancements in analytical techniques provide additional opportunities for partitioning E and T at the ecosystem scale, but their assumptions have yet to be fully 35 tested. Many approaches to partition E and T rely on the notion that plant canopy conductance and ecosystem water use efficiency (EWUE) exhibit optimal responses to atmospheric vapor pressure deficit (D). We use observations from 240 eddy covariance flux towers to demonstrate that optimal ecosystem response to D is a reasonable assumption, in agreement with recent studies, but the conditions under which this assumption holds require further analysis. Another critical assumption for many ET partitioning approaches is that ET can be approximated as T during ideal transpiring conditions, which has been 40 Biogeosciences Discuss., https://doi.

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Section: Does T/et Approach Unity?mentioning

confidence: 99%

Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities

Stoy¹,

El‐Madany²,

Fisher³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…At present, AET partitioning (T/ET) is not captured well by the models (Wei, Lee, Wen, & Xiao, 2018;Wei et al, 2017). Assessing the relationship between Ω and T/ET in the models may provide new insights into the substantial differences among model-derived Ω.…”

Section: Sources Of Errors In the Model-based Datasetsmentioning

confidence: 99%

Determinants of the ratio of actual to potential evapotranspiration

Peng

Zeng

Wei

et al. 2019

Global Change Biology

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A widely used approach for estimating actual evapotranspiration (AET) in hydrological and earth system models is to constrain potential evapotranspiration (PET) with a single empirical stress factor (Ω = AET/PET). Ω represents the water availability and is fundamentally linked to canopy–atmosphere coupling. However, the mean and seasonal variability of Ω in the models have rarely been evaluated against observations, and the model performances for different climates and biomes remain unclear. In this study, we first derived the observed Ω from 28 FLUXNET sites over North America during 2000–2007, which was then used to evaluate Ω in six large‐scale model‐based datasets. Our results confirm the importance of incorporating canopy height in the formulation of aerodynamic conductance in the case of forests. Furthermore, leaf area index (LAI) is central to the prediction of Ω and can be quantitatively linked to the partitioning between transpiration and soil evaporation (R2 = 0.43). The substantial differences between observed and model‐based Ω in forests (range: 0.2~0.9) are highly related to the way these models estimated PET and the way they represented the responses of Ω to the environmental drivers, especially wind speed and LAI. This is the first assessment of Ω in models based on in situ observations. Our findings demonstrate that the observed Ω is useful for evaluating, validating, and optimizing the modeling of AET and thus of water and energy balances.

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“…Also central to many E and T partitioning approaches is the notion that T / ET intermittently approaches 1 Nelson et al, 2018;Zhou et al, 2016;Wei et al, 2017), as suggested by modeling analyses and measurements (Wei et al, , 2018. This assumption was critiqued by Perez-Priego et al (2018), who demonstrated that T / ET was rarely greater than 0.8 in a Mediterranean ecosystem, even during dry periods when surface soil moisture was Leuning (1995) are shown for reference with the same fitted value of k. Individual half-hourly eddy covariance measurements are shown in light gray.…”

Section: Does T / Et Approach Unity?mentioning

confidence: 99%

Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities

et al. 2019

View full text Add to dashboard Cite

Evaporation (E) and transpiration (T ) respond differently to ongoing changes in climate, atmospheric composition, and land use. It is difficult to partition ecosystem-scale evapotranspiration (ET) measurements into E and T , which makes it difficult to validate satellite data and land surface models. Here, we review current progress in partitioning E and T and provide a prospectus for how to improve theory and observations going forward. Recent advancements in analytical techniques create new opportunities for partitioning E and T at the ecosystem scale, but their assumptions have yet to be fully tested. For example, many approaches to partition E and T rely on the notion that plant canopy conductance and ecosystem water use efficiency exhibit optimal responses to atmospheric vapor pressure deficit (D). We use observations from 240 eddy covariance flux towers to demonstrate that optimal ecosystem response to D is a reasonable assumption, in agreement with recent studies, but more analysis is necessary to determine the conditions for which this assumption holds. Another critical assumption for many partitioning approaches is that ET can be approximated as T during ideal transpiring conditions, which has been challenged by observational studies. We demonstrate that T can exceed 95 % of ET from certain ecosystems, but other ecosystems do not appear to reach this value, which suggests that this assumption is ecosystem-dependent with implications for partitioning. It is important to further improve approaches for partitioning E and T , yet few multi-method comparisons have been undertaken to date. Advances in our understanding of carbon-water coupling at the stomatal, leaf, and canopy level open new perspectives on how to quantify T via its strong coupling with photosynthesis. Photosynthesis can be constrained at the ecosystem and global scales with emerging data sources including solar-induced fluorescence, carbonyl sulfide flux measurements, thermography, and more. Such comparisons would improve our mechanistic understanding of ecosystem water fluxes and provide the observations necessary to validate remote sensing algorithms and land surface models to understand the changing global water cycle.

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Evapotranspiration partitioning for three agro-ecosystems with contrasting moisture conditions: a comparison of an isotope method and a two-source model calculation

Cited by 82 publications

References 89 publications

Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities

Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities

Determinants of the ratio of actual to potential evapotranspiration

Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities

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