Spatial variations in evapotranspiration over East Asian forest sites. I. Evapotranspiration and decoupling coefficient

Khatun, Rahima; Ohta, Takeshi; Kotani, Ayumi; Asanuma, Jun; Gamo, Minoru; Han, Shijie; Hirano, Takashi; Nakai, Yuichiro; Saigusa, Nobuko; Takagi, Kentaro; Wang, Huimin; Yoshifuji, Natsuko

doi:10.3178/hrl.5.83

Cited by 22 publications

(15 citation statements)

References 17 publications

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“…This is also supported by the relatively low Ω values in each site, indicating that the sites are more coupled with their microclimate, rather than each of them being controlled by local more large-scale differences [18]. However, in a study developed by Khatun et al [34], Ω values similar to the ones we have obtained here were observed. The different Ω values were explained by differences in environmental and vegetation structural attributes, rather than actual differences in vegetation type.…”

Section: Water Fluctuation Effectssupporting

confidence: 88%

“…Jarvis and McNaughton [18] also observed this increasing coupling as a result of water stress since canopies with more coupling are going to be more controlled by stomatal conductance and thus water fluctuations. Khatun et al [34] have also found this increased coupling as a result of water stress, and therefore we believe a less coupled canopy may be more resilient during periods of water stress. Growing season differences may also help to explain the discrepancies observed in the natural grassland and perennial crop sites compared to the annual cropland site.…”

Section: Water Fluctuation Effectssupporting

confidence: 62%

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Contrasting Physiological and Environmental Controls of Evapotranspiration over Kernza Perennial Crop, Annual Crops, and C4 and Mixed C3/C4 Grasslands

et al. 2019

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Perennial grain crops have been suggested as a more sustainable alternative to annual crops. Yet their water use and how they are impacted by environmental conditions have been seldom compared to those of annual crops and grasslands. Here, we identify the dominant mechanisms driving evapotranspiration (ET), and how they change with environmental conditions in a perennial Kernza crop (US-KLS), an annual crop field (US-ARM), a C4 grassland (US-KON), and a mixed C3/C4 grassland (US-KFS) in the Central US. More specifically, we have utilized the omega (Ω) decoupling factor, which reflects the dominant mechanisms responsible for the evapotranspiration (ET) of the canopy. Our results showed that the US-ARM site was the most coupled with the lowest decoupling values. We also observed differences in coupling mechanism variables, showing more sensitivity to the water fluctuation variables as opposed to the radiative flux variables. All of the sites showed their lowest Ω value in 2012, the year of the severe drought in the Central US. The 2012 results further indicate the dependence on the water fluctuation variables. This was especially true with the perennial Kernza crop, which displayed much higher soil moisture values. In this regard, we believe that the ability of perennial Kernza to resist water stress and retain higher soil moisture values is both a result of its deeper roots, in addition to its higher Ω value. Through the analysis of both the site comparison and the comparison of the differences in years, we conclude that the perennial Kernza crop (US-KLS) is more similar in its microclimate effects to the C4 (US-KON) and mixed C3/C4 (US-KFS) grassland sites as opposed to its annual counterpart (US-ARM). This has implications for the role of perennial agriculture for addressing agricultural resilience under changing climate conditions.

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Section: Water Fluctuation Effectssupporting

confidence: 88%

Section: Water Fluctuation Effectssupporting

confidence: 62%

Contrasting Physiological and Environmental Controls of Evapotranspiration over Kernza Perennial Crop, Annual Crops, and C4 and Mixed C3/C4 Grasslands

et al. 2019

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“…ET represents latent heat flux, and is a key component of water and energy balance. EC flux observations have been widely used to examine ecosystem carbon fluxes (Baldocchi, 2008;Amiro et al, 2010;Schwalm et al, 2010), ET (Ryu et al, 2008;Khatun et al, 2011), and water use efficiency (WUE) (Ponton et al, 2006;Yu et al, 2008a) worldwide. Flux observations have also been upscaled to assess terrestrial carbon and water dynamics at regional, continental, and global scales (Xiao et al, 2008(Xiao et al, , 2012Sun et al, 2011a).…”

Section: Introductionmentioning

confidence: 99%

Carbon fluxes, evapotranspiration, and water use efficiency of terrestrial ecosystems in China

Xiao

Sun

Chen

et al. 2013

Agricultural and Forest Meteorology

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250

128

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“…Single studies that have employed a consistent method to estimate across multiple species are rare (e.g. Stoy et al, 2006;Khatun et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Ideas and perspectives: how coupled is the vegetation to the boundary layer?

et al. 2017

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Abstract. Understanding the sensitivity of transpiration to stomatal conductance is critical to simulating the water cycle. This sensitivity is a function of the degree of coupling between the vegetation and the atmosphere and is commonly expressed by the decoupling factor. The degree of coupling assumed by models varies considerably and has previously been shown to be a major cause of model disagreement when simulating changes in transpiration in response to elevated CO 2 . The degree of coupling also offers us insight into how different vegetation types control transpiration fluxes, which is fundamental to our understanding of land-atmosphere interactions. To explore this issue, we combined an extensive literature summary from 41 studies with estimates of the decoupling coefficient estimated from FLUXNET data. We found some notable departures from the values previously reported in single-site studies. There was large variability in estimated decoupling coefficients (range 0.05-0.51) for evergreen needleleaf forests. This is a result that was broadly supported by our literature review but contrasts with the early literature which suggests that evergreen needleleaf forests are generally well coupled. Estimates from FLUXNET indicated that evergreen broadleaved forests were the most tightly coupled, differing from our literature review and instead suggesting that it was evergreen needleleaf forests. We also found that the assumption that grasses would be strongly decoupled (due to vegetation stature) was only true for high precipitation sites. These results were robust to assumptions about aerodynamic conductance and, to a lesser extent, energy balance closure. Thus, these data form a benchmarking metric against which to test model assumptions about coupling. Our results identify a clear need to improve the quantification of the processes involved in scaling from the leaf to the whole ecosystem. Progress could be made with targeted measurement campaigns at flux sites and greater site characteristic information across the FLUXNET network.

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Spatial variations in evapotranspiration over East Asian forest sites. I. Evapotranspiration and decoupling coefficient

Cited by 22 publications

References 17 publications

Contrasting Physiological and Environmental Controls of Evapotranspiration over Kernza Perennial Crop, Annual Crops, and C4 and Mixed C3/C4 Grasslands

Contrasting Physiological and Environmental Controls of Evapotranspiration over Kernza Perennial Crop, Annual Crops, and C4 and Mixed C3/C4 Grasslands

Carbon fluxes, evapotranspiration, and water use efficiency of terrestrial ecosystems in China

Ideas and perspectives: how coupled is the vegetation to the boundary layer?

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