Aerodynamic Resistance and Penman–Monteith Evapotranspiration over a Seasonally Two-Layered Canopy in Semiarid Central Australia

As the ratio of carbon uptake to water use by vegetation, water‐use efficiency (WUE) is a key ecosystem property linking global carbon and water cycles. It can be estimated in several ways, but it is currently unclear how different measures of WUE relate, and how well they each capture variation in WUE with soil moisture availability. We evaluated WUE in an Acacia‐dominated woodland ecosystem of central Australia at various spatial and temporal scales using stable carbon isotope analysis, leaf gas exchange and eddy covariance (EC) fluxes. Semi‐arid Australia has a highly variable rainfall pattern, making it an ideal system to study how WUE varies with water availability. We normalized our measures of WUE across a range of vapour pressure deficits using g1, which is a parameter derived from an optimal stomatal conductance model and which is inversely related to WUE. Continuous measures of whole‐ecosystem g1 obtained from EC data were elevated in the 3 days following rain, indicating a strong effect of soil evaporation. Once these values were removed, a close relationship of g1 with soil moisture content was observed. Leaf‐scale values of g1 derived from gas exchange were in close agreement with ecosystem‐scale values. In contrast, values of g1 obtained from stable isotopes did not vary with soil moisture availability, potentially indicating remobilization of stored carbon during dry periods. Our comprehensive comparison of alternative measures of WUE shows the importance of stomatal control of fluxes in this highly variable rainfall climate and demonstrates the ability of these different measures to quantify this effect. Our study provides the empirical evidence required to better predict the dynamic carbon–water relations in semi‐arid Australian ecosystems.

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“…estimate G c as a function of aerodynamic resistance to momentum transfer (r a ) following Cleverly, Chen, et al (2013):…”

Section: The Penman-monteith Equation Was Inverted (Equation 3) Tomentioning

confidence: 99%

Water‐use efficiency in a semi‐arid woodland with high rainfall variability

Tarín

Nolan

Medlyn

et al. 2019

Global Change Biology

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“…The PM method has been recommended as the standard potential evapotranspiration method by the Food and Agriculture Organization (FAO) and the World Meteorological Organization (WMO) because it is based on the physical mechanism and can be used globally in many regions without requiring the over parameterization (Tegos et al, ; J. Zhang et al, ; Zotarelli et al, ). In addition, a number of continental‐ and global‐scale evaporation models (Chen et al, ; Ferguson et al, ; Mu et al, ) and small‐scale vegetation transpiration models (Cleverly et al, ; Tukimat et al, ) have beenformed on the theoretical basis of the PM method. In most cases, the PM method also was used as the criterion to test the reliability of the calculation results obtained using other methods (Tukimat et al, ; Widmoser, ).…”

Section: Introductionmentioning

confidence: 99%

“…Zhang et al, 2016;Zotarelli et al, 2016). In addition, a number of continental-and global-scale evaporation models Ferguson et al, 2010;Mu et al, 2011) and small-scale vegetation transpiration models (Cleverly et al, 2013;Tukimat et al, 2012) have beenformed on the theoretical basis of the PM method. In most cases, the PM method also was used as the criterion to test the reliability of the calculation results obtained using other methods (Tukimat et al, 2012;Widmoser, 2009).…”

Section: Introductionmentioning

confidence: 99%

The Uncertainty of Penman‐Monteith Method and the Energy Balance Closure Problem

Hao

Zhang

et al. 2018

JGR Atmospheres

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The Penman‐Monteith (PM) method is considered the most accurate method for estimating reference crop evapotranspiration (ET0). However, the method has obvious flaws in energy balance closure. In this study, the changing trends between latent heat flux of ET0 (LEp) and surface net radiation (Rn) in China were analyzed based on observational data from 800 meteorological stations. The results showed that the multiyear average ratio of LEp/Rn was highest in the warm temperate zone and was lowest in the subfrigid zone of the Tibetan Plateau. Correspondingly, the values of LEp/Rn in these areas were ranged from 1.138 to 0.647. At the site scale, there were 61, 178, and 170 meteorological stations with daily average LEp/Rn values >1 during three periods (from January to April, May to August, and September to December, respectively). The ratio of LEp/Rn showed an obvious surface energy imbalance, and it was extremely obvious in northern China. Meanwhile, it is found that there was also great uncertainty of the ET0, which estimated based on the calculated and measured net radiation. In general, the uncertainty of ET0 was ranged from −0.955 to 1.028 mm/day and the average value of uncertainty was 0.154 mm/day. The uncertainty also showed obviously temporal variation, which was lower during April to October, but was higher in other times. The main cause of the energy balance closure problem was the overestimation of the aerodynamic component of ET0. In view of such situation, this study suggested the two ways to estimate ET0 for different regions.

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“…Energy limitations are common in maritime and mesic environments, that is, where P exceeds reference evapotranspiration (which is a function of VPD, solar radiation and aerodynamic conductance; Cleverly et al 2013a;Cleverly et al 2013b;Donohue et al 2009;Moore et al 2008). …”

Section: Discussionmentioning

confidence: 99%

Transpiration of Eucalyptus woodlands across a natural gradient of depth-to-groundwater

et al. 2017

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1Water resources and their management present social, economic and environmental 2 challenges, with demand for human consumptive, industrial and environmental uses 3 increasing globally. However environmental water requirements, that is, the allocation of 4 water to the maintenance of ecosystem health, are often neglected or poorly quantified. Further, transpiration by trees is commonly a major determinant of the hydrological balance 6 of woodlands but recognition of the role of groundwater in hydrological balances of 7 woodlands remains inadequate, particularly in mesic climates. 8In this study we measured rates of tree water use and sapwood 13 C discrimination in a 9 mesic, temperate Eucalypt woodland along a naturally-occurring gradient of depth-to-10 groundwater (DGW), to examine daily, seasonal and annual patterns of transpiration. We We conclude that even in mesic environments groundwater can be utilised by trees. We 1 further conclude that these forests are facultatively groundwater dependent when 2 groundwater depth is < 9 m and suggest that during drier-than-average years the 3 contribution of groundwater to stand transpiration is likely to increase significantly at the 4 two shallowest groundwater sites.5

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Aerodynamic Resistance and Penman–Monteith Evapotranspiration over a Seasonally Two-Layered Canopy in Semiarid Central Australia

Cited by 26 publications

References 26 publications

Water‐use efficiency in a semi‐arid woodland with high rainfall variability

Water‐use efficiency in a semi‐arid woodland with high rainfall variability

The Uncertainty of Penman‐Monteith Method and the Energy Balance Closure Problem

Transpiration of Eucalyptus woodlands across a natural gradient of depth-to-groundwater

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