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| Titel |
Determine Forest Turbulent Transport and Evapotranspiration Partition With the Help of a new Soil Water Isotope Model |
| VerfasserIn |
M. Cuntz, V. Haverd, D. W. Griffith, C. Keitel, C. Tadros, J. Twinning |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060096
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| Zusammenfassung |
| We determine simultaneously the vertical profile of forest canopy turbulent transport and
evapotranspiration ET partition in a Eucalypt forest in South-Eastern Australia for a
two-week period in November 2006. We use non-linear parameter estimation to optimise
agreement between modelled and measured vertical profiles of temperature, water vapour,
carbon dioxide, and deuterium content of water vapour. Modelled temperature and
concentration profiles are derived from Lagrangian dispersion theory together with a Soil
Vegetation Atmospheric Transfer (SVAT) model, which was enhanced by a new
isotopically enabled hydrologic scheme for coupled transport of heat, water and
stable isotopes (HDO and H218O) in soil and litter. We first present the new water
isotope model, Soil-Litter-iso1, which is suitable for use as part of a SVAT scheme
but also as part of an isotopically enabled land surface model. We show that it is
sufficiently efficient for use at regional scale, yet includes the complexity of coupled
heat and water transport enabling decomposition of the total moisture flux into
liquid and vapour components. The model permits the isotopic calculations to be
performed with thick soil layers and large times steps, resulting in significantly improved
computational efficiency compared with existing isotopically-enabled soil models of similar
complexity.
Deuterium contents of soil evaporation and vertically-resolved transpiration as a priori
estimates for the optimisation are then derived using the SVAT model with Soil-Litter-Iso for
the isotopic composition of soil evaporates and an advection-diffusion model for leaf water
and transpiration isotopes2. Predictions of deuterium in soil evaporate were validated using
soil chamber measurements, while the transpirate predictions were validated using isotopic
analyses of leaf and xylem water, combined with leaf-level gas exchange measurements.
Hence, modelled temperature and concentration profiles are generated using Lagrangian
dispersion theory combined with source/sink distributions of sensible heat, CO2, H2O and
HDO coming from the SVAT model. Optimisation of turbulent transport and ET partition
was then performed twice: once using only temperature, CO2 and H2O profiles3
and a second time including deuterium content of water vapour δD as well4. The
modelled vertical concentration profiles resulting from inclusion of δD demonstrate our
ability to make consistent estimates of both the scalar source distributions and the
deuterium content of the water vapour sources. However, introducing measurements
of deuterium in water vapour does not significantly alter resulting estimates of
turbulent transport (normalised Lagrangian time scale TL at canopy top: 0.4 ± 0.1 vs.
0.5 ± 0.1 without δD) and the ET partition (15 ± 2% soil evaporation vs. 17 ± 2%),
suggesting that the additional data and modelling required to use deuterium are
not warranted for the purpose of partitioning ET using the framework presented
here.
References
1Haverd V & Cuntz M (2010) Soil-Litter-Iso: A one-dimensional model for coupled transport of heat,
water and stable isotopes in soil with a litter layer and root extraction, J Hydrolo 388 (3-4),
438-455
2Cuntz M, Ogée J, Farquhar GD, Peylin P & Cernusak LA (2007) Modelling advection and diffusion of
water isotopologues in leaves, Plant Cell & Environ 30 (8), 892-909
3Haverd V, Leuning R, Griffith D, van Gorsel E & Cuntz M (2009) The turbulent Lagrangian time scale
in forest canopies constrained by fluxes, concentrations and source distributions, Boundary-Layer
Meteorol 30 (2), 209-228
4Haverd V, Cuntz M, Griffith D, Keitel C, Tadros C & Twining J (2011) Measured deuterium in water
vapour concentration does not improve the constraint on the partitioning of evapotranspiration in a tall
forest canopy, as estimated using a soil vegetation atmosphere transfer model. Agric. & Forest
Meteorolo 151(6), 645-654 |
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