Publication Abstracts

Friend et al. 2007

Friend, A.D., A. Arneth, N.Y. Kiang, M. Lomas, J. Ogée, C. Rödenbeck, S.W. Running, J.-D. Santaren, S. Sitch, N. Viovy, F.I. Woodward, and S. Zaele, 2007: FLUXNET and modelling the global carbon cycle. Glob. Change Biol., 13, 610-633, doi:10.1111/j.1365-2486.2006.01223.x.

Measurements of the net flux of CO2 between terrestrial ecosystems and the atmosphere using the eddy covariance technique have the potential to underpin our interpretation of regional CO2 source-sink patterns, CO2 flux responses to forcings, and predictions of the future terrestrial C balance. Information contained in FLUXNET eddy covariance data has multiple uses for the development and application of global carbon models, including evaluation/validation, calibration, process parameterisation, and assimilation. This paper reviews examples of these uses, compares global estimates of the dynamics of the global carbon cycle, and suggests ways of improving the utility of such data for global carbon modelling.

Net ecosystem exchange of CO2 (NEE) predicted by different terrestrial biosphere models compares favourably with FLUXNET observations at diurnal and seasonal timescales. However, rigorous model validation, particularly over the full annual cycle, requires information on the balance between assimilation and decomposition processes, information not readily available for most FLUXNET sites. However site history, when known, can greatly help further constrain the model-data comparison.

Flux measurements made over four vegetation types were used to calibrate the land-surface scheme of the GISS GCM, significantly improving simulated climate and demonstrating the utility of diurnal FLUXNET data. Land surface temperatures in many regions cool due to higher canopy conductances and latent heat fluxes, and the global CO2 uptake provides a useful constraint on the realism of simulated surface moisture fluxes.

FLUXNET data are used to calibrate a global production efficiency model (PEM), forced by satellite-measured absorbed radiation. This method suggests that global net primary production (NPP) increased 6.2% over 1982-1999. Good agreement is found between global trends in NPP estimated by this PEM and a dynamic global vegetation model (DGVM), and between the DGVM and estimates of global NEE derived from inversion of global atmospheric CO2 measurements. Combining the PEM, DGVM, and inversion results suggests that CO2 fertilization is playing a major role in current increases in NPP, with lesser impacts from increasing N deposition and growing season length. Both the PEM and the inversion identify the Amazon basin as the most important region for the current net terrestrial CO2 uptake (i.e. 33% of global NEE), as well as its inter-annual variability. The inversion's global NEE estimate of -1.2 Pg C/yr for 1982-1995 is compatible with the PEM- and DGVM-predicted increases in NPP after allowing for increasing drought, fire, and soil respiration. Thus there is a convergence of understanding derived from process-based models, remote-sensing based observations, and inversion of atmospheric data.

Future advances in field measurement techniques, including eddy covariance (particularly concerning the problem of night-time fluxes in dense canopies and of advection or flow distortion associated with complex terrain), will result in improved constraints on land-atmosphere CO2 fluxes and the rigorous attribution of mechanisms to the current terrestrial CO2 uptake and its spatial and temporal patterns. Global ecosystem models play a key role by linking information derived from FLUXNET measurements with atmospheric CO2 variability.

A number of recommendations concerning FLUXNET data are made, including a request for more comprehensive site data (particularly historical information), more measurements in undisturbed ecosystems, and the systematic provision of error estimates. The greatest value of current FLUXNET data for global carbon cycle modelling is in evaluating process representations, rather than in providing an unbiased estimate of net CO2 exchange.

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BibTeX Citation

@article{fr00100w,
  author={Friend, A. D. and Arneth, A. and Kiang, N. Y. and Lomas, M. and Ogée, J. and Rödenbeck, C. and Running, S. W. and Santaren, J.-D. and Sitch, S. and Viovy, N. and Woodward, F. I. and Zaele, S.},
  title={FLUXNET and modelling the global carbon cycle},
  year={2007},
  journal={Glob. Change Biol.},
  volume={13},
  pages={610--633},
  doi={10.1111/j.1365-2486.2006.01223.x},
}

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RIS Citation

TY  - JOUR
ID  - fr00100w
AU  - Friend, A. D.
AU  - Arneth, A.
AU  - Kiang, N. Y.
AU  - Lomas, M.
AU  - Ogée, J.
AU  - Rödenbeck, C.
AU  - Running, S. W.
AU  - Santaren, J.-D.
AU  - Sitch, S.
AU  - Viovy, N.
AU  - Woodward, F. I.
AU  - Zaele, S.
PY  - 2007
TI  - FLUXNET and modelling the global carbon cycle
JA  - Glob. Change Biol.
VL  - 13
SP  - 610
EP  - 633
DO  - 10.1111/j.1365-2486.2006.01223.x
ER  -

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