Submitted as: methods for assessment of models 28 Sep 2020

Submitted as: methods for assessment of models | 28 Sep 2020

Review status: a revised version of this preprint was accepted for the journal GMD and is expected to appear here in due course.

Definitions and methods to estimate regional land carbon fluxes for the second phase of the REgional Carbon Cycle Assessment and Processes Project (RECCAP-2)

Philippe Ciais1, Ana Bastos2, Frédéric Chevallier1, Ronny Lauerwald1,3, Ben Poulter4, Pep Canadell5, Gustaf Hugelius6,7, Robert B. Jackson8, Atul Jain9, Matthew Jones10, Masayuki Kondo11, Ingrid Luijkx12, Prabir K. Patra13, Wouter Peters12,14, Julia Pongratz15, A. M. Roxanna Petrescu16, Shilong Piao17,18, Chunjing Qiu1, Celso Von Randow19, Pierre Regnier3, Marielle Saunois1, Robert Scholes20, Anatoli Shvidenko21,22, Hanqin Tian23, Hui Yang1, Xuhui Wang17, and Bo Zheng1 Philippe Ciais et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, CEA-CNRS-UVSQ-U.P.Saclay, Gif sur Yvette, France
  • 2Max-Planck-Institut für Biogeochemie, Hans-Knöll-Str. 10, 07745, Jena, Germany
  • 3Université Libre de Bruxelles, Department Geoscience, Environment & Society, Bruxelles, Belgium
  • 4NASA Goddard Space Flight Center, Biospheric Sciences Lab., Greenbelt, USA
  • 5Global Carbon Project, CSIRO Oceans and Atmosphere, GPO Box 1700, Canberra, Australia
  • 6Department of Physical Geography, Stockholm University, Sweden
  • 7Bolin Centre for Climate Research, Stockholm University, Sweden
  • 8Department of Earth System Science, Woods Institute for the Environment, and Precourt Institute for Energy, Stanford University, USA
  • 9Department of Atmospheric Sciences, University of Illinois, Urbana, IL 61821, USA
  • 10Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
  • 11Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan
  • 12Meteorology and Air Quality, Wageningen University, Wageningen, the Netherlands
  • 13Japan Agencyfor Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
  • 14Centre for Isotope Research, University of Groningen, Groningen, the Netherlands
  • 15Department für Geographie, Ludwig-Maximilians-Universität München, Luisenstr. 37, München, Germany
  • 16Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
  • 17Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China
  • 18Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China
  • 19Earth System Science Center, National Institute of Space Research, Brazil
  • 20Global Change Institute, University of the Witwatersrand, Johannesburg, South Africa
  • 21International Institute for Applied Systems Analysis, 2361 Laxenburg Austria
  • 22Center of Productivity of Forests Russian Academy of Sciences, Moscow, Russia
  • 23International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, USA

Abstract. Regional land carbon budgets provide insights on the spatial distribution of the land uptake of atmospheric carbon dioxide, and can be used to evaluate carbon cycle models and to define baselines for land-based additional mitigation efforts. The scientific community has been involved in providing observation-based estimates of regional carbon budgets either by downscaling atmospheric CO2 observations into surface fluxes with atmospheric inversions, by using inventories of carbon stock changes in terrestrial ecosystems, by upscaling local field observations such as flux towers with gridded climate and remote sensing fields or by integrating data-driven or process-oriented terrestrial carbon cycle models. The first coordinated attempt to collect regional carbon budgets for nine regions covering the entire globe in the RECCAP-1 project has delivered estimates for the decade 2000–2009, but these budgets were not comparable between regions, due to different definitions and component fluxes reported or omitted. The recent recognition of lateral fluxes of carbon by human activities and rivers, that connect CO2 uptake in one area with its release in another also requires better definition and protocols to reach harmonized regional budgets that can be summed up to the globe and compared with the atmospheric CO2 growth rate and inversion results. In this study, for the international initiative RECCAP-2 coordinated by the Global Carbon Project, which aims as an update of regional carbon budgets over the last two decades based on observations, for 10 regions covering the globe, with a better harmonization that the precursor project, we provide recommendations for using atmospheric inversions results to match bottom-up carbon accounting and models, and we define the different component fluxes of the net land atmosphere carbon exchange that should be reported by each research group in charge of each region. Special attention is given to lateral fluxes, inland water fluxes and land use fluxes.

Philippe Ciais et al.

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Philippe Ciais et al.

Philippe Ciais et al.


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Short summary
The phase-2 of the Regional Carbon Cycle Assessment and Processes (RECCAP) will provide updated quantification and process understanding of CO2, CH4 and N2O emissions and sinks for ten regions of the globe. In this manuscript, we provide definitions, review different methods and make recommendations to the RECCAP community for estimating different components of the total land-atmosphere carbon exchange for each region in a consistent and complete approach.