Abstract

The African continent is facing one of the driest periods in the past three decades as well as continued deforestation. These disturbances threaten vegetation carbon (C) stocks and highlight the need for improved capabilities of monitoring large-scale aboveground carbon stock dynamics. Here we use a satellite dataset based on vegetation optical depth derived from low-frequency passive microwaves (L-VOD) to quantify annual aboveground biomass-carbon changes in sub-Saharan Africa between 2010 and 2016. L-VOD is shown not to saturate over densely vegetated areas. The overall net change in drylands (53% of the land area) was −0.05 petagrams of C per year (Pg C yr−1) associated with drying trends, and a net change of −0.02 Pg C yr−1 was observed in humid areas. These trends reflect a high inter-annual variability with a very dry year in 2015 (net change, −0.69 Pg C) with about half of the gross losses occurring in drylands. This study demonstrates, first, the applicability of L-VOD to monitor the dynamics of carbon loss and gain due to weather variations, and second, the importance of the highly dynamic and vulnerable carbon pool of dryland savannahs for the global carbon balance, despite the relatively low carbon stock per unit area.

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Acknowledgements

This research work was funded by CNES (Centre National d’Etudes Spatiales) through the Science TEC (Terre Environment et Climat) program. M.B., F.T. and R.F. acknowledge the funding from the Danish Council for Independent Research (DFF) Grant ID: DFF–6111-00258. M.B. is supported by an AXA post-doctoral fellowship. We thank DigitalGlobe for providing commercial satellite data within the NextView license program. P.C., A.V. and J.P. acknowledge funding from the European Research Council Synergy grant ERC-2013-SyG-610028 IMBALANCE-P. T.T. was funded by the Swedish national space board (Dnr: 95/16). P.C. acknowledges additional support from the ANR ICONV CLAND grant. J.Chav. has benefited from “Investissement d’Avenir” grants managed by the French Agence Nationale de la Recherche (CEBA, ref. ANR-10-LABX-25-01 and TULIP, ref. ANR-10-LABX-0041), and from TOSCA funds from the CNES.

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Affiliations

  1. Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark

    • Martin Brandt
    • , Torbern Tagesson
    • , Kjeld Rasmussen
    • , Feng Tian
    • , Guy Schurgers
    • , Wenmin Zhang
    • , Laura Vang Rasmussen
    •  & Rasmus Fensholt
  2. ISPA, UMR 1391, INRA Nouvelle-Aquitaine, Bordeaux Villenave d’Ornon, France

    • Jean-Pierre Wigneron
    • , Amen Al-Yaari
    •  & Lei Fan
  3. Laboratoire Evolution and Diversité Biologique, Bâtiment 4R3 Université Paul Sabatier, Toulouse, France

    • Jerome Chave
  4. CSIC, Global Ecology Unit CREAF-CSIC-UAB, Bellaterra, Spain

    • Josep Penuelas
    •  & Aleixandre Verger
  5. CREAF, Cerdanyola del Vallès, Spain

    • Josep Penuelas
    •  & Aleixandre Verger
  6. Laboratoire des Sciences du Climat et de l’Environnement, CEA-CNRS-UVSQ, CE Orme des Merisiers, Gif sur Yvette, France

    • Philippe Ciais
    •  & Jinfeng Chang
  7. START International Inc, Washington DC, USA

    • Cheikh Mbow
  8. CESBIO, Université de Toulouse, CNES/CNRS/IRD/UPS, Toulouse, France

    • Nemesio Rodriguez-Fernandez
    • , Yann Kerr
    •  & Arnaud Mialon
  9. International Institute for Earth System Sciences, Nanjing University, Nanjing, China

    • Wenmin Zhang
  10. NASA Goddard Space Flight Center, Greenbelt, MD, USA

    • Compton Tucker

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Contributions

J.-P.W., M.B., J.Chav., F.T. and R.F. designed the study. J.-P.W., A.A.-Y., N.R.-F., Y.K. and A.M. prepared the SMOS-IC data. P.C. and J.Chan. prepared the ORCHIDEE data, G.S. prepared the LPJ-GUESS data, C.T. prepared the high spatial-resolution satellite data. M.B., F.T. and W.Z. analysed the data. The results were interpreted by J.Chav., J.-P.W., T.T., J.P., P.C., L.V.R., K.R., C.M., L.F., A.V. and R.F. The manuscript was drafted by M.B., K.R., J.Chav., R.F., J.P.W. and P.C. with contributions by all authors.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Martin Brandt or Jean-Pierre Wigneron.

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https://doi.org/10.1038/s41559-018-0530-6