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Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands


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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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.

Author information

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.

Correspondence to Martin Brandt or Jean-Pierre Wigneron.

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Further reading

Fig. 1: Relationships between carbon density in biomass and VOD in sub-Saharan Africa.
Fig. 2: Changes in carbon stocks for 2010–2016.
Fig. 3: Shrub die-off in Senegal.
Fig. 4: Observed and simulated carbon dynamics.
Fig. 5: Hovmöller diagrams showing anomalies (z score) for Africa for each year and latitude.
Fig. 6: Climate as a driver of carbon stock dynamics.