A new tool to monitor aboveground vegetation carbon stocks: first application to the African continent

Our new study uses unprecedented data sources to measure vegetation carbon stock dynamics at continental scale. The study demonstrates that over the African continent, the net carbon balance is negative for 2010-2016, and that most of the carbon losses occurred in dryland savannahs. The results were published in the journal Nature Ecology and Evolution.

The African continent is facing one of the driest periods in the past three decades as well as continued deforestation. These disturbances from both human pressure and climate change threaten vegetation carbon stocks and highlight the need for improved capabilities of monitoring large-scale aboveground carbon stock dynamics.

Continental scale monitoring of vegetation carbon dynamics requires satellite based techniques, however, conventional satellites are limited to sensing the upper canopy layer. Consequently, the monitoring of vegetation dynamics is limited to the top green parts of the canopies which are not directly linked to aboveground biomass carbon.

Our French colleagues around Jean Pierre Wigneron (CEA, CNES, CNRS, INRA) have produced a new data set retrieved from space-borne observations of the SMOS satellite starting in 2010. The data set is based on low frequency passive microwave emissions, which are insensitive to cloud cover and green vegetation and thus able to quantify aboveground biomass carbon of the entire vegetation layer, including stems and branches, even when the vegetation is dense.

Our group had the chance to be the first group testing these new data, with groundbreaking results. For the first time, scientists were able to monitor large scale carbon stock dynamics at annual scale. The groups expect this tool to be a key in future monitoring of carbon losses and gains for national reports and large-scale efforts, such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC).

A first application to the African continent showed highly dynamic carbon stocks, and especially dryland savannahs showed surprisingly high gross losses which were caused by recent drought years. The study concludes that the new tool is close to be operational and highlights the importance of drylands in the global carbon balance.

Screenshot from 2018-03-27 15-03-42.png
Changes in aboveground vegetation carbon stocks in sub-Saharan Africa over 2010–2016. Regions with significant negative (carbon source) or positive (carbon sink) carbon changes are shown, respectively, in red or green.

© M. Brandt – Université de Copenhagen

Article at Nature Ecology and Evolution:

Brandt M, Wigneron J-P, Chave J, Tagesson T, Penuelas J, Ciais P, Rasmussen K, Tian F, Mbow C, Al-Yaari A, Rodriguez-Fernandez N, Schurgers G, Zhang W, Chang J, Kerr Y, Verger A, Tucker C, Mialon A, Rasmussen LV, Fan L, Fensholt R. 2018. Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands. Nature Ecology & Evolution 1. DOI: 10.1038/s41559-018-0530-6

Further reading:

Mongabay: new remote sensing technique used to determine carbon losses in sub-saharan africa

Article at Carbon Brief