SMOS: A new tool to monitor the carbon budget of vegetation: first application to the African continent

Category : L3

How do the vegetation carbon stocks change at the continental scale? What are the drivers of these changes? These are central questions for the sciences of Climate and for the application of international agreements on climate. A study coordinated by the University of Copenhagen1 has developed a new approach to investigate this issue. In collaboration with scientific teams2 from CEA, CNES and CNRS, INRA has coordinated the development of the new data set derived from SMOS microwave observations which is used to quantify vegetation carbon stocks. The study demonstrates that over the African continent and during the 2010-2016 period, the net carbon balance is negative (corresponding to a decrease of the quantity of carbon stored in the vegetation biomass) and that most of the carbon losses occurred in dryland savannahs. These results were published on 9th April 2018 in the journal Nature Ecology and Evolution.

Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands, Martin Brandt, et al., Nature Ecology & Evolution, Apr 9, 2018, doi:10.1038/s41559-018-0530-6

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 Copenhague

Scientists from INRA and their colleagues have produced a new data set of the vegetation index referred to as L-VOD (L-band vegetation optical depth), retrieved from space-borne observations of the SMOS satellite over 2010-2016. The data have been used to quantify annual aboveground biomass-carbon changes in sub-Saharan Africa stocks over the time period. The L-VOD index computed from SMOS observations allows sensing the whole canopy layer, while remote sensing observations made so far (including VOD indexes from high frequency microwave observations) were limited to sensing the top of the canopy, especially over relatively dense forests. In this study, the L-VOD index brings a temporal dimension to global, but static, maps of the above ground biomass.

An new tool to carry out an innovative monitoring of the dynamics of aboveground vegetation carbon stocks

This new method allows to monitor the seasonal dynamics of vegetation carbon losses and gains and also to link them with the impact of climate. The results demonstrate the key interest of SMOS L-VOD as a complementary data source for the quantification and monitoring of carbon stocks for national reports and large scale efforts in the framework of international initiatives such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC). The SMOS L-VOD index is particularly relevant to study relatively dense vegetation ecosystems where the signal measured from other remotely-sensed system saturates. It is also very relevant for semi-arid regions with little inventory data.

First applications of the new L-VOD tool to monitor carbon changes in sub-Saharan Africa

The study demonstrates there is an overall negative net carbon budget for sub-Saharan Africa (−0.10 PgC yr−1) over 2010-2016 and that the majority of the net losses occurred in drylands. In the latter regions, the gross loss per year represents approximately

5% of the dryland total carbon stocks in Africa. Overall, most of the detected decreases in carbon stocks in drylands were related to abnormally low soil moisture and rainfall conditions. The analyses showed there is a high inter-annual variability in the vegetation carbon stocks with gains during very wet years in (2011) and losses during in 2015 and early 2016, following a severe El Niño episode.

This study questions the general understandin

g that drylands may serve as carbon sinks on the long term. Indeed, the authors have found that dry years have partly reversed this trend and that drylands (especially in southern Africa) turned from being a carbon sink into a source over 2010-2016, demonstrating that climate controls short-term variations in carbon stocks at large scales.

So, in the long term we need to reassess whether woody vegetation in African savannahs will continue to be a carbon sink.


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

2 List of French teams involved:

Unité « Interaction Sol Plante Atmosphère » (Inra, Bordeaux Sciences Agro), centre Inra Nouvelle-Aquitaine

Laboratoire Evolution et Diversité Biologique (CNRS – IRD – UT3 Paul Sabatier – ENFA)

Laboratoire des sciences du climat et de l’environnement (CEA-CNRS-UVSQ)

Centre d’études spatiales de la biosphère (Cnes-CNRS-IRD-UT3 Paul Sabatier)

L Band continuation workshop update

Category : Non classé

Just a few words to say that the L band continuation workshop is now well over. We are preparing some documents and most notably a white paper. We will also put on this blog a post summarising the main findings…

RIMG0702

L band continuation workshop for the last day (Pic by A. Al Bitar)

This last week several of us attended also the ESA/ECMWF workshop at ECMWF, complementing usefully the findings of the previous week.

So stay tuned!

L Band Continuation workshop is on at CESBIO

Category : Non classé

Hello all

The L band continuation workshop is currently underway at CESBIO the agenda is
Agenda_workshop20171027

Yesterday, the presentations and exchanges were put on line by Ahmad and can be seen here.

We will continue today…

Breaking news –> SMOS new LEVEL 2 SM Version in ready!

Category : L2

Dear All

The long awaited SMOS V650 is now ready for release and thus for you to use!

We (ESA and ESLs) have prepared it  tested it, run the reprocessing from beginning to now, and the operational processor is no ready to produce it giving you access to the whole data set!

The main features of the new versions are described in the release note made available with the new distribution. It capitalises as usual on the progresses made at level 1, but the most salient features are

  • the replacement of ECOCLIMAP by IGBP which enables to have i) an up to date land use map and ii) to be aligned with SMAP and Aquarius,
  • the use of CdF matching in mixed forest nominal pixels and much more accurate and
  • relevant DQX and Chi2
  • Finally the way the current files are updated is also improved.

As  a consequence the new version is « wetter » at high latitudes and around forested areas (with also higher VODs), more retrievals are successful. In terms of metrics with respect to our usual sparse and dense networks, both correlation coefficients and RMSE  are improved but also thereis no bias at all while the SDTE remains the same.

V651-SM

Difference (V650-V620) of averaged soil moisture (4 months per year January; April, July and October) during 7 years.

V650-Tau

Difference (V650-V620) of averaged vegetation opacity (4 months per year January; April, July and October) during 7 years.

Data and documentation available at the usual ESA / Array addresses

Note that the SM NRT are being updated. CATDS L3 will also be updated, but after we have corrected an issue with L3 temporal approach algorithm.

Have fun!

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