EGU2020-19673
https://doi.org/10.5194/egusphere-egu2020-19673
EGU General Assembly 2020
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Forest above-ground biomass estimates across three decades from spaceborne scatterometer observations

Maurizio Santoro1, Oliver Cartus1, Nuno Carvalhais2, Simon Besnard2,3, and Naixin Fan2
Maurizio Santoro et al.
  • 1Gamma Remote Sensing, Gümligen, Switzerland (santoro@gamma-rs.ch)
  • 2Department for Biogeochemical Integration, Max-Planck-Institute for Biogeochemistry, Jena, Germany
  • 3Laboratory of Geo-Information Science and Remote Sensing, Wageningen University & Research, The Netherlands

The large uncertainty characterizing the terrestrial carbon (C) cycle is a consequence of the sparse and irregular observations on the ground. In terms of observations, spaceborne remote sensing has been achieving global, repeated coverages of the Earth since the late 1970s, with a continuous increase in terms of density of observations in time and spatial resolution, thus potentially qualifying as data source to fill such gap in knowledge. Above-ground biomass is a baseline for quantifying the terrestrial C pool; however, remote sensing observations do not measure the organic mass of vegetation. Above-ground biomass (AGB) of forests can only be inferred by inverting numerical models relating and combining multiple remote sensing observations. One of the longest time record of observations from space is represented by the backscattered intensity from the European Remote Sensing Wind Scatterometer (ERS WindScat) and the MetOp Advanced Scatterometer (ASCAT), both operating at C-band (wavelength of 6 cm). An almost unbroken time series of backscatter observations at 0.25° spatial resolution exists since 1991 and data continuity is guaranteed in the next decades. In spite of the weak sensitivity of C-band backscatter to AGB, wall-to-wall estimates of AGB have been derived from high-resolution SAR observations by exploiting multiple observations acquired in a relatively short time period  (Santoro et al., Rem. Sens. Env., 2011; Santoro et al., Rem. Sens. Env., 2015). We have now applied this approach to generate a global time series of AGB estimates for each year between 1992 and 2018 from the C-band scatterometer data at 0.25° spatial resolution. The spatial patterns of AGB match known patterns from in situ records and other remote sensing datasets. The uncertainty of our AGB estimates is between 30% and 40% of the estimated value at the pixel level, providing strong confidence in multi-decadal AGB trends. We identify a constant increase of biomass across most boreal and temperate forests of the northern hemisphere. In contrast, we detect severe loss of biomass throughout the wet tropics during the 1990s and the beginning of the 2000 decade in consequence of massive deforestation. This loss in biomass is followed by a steady increase during the 2000s and the beginning of the most recent decade, coming more recently into saturation. Overall, we find that the global AGB density at 0.25° steadily increased by 9% from 71.8 Mg ha-1 Pg in the 1990s to 78.1 Mg ha-1 in the 2010s. Combining our AGB density estimates with the annual maps of the Climate Change Initiative (CCI) Land Cover dataset, we show that total AGB in forests decreased slightly from 566 Pg in the 1990s to 560 Pg in the 2000s, then increased to 593 Pg in the 2010s, resulting in an almost 5% net increase during the last three decades.

How to cite: Santoro, M., Cartus, O., Carvalhais, N., Besnard, S., and Fan, N.: Forest above-ground biomass estimates across three decades from spaceborne scatterometer observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19673, https://doi.org/10.5194/egusphere-egu2020-19673, 2020.

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  • CC1: short questions, Karina Winkler, 05 May 2020

    Very impressive work! I was to slow in raising this questions in the online chat. Did you check for agreement with other available data sets such as the GlobBiOMASS for 2010? And will your AGB layers be publicly available?

    • AC1: Reply to CC1, Maurizio Santoro, 05 May 2020

      Hi Karina,

      Thanks a lot for the interest and question. GlobBiomass is a fairly decent dataset but has two issues: somewhat higher AGB in the 50-100 Mg/ha range and an almost constant AGB above 250-300 Mg/ha. I am not going into the details of why is that (a paper is going to be submitted soon). Compared to GlobBiomass, this new dataset actually has less AGB in the 50-100 Mg/ha range and captures better the high AGB above 250 Mg ha. Based on this experience, we are actually re-doing the GlobBiomass map. 

      The 25 km will be available rather soon (depends on speed of publication). THe updated GlobBiomass map will also be available as part of the CCI Biomass suite of high-res AGB data products.

      I hope this is all sufficiently clear, otherwise please ask.

      Cheers

      Maurizio