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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-251
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-251
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Jul 2020

27 Jul 2020

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This preprint is currently under review for the journal BG.

Using satellite data to identify the methane emission controls of South Sudan's wetlands

Sudhanshu Pandey1, Sander Houweling1,2, Alba Lorente1, Tobias Borsdorff1, Maria Tsivlidou3, A. Anthony Bloom4, Benjamin Poulter5, Zhen Zhang6, and Ilse Aben1 Sudhanshu Pandey et al.
  • 1SRON Netherlands Institute for Space Research, Utrecht, the Netherlands
  • 2Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
  • 3Laboratoire d'Aérologie, Université de Toulouse, CNRS, UPS, IRD, France
  • 4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
  • 5NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
  • 6Department of Geographical Sciences, University of Maryland, College Park, MD, 20740, USA

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) provides observations of atmospheric methane (CH4) at an unprecedented combination of high spatial resolution and daily global coverage. Hu et al. (2018) reported unexpectedly large methane enhancements over South Sudan in these observations. Here we assess methane emissions from the wetlands of South Sudan using two years (December 2017–November 2019) of TROPOMI total column methane observations. We estimate annual wetland emissions of 7.2 ± 3.2 Tg yr−1, which agrees with the multiyear GOSAT inversions of Lunt et al. (2019) but is an order of magnitude larger than estimates from wetland process models. This disagreement may be explained by the up to 4 times underestimation of inundation extent by the hydrological schemes used in those models. We investigate the seasonal cycle of the emissions and find the lowest emissions during the June–August season when the process models show the largest emissions. Using satellite altimetry-based river water height measurements, we infer that this seasonal mismatch is likely due to a seasonal mismatch in inundation extent. In models, inundation extent is controlled by regional precipitation, scaled to static wetland extent maps, whereas the actual inundation extent is driven by water inflow from rivers like the White Nile and the Sobat. TROPOMI emission estimates show better agreement, in terms of both seasonal cycle and annual mean, with model estimates that use a stronger temperature dependence. This suggests that temperature might be the best explanatory control for the emissions from wetlands in South Sudan. Our findings demonstrate the use of satellite instruments for quantifying emissions from inaccessible and uncertain tropical wetlands, providing clues for improvement of process models, and thereby improving our understanding of the currently uncertain contribution of wetlands to the global methane budget.

Sudhanshu Pandey et al.

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Sudhanshu Pandey et al.

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Short summary
We use atmospheric methane observations from the novel TROPOMI (Sentinel-5p) satellite instrument to estimate methane emissions from South Sudan's wetlands. Our emission estimates are an order of magnitude larger than the estimate of process-based wetland models. We find that this underestimation by the models is likely due to their misrepresentation of the wetlands' inundation extent and temperature dependences.
We use atmospheric methane observations from the novel TROPOMI (Sentinel-5p) satellite...
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