Preprints
https://doi.org/10.5194/bg-2022-2
https://doi.org/10.5194/bg-2022-2

  12 Jan 2022

12 Jan 2022

Review status: this preprint is currently under review for the journal BG.

Evaluation of Wetland CH4 in the JULES Land Surface Model Using Satellite Observations

Robert J. Parker1,2, Chris Wilson3,4, Edward Comyn-Platt5,6, Garry Hayman6, Toby R. Marthews6, A. Anthony Bloom7, Mark F. Lunt8, Nicola Gedney9, Simon J. Dadson6,10, Joe McNorton5, Neil Humpage1,2, Hartmut Boesch1,2, Martyn P. Chipperfield3,4, Paul I. Palmer8,11, and Dai Yamazaki12 Robert J. Parker et al.
  • 1National Centre for Earth Observation, University of Leicester, UK
  • 2Earth Observation Science, School of Physics and Astronomy, University of Leicester, UK
  • 3National Centre for Earth Observation, University of Leeds, UK
  • 4School of Earth and Environment, University of Leeds, UK
  • 5European Centre For Medium-Range Weather Forecasts, Reading, UK
  • 6UK Centre for Ecology & Hydrology, Wallingford, UK
  • 7Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 8School of GeoSciences, University of Edinburgh, Edinburgh, UK
  • 9Met Office Hadley Centre, Joint Centre for Hydrometeorological Research, Maclean Building, Wallingford, UK
  • 10School of Geography and the Environment, University of Oxford, Oxford, UK
  • 11National Centre for Earth Observation, University of Edinburgh, Edinburgh, UK
  • 12Global Hydrological Forecast Center, Institute of Industrial Science, The University of Tokyo, Tokyo, Japan

Abstract. Wetlands are the largest natural source of methane. The ability to model the emissions of methane from natural wetlands accurately is critical to our understanding of the global methane budget and how it may change under future climate scenarios. The simulation of wetland methane emissions involves a complicated system of meteorological drivers coupled to hydrological and biogeochemical processes. The Joint UK Land Environment Simulator (JULES) is a process-based land surface model that underpins the UK Earth System Model and is capable of generating estimates of wetland methane emissions.

In this study we use GOSAT satellite observations of atmospheric methane along with the TOMCAT global 3-D chemistry transport model to evaluate the performance of JULES in reproducing the seasonal cycle of methane over a wide range of tropical wetlands. By using an ensemble of JULES simulations with differing input data and process configurations, we investigate the relative importance of the meteorological driving data, the vegetation, the temperature dependency of wetland methane production and the wetland extent. We find that JULES typically performs well in replicating the observed methane seasonal cycle. We calculate correlation coefficients to the observed seasonal cycle of between 0.58 to 0.88 for most regions, however the seasonal cycle amplitude is typically underestimated (by between 1.8 ppb and 19.5 ppb). This level of performance is comparable to that typically provided by state-of-the-art data-driven wetland CH4 emission inventories. The meteorological driving data is found to be the most significant factor in determining the ensemble performance, with temperature dependency and vegetation having moderate effects. We find that neither wetland extent configuration out-performs the other but this does lead to poor performance in some regions.

We focus in detail on three African wetland regions (Sudd, Southern Africa and Congo) where we find the performance of JULES to be poor and explore the reasons for this in detail. We find that neither wetland extent configuration used is sufficient in representing the wetland distribution in these regions (underestimating the wetland seasonal cycle amplitude by 11.1 ppb, 19.5 ppb and 10.1 ppb respectively, with correlation coefficients of 0.23, 0.01 and 0.31). We employ the CaMa-Flood model to explicitly represent river and floodplain water dynamics and find these JULES-CaMa-Flood simulations are capable of providing wetland extent more consistent with observations in this regions, highlighting this as an important area for future model development.

Robert J. Parker et al.

Status: open (until 23 Feb 2022)

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Robert J. Parker et al.

Robert J. Parker et al.

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Short summary
Wetlands are the largest natural source of methane, one of the most important climate gases. The JULES land surface model simulates these emissions. We use satellite data to evaluate how well JULES reproduces the methane seasonal cycle over different tropical wetlands. It performs well for most regions however struggles for some African wetlands influenced heavily by river flooding. We explain the reasons for these deficiencies and highlight how future development will improve these areas.
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