Evaluating Boreal Wetland Methane Emissions in Fennoscandia using MAGIC2021 airborne measurements and Atmospheric Modelling

Boreal wetlands are components of the terrestrial carbon cycle, acting as significant natural sources of methane (CH4) in circumpolar regions. With accelerated Arctic warming, emissions from these ecosystems become hard to predict with high uncertainties on future hydrological regimes, wetland/permafrost extent, and organic matter decomposition rates, subsequently affecting CH4 emissions. Validation of accurate quantification methods for these emissions is therefore pivotal in order to better understand and manage potential climate feedbacks.

In this context, the MAGIC2021 international large-scale field campaign's airborne measurements provide key empirical data to assess CH4 emissions from boreal wetlands in Fennoscandia. Led by CNRS and CNES, the campaign took place in August 2021 and involved 70 scientists from 14 international research teams. More than twenty instruments were deployed, onboard research aircraft (in-situ and lidars), as well as on stratospheric balloons (AirCores) and on the ground (EM27/SUN). In particular, obtaining CH4 concentrations from aircraft flights within the boundary layer allowed to directly capture the signatures of wetland emissions, offering a robust dataset for model validation.

Our study employs two Lagrangian models, FLEXPART driven by ERA5 data and WRF-LPDM, to estimate wetland CH4 fluxes from these measurements. The use of these distinct Lagrangian approaches allows for cross-validation of results, enhancing the reliability of our findings. The derived fluxes are compared with outputs from two bottom-up emission models, WetCHARTs and JSBACH-HIMMELI, which simulate wetland CH4 dynamics at different scales and resolutions. This comparative analysis not only benchmarks the performance of these models against observational data but also sheds light on discrepancies in modelled bottom-up fluxes that can guide future improvements.

Contributions of this study to the session include:

• A high resolution assessment of boreal wetland CH4 emissions and atmospheric distribution, using state-of-the-art airborne observational techniques.
• Integration of multiple Lagrangian modelling frameworks to validate and corroborate CH4 flux estimates.
• A critical evaluation of bottom-up models WetCHARTs and JSBACH-HIMMELI against empirical data, advancing our understanding of model uncertainties and informing on possible enhancements in wetland CH4 emission.

This research aims to further improve our understanding of methane emission processes from boreal wetlands, which helps improve predictions about these important ecosystems. The outcomes contribute to a more accurate global methane budget and underscore the importance of synergistic observational and modelling strategies in environmental science.