Tracking 21st century anthropogenic and natural carbon fluxes through model-data integration

Project: Model-data integration to assess land carbon fluxes - This project is embedded in the project 'High-resolution monitoring of avoided carbon emissions and carbon restoration potentials from land use change', funded by German Stifterverband für die Deutsche Wissenschaft e.V. in collaboration with Volkswagen AG for the period 2020-2021. The project aims at providing updated and more reliable estimates of terrestrial land use and natural carbon fluxes by integrating observation-based datasets into global carbon cycle models. Summary: A time series of 21st century observation-based woody vegetation carbon stocks (Xu et al.,2021; https://www.science.org/doi/10.1126/sciadv.abe9829) was assimilated into the bookkeeping model BLUE ('bookkeeping of land use emissions') (Hansis et al.,2015; https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2014GB004997). Two data-integration experiments were performed to isolate anthropogenic and natural carbon fluxes. The 'transient' experiment relies on assimilating the time series of observation-based vegetation carbon stocks at each (annual) time step in BLUE. In the 'transient' experiment, changes in woody vegetation carbon between two time steps are due to the combination of environmental and anthropogenic processes. In the 'fixed' experiment, the time series of observation-based woody vegetation carbon is only assimilated in BLUE at the first time step and changes in woody vegetation carbon between two time steps are only due to anthropogenic processes. The environmental carbon fluxes were subsequently derived by taking the difference in vegetation carbon stocks between the transient and fixed experiments. All spatially explicit variables are on a geographical latitude-longitude grid with a resolution of 0.25°.