Preprints
https://doi.org/10.5194/egusphere-2024-1955
https://doi.org/10.5194/egusphere-2024-1955
02 Sep 2024
 | 02 Sep 2024

Seasonal and inter-annual variability of carbon fluxes in southern Africa seen by GOSAT

Eva-Marie Metz, Sanam Noreen Vardag, Sourish Basu, Martin Jung, and André Butz

Abstract. The inter-annual variability of the global carbon sink is heavily influenced by semi-arid regions. Southern hemispheric Africa has large semi-arid and arid regions. However, there is only a sparse coverage of in situ CO2 measurements on the southern hemisphere. This leads to uncertainties in measurement-based carbon flux estimates for these regions. Also, dynamic global vegetation models (DGVMs) show large inconsistencies in semi-arid regions. Satellite CO2 measurements offer a spatially extensive and independent source of information about the southern African carbon cycle.

We examine Greenhouse Gases Observing Satellite (GOSAT) CO2 concentration measurements from 2009 to 2018 in southern Africa. We infer CO2 land-atmosphere fluxes which are consistent with the GOSAT measurements using the atmospheric inversion system TM5-4DVar. We find systematic differences between these satellite-based carbon fluxes and atmospheric inversions based on in situ measurements pointing towards a limited measurement information content in the latter. We use the GOSAT based fluxes and additionally Solar Induced Fluorescence (SIF), a proxy for photosynthesis, as atmospheric constraints to select DGVMs of the TRENDYv9 ensemble which show compatible fluxes. The selected DGVMs allow for studying the vegetation processes driving the southern African carbon cycle. We show that the variability of photosynthetic uptake mainly drives the inter-annual variability of the southern African carbon fluxes. The seasonal cycle, however, is substantially influenced by enhanced soil respiration due to soil rewetting at the beginning of the rainy season. The latter result emphasizes the importance of correctly representing the response of semi-arid ecosystems to soil rewetting in DGVMs.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Eva-Marie Metz, Sanam Noreen Vardag, Sourish Basu, Martin Jung, and André Butz

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1955', Thomas E. Taylor, 24 Sep 2024
    • AC1: 'Reply on RC1', Eva-Marie Metz, 05 Nov 2024
  • RC2: 'Review comment on egusphere-2024-1955', Anonymous Referee #2, 15 Oct 2024
    • AC2: 'Reply on RC2', Eva-Marie Metz, 05 Nov 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1955', Thomas E. Taylor, 24 Sep 2024
    • AC1: 'Reply on RC1', Eva-Marie Metz, 05 Nov 2024
  • RC2: 'Review comment on egusphere-2024-1955', Anonymous Referee #2, 15 Oct 2024
    • AC2: 'Reply on RC2', Eva-Marie Metz, 05 Nov 2024
Eva-Marie Metz, Sanam Noreen Vardag, Sourish Basu, Martin Jung, and André Butz

Model code and software

ATMO-IUP-UHEI/MetzEtAl2024: v1.0.0 Eva-Marie Metz https://zenodo.org/doi/10.5281/zenodo.12528504

Eva-Marie Metz, Sanam Noreen Vardag, Sourish Basu, Martin Jung, and André Butz

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Short summary
We estimate CO2 fluxes in semi-arid southern Africa from 2009 to 2018 based on satellite CO2 measurements and atmospheric inverse modelling. By selecting process-based vegetation models, which agree with the satellite CO2 fluxes, we find that soil respiration mainly drives the seasonality, whereas photosynthesis substantially influences the interannual variability. Our study emphasizes the need of better representing the response of semi-arid ecosystems to soil rewetting in vegetation models.