Preprints
https://doi.org/10.5194/gmd-2021-263
https://doi.org/10.5194/gmd-2021-263

Submitted as: development and technical paper 07 Oct 2021

Submitted as: development and technical paper | 07 Oct 2021

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

A new approach to simulate peat accumulation, degradation and stability in a global land surface scheme (JULES vn5.8_accumulate_soil)

Sarah E. Chadburn1, Eleanor J. Burke2, Angela V. Gallego-Sala3, Noah D. Smith1, M. Syndonia Bret-Harte4, Dan J. Charman3, Julia Drewer5, Colin W. Edgar4, Eugenie S. Euskirchen4, Krzysztof Fortuniak6, Yao Gao7, Mahdi Nakhavali3, Włodzimierz Pawlak6, Edward A. G. Schuur8, and Sebastian Westermann9 Sarah E. Chadburn et al.
  • 1Department of Mathematics, University of Exeter, Exeter, UK
  • 2Met Office Hadley Centre, Exeter, UK
  • 3Geography Department, University of Exeter, Exeter, UK
  • 4Institute of Arctic Biology, University of Alaska Fairbanks, USA
  • 5UK Centre for Ecology & Hydrology, Bush Estate, Penicuik, Scotland, UK
  • 6Department of Meteorology and Climatology, University of Lodz, Poland
  • 7Finnish Meteorological Institute, Helsinki, Finland
  • 8Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, USA
  • 9Department of Geosciences, University of Oslo, Oslo, Norway

Abstract. Peatlands have often been neglected in Earth System Models (ESMs). Where they are included, they are usually represented via a separate, prescribed grid cell fraction that is given the physical characteristics of a peat (highly organic) soil. However, in reality soils vary on a spectrum between purely mineral soil (no organic material), and purely organic soil, typically with an organic layer of variable thickness overlying mineral soil below. They are also dynamic, with organic layer thickness and its properties changing over time. Neither the spectrum of soil types nor their dynamic nature can be captured by current ESMs.

Here we present a new version of an ESM land surface scheme (Joint UK Land Environment Simulator, JULES) where soil organic matter accumulation - and thus peatland formation, degradation and stability – is integrated in the vertically-resolved soil carbon scheme. We also introduce the capacity to track soil carbon age as a function of depth in JULES, and compare this to measured peat age-depth profiles.

This scheme simulates dynamic feedbacks between the soil organic material and its thermal and hydraulic characteristics. We show that draining the peatlands can lead to significant carbon loss along with soil compaction and changes in peat properties. However, negative feedbacks can lead to the potential for peatlands to rewet themselves following drainage. These ecohydrological feedbacks can also lead to peatlands maintaining themselves in climates where peat formation would not otherwise initiate in the model, i.e. displaying some degree of resilience.

The new model produces similar results to the original model for mineral soils, and realistic profiles of soil organic carbon for peatlands. In particular the best performing configurations had root mean squared error (RMSE) in carbon density for peat sites of 7.7–16.7 kgC m−3 depending on climate zone, when compared against typical peat profiles based on 216 sites from a global dataset of peat cores. This error is considerably smaller than the soil carbon itself (around 30–60 kgC m−3) and reduced by 35–80 % compared with standard JULES. The RMSE at mineral soil sites is also smaller in JULES-Peat than JULES itself (reduced by ~30–50 %). Thus JULES-Peat can be used as a complete scheme that simulates both organic and mineral soils. It does not require any additional input data and introduces minimal additional variables to the model. This provides a new approach for improving the simulation of organic and peatland soils, and associated carbon-cycle feedbacks in ESMs, which other land surface models could follow.

Sarah E. Chadburn et al.

Status: open (until 02 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Sarah E. Chadburn et al.

Sarah E. Chadburn et al.

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Short summary
We present a new method to include peatlands in an Earth System Model (ESM). Peatlands store huge amounts of carbon that accumulates very slowly, yet can be rapidly destabilised, emitting greenhouse gases. Our model captures the dynamic nature of peat by simulating the change of surface height and physical properties of the soil as carbon is added (from plants) or decomposed. Thus we model peat dynamics and its threshold behaviours that can lead to destabilisation for the first time in an ESM.