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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/gmd-2018-233
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2018-233
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model evaluation paper 06 Dec 2018

Model evaluation paper | 06 Dec 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).

Lower boundary conditions in Land Surface Models. Effects on the permafrost and the carbon pools

Ignacio Hermoso de Mendoza1, Hugo Beltrami2, Andrew H. MacDougall2, and Jean-Claude Mareschal1 Ignacio Hermoso de Mendoza et al.
  • 1Centre de Recherche sur la dynamique du système Terre (GEOTOP), Université du Québec à Montréal (UQAM), Montréal, Québec, Canada
  • 2Climate & Atmospheric Sciences Institute and Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, Canada

Abstract. Earth System Models (ESMs) use bottom boundaries for their land surface model components which are shallower than the depth reached by surface temperature changes in the centennial time scale associated with recent climate change. Shallow bottom boundaries reflect energy to the surface, which along with the lack of geothermal heat flux in current land surface models, alter the surface energy balance and therefore affect some feedback processes between the ground surface and the atmosphere, such as permafrost and soil carbon stability. To evaluate these impacts, we modified the subsurface model in the Community Land Model version 4.5 (CLM4.5) by setting a non-zero crustal heat flux bottom boundary condition and by increasing the depth of the lower boundary by 300m. The modified and original land models were run during the period 1901–2005 under the historical forcing and between 2005–2300 under two future scenarios of moderate (RCP 4.5) and high (RCP 8.5) emissions. Increasing the thickness of the subsurface by 300 m increases the heat stored in the subsurface by 72ZJ (1ZJ=1021J) by year 2300 for the RCP 4.5 scenario and 201 ZJ for the RCP 8.5 scenario (respective increases of 260% and 217% relative to the shallow model), reduces the loss of near-surface permafrost between 1901 and 2300 by 1.6%–1.9%, and reduces the loss of soil carbon by 1.6%–3.6%. Each increase of 0.02Wm−2 of the crustal heat flux increases the temperature at the soil-bedrock frontier by 0.4±0.01K, which decreases near-surface permafrost area slightly (0.3–0.8%), but reduces the loss of soil carbon by as much as 1.1%–5.6% for the two scenarios.

Ignacio Hermoso de Mendoza et al.
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Status: open (until 31 Jan 2019)
Status: open (until 31 Jan 2019)
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Ignacio Hermoso de Mendoza et al.
Data sets

Lower boundary conditions improvement in CLM4.5 I. Hermoso de Mendoza https://doi.org/10.5281/zenodo.1420497

Model code and software

Lower boundary conditions improvement in CLM4.5 I. Hermoso de Mendoza https://doi.org/10.5281/zenodo.1420497

Ignacio Hermoso de Mendoza et al.
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Latest update: 16 Dec 2018
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Short summary
We study the impact that the thickness of the subsurface and the geothermal gradient have in land models for climate simulations. To do this, we modify the Community Land Model version 4.5. In a scenario of rising atmospheric temperatures, the temperature of an insufficiently deep subsurface rises faster than it would in the real land. For the model, this produces faster permafrost thawing and increased emissions of land carbon to the atmosphere.
We study the impact that the thickness of the subsurface and the geothermal gradient have in...
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