Thaw processes in ice-rich permafrost landscapes represented with laterally coupled tiles in a land surface model
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Published:2019-02-18
Issue:2
Volume:13
Page:591-609
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ISSN:1994-0424
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Container-title:The Cryosphere
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language:en
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Short-container-title:The Cryosphere
Author:
Aas Kjetil S.ORCID, Martin Léo, Nitzbon JanORCID, Langer Moritz, Boike JuliaORCID, Lee HannaORCID, Berntsen Terje K., Westermann Sebastian
Abstract
Abstract. Earth
system models (ESMs) are our primary tool for projecting future climate
change, but their ability to represent small-scale land surface processes is
currently limited. This is especially true for permafrost landscapes in which
melting of excess ground ice and subsequent subsidence affect lateral
processes which can substantially alter soil conditions and fluxes of heat,
water, and carbon to the atmosphere. Here we demonstrate that dynamically
changing microtopography and related lateral fluxes of snow, water, and heat
can be represented through a tiling approach suitable for implementation in
large-scale models, and we investigate which of these lateral processes are
important to reproduce observed landscape evolution. Combining existing
methods for representing excess ground ice, snow redistribution, and lateral
water and energy fluxes in two coupled tiles, we show that the model approach
can simulate observed degradation processes in two very different permafrost
landscapes. We are able to simulate the transition from low-centered to
high-centered polygons, when applied to polygonal tundra in the cold,
continuous permafrost zone, which results in (i) a more realistic
representation of soil conditions through drying of elevated features and
wetting of lowered features with related changes in energy fluxes, (ii) up to
2 ∘C reduced average permafrost temperatures in the current
(2000–2009) climate, (iii) delayed permafrost degradation in the future
RCP4.5 scenario by several decades, and (iv) more rapid degradation through
snow and soil water feedback mechanisms once subsidence starts. Applied to
peat plateaus in the sporadic permafrost zone, the same two-tile system can
represent an elevated peat plateau underlain by permafrost in a surrounding
permafrost-free fen and its degradation in the future following a moderate
warming scenario. These results demonstrate the importance of representing
lateral fluxes to realistically simulate both the current permafrost state
and its degradation trajectories as the climate continues to warm.
Implementing laterally coupled tiles in ESMs could improve the representation
of a range of permafrost processes, which is likely to impact the simulated
magnitude and timing of the permafrost–carbon feedback.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Water Science and Technology
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