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| Titel |
Multi-scale validation of a new soil freezing scheme for a land-surface model with physically-based hydrology |
| VerfasserIn |
I. Gouttevin, G. Krinner, P. Ciais, J. Polcher, C. Legout |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 6, no. 2 ; Nr. 6, no. 2 (2012-04-02), S.407-430 |
| Datensatznummer |
250003488
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| Publikation (Nr.) |
 copernicus.org/tc-6-407-2012.pdf |
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| Zusammenfassung |
Soil freezing is a major feature of boreal regions with substantial impact
on climate. The present paper describes the implementation of the thermal
and hydrological effects of soil freezing in the land surface model
ORCHIDEE, which includes a physical description of continental hydrology.
The new soil freezing scheme is evaluated against analytical solutions and
in-situ observations at a variety of scales in order to test its numerical
robustness, explore its sensitivity to parameterization choices and confront
its performance to field measurements at typical application scales.
Our soil freezing model exhibits a low sensitivity to the vertical
discretization for spatial steps in the range of a few millimetres to a few
centimetres. It is however sensitive to the temperature interval around the
freezing point where phase change occurs, which should be 1 °C to 2 °C
wide. Furthermore, linear and thermodynamical parameterizations of the
liquid water content lead to similar results in terms of water
redistribution within the soil and thermal evolution under freezing. Our
approach does not allow firm discrimination of the performance of one approach over the other.
The new soil freezing scheme considerably improves the representation of
runoff and river discharge in regions underlain by permafrost or subject to
seasonal freezing. A thermodynamical parameterization of the liquid water
content appears more appropriate for an integrated description of the
hydrological processes at the scale of the vast Siberian basins. The use of
a subgrid variability approach and the representation of wetlands could help
capture the features of the Arctic hydrological regime with more accuracy.
The modeling of the soil thermal regime is generally improved by the
representation of soil freezing processes. In particular, the dynamics of
the active layer is captured with more accuracy, which is of crucial
importance in the prospect of simulations involving the response of frozen
carbon stocks to future warming. A realistic simulation of the snow cover
and its thermal properties, as well as the representation of an organic
horizon with specific thermal and hydrological characteristics, are
confirmed to be a pre-requisite for a realistic modeling of the soil thermal
dynamics in the Arctic. |
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