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Earth System Dynamics An interactive open-access journal of the European Geosciences Union

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Earth Syst. Dynam., 7, 611-625, 2016
https://doi.org/10.5194/esd-7-611-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
25 Jul 2016
Soil-frost-enabled soil-moisture–precipitation feedback over northern high latitudes
Stefan Hagemann1, Tanja Blome1, Altug Ekici2, and Christian Beer3 1Max-Planck-Institut für Meteorologie, Bundesstr. 53, 20146 Hamburg, Germany
2Earth System Sciences, Laver Building, University of Exeter, Exeter, UK
3Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
Abstract. Permafrost or perennially frozen ground is an important part of the terrestrial cryosphere; roughly one quarter of Earth's land surface is underlain by permafrost. The currently observed global warming is most pronounced in the Arctic region and is projected to persist during the coming decades due to anthropogenic CO2 input. This warming will certainly have effects on the ecosystems of the vast permafrost areas of the high northern latitudes. The quantification of such effects, however, is still an open question. This is partly due to the complexity of the system, including several feedback mechanisms between land and atmosphere. In this study we contribute to increasing our understanding of such land–atmosphere interactions using an Earth system model (ESM) which includes a representation of cold-region physical soil processes, especially the effects of freezing and thawing of soil water on thermal and hydrological states and processes. The coupled atmosphere–land models of the ESM of the Max Planck Institute for Meteorology, MPI-ESM, have been driven by prescribed observed SST and sea ice in an AMIP2-type setup with and without newly implemented cold-region soil processes. Results show a large improvement in the simulated discharge. On the one hand this is related to an improved snowmelt peak of runoff due to frozen soil in spring. On the other hand a subsequent reduction in soil moisture enables a positive feedback to precipitation over the high latitudes, which reduces the model's wet biases in precipitation and evapotranspiration during the summer. This is noteworthy as soil-moisture–atmosphere feedbacks have previously not been the focus of research on the high latitudes. These results point out the importance of high-latitude physical processes at the land surface for regional climate.

Citation: Hagemann, S., Blome, T., Ekici, A., and Beer, C.: Soil-frost-enabled soil-moisture–precipitation feedback over northern high latitudes, Earth Syst. Dynam., 7, 611-625, https://doi.org/10.5194/esd-7-611-2016, 2016.
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The present study analyses how cold-region physical soil processes, especially freezing of soil water, impact large-scale hydrology and climate over Northern Hemisphere high-latitude land areas. For this analysis, an atmosphere–land global climate model was used. It is shown that including these processes in the model leads to improved discharge in spring and a positive land–atmosphere feedback to precipitation over the high latitudes that has previously not been noted for the high latitudes.
The present study analyses how cold-region physical soil processes, especially freezing of soil...
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