Ninth International Conference on Permafrost ... - IARC Research

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The Influence of Snowdrift on the Geothermal Field of Permafrost: Results fromThree-Dimensional Numerical Simulations at a Local ScaleAnne-Marie LeBlancCentre d’études nordiques, Université Laval, Québec (QC), CanadaRichard FortierCentre d’études nordiques, Université Laval, Québec (QC), CanadaMichel AllardCentre d’études nordiques, Université Laval, Québec (QC), CanadaRené TherrienDépartement de géologie et de génie géologique, Université Laval, Québec (QC), CanadaIntroductionThree-dimensional (3-D) numerical simulations of thethermal regime of permafrost were carried out to studythe effect of thermal insulation of snow and the impacts ofclimate warming on the permafrost evolution. The thermalregime of permafrost is closely related to not only the climatevariability but also the surface conditions controlling theheat exchange between the ground and the air. Among theparameters affecting the surface conditions, the snow coveris probably the most important because it is recognized asa good thermal insulator preventing the ground cooling inwinter (Goodrich 1982). The spatial distribution of snow ata local scale depends on the snow falls, prevailing winds,vegetation, changes in topography, obstacles, and snowremoval. While open areas prone to strong winds arecharacterized by thin snow cover, snowdrifts form in theareas protected from the wind transport and erosion suchas depressions, thick embankments, and tall infrastructures.Since the spatial distribution of snowdrifts is highly variableat a local scale, the influence of snowdrifts on the geothermalfield of permafrost only can be modeled using 3-D numericalsimulation.Study SiteThe Inuit community of Salluit (62°12′N, 75°40′W) islocated in the continuous permafrost zone along the southernshore of Hudson Strait, in Nunavik, Canada. The village liesin a valley, and most infrastructures are built on ice-richmarine sediments.3-D Numerical SimulationA 3-D finite-element heat conduction model taking intoaccount the phase change was developed to predict thegeothermal field of permafrost in the valley of Salluit. TheQuaternary deposits and permafrost conditions in the valleywere mapped at a scale of 1:2000. These deposits werethen divided into 52 vertical layers, with layer thicknessincreasing from 0.2 m near the surface up to 5 m at a depthof 100 m. The element side varied from 2 to 50 m accordingto the dimensions of the surface conditions to be simulated.Thermal properties were then given at each voxel of the3-D model according to the previous mapping. The lowerboundary condition at a depth of 100 m corresponded tothe geothermal heat flux of 0.03 W/m 2 measured in a deepborehole in the Katinniq plateau, 150 km southeast of Salluit.The complex heat transfer function between the air and theground was simulated using simultaneous recordings ofair and ground surface temperatures at various locations inthe valley during two consecutive years. Mean monthly airtemperatures from the Canadian Regional Climate Model(Music & Caya 2007) were used to drive the simulationsfrom 1961 to 2100 according to the SRES A2 scenario(IPCC 2000).ResultsFigure 1 shows the predicted mean monthly ground surfacetemperatures (MMGST) beneath a snowdrift from October2002 to September 2003 in close match with the observedMMGST at the same location over the same period. Thepredicted MMGST at this location for the year 2099–2100is also given in Figure 1. According to SRES A2 scenario,the increase in air temperature of 6ºC over one century, from2002–2003 to 2099–2100, will shorten the winter period ofat least two months. The ground surface will be still snowfree in October 2099, and the snowmelt will take place inMay 2100; one month earlier than in 2003. The methodfor predicting the MMGST was based on the assumptionthat there is no interannual variability in snow thicknessand spatial distribution of snow. In the case of a windyenvironment such as Salluit, this assumption is valid. Evenif the variation in snow height was not simulated, the longtermmodification in MMGST is similar to the results of theSNOWPACK model presented in Luetschg et al. (2003).Figure 1. Observed and simulated mean monthly ground surfacetemperatures (MMGST) beneath a snowdrift.171
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 2. 3-D geothermal model. Snowdrifts A to K.Figure 4. 2-D section of predicted ground temperatures underneatha road embankment and a thick snowdrift in January 2100. Thedotted lines are the ground temperatures for a thin snow cover.Figure 3. Ground temperature difference between the simulationswith snowdrift surface conditions and the bare surface: (A) InJanuary 2005; (B) In January 2100.The 3-D geothermal model for the month of January 2005in the valley of Salluit is shown in Figure 2. Among the snowdriftsmapped in the valley, 11 were integrated in the model.They are identified with letters from A to K in Figure 2.Several numerical simulations were performed forassessing the thermal effect of snowdrifts. The groundtemperature difference between the simulations integratingthe snowdrift surface conditions and without integratingthese conditions is shown in Figures 3a and 3b in January2005 and 2100, respectively. Ground temperature differencesbelow the cutoff value of 0.5 C are not shown. In 2005, thethermal effect of snow insulation on ground temperaturescan reach depths as high as 100 m except for the snowdriftsA (16 m), F (42 m) and J (56 m). The surface area ofsnowdrift A is small, restricting the depth of snow influenceon ground temperatures. For similar snowdrift surface area,till and sand transmit the heat more efficiently than clay dueto their higher thermal conductivity and their lower watercontent. The thermal effect of snow on ground temperaturesis limited, therefore, under the snowdrifts F and J comparedto snowdrift H (Fig. 3a) due to the difference in soil types.In 2100, the climate warming will lead to a reductionin temperature difference at the surface: 10°C (Fig. 3b)instead of 20°C (Fig. 3a). The ground volume affected bythe snowdrifts will also decrease. In a context of climatewarming, the ground temperatures affected by a thin snowcover or under bare surface conditions will increase fasterthan the ground temperatures beneath snowdrifts.A 2-D section of predicted ground temperatures underneatha road embankment and a thick snowdrift lying on the rightembankment shoulder is shown in Figure 4 to illustrate themajor thermal effect of snowdrift. A 4 m thick talik is presentbeneath the snowdrift, while the talik is only 1 m whenconsidering a thin snow cover (dotted lines). The thermaleffect of the snowdrift propagates also underneath the roadembankment, inducing a ground warming. However, noattempt was made to take into account the water migrationat shallow depths and to accommodate thaw settlement.These two factors can influence the geothermal field ofpermafrost.ReferencesGoodrich, L.E. 1982. The influence of snow cover on theground thermal regime. Canadian GeotechnicalJournal 19: 421-432.IPCC 2000. Special Report on Emission Scenarios.N. Nakicenovic & R. Swart (eds.). UK: CambridgeUniversity Press, 570 pp.Luetschg, M., Bartelt, P., Lehning, M. & Toeckli, V. 2003.Numerical simulation of the interaction processesbetween snow cover and alpine permafrost.Proceedings of the Eighth <strong>International</strong> <strong>Conference</strong>on Permafrost, Zurich, Switzerland: 697-702.Music, B. & Caya, D. 2007. Evaluation of the hydrologicalcycle over the Mississippi river basin as simulatedby the Canadian Regional Climate Model. Journal ofHydrometeorology 8(5): 969-988.172
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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Ninth International Conference on Permafrost ... - IARC Research

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