Ninth International Conference on Permafrost ... - IARC Research

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Idealized Modeling of the Impact of Atmospheric Forcing Variables on MountainPermafrost DegradationChristian HauckInstitute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), GermanyNadine SalzmannNational Center for Atmospheric Research (NCAR), Boulder, USAIntroductionThe high-mountain Alpine cryosphere is a particularlysensitive system to climate change due to its proximity tomelting conditions. In view of probable accelerating ratesof ongoing changes concerning atmospheric, surface, andsubsurface processes in mountain regions (IPCC 2007),a great need for increased understanding of permafrostdegradation processes and corresponding new modelingtools has been identified. Traditional mountain permafrostmodel approaches focus on spatial distribution models, usingphysically-based or empirical and statistical approaches topredict the permafrost distribution over larger areas (e.g.,Noetzli et al. 2007).However, to predict possible future changes in thepermafrost distribution, the link between small-scalesubsurface characteristics, including latent heat processesand predictions from climate models, has to be established.Whereas there is a steadily increasing number of studiesusing Global and Regional Climate Model (GCM, RCM)simulations to assess permafrost evolution and its impactin arctic regions (e.g., Anisimov & Nelson 1997, Stendel etal. 2007), similar efforts for mountainous terrain have onlystarted very recently (Salzmann et al. 2007a, b). Thereby,regional to local climate scenarios, and especially mountainregions, are among the most ambitious areas for simulatingfuture climate conditions (e.g., Frei et al. 2003). In most GCM/RCM simulations, small-scale processes and influencingvariables such as surface characteristics, a realistic snowcover, topography, and lithospheric heterogeneities, as theyare typical for mountain regions, cannot be included (Stendelet al. 2007).Among those influencing variables, the duration of asignificant snow cover plays a special role, as it determinesthe amount of energy exchange between atmosphere andground and the degree of coupling between both spheres(Hoelzle & Gruber 2008). Climate warming, therefore, canonly act upon the permafrost during the snow-free period,which is usually restricted to the summer months in manyregions of the European Alps.On the other hand, the strong decoupling of atmosphereand permafrost during most of the year can be used tosimplify the necessary linking procedure between RCMresults and subsurface models. The focus of this study isto use idealized modeling of the impact of changes in airtemperature and snow cover duration on the subsurfacepermafrost temperatures. In a next step, permafrost-relevantinformation (e.g., possible trends concerning air temperatureor snow cover duration) from control and scenario time seriesof RCM simulations can be extracted using the approachesdescribed by Salzmann et al. (2007a).Atmospheric Forcing VariablesFigure 1 shows a typical example of the influence ofnet radiation and snow cover on ground temperatures inmountain permafrost regions. The example is taken from the2900 m high-altitude permafrost station Schilthorn, SwissAlps, where a more than 100 m thick permafrost layer exists(Hauck 2002, Hilbich et al. 2008). Figure 1a shows the totalground temperature change with time within the uppermost10 m of a borehole. During the time when a significantsnow cover was present (Fig. 1c and vertical black lines),temperatures within the uppermost 10 m of the boreholeremained almost constant, as the ground temperatureregime was effectively decoupled from atmosphere. Aftermelting of the snow cover in June, temperature variabilityin the borehole is high, coinciding well with the observedvariability of the radiation balance (Fig. 1b). This agreementconfirms the dominant role of the radiation balance forground temperatures in mountain permafrost terrain in theEuropean Alps.The only exception is seen right after the beginning ofsnowmelt in May, where small-scale variability of the totalground temperatures is present (Fig. 1a). Scherler et al.(submitted) showed that this feature is most probably due toinfiltrating meltwater from the snow cover.Figure 1. (a) Total temperature difference per day in the uppermost10 m in the borehole, (b) net radiation at the energy balance station,and (c) snow height at Schilthorn, Swiss Alps.95
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 tApproachFor idealized simulations, the annual variability ofradiation (or air temperature) can be approximated by asinusoidal variation, as indicated in Figure 1b. Similarly,the evolution of the snow cover can be approximated by acontinuous linear increase in early winter and a sharp lineardecrease in early summer (Fig. 1c). For idealized modelingof the impact of atmospheric forcing on the evolution ofmountain permafrost, only four atmospheric parametersneed to be varied:1. accumulated summer air temperature (e.g.,approximated by the amplitude of the sinusoidal curve);2. air temperature at the beginning of the permanentsnow cover (autumn);3. time of the buildup of the permanent snow cover; and4. time of vanishing of the permanent snow cover.The rationale for this approach can be further illustratedby analyzing multiyear time series of air temperature andsnow cover duration (Fig. 2), as well as comparing them tosubsurface temperatures. This was done in detail by Hoelzle& Gruber (2008) for two sites in the Swiss Alps (includingSchilthorn), indicating that snow cover duration and airtemperature are indeed the dominant forcing variables forpermafrost temperatures and active layer thickness.Our approach focuses on determining subsurfacetemperatures, water, and ice content evolution with aone-dimensional coupled heat and mass transfer modelsimulating mass and energy balance of the soil-snowatmospheresystem (COUP-model, Jansson & Karlberg2001). This model has been successfully applied to simulatewater and energy at Schilthorn (Scherler et al. submitted). Asa first step to using downscaled RCM scenario time series,we use idealized atmospheric forcing time series to analyzethe possible impacts of increasing summer air temperatures,for example, or a shift in the snow cover duration on thepermafrost temperatures. In a next step, these characteristicswill be extracted from simulated RCM scenario timeseries for longer time scales. For the idealized simulations,combinations of the four atmospheric parameters listedabove will be used.ReferencesAnisimov, O.A. & Nelson, F.E. 1997. Permafrost zonationand climate change in the Northern Hemisphere:results from transient general circulation models.Climatic Change 35: 241-258.Frei, C. et al. 2003. Daily precipitation statistics in RegionalClimate Models: Evalution and intercomparison forthe European Alps. J. Geophys. Res. 108(D3): ACL9-1– 9-19.Hauck, C. 2002. Frozen ground monitoring using DCresistivity tomography. Geophysical Research Letters29(21): 2016, doi:10.1029/2002GL014995.Hilbich, C. et al. 2008. Monitoring mountain permafrostevolution using electrical resistivity tomography:A 7-year study of seasonal, annual, and long-termvariations at Schilthorn, Swiss Alps, J. Geophys. Res.113: F01S90, doi:10.1029/2007JF000799.Hoelzle, M. & Gruber, S. 2008. Borehole and ground surfacetemperatures and their relation to meteorologicalconditions in the Swiss Alps. Proceedings of the <strong>Ninth</strong><strong>International</strong> <strong>Conference</strong> on Permafrost, Fairbanks,Alaska.Intergovernmental Panel on Climate Change (IPCC) 2007.Climate Change 2007: The Physical Science Basis.Summary for policy makers, 18 pp., http://www.ipcc.ch/.Jansson, P.-E. & Karlberg, L. 2001. Coupled Heat and MassTransfer Model for Soil-Plant-Atmosphere Systems.Stockholm: Royal Inst. of Technology, Dept. of Civiland Environmental Engineering, 321 pp.Noetzli, J., Gruber, S., Kohl, T., Salzmann, N. & Haeberli, W.2007. Three-dimensional distribution and evolution ofpermafrost temperatures in idealized high-mountaintopography, J. Geophys. Res. 112 (F2): F02S13,doi:10.1029/2006JF000545.Salzmann, N. et al. 2007a. The application of RegionalClimate Model output for the simulation of highmountainpermafrost scenarios. Global and PlanetaryChange 56 (1–2): 188-202.Salzmann, N. et al. 2007b. RCM-based ground-surfacetemperature scenarios for complex high-mountaintopography. J. Geophys. Res. 112: F02S12,doi:10.1029/2006JF000527.Scherler, M. et al. Submitted. Investigation of meltwaterinfiltration into the active layer of an alpine permafrostsite on Schilthorn, Switzerland. Water ResourcesResearch.Stendel, M. et al. 2007. Using dynamical downscaling toclose the gap between global change scenarios andlocal permafrost dynamics. Global and PlanetaryChange 56(1–2): 203-214.Figure 2. Air temperature and snow height at Schilthorn, SwissAlps, between autumn 1999 and 2006 (data courtesy of M. Hoelzleand PERMOS).96
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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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xvi
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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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Page 72 and 73: A Permafrost Model Incorporating Dy
Page 74 and 75: Seasonal Sources of Soil Respiratio
Page 76 and 77: Greenland Permafrost Temperature Si
Page 78 and 79: The Importance of Snow Cover Evolut
Page 80 and 81: The Account of Long-Term Air Temper
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Page 84 and 85: Adaptating and Managing Nunavik’s
Page 86 and 87: Human Experience of Cryospheric Cha
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Page 90 and 91: A Soil Freeze-Thaw Model Through th
Page 92 and 93: Mapping and Modeling the Distributi
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Page 96 and 97: Historical Changes in the Seasonall
Page 98 and 99: Rock Glaciers in the Kåfjord Area,
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