Ninth International Conference on Permafrost ... - IARC Research

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Modeling Potential Climatic Change Impacts on Mountain Permafrost Distribution,Wolf Creek, Yukon, CanadaPhilip P. Bonnaventure, Antoni G. LewkowiczDepartment of Geography, University of Ottawa, Ottawa, CanadaIntroductionDifferences in air temperature, precipitation, andvegetation cover that develop across hundreds of kilometresin lowland areas can be generated by a few hundred metresof elevation change in mountainous regions. Consequently, amountain basin located in the discontinuous permafrost zonemay span the entire range of permafrost conditions, fromisolated patches at low elevations on north-facing slopes tocontinuous permafrost on summits (Lewkowicz & Ednie2004). It is reasonable to infer that within such a basin therewill be terrain present at temperatures close to 0°C that canbe affected by changes in climate. If unfrozen, this terrainmay become permafrost during sustained climate cooling,or if permafrost, it may thaw during sustained warming orlong-term increases in snow depths. Consequently, mountainbasins with permafrost may be particularly sensitive toclimate change. However, the complexity of permafrostdistribution within them means that there have been relativelyfew attempts to model climate change impacts (e.g., Janke2005). Our goal here is to present a method that can be usedto explore the potential effects of past and future climatechange on mountain basins with permafrost.Study AreaWolf Creek Basin (60°30′N, 135°10′W) is a mountainouswatershed of approximately 190 km 2 , with elevations rangingfrom 700–2080 m a.s.l. and located 20–30 km south ofWhitehorse in the Yukon Territory. The climate is continentalwith dry, cold conditions (Wahl et al. 1987), and the basin fallswithin the zone of sporadic, discontinuous permafrost zoneaccording to the Permafrost Map of Canada (Heginbottomet al. 1995). Basin vegetation comprises boreal forest, withsub-alpine forest, a shrub zone, and an alpine tundra zoneat progressively higher elevations. Under current conditions,permafrost probability models in Wolf Creek indicate that 38to 43% of the area is underlain by permafrost (Lewkowicz &Ednie 2004, Lewkowicz & Bonnaventure 2008).MethodologyBTS measurements were collected in Wolf Creek duringthe winters of 2001 and 2002 (Lewkowicz & Ednie 2004).The spatial field of BTS was modeled in a GIS using elevationand Potential Incoming Solar Radiation (PISR) as independentvariables. Logistic regression was used to relatethe modeled BTS temperatures to the presence or absence ofpermafrost at numerous sites within the basin in late-summer.The end result of this procedure is a map of permafrostprobability at a grid cell resolution of 30 x 30 m.The effects on permafrost distribution of climate coolingor warming scenarios can be simulated by respectivelyincreasing or decreasing the values of the elevationthroughout the study area (Janke 2005). This alters themodeled BTS field which in turn affects the predictedpermafrost probabilities. We used a standard environmentallapse rate of 6.5°C/1000 m to calculate the necessary changeof elevations, a value which is less than the BTS lapserate (8.2°C/1000 m) (Lewkowicz & Bonnaventure 2008).Temperature changes of -2 to +5°C were used in order toexamine how permafrost distributions might have appearedunder equilibrium conditions similar to those of the LittleIce Age, when temperatures in the basin were lower (e.g.,Farnell et al. 2004), and for future changes through to themost aggressive temperature warming scenarios proposedby the Intergovernmental Panel on Climate Change (IPCC2007). As in previous work, we assume that permafrostprobability can be equated over many grid cells to permafrostextent.Results and DiscussionIt should be emphasized that model predictions are forequilibrium states; the model does not account for lag timesassociated with permafrost formation and degradation.Given these lag effects, the model outputs are best thoughtof as referring to the upper few metres of permafrost only.Under cooler-than-present conditions, permafrost areawithin the basin expands, doubling to about 75% for atemperature reduction of 2°C. The form of the change isapproximately linear within this range (Fig. 1). Spatially,permafrost zones become more extensive at intermediateelevations and the boundary between continuous andextensive discontinuous permafrost (90% probability)descends from about 1600 m to 1250 m, while that betweenextensive and sporadic permafrost (50% probability) changesfrom 1400 to 1100 m.Under warming conditions, such as those expectedunder IPCC projections, permafrost extent is substantiallyreduced in a nonlinear fashion. An increase of only 1°Chalves the permafrost extent in the basin, and a further1°C change reduces it to less than 10% of the basin area(Fig. 1). Boundaries of permafrost zones within the basinmove upwards so that a 1°C change causes the continuouspermafrost boundary to rise to 1700 m. At an increase of2°C, permafrost is present only on high elevation mountaintops and upper elevation north-facing slopes. A 4°C increasereduces permafrost extent to less than 1% of the basin area,and probabilities exceed 10% only on the highest mountainpeaks above 1850 m.31
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 tThe changing slope of the line in Figure 1 relates to thehypsometry of the basin (Fig. 2). The elevation zones withthe most area occur from 1200–1500 m a.s.l., and thesehave intermediate permafrost probabilities under the currentclimate. Cooling enhances permafrost probability in theseextensive zones, and permafrost also moves downwards intolower terrain. Even a warming of 1°C reduces probabilitysubstantially in these extensive areas. For large increasesin temperature, permafrost is confined to the highest peakswhich occupy only a small part of the basin, so there is littlefurther loss as warming continues.Permafrost (% of study area)8070605040302075.458.637.719.58.21030.93 0.250-2 -1 0 1 2 3 4 5Temperature Change (°C)Figure 1. Predicted percent of Wolf Creek basin underlain bypermafrost for climate change scenarios of -2 to +5°C.Percent of basin area20181614121086420700 - 800800 - 900900 - 10001000 - 11001100 - 12001200 - 13001300 - 14001400 - 15001500 - 1600Elevation1600 - 17001700 - 18001800 - 19001900 - 20002000 - 21002100 - 2200Figure 2. Hypsometric curves illustrating the percent area of WolfCreek basin in each elevation band.ConclusionsThis simple equilibrium modeling indicates thatsubstantial change in permafrost extent has probablyoccurred in Wolf Creek since the Little Ice Age, and loss ofpermafrost can be expected as the climate warms. Mountainpermafrost is highly sensitive to climatic change as groundthermal conditions vary spatially, and thus there is alwayspermafrost on the point of thaw (warming scenarios) ornonpermafrost areas ready to become perennially frozen(cooling scenarios). Although not shown here, the modelingproduces a spatial field of permafrost probabilities that maybe useful for purposes such as distributed hydrologicalmodeling or hazard mapping.AcknowledgmentsFunding was provided by NSERC, the CanadianFoundation for Climate and Atmospheric Sciences, theYukon Geological Survey, the Geological Survey of Canadaand the University of Ottawa.ReferencesBonnaventure, P.P. & Lewkowicz, A.G. Mountain permafrostprobability mapping using the BTS method in twoclimatically dissimilar locations, northwest Canada.Canadian Journal of Earth Sciences (in press).Farnell, R., Hare, P.G., Blake, E., Bowyer, V., Schweger,C., Greer, S. & Gotthardt, R. 2004. Multidisciplinaryinvestigations of alpine snow patches in southwestYukon. Arctic 57: 247-259.Heginbottom, J.R., Dubreuil, M.A. & Harker, P.T. 1995.Canada Permafrost. (1:7,500,000 scale). In: TheNational Atlas of Canada, 5 th ed., sheet MCR 4177.Ottawa: National Resources Canada.Janke, J.R. 2005. Modeling past and future alpine permafrostdistribution in the Colorado Front Range. EarthSurface Processes and Landforms 30: 1495-1508.IPCC. 2007. http://www.ipcc.ch/ipccreports/assessmentsreports.htm.Lewkowicz, A.G. & Bonnaventure, P.P. 2008.Interchangeability of mountain permafrost probabilitymodels, Northwestern Canada. Permafrost andPeriglacial Processes 19 (in press).Lewkowicz, A.G. & Ednie, M. 2004. Probability mappingof mountain permafrost using the BTS method, WolfCreek, Yukon Territory, Canada. Permafrost andPeriglacial Processes 15: 67-80.Wahl, H.E., Fraser, D.B., Harvey, R.C. & Maxwell, J.B.1987. Climate of Yukon. Canadian GovernmentPublishing Centre.32
Page 1: NICOP 2008 Ninth <
Page 6 and 7: ContentsPreface ...................
Page 8 and 9: Mapping and Modeling the Distributi
Page 10 and 11: Satellite Observations of Frozen Gr
Page 13 and 14: xiiIce Wedge Thermal Regime in Nort
Page 15 and 16: xivPermafrost Response to Dynamics
Page 17 and 18: xvi
Page 19 and 20: NICOP SponsorsUniversitiesUniversit
Page 22 and 23: Deep Permafrost Studies at the Lupi
Page 24 and 25: Effect of Fire on Pond Dynamics in
Page 26 and 27: Cryological Status of Russian Soils
Page 28 and 29: Acoustical Surveys of Methane Plume
Page 30 and 31: Permafrost Delineation Near Fairban
Page 32 and 33: Preparatory Work for a Permanent Ge
Page 34 and 35: A Provisional Soil Map of the Trans
Page 36 and 37: Martian Permafrost Depths from Orbi
Page 38 and 39: Time Series Analyses of Active Micr
Page 40 and 41: Impact of Permafrost Degradation on
Page 42 and 43: DC Resistivity Soundings Across a P
Page 44 and 45: Modeling Thermal and Moisture Regim
Page 46 and 47: A Provisional Permafrost Map of the
Page 48 and 49: Alpine Permafrost Distribution at M
Page 50 and 51: Cryogenic Formations of the Caucasu
Page 54 and 55: A Hypothesis: A Condition of Growth
Page 56 and 57: Modeled Continual Surface Water Sto
Page 58 and 59: Freeze/Thaw Properties of Tundra So
Page 60 and 61: Discontinuous Permafrost Distributi
Page 62 and 63: Thermal Regime Within an Arctic Was
Page 64 and 65: Seasonal and Interannual Variabilit
Page 66 and 67: Twelve-Year Thaw Progression Data f
Page 68 and 69: Continued Permafrost Warming in Nor
Page 70 and 71: Landsliding Following Forest Fire o
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
Page 82 and 83: The Combined Isotopic Analysis of L
Page 84 and 85: Adaptating and Managing Nunavik’s
Page 86 and 87: Human Experience of Cryospheric Cha
Page 88 and 89: HiRISE Observations of Fractured Mo
Page 90 and 91: A Soil Freeze-Thaw Model Through th
Page 92 and 93: Mapping and Modeling the Distributi
Page 94 and 95: First Results of Ground Surface Tem
Page 96 and 97: Historical Changes in the Seasonall
Page 98 and 99: Rock Glaciers in the Kåfjord Area,
Page 100 and 101: 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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