Ninth International Conference on Permafrost ... - IARC Research

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 tcontinentality and the lowest MAAT when reduced to sealevel in Norway. Typically in this area MAAT is -2.5°C to-4°C, with mean summer temperature of 8°C to 10°C andmean winter temperature -15°C to -20°C. In winter, meanmaximum snow depth is 25–75 cm. The current knowledgeon the extent and the thermal conditions of permafrost isscarce (Isaksen et al. 2008). Thawing of permafrost in thisarea may lead to subsidence of the ground surface, having asubstantial impact on, for example, the stability of mountainslopes and infrastructure. It is important, therefore, todelineate the distribution of permafrost.Modeling the Distribution of MountainPermafrostRegional permafrost modeling in southern Norway hasso far been based on maps of gridded mean annual airtemperature (MAAT), indicating permafrost as probable innon-glaciated mountain areas where MAAT is below -3°C(Etzelmüller et al. 1998, 2003). This crude approach does nottake into consideration the effects of the uneven thicknessand timing of the winter snow cover as well as the vegetationcover. In Finnmark, permafrost is presumably absent in largeforested areas although MAAT < -3°C (Isaksen et al. 2008).The reason is the influence of the forest, where more snow isaccumulated than at wind-exposed locations. The low thermalconductivity of snow efficiently insulates the ground surfacefrom the atmosphere at locations having considerable snowcover. Aiming for a better spatial representation of groundtemperature and, thus, permafrost conditions in Finnmark,ongoing work elaborates on the connection between MAATand mean annual ground surface temperature (MAGST)through the Canadian “temperature at the top of permafrost”(TTOP) model. The TTOP model uses seasonal n-factorsand air temperatures to model MAGST, and a ratio ofthawed-to-frozen conductivity of the ground to model theaverage TTOP (Smith & Riseborough 2002). In a first step,we derive seasonal n-factors based on records of air andground surface temperatures for different land cover and ofsnow parameters. As input to a regional MAGST model, weuse a land-cover map of Finnmark and gridded data of snowthickness and freezing and thawing degree-days sum of airat a resolution of 1 × 1 km. This poster presents first resultsof this ground surface temperature modeling.Isaksen, K., Farbrot, H., Blikra, L.H. & Sollid, J.L. 2008.Five year ground surface temperature measurementsin Finnmark, Northern Norway. Proceedings of the<strong>Ninth</strong> <strong>International</strong> <strong>Conference</strong> on Permafrost,Fairbanks, Alaska, 29 June–3 July 2008.Smith, M.W. & Riseborough, D.W. 2002. Climate and thelimits of permafrost: A zonal analysis. Permafrostand Periglacial Processes 13: 1-15.Tveito, O.E., Førland E.J., Heino, R., Hanssen-Bauer, I.,Alexandersson, H., Dahlström, B., Drebs, A., Kern-Hansen, C., Jónsson, T., Vaarby-Laursen, E. &Westman, Y. 2000. Nordic Temperature Maps. DNMIKlima 9/00 KLIMA, 54 pp.ReferencesEtzelmüller, B., Berthling, I. & Sollid, J.L. 1998. Thedistribution of permafrost in Southern Norway; a GISapproach. Proceedings of the Seventh <strong>International</strong><strong>Conference</strong> on Permafrost, Quebec, PQ, Canada,Centre d’Etudes Nordiques, Universite Laval,Collection Nordicana 57: 251-257.Etzelmüller, B., Berthling, I. & Sollid, J.L. 2003. Aspectsand concepts on the geomorphological significanceof Holocene permafrost in southern Norway.Geomorphology 52: 87-104.74