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Definition:
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Ground (soil or rock and included Ice and organic material) that remains at or below 0C for at least two consecutive years. Permafrost is synonymous with perennially Cryotic Ground: it is defined on the basis of temperature. It is not necessarily frozen, because the Freezing Point of the included water may be depressed several degrees below 0C; moisture in the form of water or Ice may or may not be present. In other words, whereas all perennially Frozen Ground is Permafrost, not all Permafrost is perennially frozen. Permafrost should not be regarded as permanent, because natural or man-made changes in the climate or terrain may cause the temperature of the ground to rise above 0C. The following classification may be used for Permafrost distribution models: Very High Likelihood (> 90% underlain by Permafrost): Most of this area is expected to be underlain by Permafrost. _ High Likelihood (70-90% underlain by Permafrost): Large parts of this area are expected to be underlain by Permafrost. Locally Permafrost Thicknesses of >50 m are expected depending on the topographic conditions. _ Medium Likelihood (40-70% underlain by Permafrost): Depending on the local surface characteristics and topography Permafrost is expected. Large bodies of Permafrost as well as areas with only isolated patches are possible. However, no thick (> 20m) and Continuous Permafrost layers are expected. _ Low Likelihood (10-40% underlain by Permafrost): Little Permafrost is expected in these areas. However, patches of Permafrost are possible due to local microclimatic conditions. _ Very Low Likelihood (1-10% underlain by Permafrost): Generally, no Permafrost is expected in these areas. However, sporadic exceptions are possible due to local microclimatic conditions. _ Extremely Low Likelihood (<1% underlain by Permafrost): No Permafrost is expected within these areas. However, cold caves, local Dead Ice or relict Ground Ice cannot be completely ruled out even in these areas depending on local microclimate and paleoglacial conditions.
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