| Summary: | Estimates of water flux and storage in organic‐covered, permafrost terrains require an understanding of the factors controlling soil thaw. Field studies conducted in southern Yukon Territory, Canada, showed that ground freezing and thawing commenced at temperatures between −0.14 and −0.24°C. A temperature drop below −0.6°C had little effect on unfrozen moisture content. Unfrozen moisture storage shifted abruptly between a winter period value of ca. 50 mm and a summer period value of ca. 100 mm, although soil temperatures remained close to the freezing point for extended periods. The organic soil transmitted water laterally early in the thaw period while the water table still remained in the organic soil. Following this period, water movement was mainly vertical, between the ground surface and the underlying mineral sediment. The cumulative energy consumed in melting ice (ΣQi) in the active layer was ca. 76% of the cumulative ground heat flux, and ca. 15% of the cumulative net all‐wave radiation (ΣQ*) measured over the snow‐free ground surface. A strong linear correlation between ΣQ* and ΣQi, suggests that the degree of soil thaw can be estimated from ΣQ*. Copyright © 2005 John Wiley & Sons, Ltd.
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