Ground thermal and moisture conditions at the southern boundary of discontinuous permafrost, Mongolia

The spatial distribution of ground temperature and soil moisture was observed in the region of the southern boundary of discontinuous permafrost in northeastern Mongolia. Permafrost was found beneath north‐facing forested slopes and flat pasture plains. Permafrost beneath north‐facing slopes is overlain by a wet active layer, while that beneath pasture is characterized by a dry active layer. Dry soil moisture conditions were also recognized beneath south‐facing pasture slopes where permafrost is absent. These spatial variations of soil moisture are considered to be related to the permeability of permafrost. Vertical water percolation dominates beneath permafrost‐free slopes, resulting in dry soil moisture conditions, whereas permafrost beneath north‐facing slopes acts as an impermeable layer, permitting lateral downward water movement beneath steep slopes and maintaining a wet active layer on gentle slopes. By contrast, permafrost beneath pasture is permeable because temperatures are only slightly below 0°C, and it contains large amounts of unfrozen water. This environment allows water at the bottom of the active layer to migrate into the underlying permafrost. Copyright © 2005 John Wiley & Sons, Ltd.