Mountainous permafrost zones can receive water from several sources including direct precipitation, runoff from adjacent slopes, avalanches, snow-melt and groundwater. Water output may occur through surface runoff, subsurface discharge, subsurface seepage, sublimation, vapour flux, evaporation and ground ice melt. Due to this hydrological complexity, water discharge from permafrost areas can not simply be attributed to melt of ice from the frozen ground alone. In fact, ground ice may be hundreds to thousands of years old, forming an important long-term groundwater storage that has no major influence on the yearly water balance.
To date, there have not been any long-term conclusive research programmes that have measured the full hydrological cycle. In addition to the water flow through partially saturated frozen ground, water might also flow within taliks, which are unfrozen zones that influence thermal and stress conditions of the ground. Detailed temperature records at depth help identifying such layers.
Seasonal characteristics of the hydrologic cycle may include:
o Late winter: water within the active layer is frozen and any observed discharge originates entirely from groundwater flow systems at the permafrost base or in taliks.
o Late spring/early summer: the thawing front penetrates the ground: melting snow and ice recharges the upper portion of the permafrost creating a seasonal aquifer perched on top of the frozen core.
o Summer: the majority of the free water within the upper portion of the permafrost has discharged and most of the discharge observed, other than run-off from rainfall, originates from the permafrost base or from taliks. Melt water from snow patches in depressions on the surface continues to run off through the summer.
o Late summer/early fall: the freezing front penetrates downward from the ground surface. Any remaining water is accumulated in the central portion of the active layer. Under cold permafrost conditions, two-sided freezing may occur, in which case the active layer also freezes from the permafrost table upwards (Harris et al., 2008).
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