Permafrost Thaw and the Rewiring of Northern Hemisphere Hydrology
Context: Permafrost underlies roughly one quarter of the Northern Hemisphere land area and functions as a subsurface boundary that stores ice, carbon, and water. Rapid Arctic warming is degrading this boundary, changing how precipitation, snowmelt, groundwater, and surface waters move through northern landscapes. Findings: Evidence from field networks, remote sensing, river records, and process modelling shows that thaw can increase subsurface connectivity, raise winter baseflows, drain some lakes and wetlands, create others, accelerate erosion, and export dissolved carbon, nutrients, and mercury. Responses are spatially uneven because ground-ice content, topography, vegetation, snow, and disturbance history determine whether thaw produces wetter or drier conditions. Implications: Hydrological change from permafrost thaw affects infrastructure, freshwater ecosystems, carbon cycling, and Indigenous and northern communities. Monitoring and adaptation must treat permafrost not as a static frozen layer, but as a dynamic control on watershed structure.
Introduction
Permafrost is ground that remains at or below 0°C for at least two consecutive years. It is widespread across Alaska, Canada, Greenland, Scandinavia, and Siberia, and it acts as a cryospheric framework for northern watersheds [1]. In many high-latitude catchments, frozen ground restricts infiltration, confines groundwater, supports ice-rich soils, and helps maintain lakes, wetlands, peatlands, and seasonally saturated tundra. As the Arctic warms at more than twice the global average rate, this framework is being reorganized [1].
The hydrological significance of thaw is not limited to local ground subsidence or isolated thermokarst ponds. Permafrost degradation changes the…
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