Frozen Soil Hydrological Processes and Their Effects: A Review and Synthesis

Abstract Frozen soils, including seasonally frozen ground and permafrost, are rapidly changing under a warming climate, with cascading effects on water, energy, and carbon cycles. We synthesize recent advances in the physics, observation, and modeling of frozen‐soil hydrology, emphasizing freeze–thaw dynamics, infiltration regimes and preferential flow, groundwater–permafrost interactions (including talik development and advective heat), and resulting shifts in streamflow seasonality. Progress in in situ sensing, geophysics, and remote sensing now resolves unfrozen water, freezing fronts, and active‐layer dynamics across scales, while land‐surface and tracer‐aided hydrological models increasingly represent phase change, macropore bypass, and vapor transport. Thaw‐induced activation of subsurface pathways alters recharge and baseflow, influences vegetation and biogeochemistry, and modulates greenhouse‐gas emissions. Key uncertainties persist in scaling micro‐scale processes, parameterizing ice‐impeded hydraulics, and representing abrupt thaw and wetland dynamics. We outline a tiered modeling framework, priority observations, and integration of vegetation–hydrology–carbon processes to improve projections of cold‐region water resources and climate feedbacks.