Freezing and thawing affect a multitude of physical, chemical, and biological processes in the vadose zone. Concerns over potential impacts of global warming on the spatial extent of permafrost and poorly understood hydrological and ecological processes in frozen soils have prompted renewed interest in this subject. The vadose zone research community should become more engaged in addressing contemporary challenges concerning frozen soil. This special section presents 12 papers addressing a range of topics ranging from measurement techniques and theoretical developments to field studies of seasonal freeze–thaw cycles and associated thermal and hydrological regimes in permafrost and rock glacier. It is hoped that the studies reported here will generate interest in addressing some of the fascinating challenges associated with rapid changes in the frozen vadose zone over large areas in the cold regions that may alter the hydrological and biogeochemical cycles, including greenhouse gas emissions.

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