1.IntroductionrnPermafrost is present extensively in polar,high-plateau,alpine,and mountainous regions,with a model-estimated total extent of permafrost regions at 22.79 million km2(Gruber,2012).However,among ever increasing modeling results,these estimates are based on applications of different permafrost models of various validity,but with a large range of uncertainty.Permafrost affects terrestrial ecosystems and ground hydrothermal dynamics,biogeochemical cycles,engineered infrastructures,and socioeconomic development to varied extents.Under a warming climate,permafrost has been degrading extensively.Permafrost studies have been flourish-ing due to increasing concerns on the climatic feedbacks of permafrost carbon,ecological impacts from degrading permafrost,sustainable water supplies,and engineering ramifications.