Characteristics of Spatial and Temporal Variation of Seasonal and Short-Term Frozen Soil in China in Recent 50 Years
近50年来中国季节性冻土与短时冻土的时空变化特征

Based on the quality control of daily meteorological observation data of frozen soil in China,the spatial and temporal variations of frozen soil have been investigated.The seasonal change of the frozen soil,the change of the frozen soil depth,the beginning dates and the ending dates are mainly analyzed.The results show that frozen soil occurs in most of the territory in China,including the north of the Yangtze River,Northwest China and the Tibetan Plateau.The monthly variation of seasonal frozen soil is significant.The freezing process generally began in autumn,and reached the maximum of depth and area in the end of winter.In spring the frozen soil began to thaw and finished in the summer. The thawing and freezing processes of frozen soil demonstrated different characteristics and the thawing process persisted longer and more complicatedly than the freezing process.This has a very close relationship with soil characteristics and topographic factors.In the background of global warming in the last few decades,the frozen soil showed a degradation in China.The maximum of frozen depth decreased,the beginning dates of soil freezing occurred later and the ending dates of soil freezing occurred earlier and the persisting of soil freezing shortened,as well as the soil base rose.It is in the mid 1980s that the significant abrupt change of the frozen soil happened.