Abstract:

Observed frozen soil data in Yushu Qinghai were analyzed to show the seasonal variation,beginning date and ending date of frozen soil,characteristics of no frozen soil period.Frozen soil in Yushu had obvious seasonal variations which begin from autumn,reaching maximum depth at the end of winter and melt in spring.Nonfrozen soil averaged period is 173 days.80% guarantee days were 147 days.Nonfrozen soil period is between middle June to the beginning of September.In the last 50 years,maximum frozen soil depth had stepped characters;the beginning and ending date of surface to 5 cm soil didn't have obvious trend.The beginning date of 10 cm and the deeper soil had early trend and the ending date had delay trend. All seasonal,annual mean temperature and annual minimum temperature had obvious increasing trend. This indicated that maximum depth,beginning date and ending date of frozen soil,were not always attenuation,delay or early with climate warming.They may be affected by else elements.This results was consistent with the some of scholar's studies for southern of Tibetean plateau