关键词: 青藏高原, 积温, 冻融强度, Qinghai-Tibet Plateau (QTP), accumulated ground temperature, freeze-thaw intensity

Abstract: Changes of shallow layer ground temperature can indicate the changes in active layer thickness. The soil thermal regime of the active layer was analyzed using the ground temperature data from 1977 to 2006 collected at 74 weather stations on the Qinghai-Tibet Plateau (QTP) and its adjacent areas. The results indicate that in the last 30 years the negative accumulated temperature at 5 cm depth below surface showed an increasing trend, but had different increment magnitudes in different regions. For the entire study area, the negative accumulated temperature increased 35℃ per decade. The freezing thickness of active layer showed a decreasing trend in the past 30 years in the regions. During the freezing period (cold season) the magnitude change of negative accumulated temperature was greater in the hinterland of QTP than in its peripheral areas, but it was more stably in a complete freeze-thaw cycle in the hinterland than in the peripheral areas. In the past 30 years, the values of freeze-thaw intensity (FTI) exhibited an increasing trend, which indicates that the stability of frozen ground has changed to some extent in the permafrost regions. In the QTP, latitude and altitude had a great impact on FTI. While altitude is below 4000 m, the decreasing rate of FTI with increase in altitude was different between the regions south and north of 33°N. The value in the south region was 2.5 times of that in the north region. While the altitude is above 4000 m, its impact on FTI values reduced relatively.