DU Jun, JIAN Jun, HONG Jian-chang, LU Hong-ya, CHEN Ding-mei
The annual and decadal variations of maximum frozen depth and thawing beginning date are investigated in this paper, using the data from 17 stations from 1961 to 2010 and modern statistical diagnostic methods, such as linear trend analysis, cumulative anomaly, signal noise ratio and rescaled range analysis (R/S analysis), and the variation of the maximum frozen depth in the next 50a and 100a are projected. The results show that the maximum frozen depth has displayed an increase with a rate of 1.4 cm (10a)-1 in Nyingchi in the past 50 years, but decreasing trends are observed at the other stations with a rate of (-0.7~-21.3) cm·(10a)-1, with a maximum in Nagqu. Especially, in 1981-2010, the decreasing trend of the maximum frozen depth became large, with a rate of (0.92~37.2) cm·(10a)-1, and the amplification became great with the increase of altitude. The thawing beginning date delayed with a rate of (2.1~5.2) d·(10a)-1 in Nagqu, Gyangze and Nyingchi during 1971-2010, but shifted to an earlier time with a rate of (1.8~12.7)d·(10a)-1 in others stations. In terms of decadal variation, the maximum frozen depth has decreased apparently at most stations, and the thawing beginning date has shifted to an earlier time. It is found that abrupt change of maximum frozen depth occurred in Nagqu, Amdo and Tesdang in 1984, 1987 and 1979, respectively. The results of R/S analysis show that change of maximum frozen depth has persistence with a Hurst index of larger than 0.5, demonstrating that frozen depth would decrease in most stations in future. Under the climate warming scenario with a rate of 0.044 ℃·a-1, the maximum frozen depth would continuously decrease with a rate of (1.1~77.3) cm in the next 50 a and with a rate (1.2~91.4) cm in the next 100 a. Under the climate warming rate of 0.052 ℃·a-1, the maximum frozen depth would decrease at a rate of (2.1~155) cm in the next 50 a and (2.5~183) cm in the next 100 a. obviously, the maximum frozen depth decreasing is directly related to the significant increase in air temperature and soil temperature.
