1961—2010年西藏季节性冻土对气候变化的响应

利用西藏1961—2010年17个站点最大冻土深度、土壤解冻日期等资料,采用气候倾向率、累积距平、信噪比和R/S分析等方法,分析了近50a西藏季节性冻土的年际和年代际变化特征,预估了未来50a和100a最大冻土深度变化.结果表明:近50a林芝最大冻土深度以1.4cm.(10a)-1的速度增大,其他站点均呈减小趋势,为-0.7～-21.3cm.(10a)-1,以那曲减幅最大.近30a来大部分站点最大冻土深度减幅更大,为-0.92～-37.2cm.(10a)-1,并随着海拔升高,最大冻土深度减幅在加大.近40a来当雄、江孜和林芝土壤解冻日期表现为推迟趋势,为2.1～5.2d.(10a)-1,其他站点呈提早趋势,平均每10a提早1.8～12.7d.在10a际尺度变化上,近40a大部分站点年最大冻土深度呈逐年代变浅趋势,土壤解冻日趋于提早.那曲、安多和泽当年最大冻土深度分别在1984、1987年和1979年发生了突变,从一个相对偏深期跃变为一个相对偏浅期.近40a来各站点年最大冻土深度的Hurst值均大于0.5,说明未来大部分站点年最大冻土深度仍将变薄.如果未来气候按升温率0.044℃.a-1变化,50a后西藏最大冻土深度减小1.1～77.3cm,未来100a可能减小1.2～91.4cm;气候按升温率0.052℃.a-1变化,50a后最大冻土深度减小2.1～155cm,未来100a可能减小2.5～183cm.最大冻土深度变浅显然与气温、地温的显著升高直接有关.

Response of Seasonal Frozen Soil to Climate Change on Tibet Region from 1961 to 2010

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.