西藏地温的年际和年代际变化

利用1971-2005年西藏10个站的0．8m、1．6m和3．2m逐月平均地温资料，采用气候倾向率等现代统计诊断方法，研究了近35年西藏年、季平均地温的变化趋势、气候突变和异常年份。结果表明：0．8m年平均地温在西藏东部的林芝、昌都呈现为下降趋势，其他各站以0．19～0．81℃／10a的速率升高；有5个站的1．6m年平均地温呈显著的升高趋势，升温率为0．20～0．60℃／10a；3．2m年平均地温6个站均表现为升高趋势，为0．13～0．52℃／10a，以拉萨升温率最大。在0．8m处，①大部分站点季平均地温呈明显的上升趋势，其中西藏西部、南部以夏季升幅最大，特别是狮泉河达1．61℃／10a；北部以冬季增温最突出。东部地区四分之三的季平均地温呈降温趋势。②大部分站点年平均地温呈逐年代升高趋势，而昌都表现为逐年代降低趋势。③狮泉河春、夏季平均地温分别在1996年和1983年发生了气候突变；拉萨和日喀则年、季平均地温发生的气候突变是从一个相对偏冷期跃变为一个相对偏暖期，前者出现在20世纪80年代，后者发生在20世纪90年代初；而林芝1993年夏、秋季出现的气候突变是从一个相对偏暖期跃变为一个相对偏冷期。④西藏西部年、季平均地温以异常偏高年份居多，且发生在20世纪末至21世纪前5年；南部年、季平均地温均为异常偏高年份，主要出现在20世纪90年代中后期；北部年、季平均地温异常偏高年均出现在21世纪前5年，异常偏低年份以20世纪80年代居多；东部年平均地温以异常偏低年为主。青藏铁路沿线西藏境内测站最大冻土深度以－4．5～25．4cm／10a的速率呈显著减小趋势，安多减幅最大。

Inter annual and Interdecadal Variations of Soil Temperature over Tibetan Plateau from 1971 to 2005

The variation trend,abrupt change and anomalous years of annual and seasonal mean soil temperatures at 0.8 m,1.6 m and 3.2 m over Tibet are investigated in the context of the observational data at 10 stations during the period 1971-2005 using modern statistical diagnostic methods such as the linear trend analysis. The results show that the annual mean soil temperature at 0.8 m decline in Chamdo and Nyingri of Tibet where the reduction rate is 0.15 oC/10a and 0.18 oC/10a respectively,but the increasing trends are observed at the other stations at a rate of (0.19-0.81) oC/10a (except for Tesdang,99% confidence level). Significant increasing trends of annual mean soil temperature at 1.6 m are found at five stations,with the increasing rate of (0.20-0.60) oC/10a (above 95% confidence level). Also,the increasing trends of annual mean soil temperature at 3.2 m are observed at six stations,with the rate of (0.13-0.52) oC/10a,especially in Lhasa. In the case of 0.8 m soil temperature,the following facts are found as: (1) The increasing trends of seasonal mean soil temperature are observed at most stations,with the most remarkable increasing rate in western and southern Tibet in summer,especially in Sengge Zangbu river basin where the rate is 1.61 oC/10a (99% confidence level); the maximum increasing rate is in northern Tibet in winter. But the decreasing trends of the soil temperature are found in most seasons of eastern Tibet. (2) In terms of interdecadal variations,the annual mean soil temperature increases apparently at most stations of Tibet,however it decreases in Chamdo. (3) The abrupt change of spring and summer mean soil temperature is observed in Sengge Zangbu in 1996 and 1983 respectively. The abrupt change of the annual and seasonal mean soil temperatures happens in Lhasa and Shigatse,the former in the 1980s and the latter in the early 1990s,a sudden change from the colder period to the warmer one. In addition,the abrupt change of summer and autumn mean soil temperature occurs in Nyingri in 1993,indicating a change from the warmer period to the colder one. (4) The annual and seasonal soil temperatures occur in the more anomalous higher temperature years at the end of the 1990s and the first five years of the 2100s in western Tibet,while in the mid-late 1990s in southern Tibet and the first five years of the 2100s in northern Tibet. The more anomalous lower years occur mainly in the 1980s while the anomalous lower years dominate in eastern Tibet.