西北地区季节性最大冻土深度的分布和变化特征

利用西北地区1961～2000年101个代表站的年冻土观测资料,采用EOF、REOF、小波分析方法,分析了西北地区季节性最大冻土深度的分布状况及其变化特征。结果表明,西北地区多数地区平均最大冻深在0.5～2m之间,平均2m以上的只有在新疆的天山,青海东北部的祁连山区有零星分布。近几十年来,西北地区整体最大冻深减小,上世纪90年代是近几十年来最大冻深最浅的时期,其中变化最明显的区域是新疆;西北最大冻深的变化可分为五个敏感区:西北中部区、南疆区、北疆区、青藏高原区、西北东部区。各区最大冻深随时间变化趋势有所不同,西北中部区、南疆区几乎呈直线下降,上世纪90年代的平均最大冻深均比上世纪60年代减少了0.1m,北疆区和西北东部区呈小-大-小的抛物线型式变化,最大冻深的变幅相对较小,青海高原的最大冻深则表现出与其他区域相反的变化趋势,是一个由大-小-大的变化过程,上世纪90年代比上世纪80年代平均最大冻深增加了0.57m。不同地区因其地形、土壤、控制的气候系统有所差异,变化周期有所差别,但其周期尺度基本相似。在影响冻土的因素中,干旱区以冬季气温较为显著,而半干旱半湿润区则以地温和封冻前的土壤水分的影响更为显著。

The Change Characteristics of Maximum Frozen Soil Depth of Seasonal Frozen Soil in Northwest China

Based on the observational data from 101 representative meteorological stations in Northwest China,the spatial distribution and decadal change of maximum frozen soil depth during the recent 40 years was analysed.The abnormal and evolution characteriscs was also analysed by using EOF,REOF and wavelet methods.The results showed that the maximum frozen soil depth in NW China began to decrease distinctly on a whole since the 1980's,and decreased more distinctly during the 90's.The most distinct area is Xingjiang.There are 5 main frozen anomaly regions in Northwest China,i.e.,middle NW,south Xingjiang,north Xingjiang,Qinghai Plateau,east NW.The frozen soil depth annual anomaly in the above representative areas showed different change trends,but the main trend in most areas was that the frozen depth has been decreasing since 1980's except for Qinghai Plateau,which has been increasing since 1980's.The average maxium frozen soil depth has decreased by 0.1m over the middle NW and south Xingjiang,and has decreased indistinctly over south Xingjiang and east NW,but has increased by 0.57m over Qinghai Plateau during 90's;the wavelet analysis showed that there were different variance cycles in the five regions because of the differences of controlled climatic system,the soil texture,and terrain,etc.The frozen soil depth dependsed on the temperature in winter in arid areas,but depended on the soil temperatue in winter and the soil water before freeze in semiarid and semihumid areas.