石羊河流域冬季冻土深度变化趋势及原因

Changing Trend and Reasons of Winter Maximum Frozen Soil Depth in Shiyang River Basin

利用1961~2007年石羊河流域上游、中游、下游当地气象站的冬季最大冻土深度、气温、地温、日照时数、降水量、相对湿度、蒸发、积雪资料,分析了近47 a石羊河流域冬季最大冻土深度的空间分布以及时间变化特征,进而采用相关系数法进一步探讨了冬季最大冻土深度变化的原因。结果表明：在空间分布上,石羊河流域冬季最大冻土深度分布与本地地理位置、土壤类型和海拔高度密切相关。石羊河流域冬季最大冻土深度梯度呈南—北走向,最大值出现在南部古浪,最小值出现在北部民勤。时间变化上,近47 a,石羊河流域以及流域上、中游冬季最大冻土深度呈下降趋势,而下游民勤冬季最大冻土深度则呈上升趋势,石羊河流域冬季最大冻土深度在不同时段内存在明显的6~7 a和9~10 a的周期反映,除下游民勤外在20世纪90年代都发生了突变。相关系数法分析表明,影响石羊河流域冬季最大冻土深度的气象因子是主要是热力因子,热力因子中关联最强的是极端最低地温和气温;水分因子中蒸发和冬季最大冻土深度的关联最明显。

Based on the observed meteorological data of maximum frozen soil depth,air temperature,soil temperature,sunshine hours,precipitation,relative humidity,evaporation and snow cover in winter over the upstream,middle stream and downstream of Shiyang river basin during 1961～2007,the spatial and temporal evolution of winter maximum frozen soil depth and its reasons were analyzed by correlation coefficient.The results showed that winter frozen soil depth was closely related to local geographical position,soil types and elevation above sea level.Its gradient direction was from south to north,that was big in gulang of south and small in Minqin of north in the spatial distribution.Further,the 47 a temporal changing trends of winter frozen soil depth were down in most of the basin,the upstream and middle stream of basin,but an up in Minqin over downstream of basin.It also revealed that the winter frozen soil depth had obvious variation periods of 6~7 a and 9~10 a which had some abrupt changes during 1990 s except Minqin over downstream of basin.By calculating the correlation coefficients of 10 climate factors with winter frozen soil depth,extreme minimum soil temperature and air temperature among thermal factors were major factors of influencing winter frozen soil depth,and evaporation was closely related to winter frozen soil depth in all moisture content factors over Shiyang river basin.