大通河源区多年冻土的地温特征及其影响因素分析

Characteristics of Ground Temperatures and Influencing Factors of Permafrost Development and Distribution in the Source Region of Datong River

多年冻土是一种热现象,地温是判断多年冻土特征的有效指标。通过对祁连山区东北部大通河源区多年冻土分布状况的野外考察与钻探等工作,借助于实测地温数据和地温曲线分析工具,对大通河源区39个钻孔点的多年冻土地温特征进行了对比分析,对影响多年冻土地温的主要因素进行了概括和总结。结果表明,在大通河源区,高程、植被类型、地表覆盖特征、土壤水分条件等是影响多年冻土地温的主要因素。根据尺度性划分的结果,高程是影响区域多年冻土地温变化的一级因素;随着空间尺度的下降,植被类型和地表覆盖特征成为二级影响因素;在沼泽化草甸植被覆盖区,土壤水分条件又成为影响多年冻土地温的三级影响因素。对多年冻土地温特征及影响因素的分析不仅有助于了解区域多年冻土的稳定性、预测全球气候变暖背景下的多年冻土演变和退化,还可以为寒区气候变化、生态、水文等相关领域的发展提供基础,为各项工程设施的实施和维护提供建议和指导。

Permafrost is thermally defined as the ground where temperatures have remained at or below 0℃ for a period of at least two consecutive years.Ground temperatures at depth were a valid index to make knowledge of permafrost thermal regimes and permafrost development at certain locations.Based on 39 borehole data,drilled in the summers of 2007 and 2009 at different elevations with representatives of surface characteristics of topography,geomorphology,landcover,vegetation and soil water content,and the measured ground tempera-tures in the source region of Datong River in the northeast Qilian Mountains,the characteristics of ground tem-peratures at depth at the drilling sites were analyzed using the temperature profiles,and the main factors control-ling permafrost temperatures and distribution in the study area were primarily summarized.Elevation and the el-evation-dependant MAAT（mean annual air temperature） determined the climate settings of the region and the macro-scale permafrost distribution and temperatures patterns,and thus were the first-order factors affecting per-mafrost temperatures in the source region.In the local-or micro-scale areas in low-and mid-elevation zones（el-evation generally lower than 3800 m）,however,the landcover conditions（vegetated area,bare ground or ex-posed rock）,the vegetation type（the alpine meadow or the swampy alpine meadow）,and the topsoil water con-tent（saturation or oversaturation） had some important impacts on permafrost temperatures,which could affect the permafrost occurrence at certain locations and lead to the spatial differentiation of permafrost distribution.In high-elevation zones（elevation usually exceeds 4000 m）,elevation alone could determine the presence of per-mafrost,and the local factors had effects on the gradient of permafrost temperatures with depth.The result could be as the basis of understanding the permafrost stability,and permafrost change or degradation under the climat-ic warming,also could provide the knowledge to the relevant studies of climatic changes,ecology,and hydrolo-gy in cold regions.