The Shule River Basin is located in the western part of the Qilian Mountains, where climate is very dry. According to records of borehole and measured temperature, the elevation of permafrost lower limit was determined to be 3 750 m and volume of ground ice was little because loose stratum is alluvium composed of coarse soil. The permafrost state was affected by local factors obviously. Discrepancy of a slope gradient can lead to a ground temperature difference of 0.5 ℃, while discrepancy of slope aspect can result in a ground temperature difference of 1.0 ℃. Influences of soil water content on ground temperature of shallow layers are even greater than those of slope aspect. Discrepancy of ground condition can result in significant difference in ground temperature and depth of active layer. Contrast to permafrost of central-eastern Qilian Mountains, permafrost in the Shule River source areas is not affected by ecological processes and its formation and preservation were directly driven by climate. So the permafrost of the Shule River source areas was typical of that of arid regions.
