Primary thaw date and geographical boundary of the thaw was
detected as shown in Figure 2. In the north: the thaw event
boundary runs south of the Three River Plain, Mt.
Xiaohingganling, and Mt. Dahingganling to the north of the
Desert Basin, then to the south of Mt. Henteyn, Mt. Hangayn,
and Mt. Altayn. The other area consists of regions of high
elevation, such as Mt. Tianshan, Mt. Changbai, and the Tibetan
Plateau. No thaw events occurred in the remaining (gray) areas,
like the deserts regions and south warmer areas, due to the drier
surface conditions or temperatures too high to freeze the surface
layer in winter. The primary thaw date follows clear spatial and
temporal patterns. In high elevation and high northern areas,
thaw events happen later than in lower elevation and southern
areas. On the Tibetan Plateau, at Mt. Hangayn, and at Mt.
Altayn, the thaw event occurred at the end of the first 180 days.
Those three areas are almost entirely covered by permafrost, so
only the active layer thaws in the short summer.