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Active layer thickness (ALT) is critical to the understanding of the surface energy balance, hydrological cycles, plant growth, and cold region engineering projects in permafrost regions. The temperature at the bottom of the active layer, a boundary layer between the equilibrium thermal state (in permafrost below) and transient thermal state (in the atmosphere and surface canopies above), is an important parameter to reflect the existence and thermal stability of permafrost. In this study, the Geophysical Institute Permafrost Model (GIPL) was used to model the spatial distribution of and changes in ALT and soil temperature in the Source Area of the Yellow River (SAYR), where continuous, discontinuous, and sporadic permafrost coexists with seasonally frozen ground. Monthly air temperatures downscaled from the CRU TS3.0 datasets, monthly snow depth derived from the passive microwave remote-sensing data SMMR and SSM/I, and vegetation patterns and soil properties at scale of 1:1000000 were used as input data after modified with GIS techniques. The model validation was carried out carefully with ALT in the SAYR has significantly increased from 1.8 m in 1980 to 2.4 m in 2006 at an average rate of 2.2 cm yr−1. The mean annual temperature at the bottom of the active layer, or temperature at the top of permafrost (TTOP) rose substantially from −1.1°C in 1980 to −0.6°C in 2006 at an average rate of 0.018°C yr−1. The increasing rate of the ALT and TTOP has accelerated since 2000. Regional warming and degradation of permafrost has also occurred, and the changes in the areal extent of regions with a sub-zero TTOP shrank from 2.4×104to 2.2×104km2at an average rate of 74 km2yr−1. Changes of ALT and temperature have adversely affected the environmental stability in the SAYR.

An increase of mean annual air temperature (MAAT) of about 0.2–0.4 °C on the Qinghai–Tibet Plateau as compared with the 1970s, and especially winter warming, has resulted in extensive permafrost degradation. An increase of 0.1–0.5 °C in the mean annual ground temperature (MAGT) has been observed. Discontinuous permafrost bodies and thawed nuclei have been widely detected. The lower altitudinal limit of permafrost has risen 40–80 m on the Qinghai–Tibet Plateau. The total permafrost area on the Plateau has shrunk about 10⁵ km². Permafrost degradation has caused environmental deterioration, including the destabilization of buildings, impacted upon cold regions hydrology and water resources, and accelerated desertification. Copyright © 2000 John Wiley & Sons, Ltd.

An increase of mean annual air temperature (MAAT) of about 0.2–0.4 °C on the Qinghai–Tibet Plateau as compared with the 1970s, and especially winter warming, has resulted in extensive permafrost degradation. An increase of 0.1–0.5 °C in the mean annual ground temperature (MAGT) has been observed. Discontinuous permafrost bodies and thawed nuclei have been widely detected. The lower altitudinal limit of permafrost has risen 40–80 m on the Qinghai–Tibet Plateau. The total permafrost area on the Plateau has shrunk about 105km2. Permafrost degradation has caused environmental deterioration, including the destabilization of buildings, impacted upon cold regions hydrology and water resources, and accelerated desertification. Copyright © 2000 John Wiley & Sons, Ltd.