Permafrost in the Da and Xiao Xing'anling Mountains in northeastern China is warm, thin and sensitive to climatic warming. In the 1970s, the southern limit of permafrost (SLP) was empirically correlated to the −1 to 0°C isotherms of mean annual air temperature (MAAT) in the western part of the Da Xing'anling Mountains, to about 0°C in the northern part of the Songnen Plain, and to 0 to +1°C in the eastern part of the Xiao Xing'anling Mountains. Climate warming and deforestation have led to permafrost degradation as shown by deepening of the active layer, thinning permafrost, rising ground temperatures, expanding taliks and the disappearance of permafrost patches. The present position of the SLP was estimated using the −1.0 to +1.0°C MAAT isotherms for 1991–2000. Compared to the SLP in the 1970s, areas of sporadic discontinuous and isolated patchy permafrost have decreased by 90,000–100,000 km2, or 35–37% of their total areal extent (260,000–270,000 km2) in the 1970s. Recent field observations along the Hei'he to Bei'an Highway, the proposed Mo'he to Daqing Crude Oil Pipeline route and the Hai'lar to Daqing Highway confirm these changes. Continuing northward shifting of the SLP is likely to occur during the next 40–50 years under a warming of 1.0–1.5 °C, reducing the permafrost areal extent to an estimated 35% of that in the 1970s and 1980s. Copyright © 2007 John Wiley & Sons, Ltd.

The Source Area of the Yellow River is located in the mosaic transition zones of seasonally frozen ground, and discontinuous and continuous permafrost on the northeastern Qinghai-Tibet Plateau. Vertically, permafrost is attached or detached from frost action. The latter can be further divided into shallow (depth to the permafrost table 8 m), deep (>8 m) and two-layer permafrost. Since the 1980s, air temperatures have been rising at an average rate of 0.02 • C yr −1 . Human activities have also increased remarkably, resulting in a regional degradation of permafrost. The lower limit of permafrost has risen by 50-80 m. The average maximum depth of frost penetration has decreased by 0.1-0.2 m. The temperatures of the suprapermafrost water have increased by 0.5-0.7 • C. General trends of permafrost degradation include reduction in areal extent from continuous and discontinuous to sporadic and patchy permafrost, thinning of permafrost, and expansion of taliks. Isolated patches of permafrost have either been significantly reduced in areal extent, or changed into seasonally frozen ground. Degradation of permafrost has led to a lowering of ground water levels, shrinking lakes and wetlands, and noticeable change of grassland ecosystems alpine meadows to steppes. The degradation of alpine grasslands will cause further degradation of permafrost and result in the deterioration of ecological environments as manifested by expanding desertification and enhancing soil erosion.

Northeastern China has the second largest expanse of permafrost in China, primarily known as Xing'an-Baikal permafrost. Located on the southeastern edges of the Eurasian cryolithozone, the permafrost is thermally unstable and ecologically sensitive to external changes. The combined impacts of climatic, environmental, and anthropogenic changes cause 3-dimensional degradation of the permafrost. To predict these changes on the southern limit and ground temperature of permafrost in Northeastern China, an equivalent latitude model (ELM) for the mean annual ground surface temperature (MAGSTs) was proposed, and further improved to take into account of the influences of vegetation and snow-cover based on observational data and using the SHAW model. Using the finite element method and assuming a climate warming rate of 0.048°C a 1 , the ELM was combined with the unsteady-state heat conduction model to simulate permafrost temperatures at present, and to predict those after 50 and 100 a. The results indicate that at present, sporadic permafrost occurs in the zones with MAGSTs of 1.5°C or colder, and there would still be a significant presence of permafrost in the zones with the present MAGSTs of 0.5°C or colder after 50 a, and in those of 0.5°C or colder after 100 a. Furthermore, the total areal extent of permafrost would decrease from 2.57×10 5 km 2 at present to 1.84×10 5 km 2 after 50 a and to 1.29×10 5 km 2 after 100 a, i.e., a reduction of 28.4% and 49.8% in the permafrost area, respectively. Also the permafrost would degrade more substantially in the east than in the west. Regional warming and thinning of permafrost would also occur. The area of stable permafrost (mean annual ground temperature, or MAGT≤1.0°C) would decrease from present 1.07×10 5 to 8.8×10 4 km 2 after 50 a, and further decrease to 5.6×10 4 km 2 after 100 a. As a result, the unstable permafrost and seasonally frozen ground would expand, and the southern limit of permafrost would shift significantly northwards. The changes in the permafrost environment may adversely affect on ecological environments and engineering infrastructures in cold regions. Avoidance of unnecessary anthropogenic changes in permafrost conditions is a practical approach to protect the permafrost environment. permafrost, Northeastern China, climate change, equivalent latitude model (ELM), predictionCitation:

Recently, the degradation of permafrost and marsh environments in the Da and Xiao Hinggan Mountains has become a great concern as more human activities and pronounced climate warming were observed during the past 30 years and projected for the near future. The distribution patterns and development mechanisms of the permafrost and marshes have been examined both in theories and in field observations, in order to better understand the symbiosis of permafrost and marshes. The permafrost and marshes in the Da and Xiao Hinggan Mountains display discernible zonations in latitude and elevation. The marsh vegetation canopy, litter and peat soil have good thermal insulation properties for the underlying permafrost, resulting in a thermal offset of 3℃ to 4℃ and subsequently suppressing soil temperature. In addition, the much higher thermal conductivity of frozen and ice-rich peat in the active layer is conducive to the development or in favor of the protection of permafrost due to the semi-conductor properties of the soils overlying the permafrost. On the other hand, because permafrost is almost impervious, the osmosis of water in marsh soils can be effectively reduced, timely providing water supplies for helophytes growth or germination in spring. In the Da and Xiao Hinggan Mountains, the permafrost degradation has been accelerating due to the marked climate warming, ever increasing human activities, and the resultant eco-environmental changes. Since the permafrost and marsh environments are symbiotic and interdependent, they need to be managed or protected in a well-coordinated and integrated way.

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