No abstract

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.

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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.

No abstract

Many permafrost maps in China have been compiled since the early 1960s. The scales of these maps range from the local (1:600 000) to the regional scale (1:10 000 000). The permafrost classification systems differ among these maps. The indices for permafrost classification used in these mapping projects include spatial continuity (areal extent) and thickness of the permafrost, air and ground temperatures and ground ‐ice content. All of those data have been retrieved, digitised and published in the Environmental and Ecological Science Data Center for West China. These maps represent the best understanding at the time regarding the distribution of permafrost in China and its changes over the past century. An updated map of permafrost in China, including frozen ground area, is also provided. The total area of permafrost in China is estimated at ~ 1.59 × 106 km2 (glaciers and lakes excluded), and the area of seasonally frozen ground (excluding instantaneous frozen ground) is ~ 5.36 × 106 km2. The total area of high‐altitude (plateau and mountain) permafrost in China is ~ 1.35 × 106 km2, the area of mountain permafrost is ~ 0.30 × 106 km2 and the area of plateau permafrost is ~ 1.05 × 106 km2. The latitudinal permafrost is located in the northern part of northeastern China, and its area is ~ 0.24 × 106 km2. Additionally, some suggestions are proposed for future mapping of permafrost in China. Copyright © 2012 John Wiley & Sons, Ltd.

The present distribution of permafrost on the Qinghai‐Xizang (Tibet) Plateau (QTP) is largely a relict of the permafrost formed during the late Pleistocene. It has been degrading and shrinking in areal extent under the fluctuating climates, with a general trend of warming, during the Holocene. The major criteria for the occurrence of relict permafrost include the remnants of ancient buried permafrost, relict permafrost tables, thawed sandwiches (taliks), thick‐layered ground ice, and periglacial phenomena such as pingo scars, cryoturbations, primary sand and clayey silt wedges, ice wedge casts, aeolian sand dunes and loesses, thick layers of peat, and humic soils. On the basis of 14C dating of soils, comprehensive analyses, and comparisons of the spatiotemporal distribution of relict and modern permafrost and periglacial phenomena, the evolution of permafrost and periglacial environments since the late Pleistocene was divided into seven stages: (1) the cold period at the end of the late Pleistocene (35,000 to 10,800 years B.P.); (2) the period of significant climatic change during the early Holocene (10,800 to ∼8500–7000 years B.P.), (3) the Megathermal period in the middle Holocene (∼8500–7000 to ∼4000–3000 years B.P.), (4) the cold period in the late Holocene (∼4000–3000 to 1000 years B.P.), (5) the warm period in the later Holocene (1000 to 500 years B.P.), (6) the Little Ice Age (500 to 100 years B.P.), and (7) the recent warming period (100 years B.P. to present). The conditions for permafrost development, distribution, and the paleoclimates and paleoenvironments are discussed for each stage.

Changes in the frequency and extent of wildfires are expected to lead to substantial and irreversible alterations to permafrost landscapes under a warming climate. Here we review recent publications (2010–2019) that advance our understanding of the effects of wildfire on surface and ground temperatures, on active layer thickness and, where permafrost is ice‐rich, on ground subsidence and the development of thermokarst features. These thermal and geomorphic changes are initiated immediately following wildfire and alter the hydrology and biogeochemistry of permafrost landscapes, including the release of previously frozen carbon. In many locations, permafrost has been resilient, with key characteristics such as active layer thickness returning to pre‐fire conditions after several decades. However, permafrost near its southern limit is losing this resiliency as a result of ongoing climate warming and increasingly common vegetation state changes. Shifts in fire return intervals, severity and extent are expected to alter the trajectories of wildfire impacts on permafrost, and to enlarge spatial impacts to more regularly include the burning of tundra areas. Modeling indicates some lowland boreal forest and tundra environments will remain resilient while uplands and areas with thin organic layers and dry soils will experience rapid and irreversible permafrost degradation. More work is needed to relate modeling to empirical studies, particularly incorporating dynamic variables such as soil moisture, snow and thermokarst development, and to identify post‐fire permafrost responses for different landscape types and regions. Future progress requires further collaboration among geocryologists, ecologists, hydrologists, biogeochemists, modelers and remote sensing specialists.