Search

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.

Thermokarst lakes are widespread and developing on the Qinghai‐Tibet Plateau (QTP), and they have modified hydrological processes and water balance in the region. Despite increasing attention, our understanding of the hydrological behaviors of thermokarst lakes under permafrost degradation remains limited on the QTP. In this study, water stable isotope tracers were used to characterize the spatial and seasonal hydrological changes of thermokarst lakes on the central QTP. Significant seasonal variations and factors influencing the isotopic hydrology of lakes were revealed through the ice‐free season. Substantial differences in lake‐specific input water isotope compositions (δI) among the lakes indicate two lake‐recharge regimes: rain‐dominated, and snowmelt/permafrost thaw‐dominated. We suggest that precipitation and active‐layer hydrology controlled these hydrological changes in the ice‐free season. However, under ice cover, melting of the surrounding permafrost (including ground ice) dominated the hydrology of thermokarst lakes. Importantly, a conceptual model delineates the hydrological evolution of thermokarst lakes under permafrost degradation. This study serves as a baseline for future investigations of hydrological processes and water balance relating to thawing permafrost on the QTP.

In cold regions, the occurrence of frozen ground has a fundamental control over the character of the water cycle. To investigate the impact of changing ground temperature conditions on hydrological processes in the context of climate change, a distributed hydrological model with an explicit frozen ground module was applied to an alpine watershed in the upstream area of the Hei'he River in the Qilian Mountains, northwest China. After evaluating the base model, we considered scenarios of frost-free ground and climate change. Results showed that the base model with a frozen ground module successfully captured the water balance and thermal regimes in the basin. When the frozen ground module was turned off, the simulated groundwater recharge and base flow increased by a factor of two to three because surface runoff caused by exceeding infiltration capacities at high elevations, which occurred in the base model, was eliminated. Consequently, the river hydrograph became smoother and flatter, with summer flood peaks delayed and reduced in volume. The annual mean depth where subsurface runoff was generated, was about 2.4 m compared to 1.1 m in the base model. For a warming climate, a combination of increasing evapotranspiration and reducing permafrost area results in smoother and flatter hydrographs, and a reduction in total river discharge. Although our analysis using numerical models has its limitations, it still provides new quantitative understanding of the influences of frozen ground and climate change on hydrological processes in an alpine watershed. Copyright © 2016 John Wiley & Sons, Ltd.

Inactive ice wedges are still present today at Yituli'he in the middle Da Xing'anling (Greater Hinggan) Mountains in northeastern China, which is the southernmost known site (50°37′N) with ice wedges in the Northern Hemisphere. However, it is uncertain whether the ice-wedge isotope composition, characterized by low δ18O, δD and low deuterium excess values, is representative of the isotope signature of a broader region. In this paper, the ice-wedge isotope compositions were examined in the context of the stable isotopes of precipitation from the nearby Global Network of Isotopes in Precipitation (GNIP) stations. In addition, the pollen spectra from the host sediments were analysed to provide additional information on local vegetation in order to better understand the climate conditions favouring ice-wedge formation. The pollen spectra suggest that the Yituli'he ice wedges developed during the colder and wetter period after 6000 cal. a BP. The isotopes in the Yituli'he ice wedges are consistent with the isotope background recorded in atmospheric precipitation collected at the nearby GNIP stations. When the snow-melt froze into ice veinlets, the isotope signals did not change substantially because of the strong, cold, continental anticyclones in winter as well as a strong temperature inversion that prevail in the Da Xing'anling Mountains. As the climate pattern did not change substantially, the neoglacial cold period is unlikely to have allowed for strong secondary fractionation of isotope records during ice-wedge formation. Thus, the annual isotope signature can be interpreted as a valid archive of climate data.

This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice-wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo-temperatures that are inferred on the basis of present-day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately

Recent investigations into relict periglacial phenomena in northern and western China and on the Qinghai-Tibet Plateau provide information for delineating the extent of permafrost in China during the Late Pleistocene. Polygonal and wedge-shaped structures indicate that, during the local Last Glacial Maximum (LLGM, between approximate to 35 and 10.5ka BP), the southern limit of latitudinal permafrost in northern China advanced southward at least to approximate to 38-40 degrees N in the east and to approximate to 37-39 degrees N in the west. This represents an advance of about 5-10 degrees of latitude beyond present-day permafrost limits. The lower limits of elevationally controlled permafrost on the Qinghai-Tibet Plateau and its peripheries were about 1000m lower: this permafrost was largely continuous during the LLGM. This suggests a cooling of between 4 and 10 degrees C, or more. This paper discusses the extent of permafrost during the LLGM and presents maps that have been constructed on the basis of extensive and integrative analysis of all reliable and pertinent data. The results indicate that the extent of LLGM permafrost in China was between approximate to 3.8 and 4.3x106km2. This is 80 to 100% more than that of approximate to 2.15x106km2 in the 1970s, and 120 to approximate to 150% more than that of approximate to 1.75x106km2 today.

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.

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.