Thermal Regime Of Permafrost Research Articles

Talus and its cooling effects on the thermal regime of permafrost: A review

AbstractTalus, as the product of movement and accumulation along the slope after the cracking of cliffs or steep rock walls, is a common landform in the mountain periglacial environment. Significant thermal anomalies within talus have been widely reported to be a result of cooling effects. During the cold season, the increased temperature difference between talus and the ambient environment strengthens the intensity of convection (vertical flows) and transforms into upward advection (lateral flows) and exhausts the internal warm current. During the warm season, heat is concentrated on the surface of the talus, and the internal dominant cold current moves downward along the slope by advection. The principle of the proactive cooling effects of talus has been widely utilized in railway construction within permafrost regions as embankments to alleviate degradation of the underlying permafrost. However, limited model studies have examined the cooling effects of blocky debris in nature, and in situ observations are rare. Therefore, it will be important to increase observations and develop process‐based models that couple heat conduction, convection/advection, water transfer processes, and even the latent heat of phase change. This will help to better understand the extent of the cooling effects and its impact on the thermal regime of permafrost.

Dynamic variations in thermal regime and surface deformation along the drainage channel for an expanding lake on the Tibetan Plateau

ABSTRACT The outburst of Zonag Lake in 2011 triggered a series of floods in the continuous permafrost region of the hinterland of the Qinghai-Tibet Plateau. This re-distributed the surface water in the basin and caused rapid expansion of the tail lake (Salt Lake). To avoid potential overflow of the expanding Salt Lake, a channel was excavated to drain the lake water into a downstream river. In this study, to investigate the permafrost thermal regime and the surface deformation around the expanding Salt Lake and the channel, in-situ monitoring sections were settled from Salt Lake to the downstream of the channel to obtain the permafrost temperature. Additionally, using small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), the surface deformation around Salt Lake and the channel was measured. The data showed that the ground temperature at the channel was 0.6°C higher than the natural field and the mean subsidence rate around the channel was 1.5 mm/yr higher than that at Salt Lake. These results show that the permafrost temperature in the study area changed considerably with variations in the distance from the lake/channel, and the deformation in the study area was dominated by subsidence.

Thermal Regime of Permafrost on the Western Yamal Under Climate Warming

Climate change observed in the Arctic affects all components of the natural environment, including the state of permafrost. The purpose of this study is to quantify the response of permafrost in various landscapes to changing climatic parameters. The results of long-term field observations (1978-2021) of the thermal regime of permafrost on the Western Yamal are presented. Along with the increase in mean annual air temperatures, the mean annual ground temperature over the past 43 years has increased by 1.5-2.2°C. The maximum increase of permafrost temperature values is observed on flat and polygonal tundra, the minimum increase is typical for flooded lake basins. A decrease in the annual permafrost temperature amplitude was revealed. That is caused by a rapid increase in the air temperature of the cold period, an increase in the snow thickness and an increase in soil moisture in the active layer. The shrinking in ground temperature amplitude at a depth of 5 m is 0.5-3.6°C. A trend of reducing depth of zero annual amplitude from 12-18 m (1980) to 13-16 m (2021) has been revealed.

Simulating ice segregation and thaw consolidation in permafrost environments with the CryoGrid community model

Abstract. The ground ice content in cold environments influences the permafrost thermal regime and the thaw trajectories in a warming climate, especially for soils containing excess ice. Despite their importance, the amount and distribution of ground ice are often unknown due to lacking field observations. Hence, modeling the thawing of ice-rich permafrost soils and associated thermokarst is challenging as ground ice content has to be prescribed in the model setup. In this study, we present a model scheme, capable of simulating segregated ice formation during a model spinup together with associated ground heave. It provides the option to add a constant sedimentation rate throughout the simulation. Besides ice segregation, it can represent thaw consolidation processes and ground subsidence under a warming climate. The computation is based on soil mechanical processes, soil hydrology by the Richards equation and soil freezing characteristics. The code is implemented in the CryoGrid community model (version 1.0), a modular land surface model for simulations of the ground thermal regime. The simulation of ice segregation and thaw consolidation with the new model scheme allows us to analyze the evolution of ground ice content in both space and time. To do so, we use climate data from two contrasting permafrost sites to run the simulations. Several influencing factors are identified, which control the formation and thaw of segregated ice. (i) Model results show that high temperature gradients in the soil as well as moist conditions support the formation of segregated ice. (ii) We find that ice segregation increases in fine-grained soils and that especially organic-rich sediments enhance the process. (iii) Applying external loads suppresses ice segregation and speeds up thaw consolidation. (iv) Sedimentation leads to a rise of the ground surface and the formation of an ice-enriched layer whose thickness increases with sedimentation time. We conclude that the new model scheme is a step forward to improve the description of ground ice distributions in permafrost models and can contribute towards the understanding of ice segregation and thaw consolidation in permafrost environments under changing climatic conditions.

Divergent responses of permafrost degradation to precipitation increases at different seasons on the eastern Qinghai–Tibet Plateau based on modeling approach

The Qinghai–Tibet Plateau (QTP) has responded to remarkable climate warming with dramatic permafrost degradation over the past few decades. Previous studies have mostly focused on permafrost responses to rising air temperature, while the effects of accompanying increases in precipitation remain contentious and largely unknown. In this study, a distributed process-based model was applied to quantify the impacts of increased precipitation on permafrost thermal regimes in a warming climate by employing model experiments in the source region of Yellow River (SRYR) on the eastern QTP. The results showed that the active layer thickness (ALT) of permafrost increased by 0.25 m during 2010–2019 compared to 2000 across the SRYR, which was primarily driven by climate warming. In contrast, the increased annual precipitation played a relatively limited role and just slightly mitigated active layer thickening by 0.03 m. Intriguingly, increased precipitation in the cold and warm seasons exerted opposite effects on permafrost across the SRYR. The increased precipitation in the cold season mainly promoted ALT increases, while the increased precipitation in the warm season mitigated ALT increases. In ∼81.0% of the permafrost across the SRYR, the cooling effects of warm season wetting outweighed the warming effects of cold season wetting; while at the transition zone where permafrost was unstable and degrading to seasonally frozen ground, the warming effects of cold season wetting played a relatively larger role which contributed to permafrost degradation. This study explored the physical mechanisms of permafrost thermal responses to climate wetting, thus providing a better understanding of permafrost change in a warmer and wetter climate on the QTP.

Permafrost characteristics and potential influencing factors in the lake regions of Hoh Xil, Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP) is one of the regions in the world where permafrost and lakes are widely developed. Yet, the current understanding of permafrost characteristics surrounding large alpine lakes is still not clear. Based on the observation of permafrost surrounding Zonag Lake and Yanhu Lake (>100 km2) in the Hoh Xil region since 2012, we first investigated the permafrost characteristics and potential influencing factors around large alpine lakes on the QTP. The results indicate that the large alpine lakes have only a marginal thermal effect on the surrounding permafrost. Except for the sites located at the lake bottom and adjacent to the lakeshore, cold permafrost is extensively developed around the lakes, where the mean annual ground temperature is below −1.0℃, and the permafrost thickness is generally more than 40 m. Moreover, significant differences exist in ground temperature between boreholes located in the Yanhu Lake basin and those outside the basin, which the permafrost temperature in the lake basin is remarkably lower. These phenomena are closely related to the high soil water content around lakes. Statistical results show that ground temperature decreases and permafrost thickness increases gradually with increasing soil water content. The latent heat effects play an important role in the thermal dynamics of permafrost, which can buffer the increase of permafrost temperature under climate warming. Meanwhile, the salinity of water can weaken the thermal erosion effect of the lake on the surrounding permafrost to a certain extent. Overall, the permafrost thermal regime in the lake regions is not only controlled by altitude but also affected by soil water content. This study will provide us with a basis for understanding the state and characteristics of the frozen ground around lakes in the permafrost regions of the QTP, as well as for conducting research on the interaction of frozen ground with lakes and even the atmosphere.

Automated observation of physical snowpack properties in Ny-Ålesund

The snow season in the Svalbard archipelago generally lasts 6–10 months a year and significantly impacts the regional climate, glaciers mass balance, permafrost thermal regime and ecology. Due to the lack of long-term continuous snowpack physical data, it is still challenging for the numerical snow physics models to simulate multi-layer snowpack evolution, especially for remote Arctic areas. To fill this gap, in November 2020, an automated nivometric station (ANS) was installed ∼1 km Southwest from the settlement of Ny-Ålesund (Spitzbergen, Svalbard), in a flat area over the lowland tundra. It automatically provides continuous snow data, including NIR images of the fractional snow-cover area (fSCA), snow depth (SD), internal snow temperature and liquid water content (LWC) profiles at different depths with a 10 min time resolution. Here we present the first-year record of automatic snow preliminary measurements collected between November 2020 and July 2021 together with weekly manual observations for comparison. The snow season at the ANS site lasted for 225 days with an annual net accumulation of 117 cm (392 mm of water equivalent). The LWC in the snowpack was generally low (<4%) during wintertime, nevertheless, we observed three snow-melting events between November and February 2021 and one in June 2021, connected with positive temperature and rain on snow events (ROS). In view of the foreseen future developments, the ANS is the first automated, comprehensive snowpack monitoring system in Ny-Ålesund measuring key essential climate variables needed to understand the seasonal evolution of the snow cover on land.

Modeling the Accumulation and Transition to the Relic State of Methane Hydrates in the Permafrost of Northwestern Siberia

This paper presents the results of numerical modeling of the permafrost thermal regime and thermobaric conditions of methane hydrates in the north of Western Siberia over the past 70 thousand years. The area of hydrate formation was determined and the rate of accumulation of hydrates was estimated in connection with the migration of fluid from the underlying gas-saturated layers under the conditions of cover glaciation. The estimates obtained for the change in hydrate saturation as a result of fluid migration during the 10 thousand-year glaciation period, depending on the permeability of the soil, are from 6 to 40% in the upper 350 m. Based on quantitative characteristics of the equilibrium and metastable states of methane hydrates, the conditions for the preservation of relict methane hydrates in permafrost under the paleoclimatic scenario were determined, taking into account periods of ice cover and transgression. It is shown that due to the effect of self-preservation at temperatures below –4°C, it is possible to preserve relict methane hydrates in the upper 200 m of soil under non-equilibrium conditions. The effect of lowering the temperature while the hydrates dissociate prevents the complete decomposition of the deposit and leads to an increase in the thickness of the frozen soil.

A solar compression refrigeration apparatus to cool permafrost embankment

The permafrost embankment inevitably faces the problems of permafrost degradation and thermal thaw settlement. How to actively cool embankments has always been a key issue to construct linear transportation infrastructure in permafrost regions. In this study, a solar compression refrigeration apparatus, using solar power generation to drive vapor compression refrigeration, was proposed. To verify its cooling performance, a field test was carried out in permafrost regions. The test results show that the solar compression refrigeration apparatus can actively cool permafrost. Its cooling performance is not only related to the cooling power but also affected by the ambient temperature. When the apparatus cools intermittently from top to bottom, the cooling capacity is mainly used for cooling the active layer in summer and cooling the permafrost layer in winter. In addition, it can significantly raise the permafrost table around the evaporator. Then, a numerical calculation model of the cooling embankment was established, considering climate warming, cooling power, cooling time, separation distance and buried depth. The simulation results indicate that the cooling embankment can significantly improve the permafrost thermal regime and prevent permafrost degradation. This study can provide a new approach to protecting permafrost, which is valuable for constructing linear transportation infrastructure.

Simulating the current and future northern limit of permafrost on the Qinghai–Tibet Plateau

Abstract. Permafrost has been warming and thawing globally, with subsequent effects on the climate, hydrology, and the ecosystem. However, the permafrost thermal state variation in the northern lower limit of the permafrost zone (Xidatan) on the Qinghai–Tibet Plateau (QTP) is unclear. This study attempts to explore the changes and variability in this permafrost using historical (1970–2019) and future projection datasets from remote-sensing-based land surface temperature product (LST) and climate projections from Earth system model (ESM) outputs of the Coupled Model Intercomparison Project Phase 5 and 6 (CMIP5, CMIP6). Our model considers phase-change processes of soil pore water, thermal-property differences between frozen and unfrozen soil, geothermal flux flow, and the ground ice effect. Our model can consistently reproduce the vertical ground temperature profiles and active layer thickness (ALT), recognizing permafrost boundaries, and capture the evolution of the permafrost thermal regime. The spatial distribution of permafrost and its thermal conditions over the study area were controlled by elevation with a strong influence of slope orientation. From 1970 to 2019, the mean annual ground temperature (MAGT) in the region warmed by 0.49 ∘C in the continuous permafrost zone and 0.40 ∘C in the discontinuous permafrost zone. The lowest elevation of the permafrost boundary (on the north-facing slopes) rose approximately 47 m, and the northern boundary of discontinuous permafrost retreated southwards by approximately 1–2 km, while the lowest elevation of the permafrost boundary remained unchanged for the continuous permafrost zone. The warming rate in MAGT is projected to be more pronounced under shared socioeconomic pathways (SSPs) than under representative concentration pathways (RCPs), but there are no distinct discrepancies in the areal extent of the continuous and discontinuous permafrost and seasonally frozen ground among SSP and RCP scenarios. This study highlights the slow delaying process of the response of permafrost in the QTP to a warming climate, especially in terms of the areal extent of permafrost distribution.

Thermal and mechanical characteristics of a thermal pile in permafrost regions

Cast-in-place pile foundations are widely used in permafrost regions to support buildings. The stability of cast-in-place pile foundations is highly sensitive to permafrost thermal regime changes. Permafrost degradation caused by climate change is increasing the disaster risk of cast-in-place pile foundations. However, proactive cooling methods for cast-in-place pile foundations are seldom reported. The cold energy produced by two-phase closed thermosyphons (TPCTs) can efficiently prevent the permafrost thermal regime from being disturbed by engineering activities and climate change. TPCTs were installed in a concrete pile forming a thermal pile. Then, a model experiment was conducted to explore the thermal regime, influence scope, dissipation process of cold energy, and freezing strength of the thermal pile. The results indicated that the thermal pile may significantly cool the foundation soil. Most of cold energy produced by the thermal pile dissipated during the warm period, and the cooling scope of the thermal pile can cover the area within a 40 cm (twice the pile diameter) radius around the pile. Additionally, the TPCTs can significantly improve freezing strength between the thermal pile and frozen soil. The lesson learned from this study can provide a new approach to control the thermal regime of cast-in-place pile foundation in permafrost, which was of valuable to the construction of pile foundations in cold regions.

Field Investigation on Thermal Regime of Permafrost and Talik in a River Terrace, the Interior of Qinghai-Tibet Plateau

To carry out engineering construction in a permafrost area, it is of great importance to grasp the spatial distribution of permafrost and its hydrothermal characteristics within the scope of engineering activities. Compared with the continuous permafrost area, the permafrost distribution in discontinuous permafrost area is complicated due to existence of island talik, which causes highly poor continuity and uniformity of ground hydrothermal conditions and brings great difficulty and uncertainty to the engineering geological investigation. In the present study, the spatial distribution of permafrost and the freeze-thaw process of shallow ground at the I-stage terrace of a river on the Qinghai-Tibet Plateau were studied based on field investigation including drilling, electrical resistivity tomography, and borehole temperature measurement. The results show that the relict permafrost, patchy permafrost, and island talik are distributed in the limited range of the study area. Among them, the buried depth of relict permafrost layer is in the range of 7 ~ 14 m, while the patchy permafrost layer is in the range of 3.0 ~ 17.0 m depth, and the mean annual ground temperature of both is close to -0.1°C, which belongs to extremely high-temperature permafrost. The seasonal freezing/thawing depths of shallow ground within the relict permafrost, patchy permafrost, and island talik range from 2.5 to 3.0 m. The freezing period of the seasonal freezing layer is 5.5 months, while the thawing period of the seasonal thawing layer is 6 months. The complex plane and spatial distribution of permafrost in the field are closely related to local factors such as topography, geomorphology, groundwater, and lithology of shallow ground. It is believed that the formation of the island talik in the study area is controlled by solar radiation and precipitation infiltration.

Permafrost degradation is accelerating beneath the bottom of Yanhu Lake in the Hoh Xil, Qinghai-Tibet Plateau

Lakes on the Qinghai-Tibet Plateau (QTP) have notably expanded over the past 20 years. Due to lake water level rise and lake area expansion, the permafrost surrounding these lakes is increasingly becoming submerged by lake water. However, the change process of submerged permafrost remains unclear, which is not conducive to further analyzing the environmental effects of permafrost change. Yanhu Lake, a tectonic lake on the QTP, has experienced significant expansion and water level rise. Field measurement results indicate that the water level of Yanhu Lake increased by 2.87 m per year on average from 2016 to 2019. Cold permafrost, developed in the lake basin, was partially submerged by lake water at the end of 2017. Based on the water level change and permafrost thermal regime, a numerical heat conduction permafrost model was employed to predict future changes in permafrost beneath the lake bottom. The simulated results indicate that the submerged permafrost would continuously degrade because of the significant thermal impact of lake water. By 2100, the maximum talik thicknesses could reach approximately 7, 12, 16, and 19 m under lake-bottom temperatures of +2.0, +4.0, +6.0, and +8.0 °C, respectively. Approximately 291 years would be required to completely melt 47 m of submerged permafrost under the lake-bottom temperature of +4 °C. Note that the permafrost table begins to melt earlier than does the permafrost base, and the decline in the permafrost table occurs relatively fast at first, but then the process is attenuated, after which the permafrost table again rapidly declines. Compared to climate warming, the degradation of the submerged permafrost beneath the lake bottom occurred more rapidly and notably.

Long-term energy balance measurements at three different mountain permafrost sites in the Swiss Alps

Abstract. The surface energy balance is a key factor influencing the ground thermal regime. With ongoing climate change, it is crucial to understand the interactions of the individual heat fluxes at the surface and within the subsurface layers, as well as their relative impacts on the permafrost thermal regime. A unique set of high-altitude meteorological measurements was analysed to determine the energy balance at three mountain permafrost sites in the Swiss Alps (Murtèl–Corvatsch, Schilthorn and Stockhorn), where data have been collected since the late 1990s in the framework of the Swiss Permafrost Monitoring Network (PERMOS). All stations are equipped with sensors for four-component radiation, air temperature, humidity, and wind speed and direction, as well as ground temperatures and snow height. The three sites differ considerably in their surface and ground material composition, as well as their ground ice contents. The energy fluxes were calculated based on two decades of field measurements. While the determination of the radiation budget and the ground heat flux is comparatively straightforward (by the four-component radiation sensor and thermistor measurements within the boreholes), larger uncertainties exist for the determination of turbulent sensible and latent heat fluxes. Our results show that mean air temperature at Murtèl–Corvatsch (1997–2018, 2600 m a.s.l.) is −1.66 ∘C and has increased by about 0.8 ∘C during the measurement period. At the Schilthorn site (1999–2018, 2900 m a.s.l.) a mean air temperature of −2.60 ∘C with a mean increase of 1.0 ∘C was measured. The Stockhorn site (2003–2018, 3400 m a.s.l.) recorded lower air temperatures with a mean of −6.18 ∘C and an increase of 0.5 ∘C. Measured net radiation, as the most important energy input at the surface, shows substantial differences with mean values of 30.59 W m−2 for Murtèl–Corvatsch, 32.40 W m−2 for Schilthorn and 6.91 W m−2 for Stockhorn. The calculated turbulent fluxes show values of around 7 to 13 W m−2 using the Bowen ratio method and 3 to 15 W m−2 using the bulk method at all sites. Large differences are observed regarding the energy used for the melting of the snow cover: at Schilthorn a value of 8.46 W m−2, at Murtèl–Corvatsch 4.17 W m−2 and at Stockhorn 2.26 W m−2 are calculated, reflecting the differences in snow height at the three sites. In general, we found considerable differences in the energy fluxes at the different sites. These differences help to explain and interpret the causes of a warming atmosphere. We recognise a strong relation between the net radiation and the ground heat flux. Our results further demonstrate the importance of long-term monitoring to better understand the impacts of changes in the surface energy balance components on the permafrost thermal regime. The dataset presented can be used to improve permafrost modelling studies aiming at, for example, advancing knowledge about permafrost thaw processes. The data presented and described here are available for download at the following site: https://doi.org/10.13093/permos-meteo-2021-01 (Hoelzle et al., 2021).

Isolating the Contributions of Seasonal Climate Warming to Permafrost Thermal Responses Over the Qinghai‐Tibet Plateau

AbstractClimate warming is thermally degrading permafrost. The climate warming over the Qinghai‐Tibet Plateau (QTP) is characterized by obvious seasonality and stronger winter warming in comparison with summer warming in 2000s. The contributions of seasonal climate warming to permafrost thermal responses remain unknown. Here, we isolated the seasonal warming contributions to permafrost thermal regimes through contrasting a series of specially designed numerical experiments that were composed of decadal seasonal data segments. The results reveal that permafrost thermal regime is highly sensitive to winter temperature change. Permafrost in the Three River Source region and on the Qiangtang High Plateau has undergone remarkable thermal degradation in the 2000s due to winter warming. It was estimated that each degree of rising in air temperature in summer could lead to an average increase of 0.35 m in the active layer thickness (ALT) and of 0.20°C in the mean annual ground temperature (MAGT), while for 1° winter warming, the active layer thickens by 0.16 m and the MAGT increases by 0.13°C. However, the overall impacts of winter warming have exceeded summer warming in 2000s due to a triple warming rate in winter than that in summer in this period.

Thermal regime of Cryosols and underlying permafrost in North Yakutia in the context of global climate change

The warming and an increase in the amount of solid precipitation, which became apparent in North Yakutia on the threshold of the 21st century, have led to an increase of soil temperature in winter season and of the permafrost. The heat fluxes measured in the taiga soil on the Kolyma Lowland reveal an imbalance in the annual heat gain and loss in the cryogenic ecosystem amounting to 26.3–56.1% of the incoming energy. An increase in the summer air temperatures of the 2000th caused a universal increase in the depth of seasonal soil thawing. After the drop in high summer temperatures, the active layer thickness (ALT) either continued to grow or stabilized at higher levels in the watershed ecosystems of the Kolyma Lowland; however, ALT returned to its initial values in the tundra of the Yana-Indigirka Lowland. As for the floodplain landscapes, ALT increased near-linearly over the 24 years of monitoring. The waterlogged tundra and taiga soils as well as the upland gleyzem of the Bykovsky Peninsula differed only by a temporary increase in the thawing depth. The degree of the soil and permafrost thermal regime transformation tends to increase from west to east, fitting the heterogeneity of climate changes.

Surface temperatures and their influence on the permafrost thermal regime in high-Arctic rock walls on Svalbard

Abstract. Permafrost degradation in steep rock walls and associated slope destabilization have been studied increasingly in recent years. While most studies focus on mountainous and sub-Arctic regions, the occurring thermo-mechanical processes also play an important role in the high Arctic. A more precise understanding is required to assess the risk of natural hazards enhanced by permafrost warming in high-Arctic rock walls. This study presents one of the first comprehensive datasets of rock surface temperature measurements of steep rock walls in the high Arctic, comparing coastal and near-coastal settings. We applied the surface energy balance model CryoGrid 3 for evaluation, including adjusted radiative forcing to account for vertical rock walls. Our measurements comprise 4 years of rock surface temperature data from summer 2016 to summer 2020. Mean annual rock surface temperatures ranged from −0.6 in a coastal rock wall in 2017/18 to −4.3 ∘C in a near-coastal rock wall in 2019/20. Our measurements and model results indicate that rock surface temperatures at coastal cliffs are up to 1.5 ∘C higher than at near-coastal rock walls when the fjord is ice-free in winter, resulting from additional energy input due to higher air temperatures at the coast and radiative warming by relatively warm seawater. An ice layer on the fjord counteracts this effect, leading to similar rock surface temperatures to those in near-coastal settings. Our results include a simulated surface energy balance with shortwave radiation as the dominant energy source during spring and summer with net average seasonal values of up to 100 W m−2 and longwave radiation being the main energy loss with net seasonal averages between 16 and 39 W m−2. While sensible heat fluxes can both warm and cool the surface, latent heat fluxes are mostly insignificant. Simulations for future climate conditions result in a warming of rock surface temperatures and a deepening of active layer thickness for both coastal and near-coastal rock walls. Our field data present a unique dataset of rock surface temperatures in steep high-Arctic rock walls, while our model can contribute towards the understanding of factors influencing coastal and near-coastal settings and the associated surface energy balance.

Modeled (1990–2100) variations in active‐layer thickness and ice‐wedge activity near Salluit, Nunavik (Canada)

AbstractSimulations with a one‐dimensional heat transfer model (TONE) were performed to reproduce the near surface ground temperature regime in the four main types of soil profiles found in Narsajuaq River Valley (Nunavik, Canada) for the period 1990–2100. The permafrost thermal regime was simulated using climate data from a reanalysis (1948–2002), climate stations (1989–1991, 2002–2019) and simulations based on climate warming scenarios RCP4.5 and RCP8.5 (2019–2100). The model was calibrated based on extensive field measurements made between 1989 and 2019. The results were used to estimate when soil thermal contraction cracking will eventually stop and to forecast the melting of ice wedges due to active‐layer thickening. For the period 1990–2019, all soil profiles experienced cracking every year until 2006, when cracking became intermittent during a warm period before completely stopping in 2009–2010, after which cracking resumed during colder years. Ice‐wedge tops melted from 1992 to 2010 as the active layer thickened, indicating that top‐down ice‐wedge degradation can occur simultaneously with cracking and growth in width. Our predictions show that ice wedges in the valley will completely stop cracking between 2024 and 2096, first in sandy soils and later in soils with thicker organic horizons. The timing will also depend on greenhouse gas concentration trajectories. All ice wedges in the study area will probably experience some degradation of their main body before the end of the century, causing their roots to become relict ice by the end of the 21st century.

Qinghai-Tibet Plateau wetting reduces permafrost thermal responses to climate warming

Permafrost, as one of the cryospheric indicators, is extremely sensitive to climatic changes. The Qinghai-Tibet Plateau has experienced remarkable warming and wetting since the mid-1990s. Its recent wetting alters thermal and hydrological properties in permafrost regions and inevitably affects permafrost thermal dynamics. While previous studies mostly focused on the effects of warming on permafrost, little attention has been paid to the effects of concomitant wetting. Here, a land surface model adapted for permafrost simulation is employed to quantitatively investigate the impacts of climate warming and wetting on permafrost thermal regimes by setting up a group of hypothetical numerical scenarios on the basis of historical meteorological records. The results reveal that climate wetting reduces permafrost thermal responses to warming and this effect is especially evident in the arid and semi-arid zones. It was estimated that one-degree warming induces an average increase of 0.46 m in active layer thickness (ATL) and 0.53°C in temperature at the top of permafrost (TTOP), and a 100 mm wetting in summer precipitation leads to a mean decrease of 0.35 m in ALT and 0.36°C in TTOP. Furthermore, we found through the simulations that increased summer precipitation imposes dual effects on permafrost in semi-arid high altitudes.

Simulation of the Present and Future Projection of Permafrost on the Qinghai‐Tibet Plateau with Statistical and Machine Learning Models

AbstractThe comprehensive understanding of the occurred changes of permafrost, including the changes of mean annual ground temperature (MAGT) and active layer thickness (ALT), on the Qinghai‐Tibet Plateau (QTP) is critical to project permafrost changes due to climate change. Here, we use statistical and machine learning (ML) modeling approaches to simulate the present and future changes of MAGT and ALT in the permafrost regions of the QTP. The results show that the combination of statistical and ML method is reliable to simulate the MAGT and ALT, with the root‐mean‐square error of 0.53°C and 0.69 m for the MAGT and ALT, respectively. The results show that the present (2000–2015) permafrost area on the QTP is 1.04 × 106 km2 (0.80–1.28 × 106 km2), and the average MAGT and ALT are −1.35 ± 0.42°C and 2.3 ± 0.60 m, respectively. According to the classification system of permafrost stability, 37.3% of the QTP permafrost is suffering from the risk of disappearance. In the future (2061–2080), the near‐surface permafrost area will shrink significantly under different Representative Concentration Pathway scenarios (RCPs). It is predicted that the permafrost area will be reduced to 42% of the present area under RCP8.5. Overall, the future changes of MAGT and ALT are pronounced and region‐specific. As a result, the combined statistical method with ML requires less parameters and input variables for simulation permafrost thermal regimes and could present an efficient way to figure out the response of permafrost to climatic changes on the QTP.