Rock glaciers are lobate or tongue-shaped bodies of frozen debris， which are important substitute index of permafrost boundary and widely distributed in high altitude and high latitude periglacial areas around the world. Active rock glaciers are typically moving downslope or downvalley slowly， but the climate change may cause significant increase of rock glaciers， resulting in serious geological disasters in cold regions. In addition， rock glaciers might consist of massive ice which could be important freshwater resource in arid and semi-arid areas. Based on the literature review， rock glaciers are divided into talus-derived， glacier-derived， ice cored， Kunlun Mountain type， and the formation mechanisms of different types of rock glaciers are discussed respectively. The movement of rock glacier may develop from permafrost creep， frost heave and thaw settlement， debris supply， and new ground ice formation， among others. The variation of rock glacier movement characteristics on the spatio-temporal scale is mainly affected by climatic conditions， topographic environment， internal structure， external forces， among others. The response of rock glaciers to global warming will lead to two opposite results： the acceleration or instability caused by the increase of ground temperature and the deactivation of rock glaciers caused by permafrost melting. In the context of continuous retreat of glaciers and the shortening of the duration of seasonal snow， the debris cover as a thermal insulation layer can protect the underlying ice bodies from melting， delay and reduce the response of rock glacier to climate change， thus rock glacier will become an increasingly important water resource in arid and semi-arid areas. At present， more than 13 511 rock glaciers with more than 945.51 km² of total area have been inventoried in China， but there is still a significant lack of systematic rock glacier inventory and long-term on-site monitoring and model research.

Rock glaciers are a common periglacial landform in alpine regions， and their distribution and movement patterns provide crucial insights into the state of mountain permafrost. Daxue Shan is situated at the transition zone between the Tibetan Plateau and Sichuan Basin， where the cold and rainy climate is ideal for the formation of maritime glaciers and periglacial landforms. However， the distribution of rock glaciers in this region has not been fully explored. In this study， we utilized 90 Sentinel-1A ascending SAR images acquired between June 2019 and June 2022 to apply the time-series interferometric synthetic aperture radar （InSAR） technique for deriving the mean annual surface displacement velocity over the southern Daxue Shan. We also comprehensively considered the kinematic characteristics from InSAR measurement and geomorphological characteristics from optical image interpretation to compile a rock glacier inventory. We classified rock glaciers into four types according to the geomorphological units at the upslope region directly connected to them， namely， talus-connected， debris-mantle-slope-connected， glacier-connected， and glacier-forefield-connected types. A total of 860 rock glaciers were compiled， with 67% being talus-connected and only 4% being glacier-connected. The rock glaciers are mainly concentrated in the northern part of the study area， indicating a more favorable periglacial environment for rock glacier development. Talus-connected rock glaciers are widespread in the study area with uniform distribution. Glacier-connected and glacier-forefield-connected rock glaciers are primarily distributed in the northeast region with strong glaciation， while debris-mantled-slope-connected rock glaciers are mainly found in the southwest area. Geomorphic and kinematic parameters were calculated to analyze the development and motion pattern of these rock glaciers. The area， length， and slope angle of rock glaciers are concentrated between 0.04~0.12 km2， 250~700 m， and 12°~24°， respectively. Compared to the other two types， glacier-connected and glacier-forefield-connected rock glaciers are relatively larger， longer， and located in gentler slopes. The distribution altitudes of the local rock glaciers are between 3 638~5 107 m， with no rock glacier development identified below an altitude of 3 915 m in this research area. The majority （74%） of rock glaciers face west， northwest， north， and northeast， with similar aspect distribution patterns shown by the four types of rock glaciers. Notably， no glacier-connected rock glacier faces southeast， south， and southwest. Overall， rock glacier activities in the study area are low， with a maximum and mean downslope velocity of 250.25 mm·a^-1 and 21.97 mm·a^-1， respectively， and most of them creep below 100 mm·a^-1. Rock glacier activities in the northern part of the study area are relatively more evident， indicating that abundant ice within rock glaciers interacts strongly with hydrothermal conditions in this region. Correlation coefficients between the geomorphic and kinematic parameters of rock glaciers were calculated. The correlation between the geomorphic parameters of rock glaciers reflects their development characteristics. However， no evident linear relationship was found between the geomorphic and kinematic parameters， indicating a complex mechanism of rock glacier dynamics. Based on the empirical model in the previous study， the water storage of rock glaciers in this area was primarily assessed at 0.963~1.445 km3. This study presents the first rock glacier inventory in the southern Daxue Shan， revealing the distribution and motion pattern of rock glaciers in this region. The results provide essential and reliable data for further studies on rock glaciers' hydrological contributions and mountain permafrost evolution in the southeast Tibetan Plateau. The method used in this paper for rock glacier inventory can also provide a feasible technical route for compiling large-scale rock glacier inventories in western China.

The active layer is the most thermodynamically active near-surface soil layer in the permafrost regions. It is vital to the permafrost eco-environments as it serves as the critical zone for the supply of water and nutrients for the growth of alpine/northern plants， as well as the habitats for most frequent microbial activities and critical biogeochemical cycles. It also plays an indispensable role in the exchanges of water and energy between the atmosphere and the near-surface ground. Recently， the active layer thickness （ALT） under natural and undisturbed conditions had been prevalently increased under the dual influences of climate warming and increasing anthropogenic activities， which poses significant adverse influences on the cold environment and frozen ground engineering. In this paper， we reviewed the influencing factors of the ALT under natural and undisturbed conditions in the aspects of macro-scale geology and geography and micro-scale local factors， the measurements and simulations of ALT， as well as the response characteristics of ALT to climate change. Moreover， we also discussed the impact of ALT change on the alpine ecological environment. The past modeling and observations demonstrated that the spatial heterogeneity of ALT was primarily attributed to the redistribution of solar radiation and its complex interactions with the underlying conditions. Presuming no differentiation in climate and local factors， the thicker ALT is always found in the vicinity of the lower limits of elevational permafrost or of the southern/northern limits of latitudinal permafrost. In the past three decades， ALT has increased sensitively to climate warming， which is characteristic of increasing with the rise of air temperature. The increase of ALT shows an obvious regional differentiation， among which the ALT at most of the mid-latitude alpine and mountainous permafrost regions， such as in the Tibetan Plateau and the Alps， has shown significant increasing trends， while the deepening of ALT to a certain extent was offset by the melting of ground ice and ensued thaw settlement or ground surface subsidence at high-latitude ice-rich permafrost areas. Therefore， not all sites at high latitudes have experienced significant increasing trends as revealed by the observations. However， when analyzing the sensitivity of ALT by the ratio of its changing rate to its average value， we have found that the sites in the Alps （1.46） and the Nordic regions （1.27） were the most sensitive， followed by the sites in Alaska （0.93） and on the Tibetan Plateau （0.91）， while those in Canada （0.25） had relatively low sensitivity. We conclude that the future research directions of ALT should focus on the precise simulation and mapping of ALT， the adaptive mechanisms of ALT to climate changes， the impact of changing ALT on the biogeochemical cycles， hydrological processes， and water resources and structures in cold regions， among many others.

Glaciers in Xinjiang， northwestern China， have experienced drastic retreat phenomena due to climate warming in recent decades. Glacier retreats have led to an increase in glacial meltwater runoff and accelerated the formation and expansion of glacial lakes. Especially in the core area of the Silk Road Economic Belt and climate change-sensitive areas， ice-marginal compound disasters， such as glacial surges and glacial lake outburst floods （GLOFs）， have entered a period of high incidence and acceleration. The resulting economic losses and potential risks will also become increasingly severe and prominent. Accurate mapping and monitoring of these glacial lakes is therefore critical to understanding the response of GLOF hazards to climate change. In this study， we conducted a detailed mapping of glacial lakes in Xinjiang from April to October 2022 using the DUNet semantic segmentation model and Sentinel-2 imagery， extracted the maximum boundaries of glacial lakes in Xinjiang from April to October 2022， and manually inspected to exclude non-glacial lakes and supplement glacial lakes missed due to shading. We used three-level basins to divide distribution area of glacial lakes in Xinjiang into 11 subregions. We assigned detailed attribute information to each glacial lake， such as center coordinates， perimeter， area， elevation of the center point of the glacial lake， subregion name， subregion code， absolute error， relative error， and so on. In addition， we screened out glacial lakes with an area greater than 0.06 hm². We analyzed spatial distribution of these lakes and trend of change over the past decade in conjunction with the existing inventory of glacial lakes. Results showed that the glacier mapping based on Sentinel-2 got more lake numbers and achieved lower relative errors than the existing Landsat-based inventories， with average relative errors of large （>10 hm²）， medium （>1~10 hm²）， and small （≤1 hm²） lakes are 2.29%， 10.02%， and 27.71%， respectively. The relative error of this glacial lake dataset with an area larger than 0.81 hm² is 18.36%， which meets the mapping accuracy of monitoring glacial lake changes in Xinjiang for more than 20 years. About 6 854 glacial lakes with a total area of 200.36 km² were mapped throughout Xinjiang. Specifically， small glacial lakes accounted for 70.32% of the total number of glacial lakes but only 7.51% of the total glacial lake area； medium glacial lakes and large glacial lakes accounted for 29.68% of the total number of glacial lakes， but the area accounted for 92.49% of the total area. The patterns of lake distribution are heterogeneous in different mountainous areas， and the glacial lakes are numerous in the Altai Mountains （1 474）， western Tianshan （Ili River basin） （1 170）， and southwest Tianshan （Tarim inflow area） （915）. The number of glacial lakes peaks in the altitude range of 3 300~3 600 meters. In the last 30 years， glacial lakes with areas of less than 10 hm² increased significantly in number and area， especially in the Altai and the Western Tianshan Mountains. Therefore， the regional differences in the distribution of glacial lakes in Xinjiang are significant， with a large number of small glacial lakes， which tend to be more sensitive to climate change and change more drastically and can effectively reflect the changes in regional climate and glaciers. This study provides an important dataset for monitoring and disaster assessment of glacial lakes in Xinjiang， which is essential for a deeper understanding of the response of glacial lakes to climate change and the development of effective coping strategies. Future studies will improve the construction of a multi-period glacial lake catalog database， further analyze the changing characteristics of glacial lakes in Xinjiang， and explore GLOF disaster and its coupling relationship with climate， glaciers， and other elements.

Water accumulation associated with water migration is closely related with the ice segregation， but their coupling relationship is still unclear. To decoupling the relationship of water accumulation and ice segregation， herein， the dynamics of water migration and ice segregation during the freezing and thawing of different soil types under different water supplying conditions have been investigated based on pore water pressure measurement and layer-scanning technique. Results showed that apparent water accumulation near the freezing front during the freezing of silty clay and loess tested here， but there exist differences in modes. During loess freezing under closed system， no ice segregation was observed， the pore water pressure increased， and there existed apparent liquid water accumulation during the early stage of freezing； while during the freezing of silty clay， there existed ice segregation， the pore water pressure decreased， and no apparent liquid water accumulation occurred during the early stage of freezing. The results implied that there exist two modes of water accumulation near the freezing front during soil freezing： one is the water accumulation induced by water pressure gradient induced by pore ice which results in water flowing from the frozen zone and unfrozen zone to the location near the freezing front； the other is the water accumulation induced by cryo-suction of segregation ice which results in the water flowing from the unfrozen zone to the location near the freezing front. Notably， the contribution from each mode associated with water accumulation of soil freezing depends on whether the ice segregation exists. As no ice segregation forms， water accumulation induced water pressure gradient predominates during the early stage of freezing. As there exists ice segregation during freezing， water accumulation induced cryo-suction predominates during the later stage of freezing. Investigating on different modes of water accumulations will be helpful for the exploring the mechanisms of freeze-thaw diseases and the ground ice in the cold regions.

Net shortwave radiation provides the main melting energy for mountain glaciers， which is modulated by a combination of glacier surface albedo and incoming shortwave radiation. Glacier mass balance， as a link between atmosphere and glaciers， is an important glacier parameter that characterize glacier accumulation and melting， and is sensitive to climate change. Many scholars have used the albedo method to study mass balance for an individual glacier， but less attention has been given to large-area glaciers. This study helps to understand that glacier melting is a result of climate and atmospheric changes， as well as feedback from glacier surface albedo. In order to investigate variations of glacier surface albedo from 2000 to 2022 in the Sawir Mountains and further estimate annual mass balance， two models （A-Ms and A-Mr） between albedo and mass balance were established based on MOD10A1 and MYD10A1 snow products retrieved glacier surface albedo， geodetic mass balance in the Sawir Mountains， in situ measured albedo and mass balance on Muz Taw Glacier. During ablation season， glacier albedo decreased by 0.035 in the Sawir Mountains at the rate of 0.0015 a^-1， and dates of minimum albedo appeared to have a shift towards earlier at the rate of 10 d·（10a）^-1. The A-Ms model established a linear relationship between albedo and mass balance on Muz Taw Glacier at the 95% confidence level， and indicated that a strong linear coefficient （R²=0.84） was found between albedo changes and mass balance. For A-Mr model， the R² between albedo and mass balance in cirque， valley and hanging glaciers in the Sawir Mountains were 0.81， 0.74 and 0.72 at the 99% confidence level， respectively. The reconstructed two albedo-mass balance relationships can be used to retrieve glacier mass balance. Furthermore， average annual mass balance in the Sawir Mountains estimated from A-Ms and A-Mr models were -1.24 m w.e.·a^-1 and -0.90 m w.e.·a^-1， respectively. Mass balance estimated from A-Mr model was closer to geodetic mass balance， which could better reflect mass loss in the Sawir Mountains. In addition， compared with glaciers in High Mountain Asia， glacier mass loss in the Sawir Mountains was the greatest. Glacier mass loss in the northern and western regions of High Mountain Asia was smaller than that in the southeast， and in recent years， glacier mass in High Mountain Asia had been in a state of severe loss.

The climate change in the source region of the Yellow River Basin was projected from 2121 to 2060 using eight GCMS of the Coupled model inter-comparision project Phase 6 （CMIP6） and two shared socio-economic low-carbon paths （SSP1-2.6 and SSP2-4.5）. The inter-decadal variation of discharge in the source region of the Yellow River from 2021 to 2060 was predicted by using eight GCMs climate models to drive HBV and SWAT hydrological models. The results show that： （1） In comparison with the baseline period （1995—2014）， in terms of the ensemble mean， annual mean air temperature， annual precipitation will increase by 1.3 ℃ and 1.6 ℃， by 11.6% and 11.5% under SSP1-2.6 and SSP2-4.5 scenarios， respectively. And the warming and wetting trends become obvious from 2021—2060 under the SSP1-2.6 and SSP2-4.5 scenarios in the source region of the Yellow River. （2） The multi-models ensemble mean （MEM） multi-year mean annual discharge for 2021—2060 was expected to increase by 8.6% and 8.5% under the SSP1-2.6 scenario and the SSP2-4.5 scenario， respectively. It was projected to increase in each decade from the 2020s to the 2050s under the scenario of SSP1-2.6 and SSP2-4.5. The increase degree in 2040s and 2050s is higher than 2020s and 2030s. （3） The proportion of discharge was projected to decrease by 0.1%~1.0% from May to August during 2021—2060 under both scenarios but was projected to increase by 0.1%~2.1% from April to May and September to December for most GCM_S under the SSP1-2.6 scenario and the SSP2-4.5 scenario， respectively. （4） Extremely high monthly discharge was expected to increase by 2.5%~2.7% in the water storage season under two scenarios during 2021—2060 in the source region of the Yellow River whereas the extreme high discharge in the flood season increased by 0.1% under the SSP1-2.6 scenarios but decreased by 1.3% under the SSP2-4.5 scenarios， and decreased by 0.7%~1.0% in dry season under two scenarios in the next 40 years. Extremely low discharge was projected to increase by 0.8%~1.9% in the flood season and the dry season but to decrease by 1.8%~2.3% in the storage season under two scenarios in the study region.

Deep hot-water drill is an important tool for clean drilling and sampling of subglacial lakes in polar regions. The underground return-water system is the key component of the deep hot-water drill， which mainly contains the return-water hose， heat-injection hose， submersible pump and water cavity. The return-water hose is used to extract molten water from the water cavity to the surface for recycling， while the heat-injection hose is used to inject surface hot water into the water cavity to prevent it from freezing. The thermal and flow characteristics of return-water hose and heat-injection hose are very important for the design of the downhole return-water system， however， it is not be the systematically researched and the variation of pressure loss and temperature loss is still not clear at present. In the paper， the theoretical calculation method of thermal and flow characteristics of return-water hose and heat-injection hose was firstly proposed based on Darcy-Weisbach formula and Sukhov's temperature-drop formula. Then， the numerical simulation method of thermal and flow characteristics of the two hoses was established in COMSOL Multiphysics 5.6 software， and the numerical results matched well with the theoretical calculation results. Finally， this paper systematically analyzed the influence of the factors， such as flow rate， inner diameter， length， water temperature at inlet， thermal conductivity， roughness of inner wall， ice temperature and wall thickness on the pressure and temperature loss of return-water hose and heat-injection hose. The results shows that the pressure and temperature in the return-water hose and heat-injection hose decreases linearly. In common， flow rate， inner diameter and length are the main factors affecting the pressure loss of return-water hose and heat-injection hose， while air temperature， flow rate， inner diameter and length are the main factors affecting the temperature loss. In addition， roughness of inner wall has little influence on the thermal and flow characteristics of the two hoses. When designing the downhole return-water system， the inner diameter of the return-water hose and the heat-injection hose should be increased as much as possible， and the construction depth of the return-water chamber should be reduced. The water temperature at inlet has bigger influence on the thermal and flow characteristics of the heat-injection hose compared with the return-water hose. Generally， the thermal conductivity of 0.4 W·（m·K）^-1 can ensure the return-water hose and the heat-injection hose have good thermal insulation performance and it is no longer necessary to increase the wall thickness to enhance its thermal insulation performance. The temperature loss of the return-water hose is generally not more than 2 ℃， while the temperature loss of the heat-injection hose is about 10~20 ℃. The conclusions above provided an important basis for designing a safe and efficient downhole return-water system.

The Bering Sea is a marginal sea of the Arctic Ocean， and its sea ice changes differ considerably from other marginal seas. The sea ice area （SIA） in the Bering Sea has shrunk significantly over the last decade， affecting regional hydrology， the atmosphere， and even the ecosystem， as well as the mid-latitude and our national climate systems. Lots of efforts have been conducted in the temporal and spatial characteristics of sea ice based on satellite observation， simulation， diagnostic analyses， and so on. The recent changes in sea ice in the Bering Sea are proposed， as well as the impact factors of sea ice changes. Simultaneously， the effects of Bering Sea ice changes on hydrology， atmosphere， ecosystems， and the mid-latitude climate system are summarized. According to a comprehensive review of current studies， the understanding of the mechanism of sea ice change on an intraseasonal time scale is still insufficient due to the limitation of current study approaches and observation data on seawater current， as well as a lack of systematic analysis to explore the causal relationship. It is also stated that more research on the impact of early sea ice on later sea ice， the drag effect of wind field on sea ice， the time scale of the effect of warm advection on sea ice， and the time-scale evolution of sea ice change is required.

The Three-River Source Region （TRSR） is a sensitive area of global climate change and a fragile ecological environment， and is currently facing the problems of permafrost degradation. This study analyzed the freezing and thawing characteristics of seasonally frozen ground in the TRSR before and after climate warming from 1961 to 2021 based on observations from the 18 national meteorological stations. The results show that： （1） The mean annual air temperature （MAAT） in the TRSR is -0.34 ℃ during 1961 to 2021， which is high in the east and low in the west， and an overall increase of 0.38℃·10a^-1 was observed， and the sudden change occurred in 1997， and the temperature rises significantly after the mutation； （2） The mean annual maximum seasonal freezing depth is 142.5 cm， which decreases from northwest to southeast， and degrades by 11 cm with an overall rate of 2.4 cm·10a^-1 in comparisons of that before 1997； （3） The first day of ground surface freezing is averaged on October 24， which is postponed at a rate of 1.0 d·10a^-1， and the ground surface freezing is averaged on May 18， which is advanced at a rate of 3.3 d·10a^-1 and 12 days earlier， and the first day of ground surface freezing is delayed by 14 d compared with before 1997； （4） The onset freezing of near-surface shallow soils （0~3.2 m） is 133.9 d， which exhibits a spatial tendency of west-high and east-low， and the overall decrease rate is 1.9 d·10a^-1， which has decreased by 8.8 d compared with before 1997； （5） The annual maximum freezing depth and the onset of freezing of near-surface shallow soils changed abruptly in 2004 and 2002， respectively， and the mutation time had a certain lag with the temperature. The study implicated that seasonally frozen ground is jointly affected by climate warming and anthropogenic activities. This study revealed the degradation of seasonally frozen ground in the TRSR， which may provide references for climate change and engineering construction.

Gound thermal regime plays a crucial role in the soil physical， chemical， and microbiological processes. The ground thermal regime is typically dominated by air temperature as well as local factors such as vegetation， snow cover， and soil properties. Snow cover controls the energy exchange between the atmosphere and the land and plays a decisive role in the ground thermal regime during the cold season. This study investigated the influences of seasonal snow cover on ground surface temperature in Xinjiang based on 77 stations from the China Meteorological Administration. Our results showed that the mean ground surface temperature was about -1.3 ℃ at stable seasonal snow-covered stations in the cold season during 2005—2020， while the mean snow depth was 5.9 cm， and the air temperature was -4.6 ℃. At unstable seasonal snow-covered stations， the mean air temperature was 1.4 ℃ and the ground surface temperature was 2.4 ℃. The numerical simulation results indicated that an increase in snow depth of 1 cm corresponds to an increase of 0.26 ℃ in surface offset. A change in air temperature of 1 ℃ corresponds to a difference of ground surface temperature by 0.57 ℃ in the shallow snow zone （<5 cm） and by 0.20 ℃ in the thicker snow zone （>30 cm）. Further simulation was carried out at a typical snow station during 2008-07-01—2009-06-30. The results indicated that the mean ground surface temperature below the snow increased by 2.2 ℃ as the snow density increased from 200 kg?m^-3 to 400 kg?m^-3. The mean ground surface temperature during the simulation period was -2.7 ℃， -5.5 ℃， and -3.6 ℃ for the three scenarios of the normal time series， while maintaining the same snow depth， early snowfall， and delayed snowfall. The results highlight the significant influences of snow duriation on the ground surface temperature.

Small glaciers are very sensitive to climate change， and monitoring and quantitative assessment of this type of glacier changes can help to understand the magnitude and mechanism of glacier response to climate change. In this study， we combined multi-source remote sensing data （satellite and UAV data） and meteorological data to analyze the change in area of Kuoqionggangri No. 1 Glacier in the Nyainqêntanglha Mountains， Qinghai-Tibet （Xizang） Plateau over the past 50 years， and quantitatively evaluated the magnitude of recent elevation changes and the spatial distribution of Kuoqionggangri No. 1 Glacier. The study shows that the area of Kuoqionggangri small cirque glacier shrank from （1.444±0.013） km² to （0.712±0.001） km² during 1968—2021， with a shrinkage of 50.7%， and the average rate of glacier terminus retreat was （6.23±0.71） m⋅a^-1. Based on the high-precision UAV survey data from 2020 to 2021， we found that the average elevation difference of the ice surface of Kuoqionggangri No. 1 Glacier reached （-2.41±0.69） m⋅a^-1. The average ice surface elevation change at the glacier terminus was greater than 3 m， and a decrease in the central part of the glacier in the range of 1.5 to 3 m. The study also found that glacier supraglacial streams play an important role in the spatial variation of elevation. There are 13 supraglacial streams developed on the surface of this glacier， and the average offset of the streams to the northwest from 2020 to 2021 is about 2 m. Downward and lateral erosion of the supraglacial streams resulted in causing significant spatial differences ice elevation changes at the glacier terminate.

The first working group report of the Sixth Assessment Report （AR6） of the Intergovernmental Panel on Climate Change （IPCC） summarized soil carbon storage， carbon source and sink effects， and greenhouse gas emissions under future climate scenarios in permafrost regions. The report identifies that 1 460~1 600 Pg of organic carbon is stored in surface soils and deep sediments in permafrost regions of the Northern Hemisphere （medium confidence）. As the climate continues to warm， permafrost degrades significantly， allowing soil organic matter to decompose rapidly and release into the atmosphere as carbon dioxide （CO₂） or methane （CH₄）， accelerating climate warming. Under future global warming scenarios， near-surface permafrost will decrease significantly， which will in turn release CO₂ and CH₄ into the atmosphere， resulting in a positive feedback effect of carbon-climate. The report also points out that by 2100， the CO₂ and CH₄ releases in permafrost regions are expected to be 18 （3.1~41） PgC and 2.8 （0.7~7.3） PgC for every 1 ℃ increase in temperature （low confidence）. However， due to the wide range of estimated data and limited agreement among models， as well as the incomplete understanding of driving factors and carbon models in the permafrost environment， there is low confidence in the timing and magnitude of permafrost climate feedback.

This paper systematically reviews the significant contributions of Professor Zhang Tingjun in his 40 years’ academic research career， with the principal framework of climate and frozen soil changes in cold regions and their impacts. The selected publications mainly represent innovative achievements in the following four themes. （i） He investigated permafrost and ground ice distribution in the Northern Hemisphere， including Alaskan Arctic and high mountains in west China. He led the papers （in 1999 and 2000） that estimated permafrost area and ground ice volume based on the map compiled by the International Permafrost Association， which are widely recognized and cited. （ii） He explored the physical basis of the changing frozen ground， snow cover， and other related climate elements in cold regions to reveal potential interactions of key elements of the land surface processes. He synthetically summarized the impacts and physics of seasonal snow cover on frozen ground， which provides an essential start for the research on this topic. （iii） He made efforts to develop， improve， and apply numerical models that capture critical physical processes in frozen soils. His pioneering works on permafrost numerical modeling were beneficial， effective， and operational experiences for large-scale simulations of permafrost dynamics， beyond empirical and semi-empirical methods prior. （iv） He also established cryospheric remote sensing methods for detecting freeze-thaw cycles and seasonal snow cover. Many of these achievements have greatly improved the understanding of the physical basis of the changing cold regions and thus became classic literatures in the research of frozen ground and climate change. His 40-year life of pursuing truth is also worth learning and memorizing.

Freezing and thawing index is not only of great significance to the study of frozen soil， but also a useful index to reflect climate change. The daily temperature observation values of 11 national meteorological stations in the Qilian Mountains were used to calculate the annual air and ground surface freezing and thawing indices from 1961 to 2014， and the statistical and distribution characteristics of these indices were analyzed. The temporal and spatial variation trends of the annual freezing and thawing indices were analyzed by nonparametric Mann-Kendall test， Sen’s slope estimation method and correlation analysis method. The results showed that in the past 54 years， the freezing index had a significant downward trend， and the thawing index had a significant upward trend. The annual average air freezing index， air thawing index， ground surface freezing index， and ground surface thawing index were roughly distributed between 994.3 ℃·d and 1 540.9 ℃·d， 1 828.2 ℃·d and 2 376.6 ℃·d， 744.7 ℃·d and 1 287.3 ℃·d， 2 706.0 ℃·d and 3 542.6 ℃·d， respectively. The climatic tendency rates were -6.5 ℃·d·a^-1， 6.5 ℃·d·a^-1， -7.7 ℃·d·a^-1， and 9.1 ℃·d·a^-1， respectively. From northwest to southeast， the freezing index showed the distribution characteristics of high in the middle and gradually decreasing in the east-west direction， while the thawing index was opposite； in addition to altitude and latitude， freezing and thawing index was also affected by slope aspect， surrounding topography， snow depth and human activities. The abrupt change point of freezing and thawing index time series occurred in 1994—1995， which corresponded to the abrupt change of air temperature； after the abrupt change point， the growth rates of the air and ground surface thawing indices and the decline rate of the ground surface freezing index increased， while the decline rate of the air freezing index decreased. The change rate of the ground surface freezing and thawing index was greater than that of the air freezing and thawing index during the whole study period， showing that the change of ground surface temperature was more sensitive to global warming. In addition， there was a strong linear relationship between freezing and thawing index and annual average air temperature and ground surface temperature， and the proportion of annual thawing index in the composition of annual average ground surface temperature was larger than that of the freezing index. The research results have reference significance for understanding the climate and frozen soil changes in the Qilian Mountains， further calculating the changes of frozen soil parameters and harnessing the ecological environment in the Qilian Mountains.

Climate change significantly affects the oceanic and terrestrial environment in the Arctic， and thus is directly and indirectly impacting the sources， transport pathways， and fate of persistent organic pollutants （POPs） and chemicals of emerging Arctic concern （CEACs）. The Arctic Monitoring and Assessment Program （AMAP） recently released the report “AMAP Assessment 2020： POPs and Chemicals of Emerging Arctic Concern（CEACs）： Influence of Climate Change”， which pointed out that climate warming induces the release of previously accumulated POPs from permafrost， snow and ice melt in the Arctic and the redistribution of POPs among water， sediments， snow， and air. Meanwhile， raising human activities in the Arctic under the impact of warming may result in new pollution emission sources. Global warming enhances the long-range atmospheric transport （LRAT） potential of semi-volatile POPs； while the process of “biological pump” would also be strengthened by climate change， increasing the sequestration of POPs in deep ocean and sediment. Additionally， the Arctic environment has low resilience and is sensitive to some external environmental influences due to homogeneous environmental elements and ecological scenarios. Consequently， climate change led to the changes of physical environment and ecology， which， in turn is influencing the exposure to， and potentially the effects of these contaminants on Arctic wildlife and other biota， as well as people. The assessment report revealed the high complexity of influence on POPs and CEACs in the Arctic by climate change. In the future studies， more chemicals with POPs properties need to be included in the long-term monitoring programme. Interdisciplinary efforts and cooperation among government， college， and Arctic communities needed to be strengthened.

Glacier is an important component of cryosphere. As an important fresh water resource in arid area of western China， the vulnerability of glacier change is closely related to regional social and economic development. Based on remote sensing images， this paper analyzed the characteristics of glacier change in the Chinese Altai Mountains from 1990 to 2020， constructed the evaluation framework and index system of glacier change vulnerability， demonstrated the temporal and spatial evolution pattern of glacier change vulnerability in the Chinese Altai Mountain from 2000 to 2020， and explored deeply the influencing factors of glacier change adaptability by using the obstacle degree model. The results showed that： （1） In the past 30 years from 1990 to 2020， the glacier area and volume in the Chinese Altai Mountains had decreased by about 20%， and there were significant differences in the change rate of glacier area in different counties and cities. The glacier area reduction rate in Qinghe was the largest， reaching 73%， while that in Burqin was the smallest， only 18%. （2） The glacier change vulnerability in the Chinese Altai Mountains decreased slowly at first and then experienced an accelerated increase over time， with the regional differences decreasing continuously. In spatial distribution， the glacier change vulnerability in the northwest and east was moderately high； the glacier change vulnerability in southwest was low； the vulnerability in central was the lowest. （3） The improvement of adaptability can effectively reduce the glacier change vulnerability in the Chinese Altai Mountains. Taking 2010 as the boundary， the glacier change adaptability in the Chinese Altai Mountains depended on the improvement of the regional economy and water resources in the early stage， and the improvement of adaptability in the later stage was significantly inclined towards social public income， investment， and public service quality. The ways to improve adaptability in counties and cities became more diversified and balanced.

In recent years， the retreat of global glaciers has accelerated in the context of climate warming. However， there is a positive glacier mass balance anomaly in the West Kunlun Mountains of the northwestern Qinghai-Xizang Plateau. Previous studies found that the mass gain in this region started as early as 1970s， and several glaciers have recently surged. Many large-scale glaciers are concentrated in the main peak area of West Kunlun Mountains， and the mass balance anomaly of glaciers in the West Kunlun Mountains has attracted extensive attention. However， there many states of the glacier tongue simultaneously， such as advance （normal）， shrinkage， stable and surge. The advance and retreat of glaciers are not only related to the mass balance influenced by climate change， but also closely related to the glacier velocity. Previous studies mostly focused on the former， but less on the latter. Therefore， this study uses the ITS_LIVE v01 velocity product， combined with the glacier surface elevation changes and thickness to analyze the characteristics and possible causes of glacier surface velocity change with different states of terminus dynamic in the West Kunlun Mountains from 2000 to 2018， to further understand the glacier motion and velocity changes under the same climate change scenario. The results showed that during the study period， the mean velocity of glaciers in the West Kunlun Mountains was 6.35 m⋅a^-1， and showed a fluctuating upward trend， which was caused by the mass gain caused by the thickening of glacier ［（0.15±0.02） m⋅a^-1］. The mean velocity of advanced glacier was about 4.07 m⋅a^-1， and showed an increasing trend during the study period， which was resulted by the slight mass gain， the average velocity of retreat glacier was about 4.86 m⋅a^-1， and showed an decreasing trend， this was caused by the mass loss during the period， the mean velocity of stable glacier was 3.04 m⋅a^-1， and the mass balance of this type glacier was basically stable from 2000 to 2018. In the study area， the mean velocity of advanced glacier is smaller than the retreat glacier， because the value of retreat glacier is larger than the advanced glacier. From 2000 to 2018， seven glaciers surged， and the surge period was concentrated in 2010—2015. During the study period， the thickness of the surge-type glaciers increased significantly ［（0.35±0.02） m⋅a^-1］， resulting in an acceleration in velocity. The retreat glacier with a large length in the West Kunlun Mountains experienced a surge before 2000 and in a quiet period now， mass cannot be transported from the upstream to the downstream， leading to the thinning and retreat of the glacier tongue.

As the headwaters of the Yangtze， Yellow and Lancang River， the Three Rivers Source Region （TRSR） is an important water conservation region and ecological barrier in China. In the context of climate change， the widespread frozen ground in the TRSR degrades significantly which exerts profound effects on vegetation changes and ecological environment. However， the vegetation variation characteristics and their response to climate and frozen ground change in the recent 20 years remain largely unknown. Based on the datasets for vegetation， climate and soil freeze-thaw during 2001—2020， the variation characteristics of vegetation phenology and their response to climatic and soil freeze-thaw factors over the past two decades on the TRSR were analyzed. The results show that the normalized difference vegetation index （NDVI） showed a spatial pattern of high values in the southeast and low values in the northwest on the TRSR. During 2001—2020， the vegetation on the TRSR showed an overall greening trend， with the growing season NDVI increasing by 0.017 per decade. The vegetation phenology also changed significantly， and the lengthening of the duration of the growing season ［6.3 d·（10a）^-1］ was mainly contributed by the advances of the start of the growing season （SOS） ［4.9 d·（10a）^-1］. Based on the results from statistical analysis， air temperature and precipitation were the most important dominant factors for growing season NDVI， and the sensitivities of NDVI to precipitation were larger in the relatively warm-dry region with relatively higher air temperature and lower precipitation； precipitation before the growing season was the most important dominant factor for SOS. The impact of soil freeze-thaw changes on vegetation growth showed spatial heterogeneity. The prolonged soil thaw duration could suppress vegetation growth in the relatively warm-dry region. In general， the rates of vegetation greening and growing season lengthening were higher in the seasonally frozen ground region than those in the permafrost region across the TRSR. However， permafrost degradation could suppress vegetation growth by reducing surface soil moisture content， which was more evident in the regions where permafrost was unstable or degraded into seasonally frozen ground. The results of this study could provide scientific reference for understanding vegetation and phenology changes in alpine cold frozen ground regions represented by the TRSR.

The Parlung Zangbo basin， located in the southeastern Tibetan Plateau， where the marine glaciers are most concentrated. However， due to global climate warming over recent years， these glaciers have experienced substantial losses. By applying the Open Global Glacier Model （OGGM）， we simulated the mass balance of 1 554 glaciers within the basin from 1980 to 2019. The results show that the mass balance of the entire Parlung Zangbo basin was in a continuous state of loss from 1980 to 2019， with a rate of -0.41 m w.e.a^-1. The loss was even more severe in 2000—2019， reaching -0.56 m w.e.·a^-1. Spatially， the southeast and northwest parts of the basin suffer from the most severe glacier losses， while the central and western parts have relatively less. The main causes of glacier mass loss are the increase in temperature and a slight decrease in precipitation. Through sensitivity analysis of temperature and precipitation， it was found that when the temperature rises by 1 °C， the mass balance of 71.75% of the glaciers in the basin changes at a rate of -1 000 to -500 mm w.e. a^-1. When precipitation decreases by 20%， the mass balance of 62.81% of the glaciers changes at a rate of -450 to -300 mm w.e.·a^-1. Compared to precipitation， glaciers are more sensitive to changes in temperature. Meteorological data analysis from the National Meteorological Station and reanalysis data showed that the temperature increased by more than 1.5 °C from 1980 to 2019. Total precipitation at the Bomi Station from 2000 to 2019 was 10% lower than in the previous 20 years， and the overall precipitation in the basin showed a decreasing trend. The ongoing rise in temperature， coupled with a marginal decline in precipitation， has resulted in sustained glacier mass reduction in the Parlung Zangbo basin.

The migration and accumulation of water during soil freezing， a crucial step of frost damage， has always been a frontier and important topic in the research of frozen soil physics. Since the golden age of water migration research for frozen soil in the 1970s and 1980s， there has been no major breakthrough in classical theory and scientific cognition. Many mechanical problems and key bottleneck problems involved in water migration in freezing soil still cannot be answered accurately. The damage and engineering problems related to frost heave haven’t been completely solved until now. Because of its variability， microcosm and mutation， the phase transition zone （frozen fringe） is still a “black box” in the study of water-heat transport in freezing soils. This paper reviews development history， main research progress and current situation of the research on the driving force and process of moisture migration in freezing soil， and then analyzes the physical principle and basic law of pore-water pressure and soil-water potential related to moisture migration in freezing soil. We also summarize the latest progress and main scientific problems in the theoretical characterization and experimental tests of pore-water pressure and soil-water potential， and analyze three popular theories of the moisture migration， namely capillary-， film-， and vapor-water migration theory. This paper summarizes the key bottleneck problems that restrict the breakthrough of scientific cognition for moisture migration in freezing soil and looks forward to the focus and direction in future research. The research suggests that followings should be focused on in future： 1） Strengthening the invention of instruments and the application of new technologies. 2） Focusing on the physical essence and accurate dynamic monitoring of the driving force of moisture migration. 3） Further understanding of the micro process and mechanism of the moisture migration. 4） More attention should be paid to the process of heat-mass transport and ice-water phase change from the perspective of non-equilibrium thermodynamics. 5） The development of multi-physics coupling simulation and the construction of autonomous open-source computing platform. The purpose of this paper is to systematically review current situation and future research direction， and then promote the development and improvement of the basic theory in the heat-mass transport of freezing soil， and better serve the solution of freezing-thawing disasters and environmental problems in cold regions.

The rapid retreat of Arctic sea ice has attracted extensive international attention， with far-reaching impacts on navigation periods， regional and global climate change， and geopolitical Pattern. It is of great significance to predict Arctic sea ice. In this study， the sea ice concentration， ice age data from NSIDC and ERA5 reanalysis were used to select prediction parameter schemes based on previous studies and coupled Ocean-Atmosphere model results. This study focused on the monthly-scale sea ice prediction. Five machine learning algorithms， including support vector machine （SVR）， Deep forest （DF）， LightGBM （LGB）， XGBoost （XGB） and CatBoost （CAT）， and four stacked ensemble learning models using Bayesian regression， ridge regression， Lasso regression and deep forest as meta models， three tree models LGB， XGB and CAT as base models，as well as deep neural network （DNN）， convolutional neural network （CNN） and spatio-temporal Convolution network （ConvLSTM） were compared and evaluated for the predictions of sea ice concentration and extent in 2000 test set. The results show that ConvLSTM has the best performance in the prediction of sea ice concentration， and lasso stacking ensemble learning model takes the second place. The ensemble learning model improved the prediction performance by about 1% to 4% compared with the three single tree models. In sea ice extent prediction， stacking ensemble learning model performs best. This study has laid an important foundation for the monthly-scale sea ice prediction based on the machine learning.

Dissolved organic carbon （DOC） plays a pivotal role in the global carbon cycle. At present， there are many studies about DOC in permafrost catchments of the Arctic regions， yet some studies about DOC in permafrost catchments of the Qinghai-Tibet Plateau （QTP）. To explore the spatiotemporal variability， sources， the responses to climate warming and permafrost degradation and influence factors of DOC in QTP river， here we conducted field investigations of DOC in 8 catchments （ZMD， TTH， YSP， FHS1~5） in the Yangtze River source region （YRSR）. The seasonal variations and source characteristics of DOC were deciphered using stream sampling， laboratory analyses， flux calculation， stable carbon isotopic technique （{\delta }^{\mathrm{13}}C-DOC）， and hydrological observations. The catchment characteristics including vegetation coverage， and permafrost coverage were used to study the spatial controls of DOC. The results showed that riverine DOC concentrations were low and remained relatively steady through the whole year of the YRSR， with mean concentrations varied from 1.91 mg·L^-1 to 3.69 mg·L^-1. The riverine DOC concentrations of upstream sites were higher than DOC concentrations of downstream sites. The DOC export was mainly concentrated in summer and autumn during thawed season and was much higher than the export in spring and winter. The correlation coefficient between DOC flux and river runoff reaches 0.92， suggesting intimate controls of discharge on DOC flux. The annual DOC flux of YRSR and FHS watershed were 42 539.67 t·a^-1 and 137.33 t·a^-1， respectively. The thawed season DOC flux contributed 68.06% and 79.85% of the annual DOC flux in YRSR and FHS watershed， respectively. The runoff and active layer freeze-thaw cycle process were the main factors that affect the seasonal DOC flux. The carbon isotope of DOC （{\delta }^{\mathrm{13}}C-DOC） also remained relatively steady in different seasons， varied from -37.57‰ to -21.06‰. The carbon isotope of DOC （{\delta }^{\mathrm{13}}C-DOC） was relatively lower in thawed season， which may be due to the waterborne deeper thawed soil organic carbon with relatively depleted {\delta }^{\mathrm{13}}C supplied by subsurface runoff. The isotope was enriched in downstream rather than upstream in different seasons. The source carbon isotope of DOC （{\delta }^{\mathrm{13}}C-DOC） varied from -37.694‰ to -30.411‰， including the main sources of DOC were soil organic matter and C3 plants. This study helps to understand the process and mechanism of riverine carbon transfer and transformation in the permafrost region of the Qinghai-Tibet Plateau.

The Qinghai-Xizang （Tibet） Plateau and adjacent mountainous areas experienced glacial events during MIS 3， and its scale was larger than that of the Last Glacial Maximum （LGM）. At present， the climatic drivers of the glacial advance that occurred during different subphases of MIS 3 on the Qinghai-Xizang Plateau are still not resolved. Gurla Mandhata （30°35′~30°18′ N， 81°05′~81°35′ E） is situated towards the west of the Himalayas and lies in the southwest of the Qinghai-Xizang Plateau. During the Quaternary period， multiple glaciations occurred on the planation surface of Ronggua valley， Muguru valley and Namarodi valley of Gurla Mandhata. Therefore， they well preserved a large number of Quaternary moraines. Field investigation of glacial morphology and existing ¹⁰Be exposure age dating show that multiple glaciations occurred on Gurla Mandhata during MIS 3b and MIS 3c. The glacial history of Gurla Mandhata thus provides an opportunity to investigate the drivers of glacial advance during MIS 3b and MIS 3c. According to the reconstructed chronological framework， we used glacier reconstruction tools to reconstruct paleoglacier surfaces during MIS 3b and MIS 3c of Gurla Mandhata. In addition， the accumulation area ratio （AAR） and area altitude balance ratio （AABR） methods were used to calculate the material glacier equilibrium line altitude （ELA） during MIS 3b and MIS 3c after paleoglacial restoration， which shows that the reconstructed MIS 3b and MIS 3c ELAs were 250~253 m and 348~456 m lower than that of modern times， respectively. By the precipitation-temperature and temperature lapse-rate models， we reconstructed paleoclimatic conditions of MIS 3b and MIS 3c. Model results suggested that MIS 3b temperature was 1.38~4.91 ℃ lower than that of present， with MIS 3b precipitation amounts being 50%~100% of modern values. With a MIS 3c precipitation at 140%~200% of present， MIS 3c temperature was -1.31~1.68 ℃ higher than that of present. Combining our model results with other climatic proxy records on the Qinghai-Xizang Plateau， temperature depression was identified as the main control of MIS 3b glacial advance， and abundant precipitation induced MIS 3c glacial advance.

The artificial ground freezing method is widely used in underground engineering in soft soil areas and has been rapidly developed. However， the complex stratigraphic distribution in soft soil areas and the rheological properties of frozen soil materials also bring challenges to the program design and engineering construction of the artificial ground freezing method under large-scale conditions. Based on the field surveys and the context of an estuary access project in Sanya with pipe curtain freezing method construction， considering the complexity of distribution depth on clay with different plastic states， the tensile and compressive properties of frozen fluid-plastic clay， hard-plastic clay and plastic-silty clay were studied by radial splitting and uniaxial or triaxial compression tests. The results show that the tensile properties of frozen undisturbed clays with three different plastic states are different under the radial splitting. The fluid-plastic clay and plastic-silty clay display weak strain-harden at -5 ℃， and weak strain-soften at -10 ℃ and -15 ℃， while hard-plastic clay exhibits strong strain-soften at three negative temperatures. The frozen undisturbed clays with three different plastic states show weak strain-soften under compression tests. For both the tensile and compressive stress-strain behaviors， the weak strain-harden and strain-soften behaviors of the frozen undisturbed clays with three different plastic states can be described by a modified hyperbola model of deviator stress and axial strain， and the strong strain- soften behavior can be described by a quadratic parabola model. Under the same negative temperature， the tensile strength of the fluid-plastic clay is the weakest and the deformation resistance is the strongest， the plastic-silty clay is secondary， and the hard-plastic clay has the strongest tensile resistance and the weakest deformation resistance. In the distribution range of initial tangential modulus on the frozen undisturbed clays with three different plastic states， it is largest for the plastic-silty clay， secondary for the fluid-plastic clay and smallest for the hard-plastic clay. However， the initial tangential modulus tends to increase with the decrease of temperature. The failure strain of hard-plastic clay has a tendency to increase with the increase of confining pressure， while the failure strain of fluid-plastic clay and plastic -silty clay is relatively discrete and irregular. The shear strength of fluid-plastic， hard-plastic clay and plastic-silty clay can be described by the linear Mohr-Coulomb criterion. The cohesion and internal friction angle of the three soils basically increase with the decrease of temperature. At the same temperature， the cohesive force of fluid-plastic clay is the smallest， the cohesive force of plastic-silty clay is close to that of hard-plastic clay， and for the internal friction angle， it is largest for the hard-plastic clay， secondary for the fluid-plastic clay and smallest for the plastic-silty clay. In this paper， the influence of plastic state on the tensile and compressive properties of frozen undisturbed clay is studied so as to provide data support and reference for the development of underground artificial freezing projects.

Under climate change， snow depths， snow density and snow water equivalent on global scale are undergoing numbers of changes， which further affect the hydrothermal status， biogeochemical cycle process， and structure and function of terrestrial ecosystems. The present paper reviews the current results of snow cover changes including snow depths， periods of snow cover in the Northern Hemisphere， ecologically experimental methods to simulate snow change and their pros and cons， the interaction between snow and ecosystem， and the effects of snow changes on soil nutrient turnover， soil fauna and microorganisms， root biomass and functional traits in three major terrestrial ecosystem types （grassland， shrub and forest） and their mechanisms. Thus， the main conclusions we have are： snow has the most significant warming effects in the depth of between 40 and 70 cm. The higher albedo under no snow or depth less than 40 cm may significantly reduce heat reaching the ground surface， thus soil temperature obviously decreased， and even the frequency and depth of soil freezing and thawing in winter are increased so to compensate for the huge heat loss. When the snow depth is greater than 70 cm， the latent heat of snow melting causes surface heat loss， which reduces soil temperature and weakens the heat preservation effect of snow. Increased snow cover leads carbon and nitrogen loss by accelerating soil carbon and nitrogen cycling， especially in humid habitats， but this is not the case in arid habitats. Snow reduction mainly affects root mortality， microbial activity， soil organic matter accumulation， nitrification and denitrification processes by acting on soil freeze-thaw cycles， thereby affecting soil nutrient turnover. In the grassland ecosystem， the response of soil available phosphorus content to the increase of snow cover is regulated by the ecosystem water conditions， that is， the available phosphorus increases in the humid habitat and decreases in the arid habitats. The increase of snow cover promotes the growth of plant roots in grassland ecosystem by improving the nutrient availability and water availability of shallow soil and changing the root morphological characteristics. The impact of reduced snow cover on plant root growth in ecosystems depends on the dynamic balance between negative effects （root damage and death） and positive effects （increased soil nutrient availability）. Compared with grassland and forest ecosystem， the response of plant root growth to snow cover change in shrub ecosystem was more stable. We also summarize the shortcomings and future trends in the study of effects of snow cover on belowground ecosystems. First of all， the response of phosphorus to snow cover increase is different from that of carbon and nitrogen， and it affects the coupling mechanism of soil carbon， nitrogen and phosphorus through influencing the decomposition rate of organic matter， which is very important for underground ecosystems. In the future， more attention should be paid to the response of soil phosphorus cycle and carbon， nitrogen and phosphorus coupling under snow cover change in different ecosystem environments. Secondly， at present， in the northern hemisphere， the effects of snow cover on root morphology and stoichiometric characteristics of plants in different ecosystems are not comprehensive. Further research on the response of root biomass， morphological characteristics and stoichiometric characteristics to snow cover changes in different ecosystems is still needed. Finally， to reveal the response mechanism of belowground processes in different ecosystems to snow cover changes， it is necessary to carry out more extensive and longer-term continuous field positioning observations and multi-factor comprehensive control experiments.

As one of the major alpine ecosystems， the carbon-water balance status of alpine meadows during the non-growing season is of great significance to the whole ecosystem. However， little is known about the environmental drivers of carbon and water fluxes during this season. Therefore， this study investigates the carbon and water fluxes and their influencing factors during the non-growing season （from Nov. 2022 to Apr. 2023） in alpine meadows in the Qilian Mountains based on eddy observations and meteorological gradient towers. It was found that in the alpine meadow ecosystem of the Qilian Mountains， during the entire non-growing season， the net ecosystem carbon exchange （NEE）， gross primary productivity （GPP）， and ecosystem respiration （Reco） were -18.0574 mg CO₂⋅m^-2， 27.3565 mg CO₂⋅m^-2， and 9.2991 mg CO₂⋅m^-2， respectively. The total evapotranspiration （ET） was 74.8762 mm， which was 15.0762 mm lower than the total precipitation， and the water cycle of this ecosystem was relatively balanced. Normalised vegetation index， photosynthetically active radiation and soil temperature were the main factors affecting net ecosystem carbon exchange during the non-growing season. Whereas relative humidity， precipitation and net radiation were the main factors affecting evapotranspiration in the non-growing season. The results of this study revealed the characteristics of carbon dioxide fluxes and water fluxes during the non-growing season in alpine meadows in the Qilian Mountains and their influencing factors， which provide an important reference for understanding the carbon balance process and water balance in the region and its response to climate change.

The freeze-thaw front within active layer is the interface between the frozen and the unfrozen soil layers during the freeze-thaw process， and the hydrothermal parameters of the soil layers on both sides of freeze-thaw front are significantly different. Therefore， the accurate simulation of the freeze-thaw front movement in the land surface model is essential to improve models both in simulating the hydrothermal characteristics of permafrost and simulating the energy-water balance of the land surface. In this study， the simulation depth of the Noah-MP land surface model was extended to 20 m， and the 4 soil layers of the Noah-MP land surface model was increased to 19 soil layers， and the organic matter scheme and vegetation root scheme were introduced. After these modifications， in order to strengthen the ability of the Noah-MP land surface model on simulating freeze-thaw front， the Stefan method was coupled. Then， the simulation effect of the augmented Noah-MP land surface model on the hydrothermal process of the Xidatan permafrost site was evaluated. Two experiments， CTL experiment （coupled Stefan method） and STE experiment （not coupled Stefan method）， were conducted to simulate the soil temperature and soil liquid water content of 0~20 m in 2012， and the simulation results were verified by the observed daily soil temperature and soil liquid water of 0~3.2 m and the observed yearly ground temperature of 3 m， 6 m and 10 m. The results showed that the freeze-thaw front （0 °C isotherm） obtained by interpolation of soil temperature simulation values had obvious step-like characteristics， and its maximum freeze-thaw depth was larger than the measured. Coupling Stefan method enhanced the ability of Noah-MP model to simulate the freeze-thaw front， so that the model was able to better simulate the change trend and maximum depth of the freeze-thaw front. At the same time， coupling Stefan method also improved the simulation of soil temperature. The mean RMSE and the mean MBE of the soil temperature in the soil layers of 0~3.2 m decreased to 0.89 ℃ （decreased by 44%） and -0.13 ℃ （decreased by 86%） respectively， and yearly ground temperature of 3~20 m was closer to the measured. And it also improved the simulation of the soil liquid water content. The mean RMSE and the mean MBE of the soil liquid water content in the soil layers of 0~3.2 m decreased to 0.06 m³·m^-3 （decreased by 33%） and -0.01 m³·m^-3 （decreased by 67%） respectively， and the soil water melting time of 20 cm， 40 cm， 80 cm and 120 cm in the active layer was closer to the observed. It can be seen that coupling the Stefan method that can better model the movement process of freeze-thaw front in the land surface model can greatly improve the simulation ability of the model， which is one of the effective ways to improve the land surface process model. The results of this study can provide a reference for improving the simulation of the land surface model in the permafrost area. This study will provide a reference for improving the ability of land surface model to simulate hydrothermal processes of permafrost.

Soil water availability is affected by alpine meadow degradation， which profoundly affects soil fauna diversity and ecological function. However， little knowns about the composition of soil fauna in alpine meadow ecosystems. How changes in soil water content affect their distribution and diversity during alpine meadow degradation is still unclear. Our study area was the Shule River headwaters in the western Qilian Mountains， alpine marsh meadow （AMM）， alpine meadow （AM）， alpine steppe meadow （ASM） and desertification alpine meadow （DAM） formed a gradient of degradation of the Shule River headwaters. In June and October 2021， soil mesofauna was collected using the improved Tullgren funnel method in the AMM， AM， ASM， and DAM habitats of the Shule River headwaters， at the same time soil water content was also measured in four alpine meadow habitats. Further， soil mesofauna diversity， Acarina/Collembola （A/C） ratios， and the soil biological quality index （QBS-ar） in four alpine meadow habitats were calculated， and a regression analysis was performed to determine the impact of soil water content on soil mesofauna community indices during the degradation process of alpine meadows in the Shule River headwaters. Results showed that soil mesofauna communities differed considerably between the four alpine meadow habitats， degradation of alpine meadows in the Shule River headwaters strongly affected the density changes of soil mesofauna such as mites （Acarina） and springtails （Collembola）， and their response patterns to alpine meadow degradation determined the assemblage of soil mesofauna community. Furthermore， the density， group richness， and Shannon-Wiener index in soil mesofauna communities in ASM habitats was significantly higher than those in AMM， AM， and DAM habitats in June and October in the Shule River headwaters， respectively. In October， the density and group richness of soil mesofauna communities in AMM habitats was significantly higher than those in AM and DAM habitats of the Shule River headwaters. Changes in soil mesofauna QBS-ar indices of four alpine meadow habitats during two sampling periods are consistent with the Shannon-Wiener index of soil mesofauna community， and A/C ratios over two sampling periods followed the opposite pattern. Alpine meadow degradation caused soil mites to respond differently， and there were seasonal and taxon-specific differences. The density of Oribatida in ASM habitats was significantly greater than those in the other alpine meadow habitats in June and October. As compared to AM or DAM habitats， ASM habitats had a significantly higher density of Mesotigmata in June and October. In June， the density of Prostigmata was significantly higher in ASM habitats than in AM and DAM habitats， and in October， it was significantly higher in ASM habitats than in AM and DAM habitats. Soil springtails responded in the same way to alpine meadow degradation in June and October， and the density of Entomobryidae and Isotomidae significantly outnumbered other alpine meadow species in ASM habitats. Alpine grassland degradation was associated with changes in soil moisture content and soil mesofauna community indices in the Shule River headwaters. During the degradation of alpine meadows， soil water content and the density， group richness， and Shannon-Wiener index of soil mesofauna community showed a significant quadratic curve relationship， and soil mesofauna community indices and soil water content first increased and then decreased. We also found a similar relationship QBS-ar index of the soil mesofauna community and soil water contents with other soil mesofauna community indices. In conclusion， the density， Shannon-wiener index， and QBS-ar index of soil mesofauna community in ASM habitats were higher during the degradation of the alpine meadow， indicating that a certain degree of declined soil water availability due to degradation of an alpine meadow could improve the diversity and ecological functions of soil mesofauna in the Shule River headwaters.

In high-altitude and high-altitude areas， the stability of steep mining slopes containing years of frozen layers is controlled by the mechanical properties of frozen rock layers. Excavation of the strata exposes the frozen rock layers to the air， and coupled with blasting vibrations or mechanical disturbances during excavation， the frozen rock layers gradually soften and heat melt， leading to a decrease in slope stability. With the continued global climate warming， the thermal thawing softening of frozen rock layers accelerates， further exacerbating the risk of instability in mining slopes. The strength of frozen rocks will soften during the hot melt process， which is the most susceptible stage to failure. Studying the thermal thawing softening law of frozen rocks is crucial for evaluating the stability and safety of frozen strata during the thawing process. This article conducted uniaxial compression tests on frozen rocks at different melting temperatures. Based on the restoration of rock pore structure and precise calibration of microscopic parameters， the particle flow software （PFC^2D） was used to simulate the compression failure process of frozen rocks. Based on the analysis of the initiation law and propagation law of microcracks， this paper explores the control effect of pore ice on the thermal thawing softening law of frozen sandstone. The research results indicate that： （1） the strength， elastic modulus and other parameters of frozen rock show a two-stage trend with the increase of temperature. There is a certain temperature between -4 ℃ and -2 ℃， which causes a sudden decrease in the strength and deformation parameters of the sample. （2） As the temperature increases， the failure of frozen rocks at peak stress gradually shifts from being dominated by mineral particle frameworks to being dominated by ice. When the temperature is less than -2 ℃， the degree of damage to the frozen rock skeleton is higher； When the temperature is greater than -2 ℃， the damage to porous ice is more significant. When the temperature is below -15 ℃， the initiation and propagation of microcracks are mainly controlled by the contact strength between mineral particles； When the temperature is between -2 ℃ and -15 ℃， it is mainly controlled by the contact strength between ice particles and ice minerals； When the temperature is greater than -2 ℃， it is mainly controlled by the contact strength between ice particles. （3） By analyzing the supporting and bonding effects of pore ice during the load failure process of frozen rocks， it was found that between -6 ℃ and -4 ℃， the bonding strength between ice particles and between ice minerals rapidly decayed， leading to a weakening of the supporting and bonding effects of ice， which is the essential reason for the rapid weakening of mechanical properties in this temperature range. For high-altitude and high-altitude areas， the thermal thawing softening of frozen rock layers is a core process related to their stability and safety. Therefore， studying the thermal thawing softening law and load failure process of frozen rocks is of great engineering significance.

Lakes are sensitive indicators of climate change， and studying their dynamic changes was of great significance to reveal global climate change and water resources utilization and management. Based on Landsat-5/7/8 satellites and high-resolution remote sensing images， the temporal and spatial characteristics of lake area change during 1989—2021 in Dorsodong Co-Mitijiangzhanmu Co in source region of the Yangtze River were analyzed， and the response of glacial lake and glacier to climate change was discussed. The results showed that during 1989—2021， the average area of Dorsodong Co-Mitijiangzhanmu Co was 1 011.37 km²， which expanded from 872.07 km² in 1989 to 1 119.5 km² in 2021， with an average expansion rate of 8.62 km²⋅a^-1. In terms of interdecadal variation， the lake area expanded most obviously in the early 21th century， especially in the northern， northwestern and southern parts of the lake. Growth was slowest in the 1990s. From 1990 to 2020， the area of Geladandong Glacier shrank from 797.85 km² in 1990 to 766.19 km² in 2020， a decrease of 31.66 km²， with a reduction rate of 1.106 km²⋅a^-1. Between 2015 and 2022， the glacier area decreased by 19.55 km². From 2005 to 2010， the glacier area decreased by 1.50 km². Glacier retreat accelerated from 0.51 km² in 1990 to 2.20 km² in 2010. Before 2004， glacial meltwater caused by rising temperature was the main factor of Dorsodong Co-Mitijiangzhanmu Co lake area change， with an average contribution of 66.8%. After 2004， precipitation played a leading role in the change of Dorsodong Co-Mitijiangzhanmu Co lake area. The average contribution rate of precipitation to lake area change was 57.8%. Through the analysis of net evaporation， it can be found that the net evaporation of Bangor， Shenza and Amdo all showed a downward trend year by year， especially the net evaporation of Shenza Station showed a significant downward trend， and the decline rate was 7.8 mm⋅a^-1. Therefore， it can be found that the net evaporation of Dorsodong Co-Mitijiangzhanmu Co area decreased， and the lake area also increased with the decrease of evaporation. From the perspective of mass balance and lake water volume change， the correlation between mass balance and lake water volume in Geladandong Glacier was 0.69， indicating that glacier mass loss contributes to the increase of lake water volume. The mass balance of Geladandong Glacier lost the most in 2016， the lake area increased by 16.4% and the lake water volume increased by 3.16 Gt compared with 2000. In 2005， the glacier was in a state of accumulation， the lake area was only 0.67% compared with 2000， and the lake water volume increased by 0.9 Gt compared with 2000. From 2000 to 2004， the lake area expanded by 5.1%， and the glacial meltwater was about 4.56 Gt. From 2005 to 2016， the lake area expanded by 6.9%， and the glacial melt water was about 1.94 Gt. It can be seen that the contribution rate of glacier loss to lake from 2000 to 2004 was about 80%. After 2004， the contribution of glacier loss to lake water volume will reach 40%.

The difference of slope aspect in high altitude permafrost region may cause the asymmetry of temperature field on the two slopes， and then cause uneven settlement and longitudinal cracks of infrastructure. At present， the research on the influence of slopes mainly focuses on the monitoring and simulation of the east and west slopes of the Qinghai-Xizang Railway， seldom on the other slopes. But the trend of the linear project in plateau may involve different directions， we cannot promise the railway always in one orientation in the linear engineering and the research on the status of the water and heat difference on other slope aspects is insufficient. In this study， to found a relationship of soil temperature and moisture content in Qinghai-Xizang Plateau， and study the influence of the different slopes. A monitoring entity with eight directions （known as an octagonal platform） was built in the Huashixia permafrost station， the base of the observation of the frozen soil in Qinghai-Xizang Plateau. Soil temperature and moisture content sensors were installed on the meddle of eight slopes in （10 cm， 20 cm， 30 cm） 3 depths near the surface and the top surface. To monitor and study the impact of slope aspect differences on the state of water and heat on the slope near surface. The results shew that the difference of the near surface temperature on the east to west slope was the smallest， the monthly average temperature difference from 0.1 ℃ to 2.3 ℃， and in this difference， the maximum temperature difference occurs in May； The temperature difference near the surface of the south to north slope was the largest， with the monthly average temperature difference of 1.3 ℃ to 7.7 ℃， and the maximum temperature difference occurs in February in this temperature difference. The remained near surface temperature difference of the other two relative slopes was between the east-west slope and south-north slope， and the temperature difference of the northeast-southwest slope was smaller than that of the northwest-southeast slope. From the perspective of temperature difference near the surface of slope， the north-south， whose thermal stability of linear engineering in high altitude permafrost region is better， followed by the northwest-southeast direction， the influence of slope was not significant and the temperature field was symmetrical. Similarly， the overall difference of near surface soil moisture content of the eight slopes， whose data came from 3 depths like the near surfaced soil temperature， and the device of the sensors was the same to the soil temperature， which was the smallest in the orientation of northeast-southwest， and the maximum monthly average moisture content difference was 0.06 m³·m^-3 during the melting period； The east-west slope surface difference was the largest， and the maximum monthly average water content difference in the same period was 0.11 m³·m^-3 This difference seemed on the opposite of the soil temperature. The difference of temperature and moisture content also causes a significant difference in the number of freeze-thaw cycles on different slopes， which has an important impact on the freeze-thaw damage of slope protection materials with rubble. In this research， south slope， whose freeze-thaw cycles times was the top one and higher than the west slope to 88 times， other slopes like east and northwest were close to 60 times， north slope and northeast slope were higher than west slope and northeast was higher than north. In this time， freeze-thaw cycles time in the top surface was the third high in all the slopes. The research results have a certain guiding significance for the future plateau linear engineering planning and the treatment of the different diseases of the solar and lunar slopes of the existing projects.

Freeze-thaw cycles significantly affect the water-heat-deformation interaction process of the soil-rock mixture. Therefore， this paper carried out the water-heat-deformation interaction and unconfined compressive strength test of the soil-rock mixture under unidirectional freeze-thaw cycles. Utilizing a unidirectional freeze-thaw cycling device， the soil-rock mixture sample with a rock content of 30% was prepared， and four freeze-thaw cycles were conducted according to the preset temperature change curve， with each cycle lasting 168 hours. Simultaneously， the mechanical properties of the sample both before and after freeze-thaw cycles were conducted， and the microstructural deterioration mechanism of the soil-rock mixture exposed to freeze-thaw cycles was investigated. The results show that the unidirectional freeze-thaw cycle has a significant effect on the temperature， moisture， and deformation variations in the treated sample. In the process of unidirectional freeze-thaw cycles， the melting rate of the soil-rock mixture is greater than the freezing rate. Meanwhile， the frost depth changes continuously during the freeze-thaw cycles and does not reach a stable state within the limited number of freeze-thaw cycles. The migration and redistribution of volumetric unfrozen water in soil samples occurred during the freeze-thaw processes. At the onset of the experiments， the volumetric unfrozen water content changes under the influence of temperature gradients， causing the liquid water to infiltrate downwards and leading to the accumulation of unfrozen water at the middle location of the sample， while the volumetric unfrozen water content at the top does not undergo drastic changes. Additionally， the first freeze-thaw cycle has a significant influence on the vertical deformation of the soil-rock mixture， and the net deformation of the sample increases first and then tends to be stable with the freeze-thaw cycles raised. Furthermore， the pore structure and internal arrangement of the soil-rock mixture are restructured during the unidirectional freeze-thaw cycles. The repeated expansion and contraction of soils accelerate the destruction of the skeletal structure， gradually reducing the attraction among soil particles and leading to the formation of new fractures. The unconfined compressive strength test shows that the compressive strength and deformation modulus of the sample decrease by 45.31% and 60.92%， respectively.

Climate warming has caused the permafrost degradation， accelerating the formation and expansion of thermokarst lakes or ponds， and further increasing carbon release from permafrost regions. The physio-chemical variables of sediments play a critical role on methane （CH₄） production in the thermokarst lakes and ponds. Quantifying CH₄ production from the sediment of thermokarst lakes and ponds will improve our understanding on the response of methane emissions to climate change over the Qinghai-Tibet Plateau. In this study， based on sediment samples collected from eight thermokarst lakes or ponds in the central and eastern Qinghai-Tibet Plateau， we intended to investigate the relationship between the physio-chemical variables of sediment and CH₄ production under laboratory incubation at 5 ℃， 10 ℃， and 15 ℃， respectively. The results showed that during the 50 days incubation period， the maximum CH₄ production （167.63 μg·g^-1 sediment） was found in MD-3 samples in an alpine wet meadow at the incubation temperature of 10 ℃. The minimum value （0.01 μg·g^-1 sediment） was recorded in the AD-2 sample that under a wet meadow at the incubation temperature of 15 ℃. The CH₄ production rates were higher in the sediments with relatively deeper thermokarst lakes and ponds， higher ammonia nitrogen content and lower the pH values. Meanwhile， the methane production of thermokarst lakes and ponds sediments was much higher than those in the Anduo area due to the high ammonia nitrogen and low pH values in the thermokarst lakes or ponds in the Maduo area. Temperature sensitivity of methane production （Q₁₀） of 5~10 ℃， 10~15 ℃ and 5~15 ℃ revealed that the increasing temperature has a promoting effect on 61.11% of total CH₄ production and an inhibiting effect on 18.06% of total CH₄ production. The results indicated that temperature was an important factor determining CH₄ production in the sediment of thermokarst lakes or ponds. This study investigated the effects of temperature on CH₄ production and their possible influencing factors from the sediments of thermokarst lakes or ponds， and thus provide a scientific basis for evaluating the potential and modeling of greenhouse gas emissions from thermokarst lakes or ponds.

With the rapid growth in demand for clean energy sources like natural gas， the safe storage of liquefied natural gas （LNG） has emerged as a significant challenge. Due to its excellent mechanical properties， concrete has become an important engineering material for LNG storage structures. In recent years， the development of the LNG industry has also propelled research into the ultra-low temperature performance of concrete. The performance of concrete at ultra-low temperatures greatly differs from that at normal temperatures. Current studies indicate that the compressive and tensile strengths， as well as the elastic modulus of concrete， are significantly enhanced in ultra-low temperature environments. Scholars have developed various performance prediction formulas based on experimental results and have explained the mechanism behind the enhanced performance by considering the pore water-ice phase transition process. Ultra-low temperature freeze-thaw cycle experiment results show that concrete has poor frost resistance at ultra-low temperatures， with a significant reduction in mechanical properties after just a few freeze-thaw cycles. The existing conventional freeze-thaw testing methods do not meet the requirements for ultra-low temperature freeze-thaw conditions， and there is a lack of specific standards for testing and evaluating concrete performance under these conditions. Moreover， due to differences in testing equipment and procedures， it is difficult to reference related achievements. Therefore， there is an urgent need to systematically summarize the existing experiment result of concrete performance under ultra-low temperature freeze-thaw conditions， improve the relevant standards for concrete testing under special conditions， and facilitate the development of research on ultra-low temperature concrete through in-depth analysis of a large amount of experimental data. To this end， this paper comprehensively summarizes and analyzes the progress in research on ultra-low temperature concrete testing platforms， mechanical properties at ultra-low temperatures， the mechanism of freeze-thaw damage under ultra-low temperature and large temperature difference conditions， and approaches to enhancing frost resistance and durability， both domestically and internationally. Based on the understanding and contemplation of the current state， future research directions for ultra-low temperature concrete are proposed， aiming to provide references for experimental studies on ultra-low temperature concrete.

Seasonally frozen soil is widely distributed in alpine mountains and its freeze-thaw process has profound effects on hydrological water resources and ecological environment. Research on the changes of freeze-thaw characteristic parameters and influence mechanism of seasonally frozen soil under the background of climate change can provide scientific basis for water resources management and ecological protection in alpine mountains. This study selected southern slope of the Tianshan Mountains as a typical area. Based on the observed daily data from 13 meteorological stations， including data of seasonally frozen soil （e.g. maximum frost depth， freezing period， starting date of soil freezing， and ending date of soil freezing）， air temperature， land surface temperature and precipitation， as well as reanalysis snow cover data since 1958， the spatiotemporal variations of freeze-thaw parameters of seasonally frozen soil and the driving mechanisms were analyzed using multiple linear regression statistics and spatial analysis. The results showed that： （1） The maximum frost depth of seasonally frozen soil ranged from 48.5（±11.4） cm to 96.8（±8.5） cm， the freezing period ranged from 102（±10） days to 141（±14） days， the multi-year average starting date of soil freezing were largely ranged from November 7 to November 19 and the multi-year average ending date of soil freezing ranged from March 1 to March 28. （2） The starting date of soil freezing was gradually postponed， while the ending date of soil freezing was advanced and the freezing period was shortened during 1950s—2010s. （3） The maximum frost depth showed a pattern of “higher altitude， deeper frost depth”， and it has increased significantly in the past decades in the central part of the study area. The freezing period has shortened significantly in most of the study area. （4） According to comparative analysis， temperature （air temperature and land surface temperature） is the dominant factor of the freeze-thaw parameters variation of seasonally frozen soil on south slope of the Tianshan Mountains， and the detailed impact weights are： air temperature accounts for （24.1±3.6）%， land surface temperature accounts for （12.1±3.1）%， precipitation accounts for （9.6±1.7）%， and snow cover accounts for （5.1±1.5）% by quantitative analysis.

Global changes have led to increased temperatures and accelerated glacier retreat， and a large number of radioresistant-antioxidant microbial resources have evolved at the glacier foreland. As one of the important taxa influencing the successional process of glacier frontiers， the study of radiation-antioxidant bacteria in the newly melted moraine habitats in the ice tongue area of glacier frontiers is relatively rare. Based on the phylogeny of 16S rRNA gene sequences， this study not only investigated the diversity of culturable bacteria in moraine habitats in the glacier tongue at the frontier of the Lahugou No.12 Glacier， but also screened and evaluated the strains for their radiation-resistant and antioxidant capacity. The study showed that 259 bacterial strains isolated in the study area belonged to Actinobacteria， Proteobacteria， Bacteroidetes， Firmicutes and Deinococcus-Thermus， among which the highest number of strains was found in Actinobacteria， followed by Proteobacteria>Bacteroidetes>Firmicutes>Deinococcus-Thermus. In terms of species diversity， Actinobacteria and Proteobacteria had the highest species richness. TN， TOC， WC and pH were the main factors affecting the structure of culturable bacterial communities. The strains with D₁₀ （lethality of 10%） dose of UVC irradiation intensity higher than 100 J·m^-2 accounted for 94.9% of the total culturable bacteria， and the strains with D₁₀ dose of H₂O₂ tolerance concentration higher than 10 mmol·L^-1accounted for 100% of the total culturable bacteria； among them， there were 20 strains. And the survival rate after oxidative stress of the radiation-resistant strains was above 90%. In addition， the strains with higher survival rate than Deinococcus-radiodurans R1 after oxidative stress were all radiation-resistant strains with higher than 50% survival rate after 100 J·m^-2 UVC irradiation. This study can not only provide a theoretical basis for the diversity and ecological adaptation of bacteria in the glacier foreland environment， but also provide a rich resource of radiation-resistant and antioxidant glacier bacteria for the subsequent research on the protective mechanism of irradiation and oxidative damage.

As the main body of the terrestrial ecosystem， forest soil plays an irreplaceable role in the global carbon and nitrogen cycles. Under natural conditions， the distribution of forest soil organic carbon and available nitrogen is controlled by factors such as climate and vegetation. Climate usually affects soil water and heat conditions and the distribution patterns of vegetation. Vegetation affects soil carbon and nitrogen content through its own growth and litter decomposition. However， due to the significant regional variation in response to climate warming， limited field observations and large spatial heterogeneity， the understanding of soil organic carbon and available nitrogen content and spatial distribution patterns in the deep soil of different types of permafrost zones remains largely uncertain. At the same time， in the past century， the temperature in the Greater Hinggan Mountains has experienced a warming of more than 1 ℃， and the frozen soil has degraded from continuous permafrost zone to discontinuous permafrost zone， sporadic permafrost zone or island permafrost zone. At present， there is still a lack of research on the spatial distribution characteristics and influencing factors of soil organic carbon and available nitrogen in different types of permafrost zones in the Huma River basin. Therefore， this paper selects three types of permafrost zones in the Huma River basin （discontinuous permafrost zones， sporadic permafrost zones and island permafrost zones）. Based on the spatio-temporal transformation method， we explored the spatial variation characteristics of forest soil organic carbon and available nitrogen in the process of permafrost degradation and revealed the main controlling factors and relative contributions of forest soil organic carbon and available nitrogen in the watershed. In this study， forest soil was selected as the research object. In September 2020， 16 soil profiles with a depth of 0~100 cm were selected for sample collection in discontinuous permafrost zones， sporadic permafrost zones and island permafrost zones in the Huma River basin. The soil samples were collected vertically downward from the surface into 5 layers， 0~20 cm， 20~40 cm， 40~60 cm， 60~80 cm and 80~100 cm in sequence. Three replicates of soil samples were collected at different sides of the same depth of the profile， and a total of 240 soil samples were collected. Each sampling point records basic information such as elevation， longitude， latitude， and dominant species of above-ground and surface vegetation. The effects of environmental variables such as elevation， climate， permafrost zone type and vegetation type on forest soil organic carbon and available nitrogen content were discussed based on the structural equation model （SEM）. The results showed that the contents of soil organic carbon and nitrate nitrogen in the discontinuous permafrost zone were higher than those in sporadic permafrost zone and island permafrost zone， while soil ammonium nitrogen content in the sporadic permafrost zone was higher than that in island permafrost zone and discontinuous permafrost zone. In the vertical profile， the contents of soil organic carbon and available nitrogen contents tended to decrease with increasing soil depth， and there was a significant negative correlation between soil organic carbon and available nitrogen （P<0.05）. The structural equation model clarified that vegetation type and mean annual temperature were the main controlling factor for soil nitrate nitrogen content， and mean annual precipitation had the weakest effect on soil organic carbon content； permafrost zone type and vegetation type were the main controlling factors for soil ammonium nitrogen and nitrate nitrogen content. This study is helpful to understand the distribution patterns and main controlling factors of forest soil organic carbon and available nitrogen in different types of permafrost zones in the Huma River basin， and can provide certain data support for the accurate simulation and estimation of forest soil carbon and nitrogen storage in the watershed in the future.

Taking the unified strength theory as the yield criterion of frozen surrounding rock of tunnels in cold regions under the unloading state， taking into account the influence of the non-homogeneous of surrounding rock and the intermediate principal stress effect on the strength of frozen surrounding rock， an elastic-plastic mechanical model of stress displacement of tunnels in cold regions is established， and combining with the boundary conditions of each region， the elastic solution， the plastic unified solution and the implicit equation of the radius of the plastic zone under the homogeneous and non-homogeneous state of frozen surrounding rock are calculated， discussion and analysis of stress and displacement fields respectively. The research shows that considering the heterogeneity of frozen surrounding rock， the peak value of hoop stress in plastic zone increases by 40%， the range of plastic zone decreases by 40.4%， the displacement of inner wall decreases by 9.3%， the elastic ultimate bearing capacity increases by 41%， and the plastic ultimate bearing capacity increases by 14%， which has a significant impact. The intermediate principal stress effect can give full play to the bearing potential of frozen surrounding rock， the calculated bearing capacity is significantly increased， and the plastic radius is significantly reduced. The results can provide theoretical guidance for tunnel excavation and support design and numerical simulation in cold regions.

Glacial lake outburst floods are characterized by wide range， long duration， high hazard and often accompanied by debris flow. At present， there is a lack of quantitative studies on the dynamic evolution characteristic of glacial lake outburst floods. To this end， the evolutionary characteristics of Cirenmaco glacial lake outburst flood disaster are studied based on field survey and multi-period remote sensing images， and the sediment transport model and hydrodynamic model coupling method are used to reveal the evolutionary characteristics of glacial lake outburst flood erosion. The model is based on the digital elevation model （DEM） topographic data with an accuracy of 12.5 m， simulating the inversion of the 1981 Cirenmaco glacial lake outburst flood dynamics evolution process， comparing with the actual measurement results， verifying the applicability and feasibility of the model， and conducting prediction analysis of the glacial lake outburst again， to quantitatively evaluate the characteristics of flow depth， flow velocity， erosion and deposition of glacial lake outburst flood in the evolution process. The outburst flood scours erosion on the moraine deposit of the Zhangzangbu branch ditch and the loose colluvium of the downstream ditch bank during the evolution， and the high sediment concentration flood gradually evolves into turbulent debris flow. At the 707 landslide， the flow depth is 8~10 m， the maximum flow velocity is 13.7 m·s^-1， and the erosion depth is 8~9 m. The turbulent debris flow formed a barrier dam at the main ditch deposition， with a dam height of 9~11 m， which briefly blocked the Boqu River. turbulent debris flow to the downstream landslide group of Zhangmu port for scouring side erosion， erosion depth of about 10~13 m， easy to trigger large-scale secondary disasters， turbulent debris flow reaches the hydropower station， siltation buried hydropower station intake， resulting in the failure of the hydropower station. On the whole， outburst flooding in the evolution process， the flood water to the upstream ditch bed and ditch bank for strong erosion entrainment， flood peak flow enhanced. In the midstream， turbulent debris flow laterally erodes the gully bank， and the flow velocity increases in the narrow part of the gully， and undercut erosion is enhanced. In the wide part of the channel， low velocity decreases， solid materials deposition， overall reach the balance of flushing and siltation， flood peak flow gradually decay with distance， to the downstream， channel topography open， flow velocity slows down， turbulent debris flow gradually deposition， while the lateral erosion on both sides of the channel， overall for deposition. The model can well reveal the evolutionary dynamics of glacial lake outburst flood disaster erosion characteristics.