Climate change has the potential to alter the global water cycle， resulting in an uneven spatial and temporal distribution of water resources. Furthermore， climate change can result in an increased frequency of meteorological and hydrological disasters. The Qinghai-Xizang Plateau is the most unique geological-geographical-ecological-resource-climatic unit on the Earth， known as “Asia Water Tower” and “The Third Pole”. It is the source of more than ten major rivers in Asia and is known as the “Water Tower of Asia”. With the intensification of global warming， extreme hydrological and meteorological events become more frequent on the Qinghai-Xizang Plateau. However， the complex climate and underlying surface characteristics， including glaciers， snow cover， and permafrost， limit our understanding of the response of extreme runoff to extreme precipitation in this region. Against this background， this study taking the Yarlung Zangbo River basin in the southern part of the Qinghai-Xizang Plateau as an example， this study， based on daily precipitation and runoff data， improves the method of identifying extreme streamflow and utilizes correlation analysis to investigate the relationship between extreme streamflow and extreme precipitation at different probabilities. The results indicate that extreme streamflow typically last 1~2 days in the Yarlung Zangbo River basin， and as the probability decreases， the duration of events correspondingly shortens. Extreme streamflow events with probabilities of 10%， 5%， and 1% exhibit coefficients ranged from 0.07 to 0.28 （P<0.01） with extreme precipitation， and the relationship strengthens with increasing probability of extreme precipitation. At the Nuxia Hydrological Station， the response intensity of extreme streamflow to extreme precipitation in the upper stream of Nuxia Hydrological Station is greater than that at the Nuxia and Linzhi Meteorological Station， with a lag of one day. Additionally， the response of extreme streamflow to extreme precipitation is also influenced by moisture content， vegetation conditions， and soil moisture changes in the Yarlung Zangbo River basin. The improved methods of identifying extreme streamflow in this paper can effectively capture the extreme streamflow events influenced by extreme precipitation in the Yarlung Zangbo River basin， and improve the understanding of the relationship between extreme streamflow and extreme precipitation response in high-altitude basins with complex streamflow sources. At the same time， this paper offers significant theoretical support and scientific guidance for the management of water resources and the regional economic development of the Yarlung Zangbo River basin in the context of climate change.
The accurate simulation and projection of hydrological processes are of great significance for the management and protection of water resources in the Qinghai-Xizang Plateau. However， the limited and uneven distribution of national meteorological observation stations brings a great challenge to the accurate simulation of hydrological processes in plateau areas. Utilizing multi-source precipitation data is an effective means to improve simulation accuracy. In this study， the Golmud River basin in the northern Qinghai-Xizang Plateau was selected as a case study area. The VIC-CAS model was employed using three precipitation products （ERA5， WorldClim， and TPHiPr） to represent the multi-year monthly average precipitation as the background field. The meteorological forcing data was derived through interpolation of observed data from meteorological stations， enabling simulation and analysis of the runoff process in the Golmud River basin. Additionally， future runoff predictions were made by downscaling CMIP6 climate model data. The results showed that the meteorological forcing data obtained by using the annual average precipitation of ERA5 as covariate and TPS interpolation method has the most effective simulation results， The Nash efficiency coefficient （NSE） were 0.71 and 0.70 in the calibration and validation period. The contribution of glacier meltwater and snow meltwater to annual runoff in Golmud River basin is about 14.9% and 32.5% respectively. From 1971 to 2019， under the background of slow increase of annual precipitation and significant trend of temperature rise， the increase rates of snowmelt runoff and glacier runoff were 0.28×108 m3⋅（10a）-1 and 0.03×108 m3⋅（10a）-1， respectively. The annual runoff increased at a rate of 0.54×108 m3⋅（10a）-1， and the increase of snowmelt runoff contributed more than 50%. Under the SSP2-4.5 and SSP5-8.5 scenarios， the average annual runoff of Golmud River basin from 2025 to 2100 is projected to be 10.92×108 m3 and 11.51×108 m3， with an increase rate of 0.38×108 m3⋅（10a）-1 and 0.51×108 m3⋅（10a）-1， respectively. Furthermore， it is projected that snowmelt runoff and glacier runoff in the future period will reach their inflection points in the 2020s and 2030s under both SSP2-4.5 and SSP5-8.5 scenarios， followed by a significant decrease by the end of the 21st century. This study provides valuable insights for simulating runoff in other data-scarce regions of the Qinghai-Xizang Plateau.
The young glacial erosional and depositional landforms beyond the modern glaciers on the Qinghai-Xizang Plateau and its surroundings are direct imprints of the glacier fluctuation during the past several decades or century， and contain important palaeoclimatic and palaeoenvironmental information. Studies of these landforms could provide insights into the spatiotemporal variations of these ancient glaciers. Improved logistics and the development and application of the terrestrial in situ cosmogenic nuclide （TCN） 10Be surface exposure dating techniques， are making it to be possible to investigate the young glacial landforms in the Mount Geladandong area， which locates in the west segment of the Tanggula Mountains， central Qinghai-Xizang Plateau. Here we report on 10Be surface exposure dating of six samples collected from modern glacial landforms associated with the Gangjiaquba Glacier on the eastern slope of Mount Geladandong. Dating results demonstrate that the boulders ［samples from G19-02 to G19-06 and their ages are （125±15） a、（65±13） a、（86±13） a、（96±15） a、（104±15） a］were almost not affected by nuclide inheritance， and the 10Be surface exposure ages could be used to constrain glacier fluctuations during the past century in this high-altitude area. However， a comparison of the ages of a glacially polished surface ［sample of G19-01 and its age is （11 076±688） a］ and boulders indicates that subglacial erosion by abrasion of the rock surface was insufficient （<2 m） to remove cosmogenic nuclide inventories. Thus， the apparent exposure age on the polished surface includes inheritance and overestimates the true age of this surface. Our study suggests that a cautious sampling and interpretation strategy should be adopted with bedrock samples， and the 10Be surface exposure dating techniques have potential applications for dating glacier fluctuations on a 101-year time scale in these high-altitude areas with high 10Be production rates. Meanwhile， this study also provides a new reference for the application of 10Be exposure dating technique in dating the young landforms in high altitude areas.
Against the backdrop of global climate warming and the warming effects induced by human activities， the permafrost on the Qinghai-Xizang Plateau is experiencing accelerated degradation， leading to frequent occurrences of retrogressive thaw slumps. This phenomenon not only directly impacts the regional ecological environment， but also poses a potential threat to the stability of engineering structures. This paper aims to provide a scientific basis for the prevention and prediction of thawing hazards and the assessment of climate change by reviewing the research progress on retrogressive thaw slumps in the permafrost regions of the Qinghai-Xizang Plateau by summarizing the formation mechanism， extraction methods， distribution characteristics， influencing mechanism， as well as the subsequent impacts of retrogressive thaw slumps on environment and engineering. It is concluded that the formation of retrogressive thaw slumps is the result of the interaction of various complex factors and long-term accumulation， often resulting in headward erosion， with diverse development shapes mainly controlled by slope gradients. They present various developmental shapes， mainly including elongated， branched， and multi-headed tongue shapes. Spatially， retrogressive thaw slumps show inhomogeneous distribution， which cluster in engineering corridors on the Qinghai-Xizang Plateau. Their spatial distribution is mainly controlled by terrain and permafrost conditions. Furthermore， retrogressive thaw slumps can alter soil structure and physicochemical processes， affecting regional carbon cycling， thereby increasing global or regional greenhouse gas emissions. Based on high spatial resolution remote sensing images interpretation and unmanned aerial vehicle （UAV） field verification， retrogressive thaw slumps was widespreadly monitored. Currently， research often combines Planet Cube Sat imagery with deep learning algorithms to achieve automatic identification and mapping of retrogressive thaw slumps in large-scale permafrost regions. Deep learning models such as Deep Lab V3+ show a better performance in future extensive studies of retrogressive thaw slumps. With the increasing demand for engineering construction and ecological environment protection on the Qinghai-Xizang Plateau， it is necessary to investigate the formation mechanisms， developmental characteristics， influencing mechanisms， and impacts on the environment and engineering of retrogressive thaw slumps， which will provide a theoretical foundation and scientific basis for engineering planning， prevention of retrogressive thaw slumps， and environmental protection on the Qinghai-Xizang Plateau.
Heilongjiang Province is a typical cold region in northern China， the climate change is complicated by the influence of cold air masses in winter， rich in ice and snow resources， the ice and snow economy is developing rapidly in Heilongjiang Province and the distribution of ice and snow has a significant impact on the social and economic development of the region. On the basis of the previous ecosystem services， the ice and snow ecosystem services in Heilongjiang Province are divided into three primary services： supply services， regulation services， and cultural services， and further divided into eight secondary services： freshwater resources， climate regulation， runoff regulation， farmland drought control， soil entropy conservation， air humidification， atmospheric purification， and ice and snow culture. On the basis of MODIS， statistical data and weather station data， the spatiotemporal evolution of ice and snow ecosystem service value in Heilongjiang Province from 2012 to 2022 was studied. The results show that the snow cover area in Heilongjiang Province showed an increase trend in 10 years， from 108×104 km2 in 2012 to 115×104 km2 in 2022， among which Harbin changed the most， with the change of 18.08×104 km2. Suihua City has changed a little， and the amount of change was 2.30×104 km2. Affected by global climate warming， the total value of ice and snow ecosystem services in Heilongjiang Province shows a trend of the first， and then increasing， decreasing from 3 874.11×108 RMB yuan in 2012 to 3 041.65×108 RMB yuan in 2017， and then increasing to 5 501.92×108 RMB yuan in 2022， showing the characteristics of high in north and south and low in east and west. The spatial distribution of ecosystem service value is basically consistent with the distribution of snow cover area. Among the first-level services， regulation services accounted for the largest proportion of total ecosystem services， reaching 74.11%， and supply services accounted for the smallest proportion， 10.25%， cultural services are in the middle， accounting for 15.64% of the total. Climate regulation services accounted for the largest proportion， 38.46%， and the air humidification service was the smallest， with 0.18%. In the past ten years， except for the reduction of soil moisture preservation and farmland drought control， the value of other services has increased to varying degrees. The ecological contribution of Daxing’anling Prefecture， Heihe City， Jiamusi City and Shuangyashan City is 20.45%， 18.81%， 14.97% and 10.21%， respectively， which are the main contribution factors. It is mainly located in the eastern and northern regions， which is consistent with the spatial distribution characteristics of ice and snow value. At present， the research on ecosystem services is mainly oriented to natural ecosystems such as woodlands and wetlands， and the value equivalent method is used to study the value equivalent method， compared with the functional method， the value equivalent method is simpler to evaluate the value of ecosystem services， but the accuracy is lower. Ice and snow ecosystems are always mentioned， but the spatiotemporal evolution of ice and snow ecosystem services has not been studied. In this paper， the ice and snow ecosystem in Heilongjiang Province was taken as the research object， and the functional quantity method and ecological contribution method were combined with the winter snowfall， snow cover area and snow depth in Heilongjiang Province to estimate the service value of ice and snow ecosystem in Heilongjiang Province from 2012 to 2022， and to explore its spatiotemporal evolution characteristics， so as to improve people’s understanding of ice and snow services and promote the integration of ice and snow economy and traditional economic development， in order to provide reference for the development and utilization of ice and snow resources and related policies in Heilongjiang Province.
The headwaters of the Yellow River Basin （HYRB）， located in the northeastern part of the Qinghai-Xizang （Tibet） Plateau， serves as the main source of water and is highly sensitive to climate change. However， under the background of climate warming， understanding of shifts in precipitation types and the underlying causes remains limited. This study， focusing on this important scientific issue， utilized a parameterized model of wet-bulb temperature （a precipitation pattern recognition model using surface air temperature， surface pressure， relative humidity and elevation） to differentiate precipitation types across the HYRB from 1980 to 2015. Additionally， we analyzed changes in the annual mean precipitation， rainfall， snowfall and snowfall fraction during this period using the Mann-Kendall test and the Sen’ slope estimator. We especially focused on changes in snowfall fraction （SF， defined as snowfall/total precipitation） and analyzed spatial distribution of changes of SF. In order to reduce uncertainty in the differentiation of precipitation patterns by a single product， the analysis is based on weather station observations and multi-source high-resolution meteorological datasets， including the China Meteorological Forcing Dataset （CMFD）， the ECWMF ERA5-Land （ERA5-Land）， and the Multi-Source Weather （MSWX）. Further， we used the partial correlation analysis to conduct mechanism analyses of the underlying causes of long-term changes in SF in terms of both meteorological and circulation factors， including surface air temperature， relative humidity， precipitation， surface pressure， westerly winds， Indian monsoon， East Asian summer monsoon and ENSO. The results indicate that： （1） Annual mean SF exhibited significant （P<0.05） decreasing trends （0.002 a-1）， because there was a decrease in snowfall， but rainfall increased significantly. The precipitation pattern shifted to rainfall. （2） Regionally， the percentage of grids with significant （P<0.05） decreasing trends in SF to the total grids of the HYRB was 98.31% for the ERA5-Land， 96.87% for the MSWX， and 67.62% for the CMFD. In particular， the west-central part of the HYRB exhibited a more rapid decline in SF， with Maduo （Madoi County） and Dari （Darlag County） experiencing the largest decreasing trends. （3） The three gridded datasets differed in their ability to capture the spatial variability of snowfall. Specifically， CMFD showed substantial spatial variation and presented well to spatial differences in trend of SF. MSWX was the second best， while ERA5-Land displayed a notable spatial homogeneity. （4） The annual mean SF was highly correlated with annual mean air temperature and precipitation （P<0.05）， with correlation coefficients r of -0.42 and -0.48. Moreover， westerlies also had a notable influence （r=-0.31， P=0.07）. Other factors had less effect on SF. These findings enhance our knowledge of the effects of climate warming on hydrometeorology. The identified trends and correlations offer theoretical support for the management of regional water resources in the Yellow River Basin and have important implications for water resources management across the HYRB.
In the context of global warming， the cryosphere is the second largest climate system in the world， and its changing characteristics and impacts are attracting more and more attention. In the past decade or more， the cryosphere has been shrinking all over the world. As a major part of the cryosphere， the change of snow cover will have a significant impact on climate change， ecological environment， agriculture and animal husbandry development and water resources balance. It will also affect the ecological environment， the development of agriculture and animal husbandry and the balance of water resources. The snow resources in the southern border area are extremely rich. Global warming accelerates the melting of snow and glaciers in Xizang， resulting in frequent snow and ice disasters such as avalanches， glacial lake outburst and glacial debris flow. It has a great impact on local production and residents' lives. Therefore， accurate simulation of snow depth is of great significance for hydrological processes， climate change， and ecological environment in cold regions. At present， the methods for simulating and monitoring snow depth mainly include ground snow depth observation， inversion of snow depth based on microwave remote sensing， measurement of snow depth based on satellite altimetry technology， and simulation of snow depth using snow accumulation process models. The snow accumulation process model is based on strict physical meaning and can quantitatively simulate the influence of physical environment on snow parameters， quantitatively simulating regional snow depth from a physical sense. The snow accumulation process model mainly includes single-layer snow accumulation model， medium complexity snow accumulation model， and detailed snow accumulation model. The model used in this paper is a detailed snow cover model， which is based on the layering of snow physical properties and can describe the evolution of snow microstructure over time. However， the current snow accumulation process model simulation has problems such as complex parameter settings and high uncertainty. Therefore， it is necessary to find the most suitable parameter combination for the region through parameter calibration， in order to complete the localization of model parameters. This paper innovatively applies the Crocus model for daily snow depth simulation over three years （2019—2021） at Nyalam Station， Purang Station， and Pagri Station in Xizang. Using UQ-Pyl software for model parameter sensitivity analysis and calibration， the paper constructs localized Crocus models for the aforementioned stations. The applicability of the Crocus model at Nyalam Station， Purang Station， and Pagri Station is comprehensively evaluated through correlation coefficients（R）， ratios of standard deviation （SDC）， Nash efficiency coefficients （NSE）， mean differences （BLAS） and root mean square error （RMSE）. The results show： the main sensitive parameters for the Crocus model are 20 at Nyalam Station， 15 at Purang Station， and 13 at Pagri Station； the best snow depth simulation effect of the Crocus model is achieved at Nyalam Station （correlation coefficient of 0.989， ratios of standard deviation of 0.990， Nash efficiency coefficient of 0.978， mean difference of 0.276， root mean square error of 4.280）， followed by Purang Station and Pagri Station； among these， the snow settlement， accumulation， and melting processes at Nyalam Station are well simulated， and Purang Station shows superior simulation effects when snow is thick， while Pagri Station overestimates snow depth in March-April each year， but the trend is generally consistent. The daily snow depth simulation results of three stations basically reflect the daily variation process of snow depth. The localization of the Crocus model in this paper is a useful supplement to the snow process simulation research. This paper hopes to provide scientific basis and information for understanding and revealing the snow process in Xizang Autonomous Region， and also provide strong support for improving the regional climate prediction level， effective management of water resources， disaster prevention and response.
Affected by the severely cold climate， cold region tunnels are often faced with a series of frost damage problems， such as lining ice hanging， freeze-thaw damage or cracking， road icing and drainage system freezing failure， which pose great challenges to the construction and operation of tunnels. The sub-zero temperature environment is the necessary condition for frost damage in tunnels， thus mastering the longitudinal distribution of air temperature in tunnels is the basis and premise of frost damage research and engineering control measures in cold regions. However， various tunnels differ in environmental meteorology， engineering structure and traffic conditions significantly， resulting in obvious discrepancies in the longitudinal distribution characteristics of air temperature， causing many difficulties in accurately predicting and obtaining the longitudinal distribution of air temperature inside cold region tunnels. Therefore， in order to obtain the distribution characteristics and influence factors of air temperature in cold region tunnels， literature research and statistics and analysis methods were used to collect and sort the field measuring data and related influence factors of air temperature inside 52 cold region tunnels in China. According to the distribution characteristics of air temperature inside tunnels in cold regions， they are divided into three types： symmetric， asymmetric and cut-through type， and then the length and burial depth of each type of cold region tunnels are statistically analyzed. On this basis， the influential mechanism of temperature in tunnel site area， geothermal heat of surrounding rock and ventilation in tunnel on air temperature in the tunnels is discussed. Subsequently， the natural wind， engineering construction， mechanical ventilation and traffic factors that cause air flow inside the tunnel were analyzed， and then the primary and secondary influence order of each factor was pointed out. The research results indicate that when the natural environmental factors at both ends of the tunnel portal are basically the same and the elevation difference between the two ends of the entrance is not significant， the air temperature inside the tunnel usually shows a symmetrical distribution. When there is a significant slope inside the tunnel or it is affected by the prevailing wind direction outside the tunnel， the air temperature inside the tunnel often shows an asymmetric distribution. When the tunnel length is short， the burial depth is small and unidirectional wind is prevalent， the air temperature distribution inside the tunnel often presents a cut-through type. In addition， in terms of the primary and secondary factors affecting the temperature distribution inside cold region tunnels， the environmental temperature in the tunnel site area（tunnel entrance and exit） plays a decisive role in the distribution of temperature inside the tunnel， the burial depth of the tunnel determining the geothermal effect has an important impact on the temperature inside the tunnel， and ventilation is the key factor affecting the temperature inside the tunnel. Among the various factors affecting ventilation， natural wind and longitudinal slope design are the main factors influencing the longitudinal distribution of air temperature inside tunnels with slight entrance and exit elevation differences and short lengths and tunnels with significant entrance and exit elevation differences and long lengths respectively， while engineering ancillary structures， mechanical ventilation and traffic factors are relatively secondary. This research will provide reference for the study of frost damage， insulation laying design and operation and maintenance of cold region tunnels.
The analysis of ground temperature monitoring data from the road section with thermal insulation protection measure in the high-temperature unstable permafrost region provides valuable insights into the temporal changes in ground temperature under natural conditions and on the left and right shoulders of the roadbed. This study encompasses the examination of mean annual ground layer temperature， heat budget， and permafrost table variations. Furthermore， the influence of climate warming and the sunny-shady slope effect on the thermal state change characteristics at various locations and depths of the roadbed， as well as the differences between these characteristics and the natural site， are also explored. The results of the study indicate that the sunny-shady slope effect on the left and right shoulders is particularly pronounced. Specifically， the maximum thawing depth of permafrost under the left shoulder is found to be twice that of the right roadbed shoulder. The rate of reduction of the maximum thawing depth is five times that of the right shoulder， and the declining rate of the permafrost table under the left shoulder is also 1.5 times that of the right shoulder. These findings suggest that the thermal state of the left and right shoulders is significantly different under the influence of the sunny-shady slope effect. Additionally， the right shoulder， being situated on a shady slope， may have experienced a stabilizing effect on the permafrost due to the presence of the insulation protection. This is evidenced by the fact that the artificial permafrost table on the right shoulder has been raised. This positive role of the insulation protection in stabilizing the permafrost is crucial for maintaining the integrity of the roadbed in the high-temperature unstable permafrost region. Furthermore， the study reveals that the mean annual ground layer temperature at different locations exhibits an upward trend. This growth rate gradually decreases with the increase in depth. However， it is observed that near the interface between the roadbed and the natural site on the left shoulder， the temperature growth rate is greater than that at a depth of 2.5 meters. This suggests that in this specific location， the soil layer may be subjected to stronger thermal disturbance under the influence of certain factors. To further understand the thermal state changes in the roadbed， a comprehensive analysis of the ground temperature monitoring data is conducted. This analysis involves examining the temporal variations in mean annual ground layer temperature， heat budget， and permafrost table. By comparing these parameters under natural conditions and on the left and right shoulders of the road， valuable insights into the impact of climate warming and the sunny-shady slope effect can be gained. The study also investigates the differences in thermal state change characteristics between the roadbed and the natural site. This includes analyzing the variations in maximum thawing depth and permafrost table declining rate. By quantifying these differences， a clearer understanding of the influence of the sunny-shady slope effect on the thermal state of the roadbed can be obtained. Furthermore， the study explores the role of the insulated berm in stabilizing the permafrost on the right shoulder. This involves analyzing the changes in the artificial permafrost table and the declining rate. In conclusion， the analysis of ground temperature monitoring data from the thermal insulation and protection roadbed section in the high-temperature unstable permafrost region provides valuable insights into the temporal changes in ground temperature under natural conditions and on the left and right shoulders of the roadbed. The study highlights the significant influence of the sunny-shady slope effect on the thermal state of the roadbed， particularly on the left shoulder. Additionally， the positive role of the insulation protection in stabilizing the permafrost on the right shoulder is emphasized. These findings contribute to a better understanding of the thermal dynamics in the roadbed and provide valuable information for the design and maintenance of roadbed in high-temperature unstable permafrost regions.
In recent years， under the “Belt and Road” initiative and the “transportation power” strategy actively promoted by China， the transportation infrastructure in the cold and arid regions of northwest China has been strengthened. As these constructions progress， it was inevitable to cross sections of saline soil， which created a series of challenges and problems for the construction and maintenance of the area. Problems caused by saline soils can not only be problematic during construction， but also have an impact on the long-term maintenance and operation of the facility.In the cold and arid regions of northwest China， the distribution of saline soils poses considerable challenges to infrastructure construction. In these areas， sulfate saline soil， as the most representative saline soil， exhibits a particularly obvious salt frost heave phenomenon when the temperature changes. The fluctuation of temperature， humidity and salt concentration in sulfated saline soil will cause salt heave and frost heave in the subgrade of sulfate saline soil， resulting in uneven uplift， structural relaxation and cracks on the pavement. These diseases not only affect the structural strength and stability of the roadbed， but also may cause hidden dangers to traffic safety and increase the risk of traffic accidents. In view of this， researchers and engineers have been exploring effective treatment technologies and methods to mitigate or eradicate the negative effects of saline soil. Among the many solutions， geopartition technology has been widely recognized and adopted for its economy and practicality. On this basis， this study proposes an innovative water-permeable membrane partition treatment technology， which aims to effectively control the movement of water and salt in saline soil by means of physical isolation and reduce the structural deformation and damage caused by salt frost heave.Based on the theory of porous medium and continuum media， and considering the effects of temperature change and water-salt recharge conditions on the water-salt phase transition in soil pores， a comprehensive water-heat-salt-force multi-field multiphase coupling mathematical model was established. The model covers a variety of transport mechanisms such as the movement of liquid water and water vapor， the diffusion and convection of solutes， the heat conduction， and the mechanical response of soil， which can accurately describe the complex interactions in unsaturated saline soil systems and predict the dynamic behavior of water and salt under actual conditions.In order to verify the effectiveness of the model， numerical simulation technology and laboratory model tests were used to study the water-salt migration law and salt heave deformation characteristics of unsaturated sulfate saline soil under the condition of simulating natural water and salt recharge under the condition of simulating natural water and salt recharge. By comparing the numerical simulation results with the laboratory test data， the accuracy and practicability of the model are confirmed， which provides a solid theoretical foundation for engineering application.In this study， the effects of the water-insulated and breathable membrane on the thermal migration and deformation behavior of unsaturated sulfate saline soil were analyzed. The experimental and numerical simulation results show that the water-permeable layer can significantly inhibit the vertical migration of liquid water and dissolved salts， and effectively prevent secondary salinization and structural damage of soil. In addition， the air permeability of the waterproof air permeable layer solves the problem of gas accumulation under the traditional geomembrane， and avoids the additional engineering problems caused by gas accumulation.In short， the results of this study not only provide a new technical scheme for the treatment of saline soil subgrade in cold and arid areas and other similar areas， but also provide a set of theoretical basis for engineering designers to refer to. The implementation of this new waterproof and breathable membrane treatment technology will significantly improve road stability， prolong the service life of roadbed， and reduce maintenance costs， which has important engineering practice value and wide application prospects.
This study is based on 600 meteorological stations distributed in seasonally frozen ground regions of China， the annual maximum freezing depth and temperature observation data were measured in the past 50 years from 1971 to 2020. In the 600 stations， the annual variation trends of temperature and freezing index were discussed respectively. On the basis of Stefan improved formula， the statistical relationship between the Ea factor （based on temperature freezing index） and factors such as longitude， latitude and altitude were further explored on the standard field， and established an empirical formula. Using the empirical formula to calculate the Ea factor， and verify the accuracy of it. The research shows that the Ea between the empirical formula and calculated by Stefan improved formula （based on temperature freezing index） have good fitting degree at most points， but some points at the boundary of permafrost regions have large fitting differences. In order to solve this problem， the research region was redivided into the general seasonally frozen regions and the transition regions at the boundary between the seasonally frozen regions and the permafrost regions. Correlation analysis was carried out respectively， and the relationship between the Ea and factors such as longitude， latitude， altitude were established. By comparing the observed values， it can be found that fitting degree of these points have been significantly improved. The correlation relationship was introduced into Stefan improved formula （based on temperature freezing index） for further expansion， and finally getting the empirical formula based on temperature freezing’s Stefan improved formula， which was used to calculate the freezing depth of the standard field in seasonally frozen ground regions of China. Since the E factor is relatively complicated to obtain， it is not easy to apply to engineering designs and constructions. For engineering construction sites where it is difficult to obtain the freezing depth， it calculated by using the empirical formula is similar to the observed values of meteorological stations. The combination degree is highly， which can be better provide the freezing depth as a reference for engineering constructions.
With the promotion of the Belt and Road initiative， strategic corridors are being developed in the western cold regions， necessitating numerous tunnel and slope projects in frozen rock formations. The mechanical properties of frozen rock are pivotal for ensuring the safety of construction and operation in such environments， influenced by factors like fracture structure and freezing temperature. However， the impact of fracture structure on the mechanical behavior of frozen rock masses remains poorly understood， particularly the role of fracture ice during rock mass failure. This study aims to elucidate the effects of fracture structure on the mechanical properties of frozen rock masses and the mechanism of ice fractures in the failure process. We selected medium and coarse-grained saturated yellow sandstone as our research subject and conducted uniaxial compression failure tests on sandstone samples with varying fracture dip angles （
In cold and saline soil environments， water-salt wetting-drying cycles and salt-freeze-thaw cycles can cause damage and failure to rock and soil structures. The complex coupling of heat and mass transfer with salt-soil frost heaving characteristics presents significant challenges. Understanding the frost heaving and salt expansion characteristics of sulfate saline soil under freezing conditions is essential for engineering projects and underground structures in saline soil areas. This study investigates the water-salt migration and frost heaving characteristics of silty saline soil under unidirectional freezing in an open system through experimental and theoretical research. Saline soil is a multiphase continuous porous medium composed of solid， liquid， and gas phases. Changes in water-salt content in the soil occur with temperature variations， leading to water-ice phase changes and salt-crystal phase changes， resulting in frost and salt expansion， thus generating frost heave force. The variation of frost heaving force in silty saline soil under unidirectional freezing conditions with changes in lower-end temperature， initial moisture content， salt content， and overlying load is examined， providing insights into the soil's structure and properties. We prepared silty saline soil samples containing sulfate and conducted tests using a self-developed frost heave experimental setup under unidirectional freezing conditions. Waterproof temperature sensors and pressure sensors were used to monitor temperature and frost heave force， respectively. To delve deeper into the frost heave mechanism of silty saline soil， a three-dimensional equation for water， heat， and salt forces suitable for this soil type was established. The coupled equation was based on unsaturated soil seepage， heat conduction theory， and hydrodynamic models， following the laws of mass and energy conservation， considering the effects of salt-water migration and phase change. The stress field equation was simplified from the salt expansion and frost heaving mechanisms. The PDE module of COMSOL Multiphysics software was used to create a coupled model of indoor unsaturated saline soil. In the numerical simulations， initial conditions such as soil moisture content， salt content， and temperature were set. Then， the distribution of temperature， moisture content， salt content， and frost heaving force during the freezing process was iteratively calculated based on the model’s equations. The numerical simulation results were compared with experimental data to validate the model’s effectiveness. From this study， several conclusions were drawn. Firstly， the temperature variation patterns of soil at different freezing temperatures were consistent， with lower freezing temperatures resulting in lower final and overall average temperatures， and a linear change in temperature stability values with depth. Secondly， lowering the lower-end temperature and increasing the initial moisture content promoted frost heaving force generation， while increasing overlying load and soil salinity suppressed frost heaving force. This is because lower freezing temperatures lead to higher temperature gradients during the freezing process， dominantly promoting the increase in water migration， thus facilitating frost heave force generation. Simultaneously， the stress in the frozen soil is mainly induced by the frost heave of in-situ water and migrating water， so higher initial moisture content results in greater frost heave force. An increase in salt content lowers the freezing temperature of the soil， prolonging the initiation of frost heaving. When the temperature drops below the crystallization temperature， the crystallization of ice and salt further affects the rate of water migration， inhibiting the generation of frost heave force. Under external loads， the reduction in pore size between soil particles inhibits water migration and hinders the expansion deformation caused by ice-water phase change， making it more difficult for the entire soil to undergo frost heave deformation and thus suppressing the generation of frost heave force. Lastly， the steady-state frost heaving force of silty saline soil exhibited a linear relationship with freezing temperature and a quadratic parabolic relationship with initial moisture content， overlying load， and salt content. This research provides a new method for understanding the water-salt migration and frost heaving characteristics of silty saline soil during the freezing process. This method can contribute to a deeper understanding of the mechanisms of saline soil damage in cold regions and aid in the selection of appropriate preventive measures.
Frozen soil， as a four phase cementitious matrix， composed of ice cement， soil particles， gas， and unfrozen water. Its strength is greatly affected by temperature. Therefore， the strength properties of frozen soils are more complex than those of unfrozen soils. Strength criteria of frozen soil have a wide range of applications in practical engineering， for example， strength criteria of frozen soil can be used to analyse the frozen soil slope stability. Due to the complexity of frozen soil， it is unreasonable to directly apply the strength criteria of unfrozen soil to the stability analysis and calculation of frozen soil slope engineering. To study the application of frozen soil strength criterion in the analysis of frozen soil slope stability. In this paper， representative frozen soil strength criterion proposed by Liao and Lai is selected from the existed frozen soil strength criteria， the solution of safety coefficient of frozen soil slope is derived firstly by using the Swedish strip method and the selected strength criterion； Secondly， based on the solution of safety coefficient of frozen soil slope is derived by the selected strength criterion， stability calculation and analysis of frozen soil slopes were carried out. The applicability of the selected strength criterion is verified by comparing the calculated results with the existed analysis data of frozen soil slope. The calculated results show that the safety coefficient calculated by the selected strength criterion is close to the original safety coefficient of frozen soil slope， and the error is small. The strength criterion has high accuracy and applicability in calculating the stability of frozen soil slope. Finally， considering that there are many unstable frozen soil slopes in practical engineering， based on the practicality of the project， the current prevention and control measures of frozen soil slope instability are summarized. This study can provide theoretical guidance and reference for designing， construction and maintenance of frozen soil slope in cold regions.
Since the Qinghai-Xizang Railway started operating， the subgrade problems caused by frost heave， thaw settlement and other diseases are more serious and complex than those in ordinary areas. As an important link between road and bridge， the settlement difference between subgrade and abutment seriously affects the safety of railway operation and driving comfort. Combined with the treatment methods of differential settlement in the transition section in general areas， starting from the stiffness difference， and considering the characteristics of the active layer of frozen soil， this paper puts forward the optimized structure of the transition section of pile foundation road and bridge， so as to achieve the smooth transition between the stiffness of subgrade and abutment， and analyzes the long-term effect of the optimized structure. The results show that after embedding two rows of four concrete pile foundations in the transition section subgrade， under the continuous external load and cyclic temperature load， the concrete pile foundation has little effect on the frozen soil temperature field， which can ensure the good stability of frozen soil. The differential settlement of subgrade and abutment and the rail surface angle are greatly reduced. In the global warming environment， through ANSYS simulation and analysis of temperature field and displacement field， it is found that the concrete pile foundation has little influence on the temperature field of subgrade at the transition section， and the treatment effect for differential settlement is very significant.
In order to deeply explore the energy characteristics of frozen calcareous clay and the degree of its influence under the conditions of true triaxial stress path and multi-factor interaction， this study carries out the research of true triaxial compression test of frozen calcareous clay with the help of ZSZ-2000 true triaxial permafrost test platform by adopting the design method of orthogonal test. The results show that the input energy of frozen calcareous clay is relatively low and the growth rate is slow in the initial compaction and linear elasticity stages； as the loading process progresses， the input energy gradually increases and so does the growth rate； At the damage stage， the input energy-equivalent stress curve shows an obvious jumping feature， and the sharp increase in input energy at this time indicates that the change in slope of the input energy curve is a microscopic manifestation of the unsteady development of cracks within the frozen calcareous clay. At the same time， the sudden sharp rise of the input energy curve also indicates the occurrence of instability damage. The damage curve characteristics of frozen clay are consistent with the characterization of the input energy curve， and it is reasonable to use the input energy to characterize the strength of frozen soil samples. Further analysis of extreme variance and hierarchical AHP analysis leads to a consistent order of superiority of the input energy influences： water content ω， mean principal stress coefficient b， temperature T， salinity φ， and circumferential pressure σ3. The moisture content has a significant negative effect on the input energy， the temperature and the mean principal stress coefficient （MPSC） b have a significant positive effect on the input energy， and as the value of MPSC b increases， its effect on the input energy of the frozen specimens tends to decrease， and there is an optimum MPSC b = 0.33 to maximize the increase in the input energy of the specimens. It is proposed to use the damage input energy to characterize the strength of permafrost， which provides an intuitive and comprehensive measure of the damage characteristics of permafrost by quantifying the total amount of energy absorbed by permafrost before reaching the damage state. By analyzing the damage input energy， the energy absorption and dissipation mechanism of permafrost in the stress process can be better understood， which is of practical significance for guiding the construction of permafrost projects and promoting the development of theories and models of permafrost mechanics.
In order to ensure the stability of high steep slate slope in large open-pit stope in western Sichuan Plateau， it is necessary to study the development law of the deterioration and damage characteristics of slate in the high cold area under the action of freeze-thaw cycles in different media， this paper selected the typical slate of the slope of Sichuan Jiajika spodumene mine as the research object， and divided slate into two groups， which were respectively placed in air and water for freeze-thaw cycle tests. The mass， saturated water content， longitudinal wave velocity and stress-strain curve of slate samples were tested after different freeze-thaw cycles； in order to study the deterioration damage mechanism of slate samples under the alternating action of freeze-thaw， the apparent morphology of slate patterns after freeze-thaw test was observed， and the deterioration response degree of each damage factor under the action of freeze-thaw cycle was comprehensively analyzed. The results show that： Physical and mechanical parameters of slate， such as mass， saturated water content， longitudinal wave velocity， compressive strength and elastic modulus， show obvious deterioration response during the freeze-thaw cycle， as the number of freeze-thawing increases， the mass loss rate and water absorption rate of the sample fluctuate up， the longitudinal wave velocity， uniaxial compressive strength and elastic modulus decreased， and the saturation moisture content curve showed negative exponential growth； under the alternating action of freezing and thawing， the expansion and contraction of rock samples due to temperature change， and the internal clay minerals absorb water and accumulate and expand， are the main reasons for the failure of slate； with the increase of freezing and thawing times， the deterioration rate of the slate gradually slows down and finally becomes stable； water is an important factor in the deterioration of slate， under the same number of freeze-thaw cycles， the deterioration degree and speed of slates undergoing freeze-thaw cycles in water are greater.
Global warming has triggered significant changes in the cryosphere， manifested in phenomena such as glacier retreat， snowmelt， and permafrost degradation. These transformations accelerate the conversion of solid water resources into liquid water， disrupting the long-term stability of water resource allocation in the Qinghai-Xizang Plateau’s cold regions. This paper takes the perspective of hydrological effects of cryosphere changes in cold regions， reviewing recent advancements in the understanding of hydrological processes under climate change in the Qinghai-Xizang Plateau. We analyze the current challenges and hotspots in hydrological research specific to the Qinghai-Xizang Plateau. Given that hydrological modeling is a crucial tool for studying the hydrological cycle， the structure and functionality of these models significantly influence the accuracy and direction of hydrological research. This paper summarizes the advantages and limitations of hydrological model algorithms for simulating glacier and snowmelt runoff in the plateau cold regions， and the characteristics of glacier， snow， and permafrost modules in 10 typical hydrological models. We also distill the main issues affecting the simulation accuracy of hydrological process models in this region. Our findings indicate that the limited availability of meteorological observation stations in the Qinghai-Xizang Plateau contributes to uncertainties in data input and parameter estimation. Moreover， a lack of comprehensive understanding of the intrinsic physical mechanisms governing hydrological processes in the cryosphere results in incomplete model structures， further impacting the simulation accuracy of these hydrological models. Finally， we discuss strategies for enhancing the accuracy of hydrological models through the integrated application of multivariate data and machine learning algorithms in cold regions.
In the context of climate change and intensive human activities， the water environment problem of watershed is still one of the severe challenges faced by watersheds management in China and abroad. The Taohe River basin is a typical alpine ecologically fragile basin in China， and the study of changes in water environment elements and their driving mechanisms in Taohe River basin is of great significance to the management of water environment in Taohe River basin. In this paper， the characteristics of precipitation and temperature change trends and mutation features in the Taohe River basin during the period 1990—2018 were analyzed by statistics， linear fitting and M-K trend and mutation tests. The land use transfer matrix was used to analyze the land use change characteristics of the Taohe River basin in 1990 and 2018， and the hydrological and meteorological dynamic characteristics of the Taohe River basin were revealed. On this basis， the SWAT hydrological model database was constructed by DEM， land use， soil and meteorological data， and the monthly scale simulation of runoff and water quality in the Taohe River basin was carried out. The model divided the Taohe River basin into 24 sub-basins. The meteorological data of temperature， precipitation， relative humidity， wind speed and solar radiation were input， and the weather generator was constructed by SWAT-Weather. The runoff simulation period was 1988—2018， and 1988—1989 was set as the preheating period. Due to the limited measured data， the DO simulation period is 2015—2018， and the NH3-N simulation period is 2018. The simulation calibration and verification were carried out by using the SUFI-2 calibration method in SWAT-CUP， and the R2， NSE and PBIAS indexes were selected to evaluate the simulation accuracy of the model. In order to improve the accuracy of the simulation， 22 runoff-related parameters and 37 water quality-related parameters were selected. Based on the simulation results of SWAT model， the temporal and spatial variation trend of runoff in Taohe River basin is analyzed by using water yield index and Slope trend. Finally， by setting different input conditions of precipitation， temperature and land use type， the scenario simulation was carried out for climate change， land use change and comprehensive change of climate and land use， and the driving mechanism of runoff and water quality in Taohe River basin is analyzed based on the scenario simulation results. The results show that： （1） During the past 30 years in the Taohe River basin， The interannual variation of precipitation fluctuates greatly， and the overall trend is upward， with a linear trend of 20.16 mm⋅（10a）-1； There is no significant mutation in temperature， and the overall trend is upward， with a linear trend of 0.55 °C⋅（10a）-1. The land use types in the Taohe River basin are mainly agricultural land， grassland and forest land. All land use types have changed， but the area changed slightly. （2） The SWAT model has good applicability to simulate long-term monthly runoff in the Taohe River basin； the R2 and NSE are generally above 0.6， and the absolute value of PBIAS remains within 15% The accuracy of monthly scale short-term simulation of DO is relatively high， and the accuracy of monthly scale short-term simulation of NH3-N is slightly lower， but the results in the middle and lower reaches meet the simulation accuracy requirements. The water yield in the upper reaches of the Taohe River basin is the highest， and the trend of increase is larger. The water yield in the middle and lower reaches is negatively correlated with the trend of increase in water yield. （3） Runoff is positively correlated with and controlled by precipitation， but negatively correlated with temperature. The runoff yield of each land use is agricultural land > grassland > forest land. The concentration of NH3-N is negatively correlated and controlled by temperature， but positively correlated with precipitation. The conversion of agricultural land to forest land and agricultural land to grassland significantly reduce the concentration of NH3-N. The concentration of DO is negatively related to temperature. and is almost unaffected by the other factors.
In the boreal permafrost region， forest fires not only affect the soil properties of forest ecosystems， but also the permafrost environment， soil organic carbon （SOC） and total nitrogen （TN） contents and storages. The permafrost region in Northeast China is located at the southern margin of Eurasia permafrost zone， which is undergoing extensive degradation under the influence of climate change and human activities. This affects carbon emissions， carbon and nitrogen storages in permafrost region， creating a positive feedback effect on climate warming. In this study， we selected the burned area in 2009 in Alongshan， northern Da Xing’anling Mountains， and the unburned site as a control to study the effects of different fire severity （light and severe burn） on the SOC and TN contents and storages in the permafrost region. The results showed that： （1） SOC and TN contents and storages varied significantly at different fire severities sites， and gradually decreased with increasing fire severity. Compared with the unburned site， SOC contents decreased by 9.78% and 65.11%， respectively； SOC stocks decreased by 9.29% and 68.48%， respectively； TN contents decreased by 1.99% and 52.49%， respectively； and TN stocks decreased by 3.23% and 51.61% at the light and severe burned sites， respectively. With the increase of soil depth， SOC and TN content gradually decreased； SOC storages showed a fluctuation pattern at burned site， increased first and then decreased at light burned site， and gradually decreased at severe burned site； TN storages showed a fluctuation pattern at unburned and light burned sites， and gradually decreased at severe burned site. （2） Soil temperature increased gradually with increasing fire severity. At depths of 0~100 cm， compared with the unburned sites， soil temperatures increased by （0.87±0.18） ℃ and （9.09±0.37） ℃ at light and severe burned sites， respectively； soil moisture contents （SMC） increased by （17.79±3.36）% at light burned site and decreased by （16.71±2.92）% at the severe burned site. Soil temperature and SMC decreased with increasing soil depth. （3） Redundancy analysis （RDA） showed that soil microbial biomass nitrogen （MBN） was the key factor affecting post-fire soil carbon and nitrogen contents and storages， with an explanatory rate of 65.6% （P=0.002）. SOC and TN contents were significantly positively correlated with soil temperature， SMC， NH4+-N， microbial biomass carbon （MBC） and MBN， and significantly negatively correlated with fire severity， soil depth， and pH. SOC and TN storages were significantly negatively correlated with fire severity， soil depth， soil temperature， soil bulk density， and NO3--N. In summary， forest fire has a significant effect on SOC and TN storages， resulting in the loss of SOC and TN storages， altering the distribution pattern of carbon and nitrogen pools， and reducing the stability of soil carbon and nitrogen pools. The study of forest fires on SOC and TN contents and storages is of great significance to the ecosystem carbon balance and the management of ecological environment in the cold region， and it can provide important data references for the SOC and TN storages in the boreal permafrost region.
Wetlands， serving as the third ecosystem situated between water bodies and land， possess significant ecological functions. Due to its unique geographical location and natural environmental conditions， Xizang has formed numerous distinctive natural plateau wetlands. In the Lhasa River basin， the phenomenon of wetland aggregation is particularly pronounced， with the Chabalang wetland being a crucial member of this basin. In recent years， the vigorous development of urban tourism， agriculture， and animal husbandry has led to varying degrees of degradation in wetland area， biodiversity， and wetland functions. To understand the distribution characteristics and pollution status of heavy metals in the surface sediments of the Chabalang wetland in Xizang， 19 samples of wetland surface sediments were collected in August 2021. The concentrations of heavy metals in these sediment samples were determined， and the Nemerow Pollution Index and Potential Ecological Risk Index were employed to evaluate heavy metal pollution in the study area. Additionally， the Absolute Principal Component Scores-Multiple Linear Regression model （APCS-MLR） was utilized for source apportionment of heavy metals. The results revealed that the concentrations of Cu， Cr， Ni， Zn， Pb， Cd， As， and Hg in the surface sediments of the Chabalang wetland were 1.71， 0.56， 0.65， 1.02， 1.31， 1.52， 0.92， and 1.48 times the background values in Xizang， respectively， but significantly lower than the screening values in the Soil Environmental Quality Standards for Agricultural Land （GB 15618—2018）. Compared with other plateau wetlands in Xizang， the enrichment level of heavy metals in the sediment was relatively low. The average Nemerow Pollution Index in the study area was 1.68， indicating a mild pollution level， and the average Potential Ecological Risk Index （RI） was 134.45， representing a slight ecological risk. The APCS-MLR results indicated that Cu， Zn， Pb， and Hg in the sediments of the Chabalang wetland originated from a mixed source of transportation and agricultural activities， while Cr and Ni originated from the soil parent material source， As originated from the geothermal source， and Cd originated from both the geothermal source and a mixed source of transportation and agricultural activities. The primary pathway for sediment pollution in the study area was identified as a mixed source of transportation and agricultural activities. This study elucidates the current status of heavy metal elements in the sediment of the Chabalang wetland， including their occurrence， spatial distribution characteristics， ecological risk levels， and possible sources. It provides an objective understanding of the current environmental quality of the wetland， offering scientific evidence and theoretical support for pollution prevention， control efforts， and sustainable development in the Chabalang Wetland and other similar high-altitude wetlands.
With the gradual expansion of the scale of resource development and engineering construction in the cold region， it will lead to the continuous entry of excessive heavy metals into the cold biosphere， which in turn will affect the soil ecological environment in the cold region. In this paper， we review five aspects of soil heavy metal sources and emissions， spatial distribution， migration patterns， transformation mechanisms， and remediation and treatment in cold regions through literature review. Soil heavy metals in cold regions are significantly affected by human activities， among which industrial emissions， transport， mining development and agricultural activities are important sources of soil heavy metals in cold regions. In addition， natural factors also have important contributions to the content of heavy metals in soil， mainly including permafrost degradation and soil weathering. Heavy metals have different distribution characteristics in the soil and are easy to migrate， which mainly depends on two factors， human activities and soil parent material， the nature of the soil， the properties of the heavy metals themselves and the external environment also play a role in the distribution and migration of heavy metals， Soil properties and characteristics of heavy metals themselves mainly affect the distribution and migration of local heavy metals. The climate environment can make heavy metals carry on long-distance transmission， and then affect the distribution and migration of heavy metals. Heavy metals entering the soil can have different degrees of influence on soil texture， soil temperature， soil hydrology and vegetation， etc. However， there are currently limited research findings on the remediation of heavy metals in cold region soils. Although remediation methods such as solidification and stabilization， biochar and drenching can be used for remediation of heavy metal contamination in some cold-region soils， the influence of seasonal temperature changes on the remediation effect needs to be considered. In view of the impact of heavy metals on the ecological environment of cold-region soils and the difficulty in the remediation of soil heavy metal pollution， future research needs to continue to strengthen the monitoring of heavy metals in cold-region soils， safety risk assessment and timely and necessary remediation and treatment， in order to prevent excessive heavy metals from entering the cold region and causing harm to the cold-region soil environment.
As a sensitive region to global climate change， the climate of the Tibetan Plateau has gradually changed to a warm and humid state in recent decades， and this change and the resulting permafrost changes have directly affected the hydrothermal conditions for vegetation growth. The normalized difference vegetation index （NDVI） is an important variable to characterize the growth of vegetation， and its time-series variation can well reflect the response of vegetation to natural factors. In order to more accurately characterize the impact of climate change on vegetation growth in the permafrost areas of the Qinghai-Tibet Plateau， this study selected the source of the Tuotuo River， where permafrost is relatively continuous， as the study area. Based on Landsat NDVI data， trend analysis， partial correlation analysis， and geographic detectors were used to analyze the response characteristics of NDVI in the vegetation growing season （May-September） in the study area from 2000—2021 to climate change and different terrains and vegetation types. The results show that： （1） NDVI in the growing season in the source area of the Tuotuo River showed an overall fluctuating growth trend during 2000—2021， with a growth rate of 0.013 （10a）-1， of which the NDVI growth rate was faster during the period of 2000—2010 ［0.019 （10a）-1］， and then slowed down to half of the growth rate of NDVI during the period of 2011—2021 ［0.011 （10a）-1］. The interannual changes of NDVI in different vegetation types were analyzed， and it was found that the better the vegetation development， the faster the growth rate of NDVI， among which the fastest growth rate was found in alpine swamp meadow ［0.018 （10a）-1］ and alpine meadow ［0.017 （10a）-1］， followed by alpine grassland ［0.015 （10a）-1］， and the slowest growth rate of NDVI was found in alpine desert grassland ［0.009 （10a）-1］. The analysis of the inter-annual changes of NDVI in different terrain areas showed that the growth rate of NDVI increased and then decreased with the elevation， and the growth rate was faster between 4 700~5 300 m ［>0.02 （10a）-1］；The growth rate of NDVI showed a trend of increasing first and then decreasing with the change of slope， and the fastest growth rate ［0.023 （10a）-1］ was found in the gentle slope area with a slope of 2°~6°； the growth rate of NDVI decreased with the increase of the thickness of the active layer of permafrost， and the fastest growth rate ［0.029 （10a）-1］ was found when the thickness of the active layer was less than 150 centimeters. （2） On the spatial scale， the areas with an increasing trend of NDVI in the growing season in the source area of the Tuotuo River during the period of 2000—2021 accounted for a total of 82.1% of the total area of the study area， and the area with a highly significant increasing trend accounted for 27.0%， which was mainly distributed on both sides of the river at lower elevations and in the areas near the glacier； and the areas with decreasing trend of NDVI accounted for 16.0%， which was mainly distributed in the northern part of the study area in the alpine desert grassland areas in the northern part of the study area. （3） From 2000—2021， the source area of the Tuotuo River showed an overall trend of warming and humidification， and precipitation， air temperature， solar radiation and soil water content all showed fluctuating upward trends in the growing season. 2000—2021 NDVI changes in the source area of the Tuotuo River in the growing season were most significantly affected by soil water content， and warmer temperatures would prompt the melting of the cryosphere and increase soil water content， which would improve the growth status of the vegetation； NDVI changes in the growing season showed the same trend as precipitation； NDVI changes in the growing season showed the same trend as precipitation. NDVI changes in the growing season were positively correlated with precipitation； the correlation between NDVI changes in the growing season and air temperature varied widely in space， with 55.4% of the regions showing a positive correlation and 43.8% showing a negative correlation； and NDVI changes in the growing season were negatively correlated with the solar radiation as a whole. Increased precipitation in the growing season in the source area of the Tuotuo River promoted vegetation growth in the meadow area more than in the grassland area； changes in air temperature promoted vegetation growth in the meadow area more than in the grassland area， and inhibited vegetation growth in the grassland area more than in the grassland area. （4） The spatial differentiation of NDVI in the study area is mainly influenced by soil water content， climate factors and slope， and the influence is greatest when soil water content and slope interact. This paper quantifies the effects of climatic factors and their interactions on vegetation changes using various methods through the study of NDVI changes in the source area of the Yangtze River， which further reveals the influence mechanism of regional climatic and environmental factors on NDVI changes， and provides a new basis for the study of vegetation changes and ecological environmental protection in the Tibetan Plateau region.
Geomorphological and stratigraphic evidence， as well as absolute dating results， show that the Qinghai-Xizang Plateau and its surrounding mountains， which currently hold the most widely distributed area of modern glaciers on Earth （excluding the polar regions）， experienced several significant glacier advances and retreats during the Quaternary. Multiple paleoclimatic proxies reveal that global average temperature decreased， continental ice volume increased， and sea level decreased during marine oxygen isotope stage 4 （MIS 4）， which was an ice stage of the last glacial period. Sporadic dating results suggest that individual locations on the Qinghai-Xizang Plateau have experienced glacier advances during MIS 4. In this article， the term “MIS 4 glacier advance” refers to the glacier advance that has been dated to MIS 4 based on boulder surface exposure ages. It is important to note that the glacier advance itself may not have taken place entirely during MIS 4. However， considering that the Qinghai-Xizang Plateau is home to numerous high-altitude mountains， it remains unclear where else MIS 4 glacier advances have occurred across the entire plateau. Therefore， it is also uncertain whether the MIS 4 glaciation was widespread throughout the plateau. Moreover， the scale of the MIS 4 glaciation has not been thoroughly investigated. To address the aforementioned questions， this study examines and reassesses the 10Be surface exposure ages of boulders from the Qinghai-Xizang Plateau during the MIS 4 and neighboring ice stages. The analysis is further refined using the P-CAAT method， with particular emphasis on the spatial distribution of MIS 4 moraine ridges， the climate-driven mechanisms behind the glaciation during MIS 4， and the scale of glaciers at various locations across the Qinghai-Xizang Plateau. Through statistical analysis and recalculation， the study identifies twelve groups （i.e.， twelve sites） with 10Be surface exposure ages falling within MIS 4. These groups are predominantly found in the western Qinghai-Xizang Plateau， followed by the southern and central regions of the plateau. The 10Be surface exposure ages of boulders， recalculated using the CRONUS-Earth online exposure age calculator （version 3）， were analyzed using the P-CAAT method. Various techniques were utilized to estimate the bandwidth. The formation ages of the moraine ridges were determined by interpreting the peak age and its uncertainty from the Gaussian-component with the highest probability height derived from the program run. Combined with the LR04 curve and a range of paleoclimatic proxies， the study’s findings suggest that the formation ages of these twelve moraine ridges correspond to the period when glacier retreat commenced. This indicates that these abandoned and steadily deposited moraine ridges were formed during the MIS 4 glacier advance. The formation ages of the moraine ridges in the twelve groups varied to some extent， ranging from slightly younger than 60 ka to nearly 70 ka. In summary， this paper presents the following conclusions： （1） During MIS 4， glacier advances took place across various regions of the Qinghai-Xizang Plateau， including the western， southern， eastern， and inner regions. The largest extent of glaciation was observed in the western region， followed by the southern region. In contrast， the inner region experienced the smallest scale of glaciation， which can be mainly related to the divergent amount of glacier recharge. （2） The MIS 4 glaciation on the Qinghai-Xizang Plateau was primarily influenced by variations in summer solar insolation and atmospheric CO2 concentration， and by the migration of mid-latitude westerlies in the Northern Hemisphere. These factors played crucial roles in shaping the dynamics and distribution of glaciers on the plateau. From MIS 5a to the early MIS 4， solar insolation gradually decreased to its minimum value. Consequently， the concentration of CO2 also significantly decreased， resulting in a corresponding decrease in temperature on the Qinghai-Xizang Plateau. Simultaneously， the temperature gradient between high and low latitudes in the Northern Hemisphere increased， leading to a southward migration of the strengthened westerlies. This shift in wind patterns likely brought an increased amount of solid precipitation during the winter months. The combination of lower temperature and increased winter precipitation resulted in a greater accumulation of glacier mass， ultimately driving the advance of glaciers. During the middle and late MIS 4， as the summer solar insolation continued to increase and the concentration of CO2 rapidly rose， the glaciers on the Qinghai-Xizang Plateau commenced a rapid retreat.
The evolution of the East Antarctic Ice Sheet can significantly affect global climate change since deglaciation could contribute much to sea-level dynamics. Thus， studying ice sheet history in this region is the key to understanding the Quaternary global and regional climate change. In recent years， in-situ Terrestrial Cosmic Nuclides （TCN） exposure dating has been gradually applied to the dating of glacial dynamics in the Larsemann Hills area. The data of Quaternary glacial chronology in this area can be employed further to understand the changes in the Antarctic Ice Sheet， and the dating results from this method currently require further refinement. This study summarized and homogenized 196 10Be exposure dating data from 1997 to 2022 of the Larsemann Hills and adjacent areas. These areas include the Larsemann Hills， Vestfold Hills and Rauer Group， Prince Charles Mountains， and Grove Mountains. The sampling information such as sample type， altitude， latitude， elevation， shielding factors， thickness， erosion rate， density， and AMS results were also counted. Based on distinguishing erratic and bedrock samples， we applied the newest model to all of the sample data and recalculated them. Meanwhile， the onset of biogenic sedimentation in the Larsemann Hills has been recorded with bedrock exposure data for further discussion. The results showed that the minimum exposure age of the Larsemann Hills was （4.05±0.81） ka， and the maximum exposure age was （147.01±11.80） ka. The minimum age of exposure in its adjacent areas ranged from （0.32±0.20） ka to （4 096±2 404） ka. The earliest date reaches the mid-Pleistocene， specifically MIS Gi24， spanning the entire Quaternary period. Among all the samples discussed， 17.86% have an exposure age of less than 11 ka， 83.16% have an exposure age of less than 600 ka， and 98.47% have an exposure age of less than 2.8 Ma. We divided the chronology into the Holocene （approximately 11 ka， MIS 1）， the mid to late Pleistocene （approximately 11 ka to 600 ka， MIS 1 to MIS 15）， and the early Pleistocene to late Pliocene （600 ka to 4 000 ka， MIS 15 to MIS Gi24）. We reviewed and summarized the glacial evolution history of the Larsemann Hills and adjacent areas over these periods. For the samples from the Larsemann Hills， we conducted a detailed discussion on the impact of erosion rates. We recalculated the exposure ages of the samples using erosion rates of 0 mm·a-1， 0.0007 mm·a-1， and 0.0015 mm·a-1 （modern erosion rates）. The results showed that erosion rates lead to a significant overestimation of exposure ages， and using modern erosion rates for correction resulted in model saturation. Finally， we discussed the relationship between exposure age and altitude by region. There was a clear pattern in the Prince Charles Mountains and Grove Mountains （alpine setting） but in the Larsemann Hills， Vestfold Hills， and Rauer Group （coastal setting）， glaciers primarily retreated horizontally， showing no obvious pattern. We compared the multi-source homogenized data from different regions， and the following are reached： （1） 17.86% of the samples have exposure ages less than 11 ka， 83.16% of the samples have exposure ages less than 600 ka， and 98.47% of the samples have exposure ages less than 2.8 Ma. In some regions， there are still controversies regarding the ice retreat time determined by 10Be exposure dating. （2） The resultant increase amounts to 51.57% when the erosion rate reaches 0.007 mm·a-1. When calculating exposure ages， it is important to consider reasonable erosion rates. （3） The exposure age tends to decrease with decreasing altitude. However， in low-altitude coastal areas， this trend may be offset by various factors， which require further research to explain. Future dating work in this area should be further promoted， and attention should be paid to erosion rate selection.
In order to investigate the distribution and development of temperature field in the artificial ground freezing （AGF） multi-loop pipe frozen wall， taking the Dongfeng Shaft of Qingdong Coal Mine in Huaibei city as the engineering background， a three-dimensional numerical model of the frozen temperature field was established using field measurement data and COMSOL Multiphysics software. The spatiotemporal evolution of the frozen temperature field in the soil layer of the vertical wellbore under different freezing techniques were analyzed. The research results showed that in the comparative analysis， the three-loop pipe had a faster freezing expansion speed compared to the two-loop pipe. Under the same freezing time， the average temperature of the frozen wall was 0.73 ℃ to 3.32 ℃ lower， and the effective thickness increased by 0.38 m. In the sandy soil layer， the average temperature of the frozen wall was 0.94 ℃ to 1.5 ℃ lower than that in the clay soil layer under the same freezing time， and the effective thickness increased by 0.21 m. Within the calculation scope of the frozen wellbore， the radial temperature field showed a “Saddle-shaped” distribution， with lower temperatures between the loop pipes and higher temperatures on both sides of the loop pipes. In the depth direction of the soil， the temperature gradient of different soil layers with different soil properties was more pronounced. Specifically， the three-loop pipe and the fine sand layer had lower temperatures. Around 30 d， the temperature decrease rate in the Layer II soil （sand layer with three-loop pipe） reached its maximum， about 1.12 ℃·d-1， indicating that it had entered the stage of frozen wall intersection and expansion， while other soil layers were still in the stage of temperature decrease. The arrangement of the “Long and Short Leg” frozen pipes can not only increase the excavation time of the well and shorten the construction period， but also prevent excessive freeze-thaw of the deep frozen soil， reduce the difficulty of excavation， and save construction costs. By using differential freezing method， the freezing was initiated for 30 d， and after the temperature of the seepage brine dropped to -30 ℃， the temperature of the circulation refrigerated brine was maintained， ensuring the complete success of the freezing project. This study can provide reference for similar mine freezing construction.
Artificial freezing method and grouting reinforcement method are two commonly used methods in subway tunnel construction. However， in the process of subway tunnel construction， if a complex bad geology with high water content， low soil strength and high compressibility is encountered， a single construction method sometimes cannot achieve the expected effect. Some experts and scholars have proposed to combine the two construction methods to reinforce the soil by grouting first and then freezing for complex strata. However， there is a lack of theoretical research and engineering experience in the field of subway tunnel construction. Based on this， this paper relies on a turn-back line tunnel project of Guangzhou Metro Line 3， and adopts the research method of numerical simulation. The thermal parameters and mechanical parameters measured in the laboratory test are substituted into the finite element numerical analysis software. Based on the basic theory of hydrothermal coupling， a two-dimensional finite element model is established， and the reliability of the model is verified by the measured data of the project. The development of the thaw settlement temperature field in the actual construction process of the subway tunnel is analyzed， and the development law of the surface thaw settlement displacement field is obtained， and then the best construction scheme to suppress the surface thaw settlement displacement is obtained， the main conclusions of this paper are as follows：The development of natural thawing freeze-thaw settlement displacement field gradually changes with the passage of natural thawing time. In the early stage of natural thawing， the soil began to gradually thaw. At this time， the maximum vertical displacement of thaw settlement is located on both sides of the central line above the tunnel， while the maximum displacement of soil thaw settlement below the tunnel is -39 mm， which is located below the waist of both sides of the tunnel. This displacement is much smaller than the thaw displacement above the tunnel. After 200 days of natural thawing， the growth rate of surface thaw displacement has slowed down. At the end of natural thawing， the maximum thaw settlement displacement of soil reached 340 mm， especially on both sides of the surface.The surface thaw settlement displacement gradually decreases with the increase of the grouting radius， but the effect of continuously increasing the grouting radius on the surface thaw settlement decreases sharply after the grouting radius exceeds 4 m， and when the grouting radius exceeds 5 m， the surface vertical thaw settlement displacement almost does not change with the increase of the grouting radius. Therefore， the grouting radius between 4~5 m has the best control effect on thaw settlement.The incorporation of cement is beneficial to improve the surface thaw settlement phenomenon. When the cement content exceeds 12%， the effect of cement on improving the surface thaw settlement displacement is gradually weakened. Considering the economic and environmental effects， when the grouting-freezing combined reinforcement method is adopted for this project， the cement content is set to 12%， which is the most reasonable for the control of the vertical thaw settlement displacement of the surface. When the pre-grouting-freezing combined reinforcement is adopted in this project， 12% cement content is selected， and the grouting radius is selected as 4~5 m， which can ensure that the project has high safety and economy. Compared with the original construction scheme， the surface thaw settlement can be reduced by 71%.The research shows that the natural thawing temperature field is divided into three stages rapid thawing， phase change stage and stable temperature rise. In the early stage of natural thawing， the soil is in the stage of rapid thawing， and the temperature difference between different positions in the soil is large. Then， with the passage of time， the average temperature of the frozen curtain continues to rise to -2 ℃. At this time， the frozen soil curtain enters the stage of ice-water phase change. At the end of the natural thawing period， the soil enters the stage of stable temperature rise， and the positive temperature is basically restored， and the pore ice in the soil is converted into liquid water.
