Atmospheric water vapor stable isotopes is an important tool to understand regional water cycle. We analyzed atmospheric water vapor stable isotopes and corresponding meteorological data at the Muztagata Station for Westerly Environment Observation and Research from July 26， 2017 to December 10， 2018. We found the significant diurnal， daily and monthly variations of atmospheric water vapor stable isotopes in this region. The δ18O is higher in summer and lower in autumn and winter. at the daily scale， the δ18O is positively related to the temperature and logarithmically related to the specific humidity， and show an inverse relationship with wind speed. Through multiple regression analysis， the results show that the effect of specific humidity on δ18O is stronger than temperature. Using the Hybrid Single-Particle Lagrangian Integrated Trajectory model （HYSPLIT）， we detected the possible moisture source during our observation and found that vapor sources and transport distance significantly impact on fluctuations of atmospheric water vapor stable isotopes. This study is helpful to better understand the temporal and spatial variations and climate controls of atmospheric water vapor stable isotopes dominated by the westerlies， and to provide the necessary data and key knowledge for regional water cycle.
Our research explores the influence of cloud cover on the glacier surface energy balance to better understand snow/ice-air interaction. We use the meteorological data obtained by the automatic weather station the Laohugou Glacier No.12 ablation zone located at the 4 550 m a.s.l. in 2011 to calculate the surface energy components combination with the surface energy balance model. The seasonal variation surface energy components of Laohugou Glacier No.12 are analyzed. We calculate the cloud factor through the cloud parameterization scheme and analyze the influence of cloud on Laohugou Glacier No.12 surface energy budget. The results show that： Net shortwave radiation is the most critical component of the energy source （82 W?m-2， 92%） and net longwave radiation is the primary energy output （-54 W?m-2， 61%）. Both are affected by the cloud， but the former has a more substantial cloud radiative effect （shortwave cloud radiative effect -37 W?m-2， longwave cloud radiative effect 24 W?m-2）. Cloud mainly affects the surface energy budget of the glacier by affecting radiation budget and turbulence fluxes. As the cloud increases， the glacier surface receives less energy， and the ablation rate decreases. Comparing the surface energy budget of glacier surface in other regions， we convinced that the difference depends not only on the air temperature， location， and albedo but also on the influence of altitude and cloud.
Permafrost in the Northern Hemisphere has degraded in different degree under the climate warming. Permafrost degradation may have changed the regional engineering geological conditions， topography and geomorphology， which may have a great impact on regional climate， hydrological and ecological processes， and engineering infrastructures. It is essential to assess and predict the permafrost thermal state accurately by models. Most present models used to simulate permafrost thermal state focus on the effect of ground surface temperature on permafrost changes， so their research direction is the improvement and optimization of the parameterization for air temperature and the physical process in shallow soil layer. However， the influence of the temperature field in the lower part of soil layer， which is strongly affected by historical climate and geothermal energy， on the permafrost simulation is rarely discussed. A comprehensive observation station has been established in Wudaoliang region on the Qinghai-Tibet Plateau by the Cryosphere Research Station on the Qinghai-Tibet Plateau， Chinese Academy of Sciences. Long-term continuous monitoring data， such as meteorological factors， temperature and moisture content in the active layer， ground temperature of permafrost in different depths， were recorded in the comprehensive observation station since 2004. It provides a basic-data support for the establishment of permafrost model and the sensitivity analysis of each parameter for the simulation of permafrost temperature field. In this paper， we established an one-dimensional heat conduction permafrost model to assess the influence of different lower boundary conditions on the simulation of the permafrost temperature field in Wudaoliang. In our model， not only it takes the phase change， differences in thermophysical properties between frost and thaw soil， distribution of underground ice in consideration， but also it is flexible enough to set different boundary conditions. Nine different lower boundary condition schemes were designed to evaluate the influence of different lower boundary conditions on the numerical simulation of permafrost temperature field changes from bottom to top quantitatively. The simulated permafrost temperature fields in different schemes were validated by the measured ground temperature series from 2005 to 2015. Moreover， a reconstructed historical ground surface temperature series reaching back to 1960s and a future ground surface temperature series reaching to 2100 were used to force the model to evaluate the influence of climate change on a centennial scale on the simulation of permafrost temperature field from top to bottom quantitatively. The result shows that the temperature field in the near ground surface layer （<3 m） is completely determined by the interannual climate change， while the temperature field of the permafrost in shallow layer （3~15 m） and transitional layer （15~30 m） is affected by lower boundary conditions significantly. The response of temperature field in the deep layer （>30 m） to the climate change on a centennial scale is not only related to the magnitude of climate change， but also directly related to the phase change heat. Improper lower boundary condition may have a great impact on the calculation of the permafrost degradation degree under large-scale climate change， which may lead to serious misjudgement of the temperature field in the deep layer and permafrost area. Therefore， we give some suggestions about the setting of lower boundary condition according to permafrost simulation in different scenarios as follow： if simulation the thickness or of the active layer or the interannual temperature change in the active layer， the lower boundary condition could ignore geothermal energy （set to zero geothermal flux） and be set in transitional layer or below the depth of zero annual amplitude； if simulating the change of mean annual ground temperature （MAGT） of permafrost for ten years or more， the lower boundary condition should be set to constant geothermal flux and be set below the transitional layer； if simulating the permafrost changes on centennial scale， the lower boundary condition should be set to constant geothermal flux and be set in the deep layer or below the permafrost base. This study would provide theoretical information for the selection of the lower boundary conditions in permafrost simulation researches.
Identifying the vulnerability of social-ecological system from the perspective of the coupling of human and nature is the core issue and frontier area of regional sustainable development research. Based on the Vulnerability Scoping Diagram （VSD） model which is the classical paradigm in the field of social-ecological system and vulnerability， this paper introduced the function formula of Spatially Explicit Resilience-Vulnerability and the diagnostic model of vulnerability factors to analysis the change trends and embrittlement factor of vulnerability of social-ecological system in Sunan County during 2004 to 2016. The results showed that： the exposure index ranged from 0.374 to 0.725， which shows a fluctuation trend of falling-rising-falling. Both sensitivity index and adaptability index show a trend of continuous fluctuating increase. The vulnerability index continued to rise from 0.327 in 2006 to 1.081 in 2014 and then dropped to 0.440 in 2016. The potential risks and fragility factors of the vulnerability of social-ecological system mainly come from the system’s exposure. The index of livestock density， per capita GDP， and vegetation coverage are potential risk factors that affect the fluctuation of system exposure. The support of fiscal expenditure and returning grazing to grass project are the key fragile factor of increasing the vulnerability of socio-ecological systems of this county. Therefore， to reduce the risk the vulnerability of social-ecological system， Sunan County should slow down the economic growth rate， increase the fiscal expenditure and proportion of tertiary industry in GDP， and promote the implementation of grassland ecological protection policies and its long-term sustainable governance mechanisms in the future.
Snow condition is a key indicator to measure the profitability of ski resorts. As a snow-dependent industry， ski tourism is extremely sensitive to climate change. With global warming， it is significant to assess the climate change risk of ski resorts. Snowmaking has become a standard snow management strategy to lessen the dependency on the variability of natural snow conditions. Snow models can accurately simulate snow conditions in ski resorts and provide scientific guidance for the management of the amount of artificial snow and the time of snowmaking. In this paper， we reviewed the main scientific literature on snow simulation for ski resorts. Snow models for assessing the vulnerability of ski resorts have evolved from the earliest empirical linear model to the simplified physical model and then evolved to the complex energy balance model. These models were developed from simulating only natural snow to incorporating snowmaking and grooming. According to different simulation methods of natural snow， snowmaking and grooming， snow models are classified into two categories： site-scale or semi-distributed simulation and distributed simulation. Site-scale or semi-distributed simulation methods usually employed a degree-day model or a simplified energy balance model. In these methods， snowmaking and grooming were accounted for using a few simple assumptions， and the physical properties of snow were represented in a comparatively coarse manner. Distributed simulation methods used multi-layer energy balance snow models to represent the ski resort infrastructure and the specifics of the snowmaking and grooming processes in a considerable level of detail. Moreover， we put forward some points that should be paid attention to when applying snow models to ski resorts in China. The snow models should focus on snowmaking due to the scarcity of natural snow in most regions of China and the various management modes of ski slopes should be considered. Finally， the simplified distributed snow model is considering to be more suitable for snow simulation in ski resorts due to it is unnecessary to provide a detailed description of the internal physical process of snowpack at a ski resort.
Silicon （Si） is an essential nutrient for many marine organisms， such as diatoms， and plays an important role in marine ecosystem as well as carbon cycles. Under the background of global warming， the runoff of meltwater increases rapidly with the accelerated melting of glaciers. Meanwhile， the silicate weathering gradually increases， leading to the release of a large number of Si elements with meltwater and into the downstream， which may affect the primary productivity of marine and lake ecosystems， the global carbon cycle and climate change. Recently， the research of Si related to glacier retreat has become one of the hot scientific issues globally in the background of global climate warming. In addition， we summarized the latest research achievements of Si concentrations and its δ30Si in glaciers， ice sheets and iceberg sources， analyzed the spatial variation characteristics of the Si concentration， found that the Si concentration of glacial runoff is affected by the sampling method， runoff， bedrock characteristics and other factors. Based on summarizing the existing problems in this field， it’s necessary to strengthen the field monitoring， and comprehensively utilize various isotopes method to clarify the transformation process of Si in glacial runoff in the future. Then， it is also important to assess Si fluxes into the downstream ecosystem because of melting glaciers， and thus provide scientific guidance for the significance of glacier Si assessment.
Due to global warming， glaciers in the source regions of Yangtze River faced the risks of rapid melting. Considering that， the satellite images with less cloud cover and higher imaging quality from 1986 to 2015 were selected to analyze the changes of glaciers in this area. On the basis of comprehensive understanding of local environment and image features， the boundaries of the large-scale glaciers were extracted by using band ratio method and adjusting the threshold by human-machine interaction. Additionally， the meteorological and other related datasets were used to investigate the factors affecting the glaciers changes further. The results showed that the area of glaciers decreased by 92.06 km2 during 1986—2015， and the decrease rate was 0.33%·a-1. Specifically， the area of glaciers decreased by 32.95 km2， 27.37 km2， 13.11 km2， and 18.63 km2 during 1986—1994， 1994—2001， 2001—2009 and 2009—2015， respectively， and the corresponding decrease rates were 0.47%·a-1， 0.41%·a-1， 0.17%·a-1 and 0.34%·a-1. Moreover， it can be found that the variation trends of glaciers in different subareas and various sizes were different. Particularly， the degradation and splitting phenomenon of glaciers were obvious in some parts of the study area， which could have impacts on glacier changes. The area of glaciers shrank obviously in aspect of southeast， and increased in aspect of west. As a typical glacier， the area of Ganglongjiama glacier shrank severely from 2001 to 2009， and increased slightly from 1994 to 2001. In addition， the winter precipitation decreased annually during study period， which cannot compensate the rapid melting caused by the increasing temperature.
The Three-River Source Region （TRST） includes the source regions of the Yangtze River， the Lantsang River， and the Yellow River. It has become an important ecological security barrier for China due to special location， abundant natural resources， and important ecological functions. Permafrost is essential to the alpine ecosystem in the TRST as it influences carbon sequestration， water conservation and the stability of ecological environment in cold regions. The changes of permafrost represented by the spatial and temporal variations of freezing/thawing index was considered an important influence on the alpine ecological environment. However， the long-term variation of freezing and thawing indices in the TRSR has not been fully studied over the past due to the sparse and uneven distribution of meteorological stations and observation sites. In this study， based on the monthly average temperature reanalysis data from the University of East Anglia Climatic Research Unit （CRU TS 4.03）， the temporal variation and spatial distribution characteristics of freezing and thawing indices during 1901—2018 in the TRSR were calculated and analyzed using the linear tendency and moving average method， as well as the combination of the spatial analysis in GIS. Preliminary results show that the freezing index generally decreased with a tendency of -1.1 ℃·d·a-1 during 1901—2018. The change of the freezing index could be divided into three stages： decreased at a rate of -3.4 ℃·d·a-1 from 1901 to the 1943， increased at a rate of 8.8 ℃·d·a-1 from the 1943 to the 1966， and decreased again at a rate of -4.3 ℃·d·a-1 from the 1966 to 2018. On the contrary， the variation of the thawing index fluctuated but showed an overall increasing trend of 0.34 ℃·d·a-1， and the slope was 3.3 ℃·d·a-1 from 1901 to the 1943， -3.1 ℃·d·a-1 from the 1943 to the 1981， and 2.9 ℃·d·a-1 from the 1981 to 2018. From the perspective of spatial distribution， the freezing index exhibited a decreasing trend from west to east in the TRSR （from 3 400 to 600 ℃·d）， which is consistent with the decrease of continuality of permafrost and elevation. The thawing index increased from 0 to 1 800 ℃·d from west to east. The freezing index was largest and the thawing index was smallest in the Source Region of the Yangtze River， while the freezing index of the Source Region of the Yellow River was smallest and the thawing index was largest. This study may facilitate studies relevant to the effects of degradation of frozen soil on alpine ecological environment in the TRSR.
Investigation on the distribution， post-deposition process and potential sources of mercury （Hg） in Arctic snow can not only enhance our understanding of Hg biogeochemical cycling in the cryosphere， but it is also imperative for assessing the potential exposure risk of Hg to Arctic environment. Extensive sampling of surface snow was conducted in Alaska between April and May in 2017. Spatial pattern of snow Hg distribution was discussed to explore the post-deposition process of snow Hg and its potential sources. Measurements of total mercury （THg） showed that the spatial pattern of snow Hg was governed by both atmospheric mercury depletion events （AMDEs） and nearby anthropogenic sources. The higher THg concentration was generally observed near the Arctic Ocean （such as Barrow）， and the regions in which were located near the anthropogenic sources. THg concentration showed a downward trend with depth in the Barrow snowpacks. By using correlation analysis among concentrations of major anions and cations， and THg， we concluded that THg in the Alaska snow might be mainly influenced by Arctic sea salt aerosol and anthropogenic emissions.
The hydrothermal change of frozen soil can be described by the soil freezing-thawing characteristic curve （SFTC）， which is the relationship between the unfrozen water content and the subfreezing temperature. A clear understanding of SFTC is crucial for studying the freezing process and coupled water-heat migration in frozen soil. In previous studies， the application scope of SFCT model is narrow， which can not correspond to practical needs. This study considered the influence of initial water contents and solute concentrations on unfrozen water content， proposed a new mathematical model for estimating SFTC. The Nash efficiency coefficient is generally greater than 0.95 based on validating published datasets. The new model performs well in soils with different physical characteristics， such as initial water contents， solution concentrations and it can be better and more widely used compared with the selected five literatures available SFTC models. In addition， sensitivity analysis showed that the factors affecting the parameters of proposed model are related to soil properties such as soil solution and residual water content. The new model enables us to better understand the process of water and heat transfer in soil freezing-thawing process， and serves as a solid theoretical foundation for the engineering and environmental studies and associated numerical simulation in the cold regions under climate change.
A frost mound is any mound-shaped landform produced by ground freezing combined with groundwater movement or the migration of soil moisture. It is characterized by massive ice or ice bounded strata underneath. The height of frost mound that upheaved from ground surface reveals the accumulative thickness of ground ice. So we should avoid frost mounds while engineering constructing. In course of highway building in permafrost regions in China， it was not experienced that highway embankment cut across the frost mound. But this case has encountered by Gonghe-Yushu building highway in Duogerong basin， and it would have threatened embankment stability potentially. In this work， we explore embankment stability and influence of highway constructions on ground ice under frost mound which site at mile K430+070 along Gonghe-Yushu Highway. Employing ground temperature and drilling core， we found that permafrost table under embankment has dropped to interface of ground massive ice along the section of highway cut across frost mound. The embankment would be settled consecutively because of intensely absorbing heat by black asphalt pavement in future. Where would change into thermokarst lake if permafrost has thawed completely.
Wind flow has a significant influence on the process and intensity of the ground-air energy exchange， and it is a key environmental boundary for cooled roadway embankment through heat convection adjustment in permafrost zones. Using field monitoring and numerical simulations， characteristics of wind flow field over roadway embankment in high altitude regions were studied and the effect of embankment height was investigated. The results show that the disturbed zone at the front of the windward slope is a zone with low wind speed. The wind speeds within the height from 0.5 to 2.0 m above the natural ground surface at the windward slope foot are only about 30% of the environment wind speed when the embankment thickness is 3 m. Wind speed above the embankment is greater than that of the environment wind speed at the same height. And wind speed at the windward shoulder is obviously greater than that at the center and the leeward shoulder of the embankment. The disturbed zone behind the leeward slope is a zone with low wind speed. And a vortex will develop in the zone near the leeward slope foot. Wind speed of the vortex is generally 30% of the environmental wind speed. The horizontal range of vortex is about 12 m when the embankment thickness is 3 m， and it increases linearly with increase in embankment thickness. For two separated embankments， wind speed around the leeward embankment is obviously smaller than that around the windward embankment. Taking the discrepancy of wind speed at the windward sloop feet of the two embankments not exceeding 10% of the environmental wind speed （0.35 m·s-1） as the standard， the minimum spacing between the two embankments is about 60 m with their thickness being 3 m. Therefore， in order to avoid the difference of cooling effect caused by the interaction between the embankments during the construction of embankment works， the site construction spacing of the separated convection heat exchange type cooling subgrade should not be less than 60 m.
The hight is an important factor for the long-term thermo-mechanical stability of highway embankment in permafrost zones. Moreover， the embankment with different hights will exert different impacts on the wind flow around it， which would furtherly affect the ground-air energy exchange process. In order to reveal the influence of embankment height on the wind flow around the embankment， the distribution characteristics of wind flow around highway embankment with different heights were investigated with three ambient wind speeds by the wind tunnel test. The results showed that the front of embankment was a deceleration zone of wind flow， and the range of the zone was close related to the embankment hight. When the ambient wind speed was 10 m·s-1， the deceleration zones of the embankment with the heights of 3， 4 and 5 m were 1.8， 2.2 and 2.5 times of the embankment hight （H）， respectively. Within the heights from 0.3 to 1.1 m before the windward side of embankment， the change rate of the wind speed decreased with the increasing ambient wind speed when the flow field got close to the embankment. The upper part of the embankment was the acceleration zone of wind flow， and the increase of the wind speed on the embankment shoulder was positively correlated with the height. There was a reflux zone with low wind speed at the leeward side of the embankment. The greater the embankment hight was， the wider the reflux zone would be. When the ambient wind speed was 10 m·s-1， the horizontal range of the reflux zone was 2.0H， 3.0H and 4.1H corresponding to the embankment hights of 3， 4 and 5 m， respectively. When the wind flow away from the leeward side of embankment， the wind flow recovered gradually to the natural conditions. The horizontal range of the recovery zone of the wind flow was closely related to the ambient wind speed， but had no significant relationship with the embankment hight. The horizontal range of the recovery zone of the wind flow was approximately 9.8H when the ambient wind speed was 10 m·s-1. The study could provide informative reference for the design and construction of embankment equipped with the air-cooled structures， including the crushed rock layers， ventilation ducts and thermosyphons.
The freeze-thaw cycles can cause damage to the infrastructure by affecting the soil structure in cold regions， and the macrostructure change is caused by the freezing and thawing effect that able to change the microstructure of soil. In order to explore the law of soil microstructure change under freezing and thawing， this paper takes Fuping loess with specific dry density as the research object， and performs electron microscopy scanning after 0， 4， 6， 8， 10， 50 and 100 freeze-thaw cycles. Experiments were carried out to obtain microscopic photographs. The microscopic photographs were analyzed from the three aspects of particle morphology， bonding mode and arrangement form， and the particle contact modes appearing in the microphotographs were classified by geometric model. Study the variation of the geometric model with the increase of the number of freeze-thaw cycles. The results show that with the increase of the number of freeze-thaw cycles， the size of soil particles develops toward uniformity， and the average particle size decreases first and then increases. The joint form of particles gradually changes from surface cementation to point contact. The main final regression is the surface cementation； the porosity of the soil decreases during 0~6 times freeze-thaw cycles， and the porosity increases rapidly during the 6~8 times freeze-thaw cycles， and then the number of freeze-thaw cycles increases. The porosity gradually decreases. The variation of the geometric model of granular particles gradually changes from edge contact to grain contact. The variation of geometric model of flat particles gradually changes from initial grain contact to edge contact， and finally evolves to grain contact.
Soil-water characteristic curve （SWCC） is a curve describing the relationship between soil matric suction and water content， which is the core of unsaturated soil mechanics research. Matric suction is an important stress state variable of unsaturated soil， which controls the balance between soil structure and shrinkage membrane， and is an important factor affecting mechanical properties of unsaturated soil. Loess containing sodium sulfate is widely distributed in Northwest China， and has been widely used in engineering practice. The relationship between the matric suction of loess and the content of sodium sulfate is studied by experimental test and theoretical analysis， and the law of the matric suction of loess like sodium sulfate saline soil affected by sodium sulfate is obtained. Taking the typical sodium sulfate contained in loess in Northwest China as the variable factor， the matric suction of Lanzhou loess and sodium sulfate saline soil with different salt content was measured by filter paper method， and the soil water-characteristic curve was drawn. The results show that the existence and content of sodium sulfate have a great influence on the matric suction of loess， and the higher the salt content of sodium sulfate saline soil is， the greater the matric suction is. The influence of sodium sulfate on the matric suction of loess is different under different water content： when the water content is high， the influence of sodium sulfate on the matric suction of loess is small； when the water content is low， the influence of sodium sulfate on the matric suction of loess is great. Based on unsaturated soil mechanics theory and surface physicochemical theory， assuming that the salt solution in soil does not affect the pore structure of soil， considering the influence of salt solution in soil on the capillary part and adsorption part of matric suction， a semi empirical formula is obtained， which can be used to calculate the relationship between salt content in soil and matric suction. The Kelvin radius and the thickness of adsorbed water film corresponding to each suction in the formula are calculated by the method introduced in unsaturated soil mechanics. The measured data are used to fit the three parameters in the formula. The matric suction corresponding to each water content of sodium sulfate saline soil with different salt content is calculated by the semi empirical formula， and the soil-water characteristic curve is drawn. The results show that the calculated curve is in good agreement with the experimental curve， which shows that the formula can well describe the relationship between different salt content and matric suction in saline soil. In this paper， the law of the influence of sodium sulfate content on the matric suction of loess is obtained through experiments， and the law is expressed quantitatively by theoretical derivation and semi empirical formula， which provides certain theoretical basis and data support for the future engineering practice in this area. The semi empirical formula obtained in this paper can also be applied to the calculation of soil-water characteristic curve of other saline soils， but it should be noted that the formula will not be applicable when the concentration of salt solution in soil reaches the saturation concentration.
To improve the anti-freeze and heat preservation performance of tunnels in the seasonally frozen regions， the freezing range of surrounding rock is often reduced by laying organic insulation layer such as polyurethane at present. However， due to the rapid aging speed of organic materials during the process of freeze-thaw cycles and the lack of scientific basis for insulation design， some tunnels repeatedly appear freezing-thawing damage during long-term operation. For example， the problems of lining water seepage， hanging ice， tunnel bottle water gushing， pavement freezing， lining cracking， crumbling， spalling， etc. This paper analyzes the effect of current insulating measures by establishing the heat-fluid-solid coupling calculation model， in which the Guigala Tunnel in Tibet is taken as subject investigated， and the result showed that surrounding rock within a certain length of the entrance will still undergo freeze-thaw cycles during the operation period. The boundary temperature of the surrounding rock at the section vault at a distance of 5 m from the entrance was only -0.91 ℃， and the frozen length of the key point was more than 500 m from the entrance on February 15th of the 20th year after the tunnel operation， which seriously affected the safety and stability of the tunnel structure. For the sake of meeting the requirements of antifreeze insulation， a new type of inorganic material—aerogel felt was proposed to reinforce the insulation structure of the tunnel. The material had excellent thermal insulation， flame retardant and durability， at the same time the paving was simple and easy to operate. In order to determine the length and thickness of the aerogel felt to be laid during the Guigala Tunnel operation， the radial and longitudinal temperature of surrounding rock as well as the air temperature in the tunnel were compared in detail under different thickness of aerogel felt. The evolution law of the surrounding rock and the air in the tunnel under different conditions was summarized， and the aerogel felt at the most unfavorable time was determined by data fitting. The relationship between the thickness and the vertical freezing length of the key positions of the surrounding rock was changed exponentially. According to the fitting formula， the relationship between the length and thickness of the aerogel felt should be laid out from the depth of the portal to the depth， which was the best reinforcement and maintenance method for the tunnel insulation structure. This work can provide technical support for the pre-reinforcement design of anti-freezing and insulating in Guigala Tunnel， which not only ensure the safety and economy of the tunnel structure， but also provide a reference for the insulation structure design， construction and maintenance of tunnel in seasonally frozen regions.
Due to the seasonal change of climate and day/night cycle， it is inevitably that the shallow soil is influenced by freeze-thaw cycles in cold regions. The freezing process will cause the soils to expand， and the thawing process will lead the soil to settle. At the same time， the freeze-thaw cycles can induce significant changes in the physical and mechanical property and structure of frozen soils， which will seriously threat the serviceability of some structures. The stress field of soil is one of the key factors that affects the deformation of soil during freezing-thawing process. In order to research the impact of freezing-thawing cycles on the deformation and frost heave stress characteristics of foundation soil in cold regions under different overburden pressure， the two groups frozen-thaw cycles tests are conducted. The first group tests were conducted under the constant overburden pressure in the process of freezing-thawing. In order to investigate the variation of frost heave stress in the frozen-thaw cycles process， another group were carried out under constant displacement defined. It is discovered that the freeze-thaw cycle can lead the soil expand under the 10 kPa overburden pressure， and it is compressed when the stress is 50 kPa or 100 kPa. The larger the stress is， the large settlement deformation is. The soil gradually forms a stable structure under the special stress field with increasing freeze-thaw cycles， which leads to the amount of frost heaving equal to that one of thawing settlement， namely， the coefficient of freeze-thaw stabilization is near to 1. With increasing the number of freeze-thaw cycles under the constant displacement the maximum vertical frost heave stress decreases continuously. From the measured results， it is observed that the developing trend of frost heave stress is similar with that of pore water pressure. The results indicated that frost heave stress increasing in the freezing process will compress the soils structure， which lead to the pore of the soil smaller， and it shows the pore water pressure rising. The pore of the soil will partly resilient in the thawing process， which shows the pore water decreasing. According to the principle of effective stress in frozen soil， the internal microcosmic stress mechanism of soil deformation in freezing-thawing process can be revealed by studying the distribution of pore water pressure near to the freezing-thawing interface. At the same time， the principle of frost heave stress generation in freezing process was explained under microscopic scale. Finally， through analyzing the distribution of pore water pressure under constant overburden pressure， the maximum value of frost heave stress was determined under different unfrozen water content of frozen fringe. In engineering practice， especially for water supply channels， frost heave stress is the main reason for the failure of lining structure. Therefore， the determination of the maximum frost heave stress in the process of freeze-thaw cycle is of great significance to propose a reasonable design code.
Red-mudstone is a kind of special soil. When the weathering red-mudstone was used as the filling materials，lots of engineering problems appeared， such as the uneven settlement， the lower bearing capacity and shoulder of road gushing， etc. In order to improve its mechanical properties， a certain amount of lime （Ca（OH）2） is usually added in engineering. However， the cyclic drying and wetting during operation has a great influence on the engineering properties of roadbed soil due to periodic variation of rainfall and draught. A series of unconfined compression tests were conducted to study the influence of wetting-drying cycle on the unconfined compressive strength of the stabilized red-mudstone with different content of lime. The test results show that the unconfined compressive strength of the stabilized red-mudstone increases with the increase of the content of lime. The influence of wetting-drying cycle on the unconfined compressive strength of the stabilized red-mudstone is related to the content of lime. When the content of lime is low， the compressive strength of the stabilized soil decreases with the increase of the number of wetting-drying cycles. When the content of lime is high， the unconfined compressive strength of the stabilized soil increases significantly with the increase of the number of wetting-drying cycles. The destruction model of untreated red-mudstone specimens is plastic bulging failure. Due to the increase of soil strength and brittleness， the lime stabilized red-mudstone specimens show brittle shear failure. After the wetting-drying cycle， the destruction model of lime stabilized red-mudstone specimens is cone-shape failure.
Yahuokou landslide occurred in Zhouqu County on July 16， 2019， which is located in Zhouqu-Huama active fault zone. The landslide is 1 920 m long， 50~190 m wide and 212×104 m3 in volume. It is a typical large-scale accumulation layer landslide in the long fault fracture zone. The landslide developed gradually from top to bottom along the original old sideway. The landslide developed gradually from top to bottom along the old slide. The sliding lasted about 50 days， with the maximum sliding distance of 500 m. The landslide damaged X414 County Road and chicken farm， and made Minjiang River semi blocked， affecting flood safety in flood season. The geological environment， development history， classification and block characteristics， sliding process and causes of Yahuokou landslide are systematically studied through field monitoring， UAV （unmanned aerial vehicle） measurement， geotechnical test and the historical data of the landslide. Yahuokou landslide can be divided into two grades： upper and lower， which are relatively independent. The upper landslide can be divided into two parts： The South Branch and the North Branch. On the basis of the old landslide， the North Branch of the upper landslide has been active before 2013. On July 16， 2019， the South Branch of the upper landslide began to slide violently and pushed the front of the North Branch of the landslide together to revive the slide. About 10 × 104 m3 sliding mass of the upper landslide was loaded on the lower landslide， and the lower landslide gradually expanded from the top to the bottom on July 24. The lower landslide can be divided into three sections： The upper， middle and lower. The front edge of the landslide reached the edge of Minjiang River on August 10， making Minjiang River semi-blocked. Yahuokou landslide has the characteristics of long history， long sliding time， low sliding speed and differential sliding in different grades and blocks. The main causes of landslides are the long-term active deep fault zone and fluted terrain， the weak and slippery gray black weathered and broken carbonaceous slate， the strong action of groundwater and atmospheric precipitation， and the accumulation and loading of landslides on both sides.
Debris flow disasters are widely distributed in high-elevation or high-latitude mountain areas （referred to as debris flow in high mountains， DFHM）， especially in areas where mountain glaciers and permafrost have receded rapidly. In the context of global climate change （temperature rising and higher possibility of occurrence of strong precipitation events）， the actual hazards and potential risks of DFHM have drawn increasing attention. Unlike debris flows developing in low elevation environments which are mainly triggered by precipitation， the outbreak of DFHM is also significantly affected by temperature conditions， making its formation mechanism more complicated. Although a lot of research has been carried out on DFHM at home and abroad， effective prediction and early warning and prevention and control are still very difficult. It is of great scientific value and practical significance to further strengthen the starting conditions and mechanisms of glacial debris flow. This review summarizes the recent progress on initiation study of glacial debris flow， including： the relationship between glacial debris flow outbreak and meteorological conditions， causes of typical DFHM outbreaks， failure mechanisms and models of glacier （rock， or moraine deposits）， and characteristics of moraine initiation. In the future， we should strengthen the acquisition of high spatial-temporal resolution meteorological data and the analysis and judgment of dynamic changes of material sources， and further clarify the formation conditions and development process of debris flow in alpine areas from the perspective of dynamic mechanism.
The source region of Shule River basin was selected as the study area， and the samples of river water， spring water and snow were collected between December in 2018 to November in 2019. Hydrochemical characteristics and controlling factors of different waters were analyzed qualitatively by Gibbs figure， Piper Triangular diagram and the ratio of ions. The contribution of rain （atmospheric）， evaporite， carbonate， and silicate weathering in different seasons was quantified by mass budget equations of cations （the forward model）. The results showed that the concentration of the total dissolved solids （TDS） was ordered by spring water>river water>glacier meltwater>snow water. Hydrochemical types of river water were HCO3--Mg2+?Ca2+ in winter， HCO3--Ca2+?Mg2+?Na+ in spring and HCO3--Ca2+?Mg2+ in summer and autumn. Hydrochemical types of spring water and snow water were HCO3--Ca2+ and HCO3--Ca2+?Mg2+， respectively. Due to the influence of many factors， the temporal and spatial variations of major ions in river water were different. Hydrochemical composition of river water and spring water was controlled by rock weathering， snow water was controlled by rock weathering and precipitation. The major ions of river water and spring water were derived from carbonate weathering which dominated by dolomite， silicate weathering and evaporite dissolution of halite， gypsum and sulfate minerals. The contribution of cations from atmospheric and rock weathering was different in different seasons. On the whole， the cations in river water were mainly derived from silicate weathering in winter and spring， the contribution ratio were 36.21% and 35.54%， respectively. The contribution ratio was ordered by carbonate>silicate>rain>evaporite in summer and carbonate>silicate>evaporite>rain in autumn. In general， the cations of river water mainly come from carbonate and silicate weathering.
In order to understand the variation law of extreme precipitation in flood season of the Yarlung Zangbo River basin， the quantile of extreme precipitation in a certain recurrence period was calculated by generalized Pareto distribution （GPD） method. The results indicate that the threshold at the 99th percentile was the optimal threshold for all stations in the basin. The super-threshold sequence of all stations passed the stationarity test of M-K and without an obvious mutation. The fitting effect passed K-S test， and the theoretical frequency of extreme precipitation fitted at each station was mainly consistent with the measured frequency. The large values of the scale parameters were located in the downstream of the basin， which indicates that the extreme values fluctuate considerably. The positive area of shape parameters was located in the middle and upper area of the basin， which indicates that the probability of record-breaking precipitation event was relatively high. The fitting results were consistent with the actual observations. According to the extreme precipitation values that occur once every 5 years and once every 10 years， except for the Lhaze station， the extreme precipitation values in other regions of the Yarlung Zangbo River basin exceed 30 mm， and the extreme precipitation values in Shigatse region reach 50 mm. The precipitation extremes that occur once in 20 years and once in 30 years increase very slowly in all regions. In comparison with the actual observation， it can be concluded that the level of recurrence period calculated by GPD fitting was basically in line with the reality and has certain rationality.
Glaciers are known global reservoirs for cold-adapted microorganisms. Because of the special function of cryogenic microorganisms in glacial habitats， the cold-adapted yeast biodiversity is also of increasing interest to microbiologists. The aim of this investigation was to assess the occurrence and biodiversity of airborne yeast in the air and aerosol at different elevations on the surface of the Urumqi Glacier No.1 in the Tianshan Mountains， a well-known continental glacier （Northwest China）， and to test their temperature characteristic of growth. By using membrane filtration， air aerosol were collected at three sites on the surface of the west branch of the glacier （the altitude ranging from 3 950 to 4 090 m a.s.l.）. Isolation and purification of yeast were performed by four different agar media， and all yeast strains were preliminary grouped based on their colony and microscopic morphology. Taxonomic identity and genetic variability of strains isolated were determined by internal transcribed spacer （ITS） sequence and MSP–PCR fingerprinting. The results showed that all 401 isolates were identified as basidiomycetous yeasts （Agariomycotina and Pucciniomycotina）represented by 28 species of 9 genera （Holtermanniella， Vishniacozyma， Filobasidium， Dioszegia， Rhodotorula， Rhodosporidium， Cystofilobasidium， Naganishia and Papiliotrema）， with the first four being dominant genera. H. festucosa and V. victoriae was the dominant species （22.22% and 16.91%）. Among representative strains of the 28 yeast species， only six strains were psychrophilic （the optimum temperature for growth ranging from 16 to 18 ℃）， whereas the remaining 22 strains had the optimum temperature for growth ranging from 22 to 25 ℃， indicating that they belonged to psychrotolerant yeasts. Comparative analyses of Shannon， Simpson’s and Chao indices showed the community structures of culturable airborne yeasts at the three elevation ranges on the glacier surface were somewhat different， but differences between the diversity index were not significant. More remarkably， no strains of Holtermanniella， a dominant airborne yeast genus， ware not found in otherhabitatsof the glacier， such as cryoconite sediment and supra-glacial ice core， suggesting that the harsh conditions of glacier could exert a strong selective pressure on exogenous microorganisms.
BSCs （biological soil crusts）， as ubiquitous living covers on soil surface of the enclosure grassland in the frozen ground region of the Qinghai-Tibet Plateau. However， studies on the influence of biocrusts on soil properties in the frozen ground region were fresh. Objective of the paper was to determine the influence of the biological soil crusts on soil physicochemical properties of the surface forzen soil. Field investigation was conducted and physicochemical properties of two kinds of BSCs from this region was analyzed. The results showed that BSCs occupy 37.3%~51.7% of the soil surface and the cyanobacteria crust is dominant across the study area， with a thickness of up to 12.6 mm， which was higher than the hot arid desert regions. At the same time， BSCs increase the silt particle content of 5~20 cm， but the impact is not significant， while it had remarkable effect on water holding capacity and soil bulk density. Water holding capacity of the BSCs layers increased by 10.0%~40.0% compared to the bare soils， while soil bulk density of the BSCs layer was 30.0% lower than bare soils. Both types of BSCs （dark cyanobacteria crusts and light cyanobacteria crusts） remarkably increased soil organic carbon content （TOC） of BSC layer and 0~20 cm soil layers. While both BSCs have different impact on soil total nitrogen （TN） content， dark cyanobacteria crusts had significant increase on TN in the BSCs layers and below 20 cm soil layers， but light cyanobacteria crusts only increased BSCs layer TN had no impact on the below 20 cm soil layers. Meanwhile the BSCs have no significant impact on the soil pH. Biological crust is very important in the process of vegetation degradation in alpine ecosystem. The research results provide a theoretical basis for revealing the ecological functions of biological crust in alpine ecosystem.
The accurate calculation of the water holding capacity of forest understory is especially critical for the simulation and prediction of the hydrological functions in the cold region with fragile ecological environment. In this study， the typical watershed of the Qilian Mountains in the northern foot of the Qinghai-Tibet Plateau was taken as the study area， the hydrological characteristics parameter differences of the original and scattered moss sampling methods were used to find out the effect of the sampling methods of the moss-litter hydrological parameters quantification， the undistributed moss sampled with PVC tubes， the scattered moss sampled with nylon bags and 2 596 data was obtained. The main results and conclusions were obtained as follows， the maximum water holding capacity of the undisturbed moss with an average thickness of 14.3 cm and moss-litter were 2.29 kg?m-2 and 5.42 kg?m-2， the water holding rate was 2 071% and 890%， and the water holding rate of the scattered moss was 610%. The moss-litter layer showed a significantly better water retention function than the moss layer， so it should be treated differently when we calculating the hydrological characteristic parameters. Compared with the undisturbed sample， the maximum water holding capacity of the moss layer was underestimated as much as 70.5% with a scattered sampling， that is， under the scattered sampling method， the maximum water holding capacity of the moss layer under the forest will be seriously underestimated. The soil water characteristic curve of drying conformed to a power function and the evaporation duration was 4.8~5.6 h， these key parameters will be important reference value for the modelling and forecasting of the moisture evaporation process of the forest understory. In summary， different sampling methods have significant differences in the estimation of ground cover water holding capacity. In practice， the sampling methods should be determined according to the experimental purpose and research object.
In this study， snow fence was employed to simulate artificial snow addition in an alpine swamp of permafrost region on the Tibetan Plateau. We aimed to investigate the responses of alpine swamp ecosystem to snow addition. Our results showed that： Increased snow would increase both soil moisture and temperature at the depth of 0~20 cm； Increased snow would increase vegetation height and root biomass at depth of 0~10 cm； Increased snow would decrease below-ground pools in total carbon （C）， total nitrogen （N） and total phosphorus （P） at the depth of 0~20 cm， although the C， N， P pools had increased in the roots； Increased snow also increased soil total N：P ratio with increasing available phosphorus concentration at the depth of 0~10 cm and 10~20 cm. Our results suggested that short-term snow addition had no effected community composition and above-ground biomass， but significantly increased vegetation height. Moreover， increased N：P ratio in the soil surface had indicated that snow addition could alleviate N limitation in the study region， thereby relieve the soil N deficiency for plant growth in this area. These findings provide observation data at the plot-scale for alpine ecosystem under snow change， as well as a dataset for modeling permafrost ecosystem under future climate change.
Permafrost regions are rich in natural gas resources. Gas exploration and development and gas pipeline construction thus have received increasingly more attention. The traditional and conventional techniques for pipeline design， construction and operation have encountered great challenges in permafrost regions. This paper summarizes the related key techniques for building gas pipelines in permafrost regions， including three items and fourteen sub-items， based on considerations for special permafrost environments and experiences and lessons learned from oil and gas pipeline projects in permafrost regions from the perspectives of pipeline designers and engineers. These key techniques comprise chilled transporting processes and heat-transfer calculation based on a series of techniques of coupled hydrothermal-hydraulic-mechanical modeling of the pipe-soil system， pipe crack control and strain-based design of pipelines based on a series of techniques of material and strain， grounding technology in continuous permafrost regions， cathodic protection in discontinuous permafrost regions， station foundation and pipe supports design and modular buildings and skids based on a series of techniques of public utilities， special construction equipment， building of snow and ice temporary roads and pads， low temperature welding process and welding seams inspection based on a series of techniques of construction， and risk management in natural environment， humanistic environment， social environment and new technology. It is hoped that new and innovative approaches can be inspired and envisioned for gas pipeline construction in arctic， boreal， alpine and high-plateau permafrost regions.
The difficulty of permafrost excavation and low crushing efficiency are the technical problems faced by engineering construction and foundation construction in alpine region. Mechanical breakage of frozen soil is the main method of frozen soil excavation， and the research on the mechanism of frozen soil mechanical cutting and crushing is the prerequisite and basis for improving the efficiency of frozen soil crushing. In this paper， the influences of temperature， water content and confining pressure on the complex mechanical properties of permafrost are summarized. The typical cutting mechanical models of permafrost mechanical breakage are investigated and analyzed. It is found that the breaking mode of frozen soil cutting machine is not only closely related to the mechanical properties of frozen soil， is also directly related to the cutting parameters and tool structure. There is an optimal cutting rake angle （30°~60°） during the cutting process of frozen soil， and the difference in the internal force mode of the frozen soil during deep cutting and shallow cutting will also cause different types of damage. Moreover， the mechanical properties of permafrost caused by temperature， moisture content and confining pressure will directly lead to the change of permafrost failure process and breaking mechanism， the strength of frozen soil will increase firstly and then remain stable as the temperature decreases. As the moisture content increases， it shows a trend of increasing firstly and then decreasing. Moreover， there are different failure forms such as brittleness， plastic brittle transition and plasticity. The research progress of permafrost fracture mechanism further clarifies the main influencing factors， variation characteristics and cutting damage characteristics of permafrost mechanical properties， which provides design basis for optimizing cutting parameters and cutting tool structure of permafrost mechanical fracture.
The accumulation and melting processes of snow are the important parts of the cryospheric hydrological model. Generally， the simulated snow cover and snow depth time-series by distributed hydrological model were difficult to evaluate， which mainly calibrated and validated by observed runoff data. The multi-source remote sensing snow cover and snow depth products give a good choice for evaluating the spatial-temporal patterns of snow cover and snow depth of simulation， which probably help to enhance the physical basement of model. However， due to the cryospheric components include glacier， snow cover， permafrost always distributed together in one basin， the evaluation on snow cover in one basin should base on that there are enough precipitation observation data in alpine areas of the basin， and glacier meltwater were reasonable simulated， which indicated that the large uncertainties of simulated cover were removed. There are more than 20 precipitation observation instruments were installed since 2009 in the upper reach of the Shule River basin （URSRB） with average elevation above 4 000 m a.s.l.， and the annual precipitation gradient were obtained with 14.654 mm·（100m）-1. The river runoff of Changmabao in URSRB was successfully simulated by VIC-CAS model， which coupled with glacier modules with VIC-3L model， and the simulated single glacier area changes were compared with that observed from multiple temporal remote sensing data. The simulation suggested that it well represent the glacier meltwater and glacier change. Thus， the simulated snow coverage and snow depth by VIC-CAS model were evaluated by remote sensing products in URSRB. Based on 4 383 daily MODIS surface reflectance datasets and the Long-term Snow Depth Dataset of China from 2002 to 2013， in which the snow depth algorithm developed by Che and Dai of Cold and Arid Regions Environmental and Engineering Research Institute， Chinese Academy of Sciences， the daily snow cover and snow depth simulated by VIC-CAS model were comprehensively compared in URSRB. All the forcing data， parameters， and the calibration and validation processes of VIC-CAS model in URSRB are the same with previous published literature. The comparison of stats in monthly average snow coverage and spatial pattern of annual average snow coverage in 182 sub-basins suggested that VIC-CAS model can better simulate the snow cover a in more snow year such as 2008， which has the higher relative coefficient （r） by 0.67 and lower root mean square error （RMSE） by 0.12. The simulation accuracy of VIC-CAS model is relatively lower in normal year such as 2004 with r by 0.37 and RMSE by 0.13 and less snow year such as 2013， which has r by 0.52 and RMSE by 0.09. The spatial distribution of annual average simulated snow cover has the similar patterns with that from remote sensing data， especially in more snow year， although the simulated snow coverage is less than observed by remote sensing data. The best simulation of snow coverage is located at 4 000~5 000 m a.s.l. altitude zone， which has high r by 0.44， 0.66， 0.60， and RMSE by 0.15， 0.12， 0.11 in normal year， more snow year， and less snow year， respectively， while that is the worst at 2 000~3 000 m a.s.l. altitude zone， which has r by -0.1. The consistency of snow depth between simulated and observed is high in 2008， while is low in other years. The simulated annual average snow depth is less than observed by remote sensing data. The spatial distribution of simulated snow depth suggested that it has more relationship with altitude than snow depth product， due to the later has coarse resolution. These results indicate that VIC-CAS model has a lower accuracy in the low altitude area or with thin snow， which probably comes from the related algorithm and parameterizations in snow redistribution and wind-blown snow process， which need to further enhance the observation and simulation in the future. This study provides some clues for further improving the simulation ability of hydrological model in alpine cryospheric basins.
Studying the spatial and temporal variation of vegetation coverage in the source region of the Yellow River is of great significance to understand the response of vegetation growth in permafrost area of Qinghai-Tibet Plateau under the dual effects of climate change and human activities， and to provide theoretical basis for the protection and control of the ecological environment in the source region of the Yellow River. Using Landsat as the main data source， this paper uses Multiple Endmember Spectral Mixture Analysis （MESMA） to complete the extraction of vegetative cover of 7 phases of 44 000 km2 from 1996 to 2015 in the source region of the Yellow River respectively， and analyses the change of vegetative cover from 1996 to 2015 based on transfer matrix and unvariable linear regression. The research results show： The vegetation coverage is higher in the southeast and lower in the northwest， and decreases from southeast to northwest in space. Desertification is serious in the north. This is consistent with the hydrothermal conditions in the source region of the Yellow River. From 1996 to 2004， bare land as a whole increased by 10.24%， and the unconverted area accounted for as high as 77.22%. Low coverage type， medium coverage type and medium coverage type remain basically unchanged on the whole， and the conversion is mainly to lower vegetation coverage type. The high coverage type overall decreased by 12.75%. Therefore， the vegetation coverage showed a general trend of falling. However， from 2004 to 2015， the bare land decreased by 12.91% as a whole， which was mainly converted to low coverage type. Low coverage type， low-medium coverage type and medium coverage type remained basically unchanged， and all of them were mainly converted to higher coverage type， while the high coverage type increased by 16.18% as a whole. Based on the above analysis， the overall vegetation coverage of the source region of the Yellow River showed an increasing trend. This also shows that the state in 2005， 2014 implementation of the “Three-River Source Region ecological protection and construction of the first and second phase of the project” has been effective. From 1996 to 2015， 57.25% of the vegetation coverage areas showed an increasing trend. The increased area is mainly distributed in the central and eastern part， the area around the Ngoring Lake and some areas in the north. About 16.02% of the vegetation coverage areas were basically unchanged. Areas that remain largely unchanged are concentrated in the northern and eastern desert regions， and 26.73% of the vegetation coverage areas showed a decreasing trend. The reduced area is mainly distributed in the west of the source region of the Yellow River， the north of Gyaring Lake， the northeast and southeast of the source region. The main reasons for the decrease of vegetation coverage are that the headwaters of the Yellow River and some river valleys and areas around the lake are greatly affected by human beings， and that the lower altitude of the southeastern region is greatly affected by overgrazing， as well as the disappearance of pastures in the north of Gyaring Lake. Although the vegetation coverage of the source region of the Yellow River showed an overall trend of improvement from 1996 to 2015， the area of poisonous weeds also increased from 16 060 km2 in 1996 to 22 942 km2 in 2015， which increased by 6 882 km2 in 20 years. The poisonous weeds in the source region of the Yellow River were mainly Edelweiss and Oxytropis. Edelweiss was mainly distributed in the south side of the study area. Oxytropis was mainly distributed in the north side， and the distribution area of Ajania khartensis was relatively dispersed. The increase of the area of poisonous weeds had a negative impact on the development of livestock husbandry in the source region of the Yellow River.
