In recent years， more and more attention has been paid to the ecosystem service function， and it has gradually become a hot issue for scholars. As one of the important service functions of surface ecosystem， water conservation plays a key role in regulating regional hydrological cycle， improving surface water status and maintaining the normal operation of regional ecosystem. As an important ecological security barrier， the Qilian Mountains is also one of the important water conservation functional areas in Northwest China. Based on the InVEST water wield model and the principle of water balance equation， the water production of each unit is calculated by subtracting the actual evapotranspiration from the precipitation of each unit， at last， the water conservation capacity of the study area is obtained. The model needs input of precipitation， potential evapotranspiration， soil texture， land use type， and vegetation available water grid layer. The meteorological data are from China Meteorological Data Service Center， the soil texture data are from Harmonized World Soil Database， and the soil type data are from Resource and Environment Science and Data Center， Institute of Geographic Sciences and Natural Resources Research， Chinese Academy of Sciences. The spatial and temporal variation characteristics of water yield amount and water conservation amount in the Qilian Mountains were calculated and analyzed， and the influencing factors of water conservation amount were discussed by using Pearson correlation analysis method. It is of great significance to promote the rational allocation of water resources， water management and ecosystem protection in the Qilian Mountains. The results showed that the annual average total amount of water wield and total amount of water conservation were about 93.03×108 m3 and 57.83×108 m3， respectively. The water conservation amount showed a slight upward trend and the change rate was 0.196 mm·a-1. The total amount of water conservation under different land use types was： grassland （31.87×108 m3） > woodland （16.71×108 m3） > cultivated land （4.92×108 m3） > other land （2.29×108 m3） > building land （0.63×108 m3）. In the aspect of meteorological elements， there is a significantly positive correlation between precipitation and water conservation amount in each period， there is a negative correlation between evapotranspiration and water conservation amount， and there is a positive correlation between average air temperature and water conservation amount， but the correlation is not significant. At the same time， the change of land use types in different periods also has an important influence on water conservation amount， and change of grassland area has a great influence on water conservation amount. While paying attention to regional climate change， land resources should be rationally developed and utilized， and attention should be paid to the protection of its green space ecosystem. Under the background of high and cold climate， permafrost is widely distributed in the study area， and the underground ice buried under the geomorphology of permafrost is a special form of water body. It also plays an important role in regulation of regional water resources and plateau ecological environment change. Therefore， the combination of surface water and underground ice storage of permafrost in this paper is helpful to grasp the overall change of water resources in the Qilian Mountains. In this paper， average air temperature， average surface temperature and average thickness of permafrost in the Qilian Mountains are estimated according to the empirical formula of permafrost established by predecessors. The estimated underground ice storage of permafrost in the study area is about 555.76 km3. As warming trend continues in the future， area of the warm permafrost will continue to increase， underground ice of the permafrost will melt at a faster rate， and its internal water storage will decrease accordingly. The study also has important implications for assessment and management of hydrological cycles and ecosystems in the Qilian Mountains.
Global climate warming has profound effects on forest ecosystems. Whether the environmental context affects the response of tree growth to climate change remains unkonwn. In this study， three tree-ring chronologies of Picea crassifolia at different elevation gradients were developed in the middle and eastern Qilian Mountains， respectively. The relationship between radial growth of trees and climatic factors and its stability with time were analyzed. Results showed that the Picea crassifolia in the middle of Qilian Mountains was more sensitive to precipitation and scPDSI than that in the eastern. The tree-ring width chronology was positively correlated with scPDSI from May to July of the current year in the middle of the Qilian Mountains （P<0.001）， and the eastern Qilian Mountains tree-ring width was significantly positively correlated with scPDSI in previous September and current May. It indicated that the tree growth of Picea crassifolia was mainly restricted by the soil moisture conditions from May to July of the current year in the middle of the mountains （LCH）.The eastern regions （XYH） was limited by soil moisture in September of previous year and May of the current year. As the temperature increased significantly since1980s （P<0.001）， the drought stress for tree growth was enhanced in the central and eastern regions， which caused by high temperature. After 1990s， due to the increase of precipitation in the central region and the insignificant change in the eastern region， the drought stress of tree growth in the Middle region was relieved， but it was enhanced in the eastern region. In addition， the correlation between temperature， precipitation and scPDSI of Picea crassifolia is gradually consistent in the middle and eastern Qilian Mountains， and the future climate warming may reduce the difference of tree-ring climate relationship of Picea crassifolia in the middle and eastern Qilian Mountains.
Tibetan Plateau is extremely sensitive to global warming because of its unique cryospheric geomorphy， and the warming rate is twice the global average. This research is to study and project the future trend of near-surface air temperature over the Tibetan Plateau under the background of global warming. Based on 22 earth-climate system models’ simulation data from the Coupled Model Intercomparison Project Phase 6 （CMIP6）， the spatial and temporal variations of the annual mean near-surface air temperature over the Tibetan Plateau under different scenarios from 1961 to 2100 are analyzed. These scenarios include the historical （1961—2014） and future （2015—2100） four different shared socioeconomic pathways （SSPs）： SSP1-2.6， SSP2-4.5， SSP3-7.0， and SSP5-8.5. Firstly， the performance of 22 models is evaluated by comparing their outputs with ground observation for the period 1961—2014. The ground observation is from China Meteorological Data Service Centre， including the observation data of 66 meteorological stations with complete time series. Taylor diagram， which reflects correlation coefficient， standard deviation and root mean square error， is used to evaluate the simulation ability of the models. Due to the different resolution between the models， the bilinear interpolation method is used to interpolate the data of each future model （2015—2100） into the 0.5°×0.5° grids， with a total of 1 214 grid points. Then， the future changes of annual mean near-surface air temperature over the Tibetan Plateau are analyzed by using the multi-model ensemble mean results. The results show that： through the analysis of Taylor diagram， it is found that the multi-model ensemble mean usually shows better skill than most of single models. Due to the differences of the SSP and radiative forcing， the warming trend during 2015—2100 is 0.10 ℃·（10a）-1， 0.29 ℃·（10a）-1， 0.53 ℃·（10a）-1 and 0.69 ℃·（10a）-1 under SSP1-2.6， SSP2-4.5， SSP3-7.0 and SSP5-8.5 scenarios， respectively. The SSP1-2.6 scenario indicates that the annual mean near-surface air temperature over the Tibetan Plateau remains stable after 2050 and shows a slight downward trend， while the other scenarios show a warming trend. Compared with the reference period from 1995 to 2014， the annual mean near-surface air temperature of the plateau will increase by 1.37 ℃， 2.81 ℃， 5.04 ℃ and 6.21 ℃ to 2100， respectively. With the increase of emission scenarios， the warming rate increases. The three warming centers are the Pamirs， midwest part of the northern Tibetan Plateau， and the Bayan Kara Mountains. The regions with the smallest warming trend are concentrated in the southeast of Tibetan Plateau. Compared with 1995—2014， to the middle of this century （2041—2060）， the annual mean near-surface air temperature of the Tibetan Plateau will increase by 1.37 ℃， 1.72 ℃， 1.98 ℃ and 2.30 ℃， respectively. And to the end of this century （2081—2100）， the annual mean near-surface air temperature will increase by 1.42 ℃， 2.65 ℃， 4.28 ℃ and 5.38 ℃， respectively. The future warming range in the same time period is higher than CMIP5 simulation results. Compared with the commitment of Paris Agreement to “holding the increase in the global average temperature to well below 2 ℃ above pre-industrial levels”， through this study， under any scenarios， the annual mean near-surface air temperature over the Tibetan Plateau will increase more than 2 ℃ above pre-industrial levels to the middle of this century. For the Tibetan Plateau with the cryosphere as the main geomorphic feature， it will lead to accelerated melting of glaciers and more frequent extreme weather and climate events， and it is urgent to take corresponding emission reduction measures. This study can provide a reference for the research of climate change on the Tibetan Plateau and provide a scientific basis for the formulation of mitigation strategies. Meanwhile， it also provides reference for the related evaluation and research of CMIP6 models’ results.
As an Asian water tower， the Qinghai-Tibet Plateau is extremely sensitive to global warming due to its unique cryosphere landform. At present， due to the warming of the plateau， a series of ecological and environmental problems have been caused， such as glacier retreat， frozen soil melting and so on. In recent years， the near-surface air temperature of the Qinghai-Tibet Plateau has been increasing at the rate of 0.3~0.4 ℃ （10a）-1， which is twice the global average. The near-surface air temperature increase will affect the upper atmospheric temperature in the form of long wave radiation. An important indicator of the change of upper air temperature is the 0 ℃ level height. As the lowest height of free air temperature of 0 ℃， the 0 ℃ level height is also an important indicator of global change. The height of atmospheric 0 ℃ layer determines the height of water vapor phase transition in the air. If the 0 ℃ level height is higher than the surface， the cryosphere on the surface is in a state of melting， otherwise it is in a state of freezing. Therefore， the 0 ℃ level height directly determines the state of melting of the cryosphere on the surface of the plateau. Therefore， quantifying the change of the 0 ℃ level height over the Qinghai-Tibet Plateau is very important for understanding the climate change of the plateau and the change state of the cryosphere. Based on ERA5 reanalysis data， the temporal and spatial variation of the 0 ℃ level height in summer over the Qinghai-Tibet Plateau from 1979 to 2019 is analyzed. It is found that the 0 ℃ level height in summer over the Qinghai-Tibet Plateau ranges from 4 423 to 5 972 m， with the central and southern part of the Plateau （30~32° N， 83.5~88.5° E） as the high value center， and gradually decreases in zonal direction. In the past 41 years， the 0 ℃ level height in summer over the Qinghai-Tibet Plateau has been increasing continuously. The increasing trend in the north of the plateau is greater than that in the south. The increasing trend in the Qilian Mountains is the most obvious， which is 60 m?（10a）-1， while it is slightly decreasing in the southwest of the plateau. On average， the 0 ℃ level height increases by 122 m for every 1 ℃ rise in summer near-surface air temperature over the Qinghai-Tibet Plateau. Using CMIP6 model data， it is estimated that the 0 ℃ level height in summer over the Qinghai-Tibet Plateau will increase during 2020—2100 under SSP1-2.6， SSP2-4.5， SSP3-7.0 and SSP5-8.5 social shared path scenarios， but the increasing trend under different scenarios is quite different in space. Compared with the reference period of 1979—2014， under the four scenarios， the summer mean the 0 ℃ level height of the Qinghai-Tibet Plateau will increase by 265 m， 394 m， 576 m and 729 m respectively in 2081—2100； Correspondingly， from 2081 to 2100， the area of glaciers below 0 ℃ in summer on the plateau is 79%， 86%， 94% and 98% of the second glacial catalogue data， respectively. Only from the perspective of the 0 ℃ level height change in summer， it is estimated that the accumulation area of glaciers in the Qinghai-Tibet Plateau will disappear in summer under SSP5-8.5 scenario until the end of this century， except for the Pamir Plateau and the northern Kunlun Mountains.
Following the global warming， the changes in hydrology and available water resources in arid regions are still a significant scientific problem that affects the utilization of regional water resources and flood disaster prevention and control. Utilizing long-term meteorological and hydrological datasets from 1957 to 2019， the responses of hydrological processes to climatic changes and their potential impacts were systematically analyzed in the Qarqan River Basin on the northwestern edge of the Qinghai-Tibet Plateau. In general， the significant change of the hydrological process in the Qarqan River basin occurred in the late 1990s， and the annual water resources increased by about 54.67% before and after that change. The seasonal runoffs in all seasons contributed to the increase of annual runoff， in which the increase of summer runoff contributed the most， followed by autumn， spring， and winter. The increase of precipitation （the first controlling factor） and the rise of air temperature （the second controlling factor） jointly caused the change of the hydrological process in the Qarqan River basin. In terms of seasonal runoff variations， precipitation was the main controlling factor for runoff variation in spring and summer， while the temperature was the main controlling factor for runoff variation in autumn and winter. Although the increase of runoff in the Qarqan River basin provides more freshwater for the middle and lower reaches， but the interannual variation of discharge will increase the frequency of hydrological flood and drought. It is worth noting that the cryosphere plays a crucial role in the hydrological cycle of this region， but its influence on the hydrological process is still unclear. To strengthen the monitoring of glaciers and permafrost in the Altun Alpine region will provide basic data support for further predicting the response of hydrology to climate change.
The soil moisture content of active layer is a key parameter characterizing the climate， hydrology and ecological processes in permafrost regions. For a long time， due to the limited observations in permafrost regions， soil moisture datasets， e.g.， generated through remote sensing retrievement， model simulation， data fusion and assimilation have large biases. We collected 1 072 active layer soil moisture samples in the permafrost area in the Tuotuo River source area in the hinterland of the Qinghai-Tibet Plateau during the comprehensive field campaign from October to November 2020. Based on these samples， we analyzed the active layer soil moisture characteristics in spatial， and evaluated two soil moisture products， i.e.， Global Land Data Assimilation System （GLDAS-Noah） and the reanalysis data released by the fifth-generation European Center for Medium-Range Weather Forecast （ERA5-Land）. The results showed that in the investigated region， the average active layer thickness is about 2.72 m， and the soil mass moisture content （total moisture content） of the active layer is about 14.0%. The active layer soil moisture was positively correlated with vegetation development， except for alpine swamp meadow type. In the alpine meadow and alpine grassland environment， along with the soil depth increases， the soil moisture decreased first and then increased again. The active layer soil moisture content of the of different topography presents upper slope>lower slope>middle slope>flat slope. The moisture content in the sunny slope is higher than in the shady slope， but the patterns of soil moisture profile change with depths were similar. We also compared the soil moisture in a depth of 0~350 cm in the permafrost active layer and in the same depth in talik. The soil moisture profiles along the depth both increase first， then decrease， and then increase again. But the soil moisture content in the permafrost active layer is larger than that in the same depth of talik. Compared with measured data， GLDAS-Noah assimilated moisture product is biased less than 10%， which is more accurate in this area during the investigation period than ERA5-Land reanalysis soil moisture product， and both two soil moisture products cannot correctly describe the soil moisture profiles. The results provide a scientific basis for the optimization of model freeze-thaw parameterization in a data assimilation system and the development of remote sensing moisture products.
Tuotuo River basin is one of the birthplaces of the Yangtze River， and its widely distributed permafrost has an important impact on the process of production and confluence， ecosystem， and even regional climate in the source area of the Yangtze River. The investigation and understanding of the distribution and characteristics of permafrost in this region can provide basic data support for studying the interaction between permafrost and climate， hydrology and ecology in the source region of the Yangtze River. From October to November 2020， we carried out a 50-day field investigation of permafrost in the source area of Tuotuo River and arranged 32 boreholes in different underlying surface types， different geomorphic parts， and different altitudes， with a total drilling depth of 1，200 meters. This paper is a preliminary summary of the characteristics of permafrost and the development of underground ice in the source area of the Tuotuo River based on the data of drilling and exploratory pits. The results show that the permafrost in the source region of the Tuotuo River has formed some taliks under the influence of rivers and geothermal energy to a certain extent， and its lower bound of permafrost is roughly between 4 650 m and 4 680 m. The average permafrost table depth exposed by boreholes is （2.47±0.98） m， and residual thawed interlayers exist in some areas. Affected by lithology and geothermal of shallow surface sediments， the permafrost base depth exposed by drilling holes is relatively shallow， with an average of 19.3 m， and permafrost is relatively thin， with an average thickness of 15.0 m. The maximum permafrost base depth and thickness of permafrost revealed by drilling holes are 75.0 m and 72.7 m， respectively. Topography， sediment characteristics， and geothermal conditions are the main reasons that affect the large spatial difference of permafrost thickness. The ground ice in the study area is mainly distributed at a depth of more than 15.0 m. At the same time， the shrinking pingo and lithalsa are also found. These phenomena also imply that the permafrost in the study area is in the process of degradation.
Supported by the project of the Second Tibetan Plateau Scientific Expedition and Research， a comprehensive scientific survey on permafrost in source area of the rivers and lakes on northern and southern slopes of Mt. Geladandong in the Tanggula Mountains was conducted in 2019 and 2020. The study area in the first phase of the investigation locates in source area of the Zhaga Zangbo River （upper reaches of Selin Co Lake）， and the study area in the second phase is in source area of the Tuotuo River （upper reaches of the Yangtze River）. By applying multiple technologies， such as borehole drilling， pitting， ground surface geophysical sounding， and in-situ monitoring， the first monitoring network on permafrost environment in this area was established， and the first-hand data on permafrost were obtained. The sedimentary strata and the distribution and state of ground ice on northern and southern slopes of Mt. Geladandong were compared and analyzed， indicating great differences between the two regions in sedimentary environment， and development status of permafrost and ground ice. The thermal stability of permafrost， ground ice content， and the type diversity of periglacial landforms on the northern slopes were richer than those on the southern slopes， but the distribution of frozen ground and taliks on the northern slopes was more complicated due to the influences of tectonics and resultant mosaicked distribution of geothermal gradients and river/tectonic lake taliks， because of the influence of geotectonic zone， geothermal flow anormalies， river/lake taliks， and other factors. A 100-meter borehole was drilled in source area of the Tuotuo River， which revealed the characteristics of continuously distributed ground ice with thickness greater than 50 m. It was confirmed that pingos could have developed in this area， and the largest and most complete pingo in existence on the Qinghai-Tibet Plateau was discovered and inspected. Through the investigations， nearly 12 000 samples of drill cores， surface soils， and ice/water that would be used for analysis of the physical/chemical indicators of the frozen soil， were collected. This provides the foundation for the research of permafrost environmental chemistry and reconstruction of paleo-climate and paleo-environment in source area of the rivers and lakes on northern and southern slopes of Mt. Geladandong， interior Qinghai-Tibet Plateau.
Under the background of global warming and continuous degradation of permafrost， retrogressive thaw slumps are widespread in the permafrost region of the Qinghai-Tibet Plateau （QTP）， which not only affects the regional ecological environment， but also influences the stability of engineering structures. Based on field investigations， remote sensing interpretation and meteorological data， the triggering factors， distribution characteristics and evolution process of retrogressive thaw slumps in permafrost region of the QTP were analyzed this paper. Results showed that the occurrence of active layer detachment is the main factor that induce the retrogressive thaw slumps in permafrost region of the QTP， followed by the engineering disturbance and the thermal erosion of lake water. The development process of retrogressive thaw slumps which induced by active layer detachment mainly includes three stages， they are the occurrence of active layer detachment， the collapse and retreat of the headwall and the formation of slope mudflow. The source erosion after the formation of retrogressive thaw slump will last for several years or even more than ten years until the content of ground-ice in the back edge is significantly reduced or disappeared. In terms of spatial distribution， retrogressive thaw slumps tend to be distributed on the side of the shady slope in the hilly and piedmont regions with gentle slope （3°~8°）. In addition， the retrogressive thaw slumps in permafrost region of the QTP had significantly increased in recent years， and such intensification of retrogressive thaw slumps did not increase steadily over the study period but was rather concentrated during the special years with extreme high air temperature. The research results will provide references for the future engineering planning， resource development and environmental protection on the QTP.
Iceberg calving and basal melting are the main component of mass loss of Antarctic ice shelves， which are closely related to climate warming. In particular， the Getz ice shelf is more sensitive to climate warming than the other ice shelves in the Amundsen sea sector. Long-term time series analysis of ice flow velocity and structural features over ice shelves is significant for understanding the evolving dynamics of ice shelves in the context of global climate change. Based on the Landsat series of images， this study used a multi-scale semi-automated image matching algorithm to derive the ice velocity measurements over the Getz F ice shelf from 2000 to 2017. We also extracted the structural features on the Getz F ice shelf in 2000 and 2017 via image enhancement and manual delineation. The results indicate that， the fast flow area （850~950 m?a-1） was gradually shifted to the west from 2000 to 2017， and the flow velocity generally decreased with the increase of surface elevation. The number of ice fractures in the lower and middle reaches of the ice shelf has increased significantly， and the fractures showed a trend of moving from the upper reaches to the lower reaches in the east. The flow of Getz F ice shelf is mostly fed by the Berry Glacier， the flow velocity is affected by the Modified Circumpolar Deep Water， and the front margin of the Getz F ice shelf has shown great instability.
The Arctic Northwest Passage has an important impact on the development of Arctic resources and the pattern of world trade. To address the problems of low spatial and temporal resolution and poor timeliness in the current study of spatial and temporal variability analysis of navigable suitability of the Northwest Passage， this paper made the following research. High-resolution Sentinel-1 SAR data and k-means method are used to estimate the ten-meter high spatial resolution sea ice concentration （SIC）. The navigable window of the Northwest Passage is determined through macro-tracking of long-term series and precision analysis of short-time series. Taking 70% SIC as the threshold， the cumulative number of times that the Northwest Passage failed to pass through important bays and straits was analyzed. The results show that navigation in the Northwest Passage varies with ice conditions， and its navigability is still unstable. Specifically， the ice situation in the Northwest Passage shows a pattern of light in the east and heavy in the west， light in the south and heavy in the north. The number of non-navigable nodes is less in the east and more in the west， less in the south and more in the north. Navigation of the Northwest Passage in September 2018 was the worst compared to other years during the study period. The area covered by sea ice above the navigable threshold accounts for 35.24% of the total channel area， with a total of 10 non-navigable nodes. In contrast， September 2016 and 2019 have better navigation. The A.G.—C.G.—Q.M.G.—V.S.—F.S.—P.S.—B.S.—L.S. section of the channel （Channel C） is fully navigable. Further studies through small-scale time windows revealed that the best navigable window for the Northwest Passage is late August to early September， during which a total of three fully navigable channels occur. Channel C is the best navigable route of the Northwest Passage， and its continuous navigable period is up to 30 days.
Meteorological stations in the Three-River-Source region is sparse， and only analyzing ground station data fails to reflect true snow cover on ground. In this study， based on remote sensing data， we applied gravity center model to analyze spatiotemporal dynamic characteristics of four snow cover parameters including snow cover days， snow depth， snow cover onset date and snow cover end date from 1980 to 2019. Mann-Kendall test and Sen’s slope estimation were used to analyze trends of the four snow cover parameters and climate factors. We finally explored its response to variations in annual mean air temperature and annual precipitation in the Three-River-Source region. The results indicated that snow cover days and snow depth showed downward trends， and snow cover onset date delayed and snow cover end date advanced from 1980 to 2019 in the Three-River-Source region， while air temperature and precipitation showed upward trends. Gravity center of the four snow cover parameters showed eastward trends， while gravity center of air temperature showed a westward trend. The westward speed of gravity center of air temperature was 6 times and 2 times the eastward speed of snow cover days and snow depth， respectively. These indicated that trends of the four snow cover parameters and climate factors in this region showed strong spatial heterogeneity. The increase rate of air temperature in the west was greater than that in the east， which leads to a greater decrease rate of snow cover days and snow depth in the west than in the east. It was responsible for the westward of gravity center of air temperature， and the eastward of gravity center of snow cover parameters. The Lancang River Source region had the highest rate of decrease in snow cover days and snow depth， delay of snow cover onset date and advance of snow cover end date， followed by the Yangtze River Source region and the Yellow River Source region. Further correlation analysis indicated that the increase in air temperature was primarily responsible for the decrease in snow cover days and snow depth， delay of snow cover onset date and advance of snow cover end date. Snow cover days was most sensitive to air temperature rise， followed by snow depth， snow cover onset date and end date. The correlation between annual precipitation and the four snow cover parameters was not significant. This research can provide basic data and theoretical basis for the protection of water resources and ecological environment in the Three-River-Source region.
The fractional snow cover （FSC） data can quantitatively describe the extent of snow cover in a pixel on the sub-pixel scale， and can estimate the area of snow cover more accurately than binary snow area data. The random forest regression model based on machine learning can represent high-dimensional nonlinear relationships， which can significantly improve the inversion accuracy of MODIS FSC. In this study， a new regression model， Spectral Environment Random Forest Regressor （SE-RFR） model， was constructed using random forest regression model combined with spectral and environmental information， which was used to retrieve the FSC from MODIS data in China. We used the FSC obtained from Landsat 8 surface reflectance data in a typical snow area in China as a reference value to evaluate the inversion accuracy of the SE-RFR model. Research shows that the RMSE and MAE of FSC data obtained by SE-REF are 0.160 and 0.104， respectively， which has high accuracy. The SE-RFR model is compared with the Spectral Random Forest Regressor （S-RFR） without environmental information. It shows that the random forest regression model with environmental information improves the accuracy of FSC inversion， especially in the Qinghai-Tibet Plateau region， which is influenced by environmental information， and the RMSE decreased from 0.200 to 0.181. Finally， the SE-RFR model was compared with the currently widely used MODIS FSC inversion models FSC_NDSI， MODSCAG and SSEmod. The results showed that the average RMSE of the SE-RFR model is increased by 12.0%， 8.3% and 5.5%， respectively， compared with the RMSE of the FSC_NDSI， MODSCAG and SSEmod models. In general， the SE-RFR model can accurately extract MODIS FSC， which has wide application prospects for the preparation of regional and even global FSC products.
In this paper， geodetic measurement was used to study glacier mass balance during 2000—2020 in the eastern Hindu Kush by using SRTM and ASTER stereo image pairs. In addition， CRU TS 4.04 meteorological data was applied in response of climate change for glaciers. At the same time， terrain and glacial lake data was combined with the effect in spatial variability between northern and southern regions of the eastern Hindu Kush. The result shows that： The thinning rate of glacier elevation was （-0.02±0.05） m·a-1 and the mass balance was （-0.02±0.04） m w.e.·a-1， which reflects that the eastern Hindu Kush glacier is in a weak negative mass balance. Furthermore， the thickening rate of glacier elevation in northern region was （0.08±0.05） m·a-1 and the mass balance was （0.07±0.04） m w.e.·a-1. But in southern region， the thinning rate of glacier elevation was （-0.38±0.05） m·a-1 and the mass balance was （-0.32±0.04） m w.e.·a-1. With the help of terrain and glacier area data， we find that large glaciers mainly distribute in northern region and their altitude is high， while southern region shows the opposite. Moreover， glaciers with mass gain mainly concentrate on southern slope， while mass-loss glaciers primarily spread on northern slope. According to the meteorological， terrain and glacial lake data， the reasons of mass gain in northern region is the high altitude of large glaciers and lower temperature in winter， which weakens the effect of ablation associated with summer temperature warming. Spatial distribution of glacier mass balance in northern region is similar with spatial allocation of the mean annual precipitation， which means it controls by precipitation rather than by temperature. The cause of great mass loss in southern region is the sharp rise of summer air temperature and the low altitude of glacier distribution. Finally， the continuous extending spatial variability of proglacial lakes and supraglacial lakes area partly exacerbates the spatial variability of mass balance between northern and southern regions in the eastern Hindu Kush. The ASTER L1A data is available from NASA EARTHDATA and the SRTM C DEM is from USGS. The study of glacier mass balance in Hindu Kush is rare， so it is very urgent and significant to make a full understanding of the glacier mass balance in Hindu Kush. But with the restriction of the ASTER stereo images usability， which means the coverage of cloud or the lack of data， it is only feasible to analyze eastern region of the Hindu Kush.
Five global climate models from the latest released Coupled Model Intercomparison Project Phase 6 （CMIP6） and CN05.1 meteorological data are applied to evaluate annual air temperature variations in upper basin of the Yellow River from 1961 to 2014. This study focuses on characterizing the spatiotemporal and annual variations of air temperature across upper basin of the Yellow River under seven future scenarios， combing the shared socioeconomic pathways and the representative concentration pathways （SSP1-1.9， SSP1-2.6， SSP2-4.5， SSP3-7.0， SSP4-3.4， SSP4-6.0 and SSP5-8.5）. The simulation capability of CMIP6 outputs are evaluated during the historical period （1961—2014）. We find that： Multi-model ensemble mean provides good results in characterizing spatial distribution and annual variations of air temperature dynamics across the study area. The average air temperature shows a significant upward trend ［0.03~0.82 ℃?（10a）-1］ under all seven scenarios during 2015—2100. Air temperature increased and reached the peak till the middle 21st century， and showed a slowly increasing trend till the end of the century， under the low forcing scenarios （SSP1-1.9， SSP1-2.6 and SSP4-3.4）. Under the mid and high forcing scenarios （SSP2-4.5， SSP3-7.0， SSP4-6.0 and SSP5-8.5）， the annual mean air temperature showed a continuous rising trend. Regions featured with highest temperature increasing located in western part of upper basin of the Yellow River. Air temperature in summer will rise in a relatively fast speed， while that in spring is slower. Patterns of seasonal air temperature rising shows an obvious spatial distribution， relatively fast in west and slow in east， fast in north and slow in south. In the context of global warming， a reasonable estimation of the future air temperature changes in upper basin of the Yellow River is crucial for the water resources management and study on adaptions to climate change.
The quality of meteorological forcing data is an important factor affecting the accuracy of hydrological process simulation. Based on the data recorded by eight meteorological stations in the Irtysh River basin of Xinjiang and surrounding areas， this study evaluated the applicability of the ERA-Interim reanalysis data and the China meteorological forcing dataset （CMFD）， and compared the spatial distribution of ERA-Interim and CMFD annual mean meteorological elements in the basin. The results show that： （1） the air temperature， relative humidity， downward short-wave radiation and downward long-wave radiation recorded by ERA-Interim and CMFD have high consistency with the observed data， but the consistency of precipitation and wind speed data with the observed data is poor. （2） The accuracy of temperature， relative humidity， precipitation， and downward shortwave radiation recorded by ERA-Interim on the hourly scale is slightly higher than that of CMFD data， while the accuracy of all meteorological elements recorded by CMFD on the daily scale is higher than that of ERA-Interim. Combined with the simulation results of the Noah-MP model， it is believed that the applicability of the CMFD data in the Irtysh River basin is better than the ERA-Interim data. （3） From the spatial distribution of meteorological elements in the basin obtained by the two forcing data， the annual average temperature， wind speed， relative humidity， precipitation， and downward longwave radiation obtained by ERA-Interim and CMFD are highly consistent in the basin space， but the spatial distribution of downward short-wave radiation is quite different.
Active layer deepening is a key characteristic of permafrost degradation due to global warming. Active layer variability shows significant spatial heterogeneity， especially in complex mountain environments. Based on active layer thaw depth probing in the Eboling area’s Heihe River basin of the Qilian Mountains， this study quantifies the differences in thaw depth in two types of environments： hummocks and thermokarst depressions. Focusing on the quadrate scale from June to October in 2019—2020， results indicate that the active layer depth （44.48±4.97）~（118.38±20.94） cm in hummocks， and （29.22±7.42）~（93.40±15.45） cm in thermokarst depressions. Furthermore， thawing occurs faster in hummocks than in thermokarst depressions. At the quadrate scale， the maximum thaw depth of hummocks is twice as much as that of thermokarst depressions， caused mainly by differences in soil water content. In addition， a one-dimensional heat conduction model is used to simulate the thermal state of active layer under the two kinds of microtopography. Results verify that the soil water content differences make thaw depth in thermokarst depressions shallower than in hummocks. In mountain environments， characterizing differences in thaw depth for different microtopography types serves as an important basis for providing reliable future high-precision mapping of active layer depth.
Geohazards induced by climate warming and extreme weather events have great impacts on the ecological environment and human community. In particular， in regions with more thaw-unstable， ice-rich， and warm （mean annual ground temperature >-1 °C） permafrost， climate warming and human activities have led to more frequent freeze-thaw geohazards. With the degradation of permafrost， the cohesion and shear strength of soil would be reduced， resulting in active layer detachment failures， rockfalls， mudflows， and frozen debris flows/lobes， and other frost-related geohazards in permafrost slopes. Slope instability may further aggravate the deterioration of the fragile ecological environment in permafrost regions， threatening the safe operation of engineered infrastructures. Compared with the unfrozen soil zone， the research on the stability of permafrost slopes mainly aims at ice-richer slopes. The main types of slope instability in permafrost regions include retrogressive thaw slump and active layer detachment. The former is caused by exposure and the melting of ground ice in the slope cut. The latter is by the excess pore water pressure in slope soils due to the thawing of frozen soil and the resultant excess pore water pressure reduces the soil strength， destabilizing permafrost slopes. In addition， slope instability modes in permafrost regions include gelifluction， frozen debris flows/lobes， rockfalls and creep landslides， among others. This paper reviews the latest progress on the studies on basic characteristics， influencing factors， instability mechanisms， stability evaluation methods， and mitigative measures of permafrost slope instability， identifies inadequacies， and prospects for future research.
The engineering characteristics of permafrost and its coherent geological problems are the huge challenge during the construction of pipelines in permafrost regions. Research on the pipeline-permafrost interaction is important for solving the stability problems of pipeline. In this paper， thermal and mechanical interaction of pipeline with permafrost is reviewed and discussed. It is found that previous researches focus on the quantitative description of temperature fields around the pipeline under a given or cyclic oil temperature， and the decoupling analysis of mechanical response of pipeline under differential deformation induced by frost heave or thaw settlement of pipeline foundation soil. The comprehensive in-situ monitoring data can barely be found， and systematic research on the interface characteristic between pipeline and permafrost is lack. Meanwhile， the existing anti-thaw settlement measures are classified and assessed， indicating that the application and evaluation of these mitigative measures is not supported by pipeline deformation data. Finally， the prospect of research on pipeline-permafrost interaction is presented， including strengthening the monitoring of stress and deformation for buried pipeline and secondary freezing-thawing hazards along the pipeline route， studying the interface property of pipeline-permafrost and its evolution process to establish a more reasonable contact element model， embedding interface model and permafrost model with general applicability to the finite element software to improve the reliability of pipeline-permafrost model， and evaluating performance of mitigative measures from the viewpoint of the deformation stability of pipeline.
To solve the problems of difficult excavation of shaft frozen soil and low efficiency of manual excavation， a new type of gravity shaft tunnelling machine was invented. The machine has well adaptability in the excavation of shaft frozen soil. The invasion depth of cutting pick is an important factor affecting the efficiency of excavation of frozen soil. The cutting pick is used to continuously roll downward and walk to excavate frozen soil. In this study， three-dimensional software is used to establish the model， and the parameters of frozen soil constitutive model are optimized through the Hopkinson pressure bar impact test and the original parameters of HJC compression damage model. Then， the finite element analysis software is used to simulate the rolling excavation of frozen soil under different invasion depths of cutting picks， and the variation laws of three-dimensional force of cutting picks， stress and strain of frozen soil under different destruction depths of depressions are obtained. And it is convenient to visually study the process of cutting pick excavation of frozen soil and seek the optimal invasion depth of cutting picks. The simulation results show that with the increase of the invasion depth of the cutting pick， the three-dimensional force of cutting pick increases， the area of the frozen soil depression expands， and the stress and strain of the frozen soil decreases downward without boundary. The stress and strain in the contact area between the frozen soil and the cutting pick is the largest， and the stress and strain in the frozen soil area away from the cutting pick decreases gradually. The stress and strain variation laws are related to the characteristics of the frozen soil in the continuous rolling excavation of the cutting pick. When the uniaxial compressive strength of frozen soil is 9 MPa， there is an optimal intrusion depth of 4 cm in the frozen soil excavation process by cutting pick rolling. The destruction characteristics of frozen soil are obvious， and the efficiency of frozen soil excavation by cutting pick rolling is the highest and the energy consumption is low.
Silt is widely distributed in China and heavily involved in various engineering applications. The soil is high sensitive to frost heaving， hence the frost heaving characteristics should be taken into account when engineering is constructed in frozen regions. In order to restrain the impact of frost heaving of silt and reduce the carbon footprint， the randomly distributed short-cut anticorrosive wheat straw is used to reinforce silt. Frost heaving tests are carried out on unreinforced and reinforced silt via one-dimensional freezing in the open system. The influence of straw content and straw length on the frost heaving characteristics of silt are investigated. The results suggested that straw reinforcement can significantly inhibit the frost heaving of silt. A small amount （0.2%， 0.4%） of the straw content can change the soil from strong frost heaving silt to weak frost heaving or non-frost heaving silt； for a given test condition， the frost heaving ratio of the soil increases linearly with the increase of straw content in the test range， but the values of reinforced soil are much smaller than that of the unreinforced soil， and a small amount of straw content can inhibit the frost heaving； an optimum straw length can be found for a given straw content， at which both the frost heaving deformation and frost heaving ratio of reinforced soil reach the minimum value.
The competition among world powers for the frontier of Antarctic science and technology， geopolitics， development and utilization rights is becoming increasingly fierce. The construction and operation of Antarctic aviation infrastructure in China is conducive to enhancing China’ s comprehensive influence in the Antarctic， expanding the scale of Antarctic scientific investigation and meeting the needs of rapid delivery of personnel and materials. Therefore， the strategic development value of Antarctic airport construction is prominent， and compacted snow runway is the preferred form of large airport pavement in Antarctic construction in China. Artificial ice samples were prepared by the method of compacted snow. Combined with the aircraft load characteristics of ice and snow runways， under the temperature of -10 ℃， with 1.0 MPa as the average loading stress， 0.03 Hz as the loading frequency， the stress amplitude of 0.2~1.0 MPa， and the cycle number of 100~900 as the cycle conditions， the compressive strength test of compacted snow ice under cyclic loading at the strain rate of 1.0×10-3~1.0×10-1 s-1， and the compressive strength test of compacted snow ice under monotonic loading at the strain rate of 5.0×10-4~1.0×10-1 s-1. The results show that the compressive strength of compacted snow ice under monotonic loading increases with the increase of strain rate in the ductile region， reaches the maximum in the ductile-brittle transition region， and then decreases significantly in the brittle region. In the range of high strain rate and a certain number of cycles， the cyclic load has a strengthening effect on the compressive strength of compacted snow ice. When more than a certain number of cycles， the cyclic load will weaken the compressive strength of compacted snow ice. The test results obtained in this paper can provide a theoretical basis for the design and maintenance of compacted snow track.
In Qinghai， engineering construction is affected by the effects of freeze-thaw cycles and the properties of loess. Lime and loess are often mixed as cushion materials to meet engineering requirements， but the freezing and thawing effects still affect the performance of the foundation soil. To explore the adverse effects of climate changes in Qinghai’s seasonal regions on the foundation soil， three temperature control curves （1#， 2# and 3# temperature control curves） are selected by using the frost heave circulation box to simulate the change law of temperature in Qinghai. Through the unconfined compressive strength （UCS） test and SEM， XRD microscopic test， to analyze the change trend of different temperature control curves on the strength and microstructure of lime-improved loess. The results show that the stress-strain relationship of lime-improved loess was strain-softening. During the 0~6 freeze-thaw cycles， the UCS of the sample gradually decreased with the increase in the number of freeze-thaw cycles， and its strength increased after the freeze-thaw cycles. The distribution of pores in the lime-improved loess at 6 freeze-thaw cycles was more than that at 20 times. And with the increase of the number of melting cycles， the contact mode between particles changed from point-to-point， point-to-surface contact to surface-to-surface contact. The micro-quantitative parameters of lime-improved loess changed more obviously when experiencing the temperature control curve of 1# than when experiencing the temperature control curves of 2# and 3#. The pores of the lime-improved loess were smoother and the structure arrangement was more disordered when going through the 1# temperature control curve. The 1# temperature control curve had relatively weak influence on the structure and strength of the lime-improved loess.
Runoff variation is an important indicator reflecting the regional climate and underlying surface changes in the typical plateau region， Yarlung Zangbo River basin. Facing the global warming， there is still a lack of study on the influence of climate and underlying surface changes on the runoff of the Yarlung Zangbo River Basin because of its scarce observation data. Therefore， based on the daily meteorological data and the monthly hydrological data of Nuxia station during 1986—2010， as well as dynamic land use data， this study comprehensively investigated the influence of climate and underlying surface changes on runoff at different period from 1991 to 2010 in the Yarlung Zangbo River basin， with the final goal of clarifying the discharge variation mechanism of the high-altitude watershed by means of the improved distributed hydrological model in association with different simulation strategies. The results suggested that： （1） During 1991—2010， the contribution rate of climate change and underlying surface change to runoff variation varied greatly in different periods， and the contribution rate of climate change to runoff variation was higher than that of underlying surface change， which increased runoff during the period. （2） In spatial perspective， the contribution of climate change to runoff was larger in the upper and middle reaches， but smaller in the northeast of the lower reaches where the underlying surface changes contributed relatively large. （3） Runoff from snow and ice ablations tended to increase with climate warming， their average contribution to the annual total runoff of the basin was in the range of 21.1% to 48.6% approximately， and the average long-term contribution was about 33.6%. The snow-ice melting runoff started to increase from April of a year， reached to the maximum in August of the year， and approached to the end of ablation in October in general. The implementation and findings of this study is not only the need of basic research on hydrology and water resources in the Yarlung Zangbo River basin， but also has important theoretical significance. At the same time， it can also provide scientific theory and decision-making basis for the protection， planning and management of water resources in the basin， which has important practical significance.
Under the climate warming， the severe melting of glacier， snow and frozen soil， which have resulted in the evolution of runoff and the generation of water cycle mechanism in the cold watershed. By summarizing the research on the water chemistry characteristics of various water bodies in the source area of the Yangtze River. Research progress of ecological hydrology based on hydrochemical characteristics in the source region of the Yangtze River mainly includes： （1） The water vapor source of precipitation is mainly controlled by westerly circulation and monsoon circulation in the source region of the Yangtze River. （2） The hydrochemical characteristics of glacier snowmelt water is affected by the intensity， duration and fresh snow melt water of melting water. At the same time， there may be hydrochemical exchange among ice snow melt water， snow cover and glacier meltwater. （3） Supra-permafrost water is supplied by precipitation， glacier snowmelt water， and ground ice meltwater， which causes random fluctuation of hydrochemical characteristics. The area with an altitude of 4500 m is sensitive to the ion control source in the study area. （4） With the increase of altitude， the dilution effect of rainfall direct recharge on chemical ions in river water gradually weakens. At the same time， precipitation from 4500 m to 5000 m has the greatest effect on ion concentration in river water， while rivers above 5000 m are mainly supplied by glacier snowmelt water， and the changes of precipitation and ablation period have little impact on hydrochemical characteristics of river water. The research results can provide scientific basis for more systematic understanding of the hydrological effect caused by the change of underlying surface in cold region and provide decision-making basis for rational development and utilization in the cold regions.
With the population growth and the economic and social development， the contradiction between supply and demand of water resources is on the increase day by day. It is a crucial new task to save， protect， manage， rationally develop， efficiently utilize and optimize allocation of water resources comprehensively. As an important way to study the sustainable utilization of water resources， entropy weight method can eliminate small contribution to the evaluation results in the index system of indicators， reduce the influence of human factors on the subjective weight， and thus more accurate calculation results are achievable， which can objectively reflect the status quo of water resources and water environment. For this reason， the method is widely used in the evaluation of water resources and water environment， which will provide scientific basis for efficient utilization of water resources and comprehensive evaluation of water environment. This article explored the origin of the entropy weight method and development process in the evaluation of water resources and environment， discussed and summarized the four applications of the entropy weight method in water resources quantity， water resources carrying capacity， water environmental quality and water ecological environment assessment and found the entropy weight method shows a good application prospect in the evaluation of water resources and water environment. Meanwhile， in view of the shortcomings of entropy weight method in water resources and water environment assessment， some improvements are suggested， which will provide new ideas for the research direction of water resources and water environment assessment. In addition， the future of entropy weight method is forecasted： by combining the entropy weight method with other methods innovatively， a reasonable and comprehensive evaluation index system can be built， and applied in the development trend of water resources utilization and spatio-temporal pattern evolution.
Taniantaweng Mountains （30°45′~30°11′ N， 96°30′~97°30′ E） is situated towards the west of the Hengduan Mountains and lies in the transition zone of the southeastern Qinghai-Tibet Plateau （QTP） and the Yunnan-Guizhou Plateau （YGP）. During the Quaternary period， multiple glaciations occurred on the planation surface of the middle section of Taniantaweng Mountains； hence， it contains numerous typical glacial erosional and depositional landforms. The Quaternary glaciers in this area are marine glaciers， maintained by precipitation brought by the South Asian monsoon. Thus， the advances and retreats of these Quaternary glaciers directly reflect the fluctuations of the South Asian monsoon and are highly important for Quaternary glacial research. The Qinggulong Valley is about 7 km long and possesses numerous groups of preserved moraines in clear and complete formations. Moraine QM3 was distributed within an altitude range of 4 600 to 5 250 m， and extended from upstream to downstream for approximately 7 km. ESR and OSL dating results reveal that these moraines were formed during the LGM and correspond to MIS 2. Moraine QM2 was preserved at altitudes between 5 290 and 5 175 m in the cirque， displayed a greyish-yellow colour and an arcuate distribution and was recorded lying across the cirque mouth. Moraine QM1 was distributed 5 360~5 270 m， and massive granite debris were scattered on the surface. Here， we investigated the QM2 moraine history of the Qinggulong Valley using cosmogenic 10Be surface exposure dating techniques. The three samples for QM2 yielded ages of （6.13±0.37）， （8.83±0.53） and （8.37±0.50） ka， and we assigned an age range of 8.83 to 6.13 ka to this moraine， indicating a glacial event during the early-mid Holocene. In order to make regional comparisons we recalculated the 10Be ages for surrounding mountains using data compiled from previously published literature. Combined with other dating results （OSL and 14C）， we suggest that the early-mid Holocene occurred on the eastern and southeastern QTP. Air temperature and precipitation are two major factors affecting glacier change. The water vapor carried by the southwest monsoon， which influences the development of glaciers in Taniantaweng Mountains， is obstructed by high terrain barriers above 6 000 m. Thus， the precipitation reaching the Taniantaweng Mountains is significantly reduced， resulting in much smaller glaciers compared with those in glaciated areas with abundant precipitation， such as the southeastern QTP. Pollen from cores of Lake Rencuo and Hidden in southeast Tibet demonstrated that the mean air temperature in January was likely 2~3 ℃ higher than present， and mean annual precipitation during the 8~6 ka BP was 100 mm greater than the current values. At high altitudes abundant precipitation fall as snow， which led to positive glacial mass balance and glacial advance. The glacial advance in Taniantaweng Mountains during the early-mid Holocene may have resulted from an increase in precipitation from the southwest monsoon. At present， the geochronological evidence of the early-mid Holocene glacial advance event in the eastern QTP is primarily based on TCN， OSL， and radioactive 14C. The dating technology used in the current study is limited by the complex geological and geomorphic processes that have occurred in this region， and by the particularities of glacial deposition in mountain areas. Furthermore， the resolution of the glacial geomorphic age since the Holocene is insufficiently high， leading to large uncertainties in the chronological data. There are also few geochronology data available to support the glacial advance in this period. Therefore， in this study， we aim to provide an initial chronological framework and preliminary results for the early Holocene glacial advance. More accurate glacial geochronology data are required to further understand the early-mid Holocene glacial advance in the QTP. This study provides a new basis for investigating the dynamic relationships amongst glaciations， changes in the South Asian monsoon， and global climate change.
Due to the lack of snow cover extent dataset with slightly high spatiotemporal resolution and high accuracy in the Northern Hemisphere from 1981 to 1999， we used NOAA-AVHRR version 4 surface reflectance data as the basic input data and Landsat-5 TM snow maps as reference maps， to obtain the optimal threshold of snow discriminant algorithm based on multi-indicator multi-level decision tree. Then， combined with the cloud discrimination algorithm， we produced the Northern Hemisphere AVHRR L1 （Level 1） daily snow cover extent dataset. In addition， aimed at the complete lack of AVHRR dataset in high latitudes and partial lack of data in low latitudes， we filled the gaps of AVHRR L1 dataset by the Northern Hemisphere 0.25° snow depth dataset， and generated AVHRR L2 （Level 2） daily snow cover extent dataset. Finally， taking 2 546 ground snow depth stations measurements from 1981 to 1999 and 939 Landsat-5 TM snow maps as validation data， accuracy of the Northern Hemisphere AVHRR daily snow cover dataset was accessed. The results showed that overall accuracy （OA） of AVHRR L1 and L2 dataset is 81.8% and 82.2%， user’s accuracy （UA） is 83.7% and 83.8%， and producer’s accuracy （PA） is 81.7% and 84.2%， respectively. These accuracies were relatively high， and commission error and omission error were relatively balanced. Furthermore， we used Landsat-5 TM snow maps for L2 dataset to perform accuracy assessment. The results showed that OA of L2 dataset is 90.3%， UA is 90.2% and PA is 99.1%. Therefore， our product has virtually provided more reliable snow knowledge over the Northern Hemisphere， and thereby can better serve for study on global snow cover change.
The interaction between permafrost and atmosphere is mainly accomplished through the thermal and hydro-dynamics in the active layer. In background of climate change， the simulation of freezing-thawing process， active layer thickness map and variation-prediction are the basis of studying ecological environment， hydrology， engineering and carbon cycle of permafrost regions. For this paper， we summarize the application of different revised Stefan equations in simulating freezing-thawing process and active layer thickness， as well as its significant application in multi-layer soil， and then discuss the possible questions in its implication. Stefan equation revealed the linkage between change of surface temperature （or air temperature） and freezing-thawing process of ice （or soil） in a simple form， which significantly simplified the analysis and calculation of freezing-thawing process of soil. Stefan equation， with less parameters， simple form and reliable simulation results， is widely used to simulate freezing-thawing process. Also， more and more studies focusing on coupled it to climate model， land surface model and hydrological model. Stefan equation was originally proposed in the study of lake ice formation in the Arctic region and later widely used in permafrost. It was improved by considering soil water content， difference between ground and air temperature on different underlying， topography， precipitation and other factors， and even was applied to simulate freezing-thawing process of heterogeneous soil. However， on the Qinghai-Tibet Plateau， Stefan equation is widely used for simulating spatial distribution of active layer thickness of permafrost for homogeneous soil but rarely applied to heterogeneous soils. Therefore， it is necessary to further study that Stefan equation simulated freezing-thawing process for multilayer soil in the future， which will provide a basic method for accurately studying the response of permafrost to climate change.
With acceleration of industrialization process， water pollution and heavy metal pollution incidents in the soil have gradually increased， and management and remediation of the environment has become an urgent need. When freezing technology is used to purify and remediate contaminated soil and water， only “cold energy” is input to the formation. There is no secondary pollution in the treatment process， which makes the freezing technology receive more and more attention in the environmental field. This paper introduces in detail the mechanism of freezing technology to remediate polluted water and soil and summarizes the application status and latest research progress of freezing technology in sewage， sludge and heavy metal contaminated soil. The mechanism of freezing remediation is to achieve the directional drive and enrichment of pollutants through the self-purification effect of ice and the principle of solid-liquid phase equilibrium. However， due to adsorption and retardation between cohesive soil particles， the difficulty of remediation of heavy metal contaminated soil with single method is more complicated. Freezing technology combined with other remediation technology is a new treatment method. The low permeability of frozen soil can effectively reduce the migration speed of pollutants to block different types of pollutants and form a frozen barrier to prevent pollutants diffusion. Freezing remediation technology has a good market application prospect in environmental remediation.
