Central Qinghai-Tibetan Plateau Research Articles

Influence mechanism of seasonal rainfall on hydrothermal changes of permafrost active layer in the central Qinghai-Tibet Plateau

Influence mechanism of seasonal rainfall on hydrothermal changes of permafrost active layer in the central Qinghai-Tibet Plateau

Re-intensification of flash drought in western China over the past decade: Implications of fluctuating wetting trend

Climate changes and human activities have led to a rise of frequency and intensity of the global flash droughts, resulting in severe consequences for ecosystems, agriculture, and human societies. However, research dedicated to flash droughts in the dryland of western China is relatively limited, leaving their evolutionary characteristics and development processes of these phenomena unclear. To bridge this gap, this study analyzed the spatiotemporal characteristics of flash droughts in western China from 1981 to 2020, based on the standardized evapotranspiration stress index. Additionally, we investigated the development mechanisms by taking meteorological conditions and soil moisture into account. The findings revealed that the northern Qinghai-Tibet Plateau, western Qilian Mountains, and western and southern Loess Plateau are hotspots of flash droughts, characterized by rapid development rates. Across most of the study area, flash drought events persisted between 25 and 30 days. Adequate precipitation is necessary before the onset of flash droughts in western China, while water scarcity and high temperatures played crucial roles in driving the mid-stage of flash droughts. Within the context of the observed “warming and wetting” trend, the average flash droughts occurrence from 2011 to 2020 was approximately 16 % lower than that from 1981 to 1990, and there was a significant annual decrease in spatial coverage of 0.01 % per year. However, in the “wetting in west, drying in east” trend, the spatial coverage of flash droughts has shifted from a declining trend to an insignificant increasing trend since 2000 in the study area, with significant regional differences between the western and eastern regions. Over the past decade, flash droughts had once again intensified in the central Qinghai-Tibet Plateau and the Loess Plateau due to warming and fluctuating wetting trends, raising significant concerns for future ecosystem and agricultural water management in these regions.

Estimation of shallow groundwater recharge in central Qinghai-Tibet Plateau by combining unsaturated zone simulation and improved water table fluctuation method

Accurate estimation of groundwater recharge (GR) is crucial for sustainable groundwater use, particularly in alpine regions that are sensitive to climate change response. However, quantifying the amount of GR in these areas is challenging due to the absence of measurement data and an unclear understanding of the GR mechanism. In this paper, we proposed a new method (HS-IWTF) for estimating GR in the central Qinghai-Tibet Plateau. The method utilized Hydrus-1D to create an unsaturated zone soil water transport model, which provides a reference value for specific yield (Sy). Additionally, the method incorporated the impact of groundwater potential decline at various freeze–thaw stages to improve recharge estimation. The results showed that HS-IWTF method can be better applied for estimating GR in alpine regions. The simulated recharge of groundwater though vertical infiltration ranged from 191.7 to 217.8 mm/yr, primarily from precipitation infiltration. The total GR ranged from 312.1 to 405.0 mm/yr, with significant recharge contributed by snow and ice thaw and lateral runoff. The HS-IWTF method is more precise and reliable than simulated infiltration and traditional water table fluctuation (WTF) method in reflecting recharge changes at various monitoring sites during each freeze–thaw period. The thawing process period (0.95 mm/d, 11 %) and the complete thawing period (1.07 mm/d, 61 %) contributed more recharge at higher recharge rates due to improved recharge sources and conditions. The air temperature rise promoted the degradation of the cryosphere and raised the ratio of recharge precipitation (GR/PT), particularly in regions with high altitude and proximity to permafrost and glaciers where recharge was significantly high during the freezing period. This study provides valuable information on the measurement of GR in alpine regions and the crucial role of freeze–thaw processes in GR.

Control of local topography and surface patterning on the formation and stability of a slope permafrost peatland at 4800-m elevation on the central Qinghai-Tibetan Plateau

Some sloping peatlands in northern regions often develop surface microtopographic patterns to maintain their water balance and ecosystem functioning. However, we do not know whether and how spatial patterning would influence the water balance and peat formation of permafrost-affected peatlands in relatively dry regions. Here we used data from the field observations and Unmanned Aerial Vehicle (UAV) survey of a slope peatland at an elevation of around 4800 m in the hinterland of the Qinghai-Tibetan Plateau (QTP) to document and understand the topographic controls of water balance and vegetation growth. Our terrain analysis result shows that the peatland—located on the middle section of a hillslope—has a gentle slope of 5.6° ± 2.5°, while the non-peatland upper section has a steep slope of 12° ± 4.5°. The great upstream catchment area and the presence of shallow impermeable permafrost likely create a saturated condition for peat formation. Our UAV results show obvious spatial patterning of abundant pools and ridges across this peatland, and pool sizes and ridge abundance increase with increasing slopes, suggesting that slope-controlled water flow gradient is the main driver of ridge formation and that ridges is to slow down the runoff. UAV-derived greenness values show a positive relationship with the total pool extent locally (R2 = 0.60) and decrease with increasing distance from the individual pools, suggesting sensitive responses of vegetation growth to surface moisture. Thus, enhanced vegetation growth and likely resultant great peat accumulation immediately around pools potentially further differentiate surface microtopography, strengthening the pool stability. We conclude that the local slope gradient, surface patterning (pools and ridges) and permafrost interact together to regulate water flow and maintain water balance, which in turn regulate the vegetation growth, peat accumulation and peatland stability. Our study implies that the delicate water balance maintained partly by microtopography is sensitive to climate change—especially potential extreme hydroclimate events—and natural and human-induced disturbances that may modify the surface patterning and weaken the peatland’s stability, affecting the carbon sequestration ability of this type of peatlands.

Lakes-scale pattern of eukaryotic phytoplankton diversity and assembly process shaped by electrical conductivity in central Qinghai-Tibet Plateau.

Phytoplankton are the main primary producers in aquatic ecosystems and play an important role in food web and geochemical cycles. Its diversity, community structure, and assembly process are influenced by several factors. Alpine lake ecosystems are relatively weak and extremely sensitive to global climate change. However, the impact of climate change on phytoplankton in Qinghai-Tibet Plateau lakes and their responses are still unclear. In this study, we analyzed the diversity, environmental drivers, and assembly process of phytoplankton community in the central QTP lakes. The phytoplankton of these lakes can be primarily distinguished into freshwater and brackish types, with significant differences in species diversity and community dissimilarity. Both shared nearly same key environmental factors that significantly affecting phytoplankton such as EC, and brackish lakes were also positively correlative with TN. Stochastic process was predominant in phytoplankton assembly. Additionally, freshwater and brackish lakes were dominated by dispersal limitation and heterogeneous selection respectively. Alpine lakes had significant EC thresholds, and their diversity and assembly processes changed significantly around the thresholds. The present findings have important implications for understanding and predicting the response of lake phytoplankton communities to climate change and for making decisions to protect the ecological resources of alpine lakes.

Climatic characteristics of precipitation change and its multiscale causes over Central Qinghai–Tibet Plateau

AbstractRegional climates have changed as a result of global warming, which has sped up cirrus circulation and altered the temporal and spatial distribution of precipitation. As climate change intensifies, the pattern of precipitation in the Hoh Xil (HX) region has changed. The dislocation of rain and heat in summer hinders ecological restoration and brings great ecological threat. And it is important to clarify the causes and scopes of the midsummer drought (MSD). In this study we highlight the causes of MSD in terms of water vapour transport, circulation structure and the related influencing factors. We found that (1) the HX region gradually entered a drying‐warming process as MSD developed after 2005. (2) The change in the water vapour balance is the direct cause of MSD in the HX. (3) As a typical climate key zone, the HX is located in the transition region between the westerlies and the Indian monsoon. (4) Regional evaporation capacity is the main factor affecting the occurrence of MSD. The dominant factor shifted from being energy to water with the occurrence and enhancement of MSD. This study complements the scarce research on precipitation anomalies in the HX, provides support for clarifying the impact of climate change on the Qinghai–Tibet Plateau (TP) and contributes to understanding the trends and mechanisms of climate change over the TP under global warming.

A new perspective for assessing hydro-meteorological drought relationships at large scale based on causality analysis

Correlation analysis is the common method to evaluate the relationship between two variables; however, it may sometimes cause spurious correlations. Specifically, in the field of hydrometeorology, with the impacts of climate change and human activities, correlation analysis is difficult to identify the true relationship between variables, and thus, causality analysis should be adopted instead. This study analyzed the causal relationship between meteorological drought and hydrological drought in different climatic regions of China by using convergent cross mapping (CCM). We improved the identification of CCM convergence by using the coefficient of variation and applied it in the field of large-scale hydrometeorology. The results of correlation analysis were compared, and the applicability of causality analysis was explored. The results revealed that: In Southeast China, the correlation and causality between meteorological drought and hydrological drought were both large. In Northeast China and central Qinghai–Tibet Plateau, the correlation between meteorological drought and hydrological drought was small, but the causality was large. In view of the spurious correlation, introducing causality analysis can better explain the relationship between meteorological drought and hydrological drought, especially in areas with snowmelt runoff. Overall, CCM can provide valuable causal information from common time series in the field of large-scale hydrometeorology and has a wide range of application values. However, causality analysis cannot explain the positive or negative relationship between variables. Therefore, when analyzing the relationship between variables, the advantages of the two methods should be given full play.

Impacts of climate change on herpetofauna diversity in the Qinghai-Tibetan Plateau.

Although numerous studies on the impacts of climate change on biodiversity have been published, only a handful are focused on the intraspecific level or consider population-level models (separate models per population). We endeavored to fill this knowledge gap relative to the Qinghai-Tibetan plateau (QTP) by combining species distribution modeling (SDMs) with population genetics (i.e., population-level models) and phylogenetic methods (i.e., phylogenetic tree reconstruction and phylogenetic diversity analyses). We applied our models to 11 endemic and widely distributed herpetofauna species inhabiting high elevations in the QTP. We aimed to determine the influence of environmental heterogeneity on species' responses to climate change, the magnitude of climate-change impacts on intraspecific diversity, and the relationship between species range loss and intraspecific diversity losses under 2 shared socioeconomic pathways (SSP245 and SSP585) and 3 future periods (2050s, 2070s, and 2090s). The effects of global climatic change were more pronounced at the intraspecific level (22% of haplotypes lost and 36% of populations lost) than the morphospecies level in the SSP585 climate change scenario. Maintenance of genetic diversity was in general determined by a combination of factors including range changes, species genetic structure, and the part of the range predicted to be lost. This is owing to the fact that the loss and survival of populations were observed in species irrespective of the predicted range changes (contraction or expansion). In the southeast (mountainous regions), climate change had less of an effect on range size (>100% in 3 species) than in central and northern QTP plateau regions (range size <100% in all species). This may be attributed to environmental heterogeneity, which provided pockets of suitable climate in the southeast, whereas ecosystems in the north and central regions were homogeneous. Generally, our results imply that mountainous regions with high environmental heterogeneity and high genetic diversity may buffer the adverse impacts of climate change on species distribution and intraspecific diversity. Therefore, genetic structure and characteristics of the ecosystem may be crucial for conservation under climate change.

Autumn migration of black-necked crane (Grus nigricollis) on the Qinghai-Tibetan and Yunnan-Guizhou plateaus.

Despite previous research efforts, the majority migration routes of the black-necked cranes (Grus nigricollis) have remained veiled. In this study, we utilized satellite telemetry data from 45 cranes between 2015 and 2021 to unveil critical insights. Our results revealed 11 distinct autumn migration routes and one sedentary flock, of which eight routes and the sedentary flock were previously undocumented. Our findings highlighted the remarkable diversity in the migration routes of black-necked cranes, especially in terms of migration orientations, spatial-temporal patterns, and altitudinal movement patterns. Cranes breeding on the eastern, northern, and central Qinghai-Tibetan Plateau migrated southward, while those on the northern slopes of the Himalayas migrated eastward, westward, northward, or opted to remain sedentary. Moreover, we expanded the known range of migration distances to 84-1520 km at both ends (excluding sedentary individuals) and identified two long-term (Da Qaidam and Chaka) and one short-term (Gyatong grassland) stopover sites. Furthermore, our study revealed that the breeding colonies in the Qilian Mountains on the northeastern Qinghai-Tibetan Plateau utilized long-term stopover sites before embarking on significant altitude ascent, while other flocks displayed more urgent migration patterns, preferring to roost only at night. By unveiling the near-complete autumn migration routes of black-necked cranes, our research has contributed to discovering the critical habitats and connectivity among various breeding colonies, which is instrumental in developing effective seasonal conservation plans.

Distribution Characteristics of Groundwater Table in the Nagqu River Basin, Central Qinghai-Tibet Plateau

Distribution Characteristics of Groundwater Table in the Nagqu River Basin, Central Qinghai-Tibet Plateau

Deep convective clouds observed by ground-based radar over Naqu, Qinghai–Tibet Plateau

The deep convective clouds (DCCs, 20 dBZ echo top exceeding 14 km) and intense DCCs (IDCCs, 40 dBZ echo top exceeding 10 km) over Naqu, a city featuring the most active convection in the central Qinghai–Tibet Plateau, were analyzed on the basis of data derived from the Naqu C-band radar within a radius of 100 km. The most frequent DCCs occur in July and at 15:00 LT (local time), in terms of monthly and diurnal variations, respectively. The geographic distribution of the DCCs seems to be related to the topography. The centers featuring the most frequent DCCs correspond to some certain hilly areas, while the ratio of IDCC to DCC is greater in some specific flat areas, which may be because the hilly topography is conducive to triggering convection but is unfavorable to the full accumulation of unstable energy. The DCCs (IDCCs) have average 20, 30 and 40 dBZ echo tops of approximately 15.8 (16.5), 12.3 (14.1) and 9.9 (11.3) km, and average areas of the regions with a composite reflectivity >20, 30 and 40 dBZ of approximately 120.3 (196.1), 37.4 (75.3) km2 and 9.2 (14.6) km2, respectively. The maximum reflectivity and horizontal extents of 20 and 30 dBZ radar echoes tend to occur at the level around −20 °C. The average horizontal extent of DCCs is much smaller than that suggested by the satellite-based radar data. In the diurnal variations in the vertical and horizontal extents of DCCs, the parameters related to 30 dBZ always increase more slowly and decrease more rapidly than those related to 20 dBZ in the afternoon, which is attributed to the generally weak convection characteristics of DCCs. The strongest convection may be around 16:00 LT in Naqu.

Effects of seasonal rainfall variations on the hydrothermal state and thermal stability of the permafrost active layer in the central Qinghai-Tibet Plateau of China

Rainfall significantly impacts the hydrothermal state and thermal stability of the permafrost active layer by modifying surface energy boundary conditions. The quantitative characterization of hydrothermal changes in the Qinghai-Tibet Plateau has long been a crucial issue, yet the mechanisms underlying the effects of seasonal rainfall on the hydrothermal state within the permafrost active layer remain poorly understood. Therefore, this study investigated the influence of seasonal rainfall variations on the hydrothermal state within the permafrost active layer based on a water-vapour-heat coupled model that optimises the surface energy balance boundary conditions. The results show that regardless of whether the spring rainfall changes or not, the Bowen ratio is >1, indicating that the main energy exchange mode between the atmosphere and surface is sensible heat flux. But following the increase in rainfall in summer and autumn, the Bowen ratio is <1, indicating that the main energy exchange mode is latent heat flux. Meanwhile, increased seasonal rainfall leads to an increase in liquid water flux and a decrease in water vapour flux, whereas decreased seasonal rainfall leads to the opposite trend. Heat conduction, water vapour thermal convection, and water vapour diffusion latent heat decrease with increasing rainfall in various seasons. However, liquid water thermal convection increases with increasing rainfall during various seasons. Seasonal rainfall variations ultimately affect permafrost thermal stability by influencing water-vapour migration and energy changes within the permafrost active layer. Among them, the active layer thickness remains basically unchanged after the spring rainfall increases by 2.0 times, whereas it decreases by 4 and 6 cm after the summer and autumn rainfall increase by 1.5 and 2.0 times, respectively. Additionally, when the rainfall during spring, summer, and autumn decreases by 2.0, 1.5, and 2.0 times, respectively, the active layer thickness increases by 7, 6, and 3 cm, respectively. Therefore, increased seasonal rainfall can alleviate permafrost degradation. Otherwise, it is unfavourable for the preservation of permafrost thermal stability.

Co-management for sustainable development and conservation in Sanjiangyuan National Park and the surrounding Tibetan nomadic pastoralist areas

The Qinghai-Tibet Plateau plays an essential role in national to regional ecological security, biodiversity conservation, and sustaining livelihood. An array of natural resource management, environmental conservation, and ecological restoration projects have been trialed and implemented in recent years in the vast Sanjiangyuan region of the central Qinghai-Tibet Plateau, aiming especially to ensure socio-ecologically appropriate and sustainable development of animal husbandry in the alpine grasslands. Novel approaches in China have included the introduction of more collaborative approaches in protected area management and the development and formal establishment of a new multi-purpose national park system. Many milestones have been achieved. However, such developments are driven largely by national and global goals and very little has been heard to date directly from the people most affected: those residing within the protected landscapes, i.e. the community stakeholders themselves. This empirical, perceptions-based study aims to partially fill this gap, drawing on the results of focus group discussions with community representatives supplemented by key informant interviews and a targeted review of the literature, to provide synthesized feedback and priority recommendations for improving “community co-management” collaborations for the joint benefit of Tibetan herders and protected areas. The mixed-method approach employed in this study was based on a conceptual model derived from Elinor Ostrom’s social–ecological systems framework, calibrated to local residents’ self-assessments of their household well-being. Results highlight how the most recent configuration of China’s national park model (i.e., its form and the approaches it utilizes) is generally deemed successful by community stakeholders, albeit with some notable perceived limitations mainly relating to a sense of lack of fairness and inclusiveness in the “one household, one post” co-management mechanism. The paper closes with discussion and recommendations around fundamental issues of equity, empowerment, and gender, finally pointing to the significance and, ultimately, the need to move even beyond co-management per se and to adopt a model of inclusive governance for conservation wherein joint deliberations and decision-making amongst diverse stakeholders are prioritized over the simple implementation of externally developed programs and management plans.

Effects of climate change and anthropogenic activity on ranges of vertebrate species endemic to the Qinghai-Tibet Plateau over 40years.

Over the past 40years, the climate has been changing and human disturbance has increased in the vast Qinghai-Tibet Plateau (QTP). These 2 factors are expected to affect the distribution of a large number of endemic vertebrate species. However, quantitative relationships between range shifts and climate change and human disturbance of these species in the QTP have rarely been evaluated. We used occurrence records of 19 terrestrial vertebrate species (birds, mammals, amphibians, and reptiles) occurring in the QTP from 1980 to 2020 to quantify the effects of climate change and anthropogenic impacts on the distribution of these 4 taxonomic groups and estimated species range changes in each species. The trend in distribution changes differed among the taxonomic groups, although, generally, ranges shifted to central QTP. Climate change contributed more to range variation than human disturbance (the sum of the 4 climatic variables contributed more than the sum of the 4 human disturbance variables for all 4 taxonomic groups). Suitable geographic range increased for most mammals, amphibians, and reptiles (+27.6%, +18.4%, and +27.8% on average, respectively), whereas for birds range decreased on average by 0.9%. Quantitative evidence for climate change and human disturbance associations with range changes for endemic vertebrate species in the QTP can provide useful insights into biodiversity conservation under changing environments.

Co- and Postseismic Deformation of the 2020 Mw 6.3 Nima (Tibet, China) Earthquake Revealed by InSAR Observations

On 22 July 2020, an Mw 6.3 earthquake occurred in Nima County, central Qinghai-Tibet Plateau, China. We used the synthetic aperture radar interferometry (InSAR) technique with Sentinel-1 images to retrieve the line of sight (LOS) coseismic deformation fields which indicate that the maximum surface displacement reached ~30 cm. We then processed a series of interferograms spanning one year after the Nima earthquake with the Small Baseline Subset Interferometric SAR (SBAS-InSAR) technique. The maximum cumulative postseismic LOS surface displacement reached ~8 cm and approximately followed a logarithmic function over time. The inversion of the fault geometry and co- and afterslip distribution shows that the epicenter location was (33.18°N, 86.88°E) at a depth of 7.4 km, and the causative fault had an N29.1°E strike and 50.2° dip. The most coseismic slip was concentrated at depths between 3 to 12 km with a peak value of 2.0 m at 7.4 km, whilst most afterslips were concentrated at depths between 0 to 12 km with a peak value of 0.2 m at 5 km. The postseismic moment energy was about 5.04 × 1017 N∙m 308 days after the event, which was approximately 13.8% of the coseismic moment energy. By analyzing the contribution of afterslip and poroelastic rebound to postseismic deformation, it was concluded that afterslip was the main early postseismic deformation mechanism. Future attention should be paid to the northern segment of the West Yibug Caka fault and East Yibug Caka fault.

Accumulation pattern and risk assessment of metal elements in permafrost-affected soils on the Qinghai-Tibet Plateau

Permafrost-affected soils can serve as a major reservoir of metal elements (MEs) from anthropogenic sources by atmospheric transport. Understandings of the contents, sources, and ecological risks of MEs in high-altitudinal permafrost regions are helpful to mitigate environmental and human health hazards under climate change. Thus, we investigated the concentrations of 21 MEs of topsoil (0–50 cm) and evaluated the environmental quality using the ecological risk assessment methods in permafrost regions on the central Qinghai-Tibet Plateau (QTP). The results showed that (1) Ca, Al, Fe, K, Mg, Ti, and Mn (max values in mg/kg d.w.: 7.61 × 104, 5.93 × 104, 3.12 × 104, 2.33 × 104, 1.49 × 104, 0.52 × 104, and 0.06 × 104, respectively) were abundant in all sampling sites. (2) The concentrations of most MEs in the alpine wet meadow were the highest, followed by the alpine meadow and alpine desert steppe. (3) Land cover types and soil properties (soil organic carbon, pH, and soil texture) were associated with MEs. (4) Ca, Al, Fe, K, Mg, Mn, Rb, Sr, Th, Zn, V, Ni, As, Pb, Cu, and Co likely originated from geogenic/pedogenic processes, and Ti, Cr, Cd, and Hg were enriched by both natural and anthropogenic sources. (5) The modified contamination degree indicated that sampling sites in permafrost regions of the QTP were in a low pollution state, while the geoaccumulation index and enrichment factor have revealed that 37.14 % of soils showed moderate pollution of Hg, and 84.44 % of soils had moderate to high enrichment levels for Cd. This study reveals accumulation patterns of MEs in permafrost regions and provides a scientific basis for the research on the ecological security of MEs in permafrost regions influenced by climate change.

Increasing Negative Impacts of Climatic Change and Anthropogenic Activities on Vegetation Variation on the Qinghai–Tibet Plateau during 1982–2019

Climate change, combined with ever-increasing anthropogenic activities, has had significant impacts on the vegetation of the Qinghai–Tibet Plateau (QTP). This study quantitatively analyzed the impacts of climate change and human activities on vegetation variation on the QTP from 1982 to 2019 based on AVHRR NDVI data and the residual trend method. The main results were as follows: (1) From 1982 to 2000, the vegetation of the QTP had an obvious restoration process, whereby 67.8% of vegetation coverage areas experienced an increasing trend, while it had a large range of degradation during 2001–2019, especially in the central QTP. (2) The positive effect of climate change on the vegetation of the QTP decreased, and the negative impact increased. The area of positive impact decreased from 68.54% in 1982–2000 to 47.13% in 2001–2019, while the negative-impact area increased from 31.46% to 52.87%. (3) The area negatively affected by human activities increased from 57.68% in 1982–2000 to 79.46% in 2001–2019 and was mainly concentrated in the grassland of the central QTP. The findings of this study provide a scientific basis for vegetation restoration and management in the QTP region.

Thermal-Moisture Dynamics at Different Underlying Surfaces in Permafrost Regions of the Central Tibetan Plateau by considering the Effect of Rainfall

The Qinghai-Tibetan Plateau (QTP) has undergone an increase in rainfall and a drastic alteration in the moisture-heat regime in active layers and engineering. To investigate the water and heat responses of natural ground and engineering to rainfall, the differences in energy on the ground surface and the thermal-moisture dynamics of different permafrost underlying surfaces were discussed. Based on the meteorological data in 2013 observed at the Beiluhe observation station, three types of underlying surfaces (i.e., natural ground, asphalt pavement, and gravel pavement) were selected to compare the differences in energy balance at the ground surface, water-energy transport process, and coupling mechanism in active layers under rainfall conditions by a coupled water vapor-heat model of the unsaturated frozen soil. The results show that the asphalt pavement greatly increases the surface net radiation and soil surface heat flux, decreases the surface evaporation latent heat, and cuts off the moisture migration between the atmosphere and the active layer. The gravel pavement significantly increases the surface evaporation latent heat to lower the soil surface heat flux, and the amount of moisture in shallow soil is strongly influenced by rainfall and evaporation. Therefore, the moisture migration and accumulation under the asphalt pavement are dominated by the water vapor flux under thermal gradients, whereas the liquid water under the water potential gradients is the major source of moisture migration under the gravel pavement. The heat transfer in the shallow active layer is dominated by heat conduction. The effect of heat conduction, water vapor migration, and phase transition on the soil temperature is evident for the asphalt pavement, while the impact of liquid water migration on the shallow soil temperature for the gravel pavement is significant in the thawing period. As a result, the soil temperature relationship between different underlying surfaces is asphalt pavement&gt;gravel pavement&gt;natural ground. The thickness of the active layer gradually decreases. Although rainfall infiltration promotes the liquid water convection of the gravel pavement, the decrease in heat flux is less than the increase in thermal conductivity. In general, the construction of asphalt pavement and gravel pavement accelerates the degradation of permafrost. The results can provide theoretical and simulated guidance for the stability prediction and analysis of various underlying surfaces in the central QTP where rainfall is increasing.

Abrupt increase in thermokarst lakes on the central Tibetan Plateau over the last 50 years

Thermokarst lakes are an important ecosystem component in permafrost terrains; therefore, quantifying changes in these lakes is important for evaluating the water balance and carbon budget on the Qinghai-Tibet Plateau (QTP). In this study, we utilized high spatial resolution aerial and satellite images from 1969, 2010, and 2019 to quantify changes in thermokarst lakes > 0.1 ha across four regions on the central QTP. The results indicated an overall significant increase in the lake number (+158%) and surface area (+123%) for all study regions over the last five decades, despite variations in change in these trends among the different landform types. Changes in individual lake processes indicated that the above lake changes were mainly characterized by a significant increase in the number of small lakes and area enlargements of large lakes, whereas thermokarst lake drainage only occurred in some gentle slope areas. By analyzing the potential factors that drive changes in thermokarst lakes in the study region, we found that persistent climate warming and the increasing of precipitation were the most likely explanations for the observed results. With continued climate warming and permafrost degradation, we expect a persistent increase in the number and surface area of thermokarst lakes; however, the probability of lake drainage may also increase with lake expansion.

Monitoring Regional-Scale Surface Deformation of the Continuous Permafrost in the Qinghai–Tibet Plateau with Time-Series InSAR Analysis

As an important indicator of permafrost degradation, surface deformation is often used to monitor the thawing and freezing process in the permafrost active layer. However, due to the large area of the continuous permafrost of the Qinghai–Tibet Plateau (QTP) and the large amount of data processed by conventional time-series InSAR, previous studies have mostly focused on local area investigations, and regional characteristics of surface deformation of the continuous permafrost area on the QTP are still unclear. In this paper, we characterized surface deformation in space and time over the main continuous permafrost area on the QTP, by analyzing 11 ascending and 8 descending orbits of Sentinel-1 SAR data acquired between 2018 and 2021 with the time-series InSAR processing system LiCSAR. The reliability of the InSAR deformation results was verified by a combination of leveling measurement data, the intercomparison of overlapping area results, and field verification. The results show that the permafrost regions of the central QTP exhibited the most significant linear subsidence trend. The subsidence trend of permafrost on the QTP was mainly related to the thermal stability of permafrost, and the regions with larger subsidence rates were concentrated in sub-stable, transitional and unstable permafrost areas. We also found that, according to analysis of time-series displacement, the beginning and ending times of permafrost thawing were highly spatially heterogeneous, with the time of maximum thawing depth varying between mid-October and mid-November, which was probably attributed to the active layer thickness (ALT), water content in the active layer, and vegetation cover in these regions. This study is of great significance for understanding the changing trend of permafrost on the QTP under the background of climate change. In addition, this study also demonstrates that combination of Sentinel-1 SAR images with the LiCSAR system has significant potential for detecting permafrost deformation with high accuracy and high efficiency at regional and global scales.