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Permafrost ground ice melting could alter hydrological processes in cold regions by releasing water. Currently, there is a lack of gridded data of ground ice from the Qinghai‐Tibet Plateau (QTP). Using 664 borehole sample records, we applied a random forest (RF) method to predict the ground ice content of permafrost between 2 and 10 m depth in three layers (2–3, 3–5, and 5–10 m) at a spatial resolution of 1 km. The RF predictions demonstrated an R2 value exceeding 0.80 for all three layers with a negligible positive overestimation (0.98%–1.85%). The ground ice content of the first layer (2–3 m) can be predicted primarily using climate variables, but the contribution of terrain and soil variables increases as the depth increases. The total water storage of ground ice across the QTP permafrost (2–10 m depth) is approximately 3330.0 km3, with 403.5 km3 in the 2–3 m layer, 857.2 km3 in the 3–5 m layer, and 2069.3 km3 in the 5–10 m layer. This study generated for the first time a gridded dataset of the shallow permafrost ground ice content across the entire QTP which can be used to improve simulations of hydrological processes in the permafrost regions. [ABSTRACT FROM AUTHOR]

In this study, Cu-doped ZnO was prepared via the facile one-pot solvothermal approach. The structure and composition of the synthesized samples were characterized by XRD (X-ray diffraction), TEM (transmission electron microscopy), and XPS (X-ray photoelectron spectroscopy) analyses, revealing that the synthesized samples consisted of Cu-doped ZnO nanoparticles. Ultraviolet–visible (UV-vis) spectroscopy analysis showed that Cu-doping significantly improves the visible light absorption properties of ZnO. The photocatalytic capacity of the synthesized samples was tested via the disinfection of Escherichia coli, with the Cu-ZnO presenting enhanced disinfection compared to pure ZnO. Of the synthesized materials, 7% Cu-ZnO exhibited the best photocatalytic performance, for which the size was ~9 nm. The photocurrent density of the 7% Cu-ZnO samples was also significantly higher than that of pure ZnO. The antifungal activity for 7% Cu-ZnO was also tested on the pathogenic fungi of Fusarium graminearum. The macroconidia of F. graminearum was treated with 7% Cu-ZnO photocatalyst for 5 h, resulting in a three order of magnitude reduction at a concentration of 105 CFU/mL. Fluorescence staining tests were used to verify the survival of macroconidia before and after photocatalytic treatment. ICP-MS was used to confirm that Cu-ZnO met national standards for cu ion precipitation, indicating that Cu-ZnO are environmentally friendly materials. [ABSTRACT FROM AUTHOR]

The freeze–thaw (F-T) cycle of the active layer (AL) causes the "frost heave and thaw settlement" deformation of the terrain surface. Accurately identifying its amplitude and time characteristics is important for climate, hydrology, and ecology research in permafrost regions. We used Sentinel-1 SAR data and small baseline subset-interferometric synthetic aperture radar (SBAS-InSAR) technology to obtain the characteristics of F-T cycles in the Zonag Lake-Yanhu Lake permafrost-affected endorheic basin on the Qinghai-Tibet Plateau from 2017 to 2019. The results show that the seasonal deformation amplitude (SDA) in the study area mainly ranges from 0 to 60 mm, with an average value of 19 mm. The date of maximum frost heave (MFH) occurred between November 27th and March 21st of the following year, averaged in date of the year (DOY) 37. The maximum thaw settlement (MTS) occurred between July 25th and September 21st, averaged in DOY 225. The thawing duration is the thawing process lasting about 193 days. The spatial distribution differences in SDA, the date of MFH, and the date of MTS are relatively significant, but there is no apparent spatial difference in thawing duration. Although the SDA in the study area is mainly affected by the thermal state of permafrost, it still has the most apparent relationship with vegetation cover, the soil water content in AL, and active layer thickness. SDA has an apparent negative and positive correlation with the date of MFH and the date of MTS. In addition, due to the influence of soil texture and seasonal rivers, the seasonal deformation characteristics of the alluvial-diluvial area are different from those of the surrounding areas. This study provides a method for analyzing the F-T cycle of the AL using multi-temporal InSAR technology. [ABSTRACT FROM AUTHOR]

Relict permafrost presents an ideal opportunity to understand the impacts of climatic warming on the ground thermal regime since it is characterized by a mean annual ground temperature close to 0 ∘ C and relatively thin permafrost. The long-term and continuous observations of permafrost thermal state and climate background are of great importance to reveal the links between the energy balance on hourly to annual timescales, to evaluate the variations in permafrost thermal state over multiannual periods and to validate the remote sensing dataset. We present 11 years of meteorological and soil data from the Mahan Mountain relict permafrost site of northeastern Qinghai–Tibet Plateau. The meteorological data comprise air and land surface temperature, relative humidity, wind speed and direction, shortwave and longwave downwards and upwards radiation, water vapor pressure, and precipitation on a half-hour timescale. The active layer data include daily soil temperature and soil volumetric water content at five different depths. The permafrost data consist of the ground temperature at 20 different depths up to 28.4 m. The high-quality and long-term datasets are expected to serve as accurate forcing data in land surface models and evaluate remote-sensing products for a broader geoscientific community. The datasets are available from the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.271838, Wu and Xie, 2021). [ABSTRACT FROM AUTHOR]

Relict permafrost presents an ideal opportunity to understand the impacts of climatic warming on the ground thermal regime since it is characterized by mean annual ground temperature close to 0 °C and relatively thin permafrost. The long-term and continuous observations of permafrost thermal state and climate background are of great importance to reveal the links between the energy balance on hourly to annual timescales, to evaluate the variations of permafrost thermal state over multi-annual periods and to validate the remote sensing dataset. Until now there are few data available in relict permafrost regions although those data are important to understand the impacts of climate changes on permafrost especially in the boundary regions between permafrost and seasonally frozen ground regions. In this study, we present 11 years of meteorological and soil data in a relict permafrost site of the Mahan Mountain on the northeast of the Qinghai-Tibet Plateau. The meteorological data are comprised of air and ground surface temperature, relative humidity, wind speed and direction, shortwave and longwave downward and upward radiation, water vapor pressure, and precipitation on half-an-hour timescale. The active layer data include daily soil temperature and soil moisture at five different depths. The permafrost data consist of ground temperature at twenty different depths up to 28.4 m. The high-quality and long-term datasets are expected to serve as accurate forcing data in land surface models and evaluate remote-sensing products for a broader geoscientific community. The datasets are available from the National Tibetan Plateau/Third Pole Environment Data Center (https://doi.org/10.11888/Cryos.tpdc.271838, Wu and Xie, 2021). [ABSTRACT FROM AUTHOR]

Permafrost has great influences on the climatic, hydrological, and ecological systems on the Qinghai–Tibet Plateau (QTP). The changing permafrost and its impact have been attracting great attention worldwide like never before. More observational and modeling approaches are needed to promote an understanding of permafrost thermal state and climatic conditions on the QTP. However, limited data on the permafrost thermal state and climate background have been sporadically reported in different pieces of literature due to the difficulties of accessing and working in this region where the weather is severe, environmental conditions are harsh, and the topographic and morphological features are complex. From the 1990s, we began to establish a permafrost monitoring network on the QTP. Meteorological variables were measured by automatic meteorological systems. The soil temperature and moisture data were collected from an integrated observation system in the active layer. Deep ground temperature (GT) was observed from boreholes. In this study, a comprehensive dataset consisting of long-term meteorological, GT, soil moisture, and soil temperature data was compiled after quality control from an integrated, distributed, and multiscale observation network in the permafrost regions of QTP. The dataset is helpful for scientists with multiple study fields (i.e., climate, cryospheric, ecology and hydrology, meteorology science), which will significantly promote the verification, development, and improvement of hydrological models, land surface process models, and climate models on the QTP. The datasets are available from the National Tibetan Plateau/Third Pole Environment Data Center (https://data.tpdc.ac.cn/en/disallow/789e838e-16ac-4539-bb7e-906217305a1d/ , last access: 24 August 2021, 10.11888/Geocry.tpdc.271107, Lin et al., 2021). [ABSTRACT FROM AUTHOR]

The comprehensive understanding of the occurred changes of permafrost, including the changes of mean annual ground temperature (MAGT) and active layer thickness (ALT), on the Qinghai‐Tibet Plateau (QTP) is critical to project permafrost changes due to climate change. Here, we use statistical and machine learning (ML) modeling approaches to simulate the present and future changes of MAGT and ALT in the permafrost regions of the QTP. The results show that the combination of statistical and ML method is reliable to simulate the MAGT and ALT, with the root‐mean‐square error of 0.53°C and 0.69 m for the MAGT and ALT, respectively. The results show that the present (2000–2015) permafrost area on the QTP is 1.04 × 106 km2 (0.80–1.28 × 106 km2), and the average MAGT and ALT are −1.35 ± 0.42°C and 2.3 ± 0.60 m, respectively. According to the classification system of permafrost stability, 37.3% of the QTP permafrost is suffering from the risk of disappearance. In the future (2061–2080), the near‐surface permafrost area will shrink significantly under different Representative Concentration Pathway scenarios (RCPs). It is predicted that the permafrost area will be reduced to 42% of the present area under RCP8.5. Overall, the future changes of MAGT and ALT are pronounced and region‐specific. As a result, the combined statistical method with ML requires less parameters and input variables for simulation permafrost thermal regimes and could present an efficient way to figure out the response of permafrost to climatic changes on the QTP. Key Points: The combined statistical method with machine learning is efficient to obtain the thermal regime of permafrost on the Qinghai‐Tibet Plateau (QTP)The present permafrost area on the QTP is ∼1.04 × 106 km2, and the average mean annual ground temperature and active layer thickness are −1.35 ± 0.42°C and 2.3 ± 0.60 m, respectivelyThe future changes of permafrost are projected to be pronounced due to climate change, but region‐specific [ABSTRACT FROM AUTHOR]

Permafrost on the Qinghai–Tibet Plateau (QTP) has undergone degradation as a result of recent climate change. This may alter the thermo‐hydrological processes and unlock soil organic carbon, and thereby affect local hydrological, ecological, and climatic systems. The relationships between permafrost and climate change have received extensive attention, and in this paper we review climate change for permafrost regions of the QTP over the past 30 years. We summarize the current state and changes in permafrost distribution and thickness, ground temperature, and ground ice conditions. We focus on changes in permafrost thermal state and in active‐layer thickness (ALT). Possible future changes in ground temperature and ALT are also discussed. Finally, we discuss the changes in hydrological processes and to ecosystems caused by permafrost degradation. Air temperature and ground temperature in the permafrost regions of the QTP have increased from 1980 to 2018, and the active layer has been thickening at a rate of 19.5 cm per decade. The response of permafrost to climate change is not as fast as in some reports, and permafrost degradation is slower than projected by models that do not account for conditions deep in permafrost. [ABSTRACT FROM AUTHOR]

The dynamics of permafrost (including the permafrost thermal state and active layer thicknesses (ALT)) across the Qinghai-Tibetan Plateau (QTP) have not been well understood on a large scale. Here we simulate the ALT and permafrost thermal state using the Geophysical Institute Permafrost Lab version 2 (GIPL2) model across the QTP. Based on the single-point simulations, the model is upscaled to the entire QTP. The upscaled model is validated with five investigated regions (IRs), including Wenquan (WQIR), Gaize (GZIR), Aerjin (AEJIR), Xikunlun (XKLIR), and Qinghai-Tibetan Highway (G109IR). The results show that the modified GIPL2 model improves the accuracy of the permafrost thermal state simulations. Due to our simulated results on the QTP, the average ALT is of 2.30 m (2.21-2.40 m). The ALT decreases with an increase in the altitude and decreases from the southeast to the northwest. The ALT is thin in the central QTP, but it is thick in the high-elevation mountain areas and some areas surrounding glaciers and lakes. The largest ALT is found in the border areas between permafrost and seasonally frozen ground regions. The simulated results of the MAGT (the mean annual ground temperature) indicate that most of the permafrost is substable, which is sensitive to climate warming. The simulated results would be of great significance on assessing the impacts of permafrost dynamics on local hydrology, ecology, and engineering construction. [ABSTRACT FROM AUTHOR]

The Noah land surface model (LSM) can simulate well the hydrological and thermal processes of permafrost in the Qinghai-Tibet Plateau (QTP) and provides more permafrost metrics than those of statistical empirical models. The aim of this study was to develop a prototype for permafrost modelling by Noah and validate the model with field data. This was accomplished by modifying Noah, introducing a new thermal roughness scheme, a parameter calibration method and extending the simulation depth to allow for soil heterogeneity. The modified Noah LSM was validated using observations from the Tanggula meteorological station. Key permafrost metrics were simulated, including mean annual ground temperature (MAGT) at the depth of zero annual amplitude (DZAA), active layer thickness (ALT) and ground ice content of the West Kunlun area in the QTP. The permafrost distribution of the West Kunlun was mapped using the simulated MAGT and compared to a permafrost distribution map based on field observations. Data from ten boreholes were used for verification. The simulation error of the MAGT is less than 1.0 °C for eight boreholes, and the ALT simulations have relative errors of less than 25 per cent for seven boreholes. The Kappa coefficient for the two maps is 0.70. Permafrost characteristics including the distribution of different permafrost types, DZAA, ALT, MAGT and ground ice content in the West Kunlun are strongly influenced by altitude and the local environment. Such permafrost modelling can be extended to the rest of the QTP. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT To determine the relationship between soil organic matter (SOM) decomposition and chemistry in the permafrost region of the Qinghai-Tibet Plateau (QTP), 300-day laboratory incubations at 25°C and chemical fractionation were performed to characterise the mineralisation dynamics of organic carbon from soils under five vegetation conditions. The respiration rates in wet meadows were the highest, followed by the Kobresia pygmaea meadow and K. robusta meadow. After the incubation period, all four fractions of SOM - non-polarity soluble, water soluble, holocellulose and lignin contents - showed some decline, and the SOM decreased by 16-20 per cent in soils of the steppe, meadow and wet meadow. These results suggest that a large proportion of the organic matter in soils of the permafrost region in the QTP is mineralisable. Based on the changes in chemical fractions of organic matter, it could be determined that soils with higher water-soluble fractions had higher rates of carbon mineralisation, while the mechanisms involved in the respiration of different chemical fractions are complicated. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study, the ground surface temperature (GST) records from 16 meteorological stations, which are located in or adjacent to permafrost regions on the central Qinghai-Tibet Plateau (QTP), are analysed using Mann-Kendal test and Sen's slope estimate methods. We revealed that the GSTs have shown statistically significant warming. On average, mean annual ground surface temperature has increased at a rate of 0.60 °C decade−1 over the period of 1980-2007, which is more pronounced than the increase of mean annual air temperature on the plateau. The winter ground surface warming is especially prominent, which is similar to the seasonal trends in changes of air temperature. As important parameters to assess the changes of ground thermal regime in cold regions, surface freezing and thawing indices were also studied. The nonparametric statistic test and estimate indicate that surface freezing and thawing indices both show significant variations (−111.2 and 125.0 °C d decade−1, respectively) on the central QTP. The intensive ground surface warming is responsible for the concurrent increase in permafrost temperatures at the long-term observation sites on the plateau. The close correlations between ground surface and permafrost temperatures indicate that the dramatic ground surface warming could have significant influence on the change of permafrost thermal regime in the study region. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

ABSTRACT Soil organic carbon (SOC) contents were examined beneath two grassland vegetation communities and cold desert sites in permafrost areas of the central western part of the Qinghai-Tibet Plateau. Mean SOC stocks in the top 150 cm were 7.73 kg m-2 for Stipa roborowskyi communities and 3.72 kg m-2 for Carex moorcroftii communities, but only 1.84 kg m-2 for cold alpine desert. More than 80 per cent of SOC stocks beneath the grasslands were in the top 100 cm. Correlation analyses showed that SOC stocks in the top 150 cm are linked to soil moisture content, and the vertical distribution of SOC is mainly affected by depth and soil moisture content. Moisture content and vegetation communities are therefore important factors associated with SOC content in this cold, arid area, while active-layer thickness, vegetation cover and topographical factors play non-significant roles in SOC distribution. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Spatial information of particle size fractions (PSFs) is primary for understanding the thermal state of permafrost in the Qinghai-Tibet Plateau (QTP) in response to climate change. However, the limitation of field observations and the tremendous spatial heterogeneity hamper the digital mapping of PSF. This study integrated log-ratio transformation approaches, variable searching methods, and machine learning techniques to map the surficial soil PSF distribution of two typical permafrost regions. Results showed that the Boruta technique identified different covariates but retained those covariates of vegetation and land surface temperature in both regions. Variable selection techniques effectively decreased the data redundancy and improved model performance. In addition, the spatial distribution of soil PSFs generated by four log-ratio models presented similar patterns. Isometric log-ratio random forest (ILR-RF) outperformed the other models in both regions (i.e., R2 ranged between 0.36 to 0.56, RMSE ranged between 0.02 and 0.10). Compared with three legacy datasets, our prediction better captured the spatial pattern of PSFs with higher accuracy. Although this study largely improved the accuracy of spatial distribution of soil PSFs, further endeavors should also be made to improve model accuracy and interpretability for a better understanding of the interaction and processes between environmental predictors and soil PSFs at permafrost regions. [ABSTRACT FROM AUTHOR]

Lakes on the Qinghai–Tibetan Plateau (QTP) have experienced significant changes, especially the prevailing lake expansion since 2000 in the endorheic basin. The influence of permafrost thawing on lake expansion is significant but rarely considered in previous studies. In this study, based on Landsat images and permafrost field data, the spatial-temporal area changes of lakes of more than 5 km2 in the endorheic basin on the QTP during 2000–2017 is examined and the impact of permafrost degradation on lake expansion is discussed. The main results are that permafrost characteristics and its degradation trend have close relationships with lake changes. Lake expansion in the endorheic basin showed a southwest–northeast transition from shrinking to stable to rapidly expanding, which corresponded well with the permafrost distribution from island-discontinuous to seasonally frozen ground to continuous permafrost. A dramatic lake expansion in continuous permafrost showed significant spatial differences; lakes expanded significantly in northern and eastern continuous permafrost with a higher ground ice content but slightly in southern continuous permafrost with a lower ground ice content. This spatial pattern was mainly attributed to the melting of ground ice in shallow permafrost associated with accelerating permafrost degradation. Whereas, some lakes in the southern zones of island-discontinuous permafrost were shrinking, which was mainly because the extended taliks arising from the intensified permafrost degradation have facilitated surface water and suprapermafrost groundwater discharge to subpermafrost groundwater and thereby drained the lakes. Based on observation and simulated data, the melting of ground ice at shallow depths below the permafrost table accounted for 21.2% of the increase in lake volume from 2000 to 2016. [ABSTRACT FROM AUTHOR]

Abstract The variations in land surface heat fluxes affect the ecological environment, hydrological processes and the stability of surface engineering structures in permafrost regions of the Qinghai-Tibetan Plateau (QTP). Based on observation data from a meteorological station in the Tanggula site in 2005, which is located in a permafrost region on the QTP, the performances of seventeen selected the phase 5 of the Coupled Model Intercomparison Project (CMIP5) were evaluated. The results showed that these simulations did not perform well using sensible heat flux, downward shortwave radiation or upward shortwave radiation, and differences exist among the models. The average multimodel ensemble results were similar to the observed land surface heat fluxes. The results revealed that the monthly average latent heat flux and the net radiation were small in December and January and large in May, June and July. The fluctuation in the soil heat flux was well correlated with the net radiation, and the sensible heat flux was negative in January and December in northwest of the Plateau. The latent heat flux was the strongest over the southeastern QTP from May to August, and it decreased over the northwestern QTP. In contrast, the sensible heat flux was the weakest over the southeastern QTP, and it gradually increased and became dominant over the northwestern QTP. The results also indicated that there was a good correlation between the surface heating field intensity and the net radiation, with a correlation coefficient of 0.99; this indicates stronger heating over the eastern QTP than over the western QTP and stronger heating over the southern QTP than over the northern QTP. Furthermore, the Bowen ratio was higher during the freezing and thawing stages than that during the completely thawed stage. This ratio was larger over the central and northeastern QTP and smaller along the northwest edge of the QTP, which was lower (range from −0.81 to 4.86) due to the overestimation of precipitation, a smaller difference between the simulated monthly average surface temperature and the observed air temperature, and a decrease in wind speed when using the CMIP5 models in the permafrost region of the QTP. This research provides a foundation for understanding land surface heat flux characteristics in the permafrost regions on the QTP under climate change. Highlights • Evaluate the performance of the CMIP5 model in the permafrost regions of the QTP. • Analyze variations in the spatial distribution of land surface heat flux values on the QTP. • Demonstrate the effect of the freezing and thawing process on land surface heat fluxes. [ABSTRACT FROM AUTHOR]

Soil thermodynamic properties are critical for determining the soil freezing and thawing depths of active layers which is highly important for the hydrology and energy balances of permafrost regions. Here, three soil thermal conductivity parameterizations were evaluated against detailed field measurements at two field sites in the permafrost region of Qinghai-Xizang (Tibet) Plateau (QXP). The results revealed that the comprehensive parameterization based on different schemes for calculating soil thermal conductivity is relatively close to the measured values in unfrozen soil, and Johansen's parameterization is the best in the frozen soil. Then, we first combined three thermal conductivity parameterizations with a freeze-thaw algorithm to simulate freezing and thawing depths of multi-layered soil. The analysis showed that the average percentage difference between the observed and calculated soil thawing depth values for the Johansen's and comprehensive parameterization was 10.42% and 8.49% at Tanggula (TGL) and Xidatan (XDT), receptively. It indicated that the comprehensive parameterization with freeze-thaw algorithm simulated the soil thawing depth more similarly to the observed data for multi-layered soil. These findings can also be incorporated into other land surface, hydrological or ecosystem models to simulate the freeze-thaw cycles in permafrost regions. [ABSTRACT FROM AUTHOR]

• Analysis the hysteresis characteristic of ground temperature with depth increasing. • Develop models to obtain ground temperatures from air temperature. • Compare the models used to estimate ground temperature at different depths. • Evaluate the applicability of these models in the permafrost regions on the QTP. Air and ground temperatures are important factors contributing to land and atmosphere processes as well as ecosystem dynamics. This paper presents a simple model for simulating ground temperature from air temperature in the permafrost regions on the Qinghai-Tibetan Plateau (QTP). The model takes hysteresis between daily air temperature and ground temperature into consideration as well as exponential and linear functions for annual average ground temperatures at different depths. Results indicate an evident hysteresis in ground temperature with increasing depth. By taking hysteresis into account, the developed model provides improved daily ground temperature estimates compared to those obtain from the original linear regression, at Xidatan (site QT09) and Kunlun Pass (site CN06) in the permafrost regions on the QTP, with an average root mean square error (RMSE), normalized standard error (NSEE), and mean absolute error (MAE) of 1.12 °C, 0.41, and 0.84 °C for QT09, and 1.41 °C, 0.29 and 1.10 °C for CN06, respectively, at all depths. The results indicate that the model that takes hysteresis into account provides monthly ground temperatures that are closest to field observations, with an average RMSE, NSEE, and MAE of 0.63 °C, 0.24, and 0.50 °C, respectively, at QT09 site and 0.92 °C, 0.18 and 0.63 °C, respectively, at CN06 site. In addition, the simulation accuracy of the average annual ground temperature is significantly improved by using the combined exponential and linear model, and this is particularly relevant when drilling boreholes at great depths in permafrost regions. Therefore, these models provide a useful and simple method for simulating ground temperature and modeling permafrost changes under global warming conditions. [ABSTRACT FROM AUTHOR]