Research in Cold and Arid Regions最新文献

As an important component of carbonaceous matters, dissolved organic carbon (DOC) can absorb and scatter the solar radiation at ultraviolet and blue wavelengths. The wet deposition process has great impact on the concentration and light absorption ability of precipitation DOC, affecting the climatic effect caused by DOC in the atmosphere. In this study, light absorption and fluorescence characteristics of precipitation DOC was investigated in the central Tibetan Plateau (TP). The results showed that the mean DOC concentration and mass absorption cross-section measured at 365 nm (MAC₃₆₅) in Tanggula (TGL) station were 0.59 ± 0.42 mg/L and 0.37 ± 0.19 m²/g, respectively, while both values showed much higher volatilities than those of aerosols. DOC concentrations had significant negative correlation with the precipitation amount, while MAC₃₆₅ values increase with the precipitation amount in TGL station. Therefore, DOC with high light-absorbing ability was preferred to be retained in the atmosphere during wet deposition. In this study, precipitation DOC contained three fluorescent components (one humic-like component and two tyrosine-like components) mainly from local biomass burning sources. DOC concentration showed a negative relationship with MAC₃₆₅ value in TGL station. The wet deposition of DOC with low light-absorbing ability can reduce the strong negative radiative forcing caused by secondary organic aerosol due to high proportion of DOC in secondary organic carbon. Similar phenomenon was also found in Nam Co, Lulang and Everest stations of previous study, which may have a potential impact on radiative forcing in the atmosphere of TP.

This paper aims to assess the influence of moisture content changes during rainfall on the stability of loess high-fill slopes by taking a loess high-fill slope in Lanzhou City as an example. First, according to the moisture content monitoring data collected from a slope online monitoring system, direct shear tests were performed on soil samples of different moisture content to determine the relationship between the shear strength parameters and moisture content. Next, a coupled hydro-mechanical model with soil shear strength related to moisture content was established and used to analyze 16 working conditions with various rainfall intensities and durations for two cases: shear strength parameters from the site exploration report and those from this study. Finally, the results from the two cases were compared regarding the changes in stresses and displacements after rainfall infiltration to analyze the influence of moisture content on the stability of loess high-fill slopes. The conclusions are as follows: (1) Segmental relationship equations of cohesion and angle of internal friction were established for loess with various moisture content. (2) Under the conditions of different rainfall intensities, significant differences were observed in the trends of slope stress and displacement changes. (3) The slope displacement occurred in the shallow soil layer within about 12.5 m from the slope top, and the plastic strain concentrated in the soil layer within about 6 m from the slope top. (4) The results of slope stability analyses based on moisture content monitoring data are more in line with the observed.

Bentonite, consisting of clay minerals of the montmorillonite group, has been widely used as an adsorbent and backfill material in nuclear waste disposal and groundwater remediation. It is challenging to use bentonite as a filling material in cold regions since bentonite is highly sensitive to thermal environmental changes, during which its bulk volume and microstructure change significantly. In this study, a series of one-dimensional and three-dimensional freeze-thaw tests were carried out within a closed system to investigate the influencing factors of the deformation of bentonite under freeze-thaw cycles. Results show that the initial soil water content greatly impacts bentonite's deformation during freeze-thaw cycles. For an initial higher degree of saturation (S_r), the expansion caused by the formation of ice lenses has a greater impact than the shrinkage induced by dehydration, ice-cementation, and so on. Conversely, bentonite tends to shrink at a lower degree of saturation during freezing. And the critical degree of saturation that determines bentonite's behavior of frost heave or frost shrinkage seems to be roughly 0.8. As the number of freeze-thaw cycles rises, initially uncompacted bentonite clay becomes more compacted, and initially compacted bentonite clay remains unchanged.

There are a large number of lakes, rivers, and other natural water bodies distributed in the permafrost area of the Qinghai-Tibet Plateau (QTP). The changes in water bodies will affect the distribution of water resources in surrounding areas and downstream areas, resulting in environmental impact and bringing potential flood disasters, which will induce more serious issues and problems in alpine and high-altitude areas with a fragile habitat (such as the QTP in China). Generally, effective, reasonable, and scientific monitoring of large-scale water bodies can not only document the changes in water bodies intuitively, but also provide important theoretical reference for subsequent environmental impact prediction, and disaster prevention and mitigation in due course of time. The large-scale water extraction technology derived from the optical remote sensing (RS) image is seriously affected by clouds, bringing about large differences among the extracted water result products. Synthetic aperture radar (SAR) RS technology has the unique advantage characteristics of all-weather, all-day, strong penetration, and not being affected by clouds, which is hopeful in extracting water body data, especially for days with cloudy weather. The data extraction of large-scale water bodies based on SAR images can effectively avoid the errors caused by clouds that become prevalent at present. In this paper, the Hoh Xil Salt Lake on the QTP and its surrounding five lakes are taken as the research objects. The 2-scene Sentinel-1 SAR image data covering the whole area on 22 August 2022 was used to verify the feasibility of extracting water body data in permafrost zones. Furthermore, on 22 August 2022, the wealth here was cloudy, which made the optical RS images, e.g., Sentinel-2 images full of clouds. The results show that: using the Sentinel-1 image and threshold segmentation method to extract water body data is efficient and effective with excellent results in permafrost areas. Concretely, the Sentinel-1 dual-polarized water index (SDWI), calculated by combining dual vertical–vertical (VV) polarized and vertical–horizontal (VH) polarized data is a useful index for water extraction and the result is better than each of the VV or VH polarized images.

The changes in pore structure within soil-rock mixtures under freeze-thaw cycles in cold regions result in strength deterioration, leading to instability and slope failure. However, the existing studies mainly provided qualitative analysis of the changes in pore or strength of soil-rock mixture under freeze-thaw cycles. In contrast, few studies focused on the quantitative evaluation of pore change and the relationship between the freeze-thaw strength deterioration and pore change of soil-rock mixture. This study aims to explore the correlation between the micro-pore evolution characteristics and macro-mechanics of a soil-rock mixture after frequent freeze-thaw cycles during the construction and subsequent operation in a permafrost region. The pore characteristics of remolded soil samples with different rock contents (i.e., 25%, 35%, 45%, and 55%) subjected to various freeze-thaw cycles (i.e., 0, 1, 3, 6, and 10) were quantitatively analyzed using nuclear magnetic resonance (NMR). Shear tests of soil-rock samples under different normal pressures were carried out simultaneously to explore the correlation between the soil strength changes and pore characteristics. The results indicate that with an increase in the number of freeze-thaw cycles, the cohesion of the soil-rock mixture generally decreases first, then increases, and finally decreases; however, the internal friction angle shows no apparent change. With the increase in rock content, the peak shear strength of the soil-rock mixture rises first and then decreases and peaks when the rock content is at 45%. When the rock content remains constant, as the number of freeze-thaw cycles rises, the shear strength of the sample reaches its peak after three freeze-thaw cycles. Studies have shown that with an increase in freeze-thaw cycles, the medium and large pores develop rapidly, especially for pores with a size of 0.2–20 μm. Freeze-thaw cycling affects the internal pores of the soil-rock mixture by altering its skeleton and, therefore, impacts its macro-mechanical characteristics.

Forest canopy in a deciduous forest has significant sheltering effects on the sub-canopy solar radiation, significantly influencing the energy balance of snow and permafrost beneath the forest and their spatial distribution. This study employs a digital camera mounted with a fisheye lens to acquire photographs at various times in a growth cycle of the forest canopy at three selected sites in a deciduous forest near the Greater Khingan Mountains Forest Ecological Station, Northeast China. The vegetation types and conditions at the selected sites include P1 in Ledum-Claopodium-L. dahurica, P2 in Carex tato-L. dahurica, and P3 in Betula fruticosa-L. dahurica. After necessary image processing, these photographs were used to identify the canopy structure and its impacts on the sub-canopy solar radiation. Results show that fisheye photographs can successfully capture the forest canopy structure and are useful in estimating the sub-canopy solar radiation. The order of sheltering effects from the largest to the smallest on sub-canopy solar radiation at three selected sites is P3, P1, and P2, highly depending on the canopy density. Then sub-canopy solar radiation was calculated using fisheye photographs and an algorithm validated by in-situ observed solar radiation beneath the canopy at P1 and P3. The results are reasonable, although the accuracy seems compromised due to the mismatch of conditions for calculation and observation. Results also show that the mean annual solar radiation above the canopy was about 148.3 W/m² in 2018, and the mean annual solar radiation values beneath the canopy were about 90.0, 123.8, and 61.0 W/m² at P1, P2, and P3, with only 60%, 84%, and 42% of the total solar radiation penetrating through the canopy, respectively. Even in winter, when the trees are leafless, the canopy sheltering effects cannot be ignored in dense forests. Despite the limitations, fisheye photographs and related algorithms are useful in investigating the forest canopy structure and its impacts on sub-canopy solar radiation.

As a unique hydro-geological phenomenon in permafrost regions, the seepage of supra-permafrost groundwater will carry a large amount of heat and cause differential settlement in the embankment. This paper presents the results of a field study monitoring the supra-permafrost groundwater levels on both sides of an embankment in permafrost regions. It describes a two-dimensional coupled hydro-thermal model and uses it to analyze the influence of seepage on its temperature field considering climate warming. The results show that seepage exacerbates permafrost thawing and thickens the active layer. The thermal influence on the sunny side of the embankment toe is more significant than that on the shady side, which will cause differential settlement in the embankment. After 50 years of operation, the embankment soil temperature with seepage during freezing is 0.2 °C warmer than that without seepage, and the thermal influence diminished with the increase in depth. Additionally, seepage influences the thermal regime in vertical and horizontal directions of the embankment. During freezing seasons, the thaw depth increases, and the horizontal thaw range decreases. During thawing seasons, the thaw range grows both vertically and horizontally.

Climate change is the dominant factor affecting the hydrological process, it is of great significance to simulate and predict its influence on water resources management, socio-economic activities, and sustainable development in the future. In this paper, the Xiying River Basin was taken as the study area, China Atmospheric Assimilation Driven Data Set (CMADS) and observation data from the Jiutiaoling station were used to simulate runoff of the SWAT model and calibrate and verify model parameters. On this basis, runoff change of the basin under the future climate scenario of CMIP6 was predicted. Our research shows that: (1) The contribution rates of climate change and human activities to runoff increase of the Xiying River are 89.17% and 10.83%, respectively. Climate change is the most important factor affecting runoff change of the Xiying River. (2) In these three different emission scenarios of SSP1-2.6, SSP2-4.5 and SSP5-8.5 in CMIP6 climate model, the average temperature increased by 0.61, 1.09 and 1.74 °C, respectively, in the Xiying River Basin from 2017 to 2050. Average precipitation increased by 14.36, 66.88, and 142.73 mm, respectively, and runoff increased by 15, 24, and 35 million m³, respectively. The effect of climate change on runoff will continue to deepen in the future.

The Singing Sand Mountain and Crescent Spring Scenic Spot in Dunhuang, Northwest China is a world-renowned desert attraction that is also an integral component of the Dunhuang UNESCO Global Geopark. This scenic area underwent a 30-year transformation, i.e., from a severe sand risk with spring water threatened by sand burial due to dune deformation, to restoration of the original sand flow field and mitigation of the sand burial problem. The current paper summarizes the research on the intensive monitoring of the dynamic change of star dunes near the spring, observation of wind and sand flow movement, and then restoring the harmonic vibration of the sand particles (singing sand) that were previously silenced. The existing and prospective impacts of anthropogenic and natural forces on the deformation of the sand dunes are investigated by integrated methods, guiding the implementation of mitigating measures with significant ameliorative effects. Contrast to common sand control practices that aim to reduce wind speed and stop blown sands, our research highlights the importance of maintaining the natural wind flow field in stabilizing surrounding dunes. These mitigation measures consist of removing excessive vegetation and newly constructed buildings to recover the original wind flow field and sand transport activity. Such research and mitigation efforts ensure the scientific protection and restoration of the special desert landform, and contribute to the mutual enhancement of the conservation and exploitation of this desert scenic spot and similar sites.

Under the goal of “Carbon Emission Peak and Carbon Neutralization”, the integrated development between various industries and renewable energy (photovoltaic, wind power) is of great significance in China. This paper summarizes the relevant policies, integration schemes and typical cases of the integrated development between renewable energy and other industries. First, the development status of wind and solar generation in China is introduced. Second, we summarize the relevant policies issued by the National Development and Reform Commission, National Energy Administration and other departments to promote the integrated development in photovoltaic and wind power generation in China. Third, eight kinds of photovoltaic three-dimensional development models are described, including “photovoltaic + agriculture, industry, environmental protection, transportation, architecture, communication, hydrogen and ecology”. Fourth, eight kinds of wind power three-dimensional development models are summarized, including “Offshore wind power + marine ranch, marine energy, marine tourism, marine oil and gas, hydrogen, communication, Energy Island” and “Onshore wind power + courtyard”. In the future, the promotion and application of the above integrated development projects will be accelerated. This overview aims to provide reference for the design in photovoltaic and wind energy systems and help potential investors to make decisions.