Glacial meltwater is a major carrier of nutrients and bioactive compounds, and meltwater chemistry is an important way to study the glacier drainage system and its dynamic characteristics to gain insights into the biogeochemical cycling process and explore the relationship between deglaciation and climate change. With accelerated melting of glaciers and increases in erosion and weathering, meltwater chemistry has undergone significant changes, which may have significant impacts on downstream water quality, the water environment, and ecosystems. In this study, the contents of inorganic chemical components and their spatial and temporal variations, solute sources and their proportions, and the relationship between chemical weathering and carbon cycling in global glacial meltwater were reviewed. The results indicated that meltwater chemistry is affected by various factors, such as the nature of the bedrock, the drainage system, the physical chemistry, and the topography and geomorphology. To provide references for future research on the relationships among the cryosphere, carbon cycle, and climate change, it is essential to strengthen simultaneous and continuous monitoring of hydrometeorological parameters and inorganic and organic chemical components in meltwater, evaluate the ecological and environmental effects of solutes sourced from glaciers, and examine the relationships among the coupled mechanisms of chemical weathering in glacial regions, solute mobilisation, and atmospheric CO₂ balance.

River width is one of the key parameters for studying river dynamic processes and hydrological and hydrodynamic models. Compared with traditional hydrological stations, satellite images can achieve large-scale observations of river width. Based on Sentinel-2 imagery, Google Earth Engine (GEE) and RivWidth tool, a new river connectivity construction method was developed to improve the computational efficiency of RivWidth tool for river width extraction, and the monthly river width dataset (MRWD) with a 10-m spatial resolution from 2019 to 2021 in the upper reaches of the Yellow River was generated by the improved algorithm. The results show that the river connectivity construction method developed in this study (referred to as the connection method) improves the computing efficiency of RivWidth tool by 24.7%. The comparison and verification results with the in-situ river width and GRWL (Global River Widths from Landsat) river width show that the mean absolute percentage error (MAPE), root mean square error (RMSE) and relative root mean square error (RRMSE) of MRWD are respectively 7.82%, 11.62 m, and 8.84%. The MRWD includes 6.1×10⁶ river width estimations, covering 2035 km of rivers in the upper reaches of the Yellow River, of which 41% are narrower than 100 m, more than 85% are less than 500 m, and 2% are more than 1000 m. The MRWD generated in this study can provide an important reference for surface water resources management.

To quantitatively explore the adjustments in the wandering intensity in a wandering reach of the Lower Yellow River (LYR) since the operation of the Xiaolangdi (XLD) Reservoir, the calculation method of a new wandering index (WI) was proposed. In addition, Landsat images were collected to perform an analysis of the spatio-temporal variations in the wandering intensity and their response to major influencing factors. The results indicate that the wandering intensity in the wandering reach integrally presented a decreasing trend during the period from 2000 to 2022, with the value of WI decreasing from 0.918 to 0.674 and changing rate being fast to slow. Specifically, the wandering intensity in the Tiexie-Yiluohekou reach and Huayuankou-Jiahetan reach has decreased, while the Yiluohekou-Huayuankou reach maintained and the Jiahetan-Gaocun reach increased. Furthermore, the wandering intensity adjustments had close relations to the flow-sediment regime, riverbed boundary conditions and local river regime evolution. For flow and sediment regime, the decrease of wandering intensity in the wandering reach was significantly attributed to the sharp reduction in the incoming sediment volume and rising-recession rate of floods in the LYR owing to the operation of XLD Reservoir, which resulted in the riverbed erosion and flow concentration in the downstream channel. Regarding riverbed boundary conditions, the wandering intensity in the sub-reaches with strong lateral restrict caused by banks or channel regulation works tended to decrease. Also, the increase in the longitudinal stability of the riverbed was one of the reasons why the wandering intensity in the wandering reach declined with a slower changing rate in the later stage. Concerning about propagation of river regime adjustments, the frequent occurrence of avulsion in the Jiahetan-Gaocun reach during the later period was mainly attributed to the river regime evolution in the inlet reach between Zhuzhai to Dongbatou.

The loess-paleosol sequence in the Zoige Basin is a geological record of the surface processes and evolution after the paleolake disappeared in this region. The Ouqiangcun (OQC) profile of the secondary terrace of the Yellow River in the Maqu reach was selected as the focus of this study. Based on the comprehensive investigation of multiple proxies, such as the grain-size distribution, magnetic susceptibility, total organic carbon, chroma, elements, and optically stimulated luminescence age, the following conclusions were obtained: (1) Continuous aeolian dust accumulation began on the Yellow River secondary terrace around 10 ka BP, and the developed loess-paleosol sequence from bottom to top was fluvial sediment (T_2-al, >10.0 ka)→loess (L₁, 10.0-8.5 ka)→paleosol (S₀, 8.5-3.0 ka)→topsoil (L₀+MS, 3.0-0 ka). (2) The OQC profile was in the primary chemical weathering stage where plagioclase was mainly decomposed and potassium feldspar was not decomposed (CIA value is between 48.20 and 63.08). While the paleosol was slightly increased when compared with the loess layers, this enhancement was limited, and it had not progressed to the moderate weathering stage. (3) Around 10 ka BP, the climate of the Zoige Basin was dry and cold, aeolian sand activity was prevalent, and continuous wind-dust accumulation began to occur on the gentle terrace, which formed loess L₁. Around 8.5 ka BP, the climate was warm and humid, the activity of the aeolian sand was obviously weakened, and the weathering of the pedogenesis was dominant. Paleosol with black and gray characteristics was formed during this period. Around 3.0 ka BP, the climate changed to cold and dry and the aeolian sand activity was intense. The development of paleosol was interrupted, it was covered by loess L₀, and the modern soil was formed. (4) The loess-paleosol sequence of the Zoige Basin was significantly different in terms of the macroscopic morphology, stratigraphic age and physical property parameters when compared with those of the Loess Plateau. This suggests that the environmental significance of these parameters in the high-cold area (Zoige Basin) may be different from that in the monsoon humid area (Loess Plateau). The findings provide basic data to support the study of the chronology of aeolian sediments and the extraction of environmental information in the Zoige Basin.

As a crucial ecological service provider and a key regional growth pole, the upper reaches of the Yangtze River faces significant environmental pressure due to enormous resource consumption during rapid economic development, posing a threat to the stability of its ecosystem. Based on the panel data from 47 prefecture-level and above cities in the upper reaches of the Yangtze River from 1998 to 2021, this paper comprehensively used Dagum Gini Coefficient, kernel density estimation, Markov Chain, spatial convergence model and other methods to deeply analyze the spatiotemporal pattern of environmental pressure. The results are as follows: (1) During the sample period, the overall pressure showed a slight upward trend in an inverted "V"-shaped pattern. The environmental cost of economic growth was high in the early stages, but the environmental risk was effectively controlled in the later stages. (2) The pressure demonstrated a pattern of "high in the east and low in the west" and "high-pressure areas contracted and low-pressure areas expanded". The three urbanized areas in the east, especially Chengdu-Chongqing region, were the pressure centers. However, due to the implementation of the environmental protection policies in the Yangtze River Basin, the scope of high-pressure cities significantly decreased. (3) The overall difference of the pressure exhibited a gently periodic fluctuating trend, with regional difference, net inter-regional difference, and hypervariable density tending towards a state of equilibrium. There were a few stable high-pressure cities in Yunnan-Guizhou region. (4) The evolution of the pressure shifted from a "multi-polar differentiation" trend to a "low-pressure concentration" trend. Initially, there were significant gradients in environmental pressure among cities, but in the later stages, most cities tended to converge towards lower pressure levels. (5) The relative situation of the pressure showed strong stability, but gradually decayed over time, and there existed spatial infiltration effect on the pressure changes. (6) The convergence trend of the pressure was robust, and the spatial proximity accelerated the convergence of environmental pressure. The tightening of environmental policies in the later stages further accelerated the convergence process. This study could provide decision-making support for strengthening ecological security barrier in the study area.

Integral early urban evolution of prehistoric city sites are intimately related to regional environmental factors such as climate, geomorphology, and hydrology. However, current research is inadequate in considering the regional environmental factors associated with prehistoric city sites. This study utilizes the Shangjinhu Lake sedimentary record and a comprehensive chronological framework of the ancient city of Zoumaling, a typical site in the middle Yangtze River. By analyzing climatic proxies such as elemental geochemistry, it offers a reconstruction of the regional depositional environment of the Zoumaling site during the mid-late Holocene. Furthermore, it explores the connection between regional environment and human activities. The study indicates that: (1) During 6.4-5.3 ka BP, the CIA, Rb/Sr, and Mn/Ti values were generally high, and the Be and Saf values showed an opposite trend, indicating a warmer and wetter climate. The ancestors of the lower Qujialing culture constructed the city of Zoumaling. (2) During 5.3-4.7 ka BP, the values of CIA, Rb/Sr, and Mn/Ti reached their peak, and the climate was warm and humid. Rice agriculture flourished and the Qujialing culture in Zomaling city reached its heyday. Specifically, between 4.7 and 4.6 ka BP, a significant rise in grain size parameters indicates that the ancient city was subjected to flood events due to intense precipitation. (3) During 4.7-4.2 ka BP, the climate became cooler and drier. Consequently, the Shijiahe culture within the Zomaling city began to decline gradually. (4) During 4.2-2.4 ka BP, the CIA, Rb/Sr, and Mn/Ti values fell to their lowest, indicating a shift to cooler and drier climate conditions, and the ancient city was abandoned around 3.9 ka BP. (5) During 2.4-0.3 ka BP, CIA and Rb/Sr values rebounded and Saf and Be values decreased, indicating a warming climate. Around 0.8 ka BP, the Shangjinhu Lake was formed. During 0.3-0.1 ka BP, the values of CIA and Rb/Sr decreased sharply, and Be and C/N values increased, indicating a cold and arid climate at Zomaling during the heyday of the Ming-Qing Little Ice Ages. The primary productivity was high due to frequent human activities like land reclamation. The Zomaling city primarily depended on the Sheziling waterbody for its water supply. During the rainy season, the west water gate was opened to release flood water into the Shangjinhu Lake via the trench. During the dry season, the west water gate was closed, and water was drawn from the external Sheziling waterbody to supply the city. In the later period, as the climate turned cooler and drier, the depletion of water bodies caused the moat system of the Zoumaling city to become ineffective, resulting in its abandonment.

Currently, most studies on the response of lake ecosystems on the Tibetan Plateau to climate warming over the past 200 years have focused on deep lakes, whereas studies on ecosystems characterized by many shallow lakes are scarce. In this paper, we selected the shallow lake Zhenbu Co on the southeastern Tibetan Plateau as the research object. Based on ²¹⁰Pb and ¹³⁷Cs dating of sediments and high-resolution diatom identification, the changes in the diatom assemblage over the past 200 years were reconstructed. Combined with total organic carbon (TOC), total nitrogen (TN) and carbon-nitrogen ratio (C/N) of the sediments, the response of the lake ecosystem to climate change was explored. The results showed that during 1820-1950 AD, the content of Encyonema lange-bertalotii in sediment was high, indicating the abundant aquatic plants and high lake-water transparency in Zhenbu Co. Since 1950 AD, the diatom assemblages shifted, decreasing rapidly in Encyonema lange-bertalotii content and increasing in small Fragilaria content, which indicated a decline of aquatic plants and decreased lake-water transparency. Meanwhile, the contents of TOC and TN increased, and the C/N decreased, which indicated that the productivity and nutrient level of the lake increased, and the percentage of algae in the lake organic matter increased. Rapidly rising temperature, increased precipitation (i.e., more nutrients entering into the lake), and enhanced human activities (i.e., the appearance of new temples in the watershed) may have jointly led to higher lake productivity and algal bloom content, as well as lower aquatic plant content and decreased water clarity. Eventually, the diatom assemblages abruptly shifted. Based on our results, shallow lakes may face ecosystem shifts in the context of climate warming and humidification on the Tibetan Plateau, and the monitoring and protection of such lakes should be strengthened in the future. The timeline of the abrupt shift of the plateau shallow lake ecosystem in this paper is basically consistent with that in China and other parts of the world, which also provides new evidence for determining the stratigraphic marker of the Anthropocene. Thus, the lakes of the Tibetan Plateau can serve as natural laboratories for studying the Anthropocene.

Clarifying the modern process of alluvial pollen is the foundation for reconstructing the ancient environment of the watershed. Although research on the transport of pollen in rivers has started early both domestically and internationally, further research is needed on how pollen is transported and what factors affect it after entering rivers. This paper selects sampling sections for the main stream and tributaries of the middle and lower reaches of the Yellow River, collects river water and sediment samples during the flood season for pollen analysis, and uses methods such as geographic detectors to explore the distribution characteristics and influencing factors of pollen. The results show that: (1) The vegetation composition varies in different watersheds, and there are significant differences in the percentage and concentration of pollen types. The pollen concentration in the main stream of river water is higher than that in the tributaries, while the percentage and concentration of sediment pollen in the main stream are generally lower than those in the tributaries. (2) The concentration of suspended solids is the main factor affecting the concentration of pollen in the Yellow River, and it is particularly prominent outside the Shanxi-Shaanxi Gorge. Furthermore, excessive coarse sand and rapid flow velocity may be the reasons for the high concentration of suspended solids and low concentration of pollen in the main stream of the Shanxi-Shaanxi Gorge. (3) The sediment clay content is the main factor affecting the pollen content of sediment, and the interaction between clay and silt, clay and flow velocity is more prominent. After the Yellow River exited the Shanxi-Shaanxi Gorge, the concentration of sediment pollen and clay particles significantly increased. (4) The changes in pollen concentration in the river water before and after the reservoir are consistent with those in suspended solids, while the changes in sediment pollen concentration are consistent with those in clay particles. Compared to water samples, the decrease in pollen concentration in sediment after the reservoir is more pronounced. (5) There is a good correspondence between river pollen and topsoil pollen, which can better reflect the overall vegetation landscape of the watershed. The results can provide support for paleoenvironmental reconstruction using alluvial deposits or lake sediment pollen injected by rivers.

The Hengduan Mountains Region is one of the regions with the most densely distributed and severe flash flood disasters in China. It is also the key area for major engineering projects and beautiful countryside construction in southwest China. However, previous studies have not systematically summarized the development characteristics and formation modes of flash flood disasters in this region, which restricts the development and establishment of flood control theory and technical system in the southwestern mountains. This paper focuses on the physical processes of generation, movement and hazard-formation of flash flood disasters in the Hengduan Mountains. It clarifies the dominant disaster-inducing conditions (multiple humid monsoon circulation conditions, high potential energy conditions and high heterogenous underlying surface conditions) and disaster development characteristics (high spatio-temporal heterogeneity, highly concentrated energy, disaster chain and clustered occurrence) of flash floods in the Hengduan Mountains. Based on the entire processes of flash flood disasters, three major formation modes are summarized: the runoff generation of vegetation-hydrology-soil coupling dominated by high hydraulic gradient in mountainous areas, strong runoff-sediment coupled movement, and serious disaster losses due to high exposure of disaster bearing objects. Finally, based on the issues in previous research, four future research challenges for flash flood disasters in the Hengduan Mountains are proposed. Our work contributes to the development of disaster prevention and reduction research, including basic theoretical system, precise risk assessment of regional disasters, and fine early warning and forecasting of flash floods.

Superheavy rain is an extreme weather phenomenon, and the resulting flood disasters can cause significant losses to the socio-economy. The railway system serves as the backbone of the national economy, with railway hubs functioning not only as centers for line connections but also as centers for the distribution of passenger and freight flows. Additionally, hubs are subject to the effect of correlated networks and other processes, which suggests that superheavy rain at a given hub propagates and amplifies the impact of this disaster outward through transportation routes, ultimately affecting the entire railway network. In this paper, we systematically analyzed the impact process and disaster propagation mechanism of the Zhengzhou superheavy rainfall event that occurred on July 20, 2021, on the railway network of China using disrupted train data. The results showed that: (1) From the early to middle periods of flooding, the number of affected nodes in the railway network of China gradually increased. The intensity of the disruptions decreased from the center of the flooding impact toward the periphery. The disrupted transportation routes expanded from local routes to the interconnected network, and the disrupted network spread from the center of the impact of flooding toward the periphery within the meter-shaped network. At the late period of the flooding impact, the number of disruption nodes and intensity of the disruptions decreased. Nodes with high disruption intensity values and disrupted networks contracted from the periphery toward the center of the flooding impact. (2) When different disaster-bearing bodies (high-speed and conventional railways) face the same impact, the shape and structure of the transportation network respond differently. High-speed railways are more sensitive and exhibit higher resilience. (3) The hierarchical nature of the disruptive network is significant, and the preferential link effect is obvious. The impact of the disaster is first transmitted to directly related nodes and lines before propagating further. When the hierarchical nature is reduced, the preferential link effect decreases, clustering is reduced, the number of regional small groups decreases, the degree of integration increases, and the transmission efficiency increases. Conversely, when the hierarchical nature increases, the opposite effects can be observed. (4) Due to integration, correlation, and conduction within the transportation network, when it is impacted by disasters, disruptions not only occur at the disaster center but also at related nodes, lines, and correlated areas. This paper provides a systematic basis for improving the disaster prevention and reduction capabilities of China's railways and achieving safe and reliable operation.

Sandy lands are important geographical units in semi-arid region in northern China, and runoff is one of the main transport forces of sediments in these areas. Extraction of river network and quantitative estimation of sediment input and output caused by surface water flows are of great significance for understanding the surface dynamic process and geomorphic evolution in the Mu Us sandy land of northern China. In this study, Sentinel-2 satellite remote sensing images with a 10-m spatial resolution and Copernicus Digital Elevation Model (COPDEM) were used to automatically extract the river network in exorheic regions of the study area by a combination of water index and stream burning method. Based on the Budyko model, a method for estimating annual average water loss in semi-arid region was established by using precipitation and potential evapotranspiration data. Then, the method was used to quantitatively evaluate annual water erosion of surface sediments in the Mu Us sandy land. Our results show that the Jialu River has the highest density of river network in the exorheic regions of Mu Us sandy land, followed by Tuwei River and Wuding River, and the Kushui River has the lowest density. Under erosion and deposition by runoff, the amount of sand materials transported into the Mu Us sandy land was about 7 million t/a, the amount of sand materials eroded out of the sandy land was about 45 million t/a from 1992 to 2021, and the average annual erosion by runoff was about 38 million t. Interpretation of remote sensing images helped to add more hydrological information to obtain river network in the semi-arid regions. Based on available hydrometeorological data, average annual water erosion in the semi-arid regions is estimated. The interpretation of remote sensing images, combined with climate data ananysis (potential precipitation-evaporation balance), runoff and surface erosion model, realized a quantitative assessment of surface water erosion in the semi-arid regions. This study provides a new apporach for quantitative assessment of geomorphologic process in arid and semi-arid regions where observational data are limited.

The prevention and control of air pollution in the Qinghai-Tibet Plateau (QTP) is imperative to meet the goals of the Blue-Sky Protection Campaign, to protect the ecological security barrier, and to achieve high-quality and sustainable economic development. Based on the long time-series fine particulate matter (PM_2.5) data with a high spatial resolution, the spatial autocorrelation model was adopted to analyze the static spatial correlation characteristics of county-scale PM_2.5 concentrations in the QTP. Furthermore, the dynamic evolution and long-term transfer trend of PM_2.5 distribution were explored by combining traditional and spatial kernel density estimation. Finally, the spatial Markov chain model was used to characterize the spatial transfer characteristics of county-scale PM_2.5 concentrations in the study area. The results showed that: (1) On the county scale, the PM_2.5 concentrations started with a higher value, and the spatial lock-in characteristics were significant. PM_2.5 emissions were high in the following areas: southern Xinjiang, and Qaidam Basin, Xining city, and Haidong city of Qinghai province. (2) The county-scale PM_2.5 concentrations presented significant spatial correlation characteristics, and the local spatial correlation was mainly dominated by two homogeneous spatial correlations: H-H and L-L. (3) The PM_2.5 concentrations in counties of the QTP showed an overall decline in the distribution and dynamic evolution, and the local differences were still large. Furthermore, there was a "club convergence" phenomenon when spatial conditions were not considered. When the spatial influence of adjacent regions was considered, the spatial convergence pattern and significant spatial positive correlation were presented. Under the condition of a three-period time lag, the “siphon effect” in the area with high PM_2.5 concentrations was enhanced. Additionally, the results revealed that the combined effect of PM_2.5 emissions from different regions would affect the future spatial distribution of PM_2.5 in the QTP. (4) The spatial transfer trend of PM_2.5 concentrations was stable at the county level, and it is difficult to realize the jump transfer in the level of county units. This study provides a theoretical reference for identifying the spatial dynamic evolution characteristics of PM_2.5 concentrations in the QTP on the county scale and implementing targeted air pollution prevention and control measures to construct ecological civilization in the plateau region.