The Tibetan Plateau (TP), often referred to as the 'Asian Water Tower', plays a critical role in regulating the hydrological cycle and influencing global climate patterns. Its unique topography and climatic conditions result in pronounced seasonal freeze-thaw (FT) dynamics of the land surface, which are critical for understanding permafrost ecosystem responses to climate change. However, existing studies on FT dynamics over the TP are limited by either short observational periods or deficiency in accuracy, failing to capture the long-term FT processes comprehensively. This study presents a novel satellite-based approach for monitoring the FT dynamics over the TP from 1979 to 2022, utilizing passive microwave observations. We developed a new algorithm that integrates discriminant function algorithm (DFA) with a seasonal threshold algorithm (STA), employing the freeze-thaw index (FTI) as the classification variable to determine optimal FT thresholds. The strong performance of the algorithm was confirmed by in-situ validation, with an overall accuracy of 91.46%, a Kappa coefficient of 0.83, and an F1-score of 0.92, outperforming other remote sensing-derived FT products such as SMAP (OA = 89.44%, Kappa = 0.79, F1 = 0.89). Results reveal significant changes in surface freeze-thaw dynamics over the past four decades. Between 1988-2022, frozen days exhibited a significant decreasing trend of -0.19 daysyear(-)(1), primarily attributed to the delayed freeze onset (0.19 daysyear(-)(1)), while thaw onset showed no significant trend. Spatially, permafrost regions experienced a more pronounced decrease in frozen days and earlier thaw onset compared to seasonally frozen regions. Moreover, marked interannual trend differences in FT processes were observed across elevation gradients, with higher elevations showing more negative trends in frozen days and thaw onset. This study provides a reliable and up-to-date analysis of surface FT process changes over the TP, informed by long-term satellite-based observational perspectives. These analyses revealed marked spatial heterogeneity in surface FT dynamics across the TP region, underscoring the impacts of climate change on the cryosphere and hydrology.

Climate change is reshaping the risk landscape for natural gas pipelines, with landslides emerging as a major driver of technological accidents triggered by natural hazards (Natech events). Conventional Natech risk models rarely incorporate climate-sensitive parameters such as groundwater levels and soil moisture, limiting their capacity to capture evolving threats. This study develops a probabilistic model that explicitly links climate-driven landslide susceptibility to pipeline vulnerability, providing a quantitative basis for assessing pipeline failure probability under different emission projection scenarios. Using Monte Carlo simulations across five regions in China, the results show that under high-emission pathways (SSP5-8.5), pipeline failure probability in summer increases dramatically. For example, from 0.320 to 0.943 in Xinjiang, 0.112 to 0.220 in Sichuan, and 0.087 to 0.188 in Hainan. In cold regions, winter failure probability more than doubles, rising from 0.206 to 0.501 in Heilongjiang and from 0.235 to 0.488 in Beijing. These shifts reveal an overall increase in risk, intensification of seasonal contrasts, and, in some areas, a reconfiguration of high-risk periods. Sensitivity analysis highlights groundwater levels and soil moisture as the dominant drivers, with regional differences shaped by precipitation regimes, permafrost thaw, and typhoon impacts. Building on these insights, this study proposes an AI-based condition-monitoring framework that integrates real-time climate and geotechnical data to support adaptive early warning and safety management.

Permafrost soils contain approximately twice the amount of carbon as the atmosphere and this carbon could be released with Arctic warming, further impacting climate. Mosses are major component of Arctic tundra ecosystems, but the environmental drivers controlling heat penetration though the moss layer and into the soil and permafrost are still debated, especially at fine spatial scales where microtopography impacts both vegetation and soil moisture. This study measured soil temperature profiles (1-15 cm), summer thaw depth, water table depth, soil moisture, and moss thickness at a fine spatial scale (2 m) together with meteorological variables to identify the most important controls on the development of the thaw depth during two Arctic summers. We found a negative relationship between the green moss thickness (up to 3 cm) and the soil temperatures at 15 cm, suggesting that mosses insulated the soil even at high volumetric water contents (>70%) in the top 5 cm. A drier top (2-3 cm) green moss layer better insulated deep (15 cm) soil layers by reducing soil thermal conductivity, even if the moss layers immediately below the top layer were saturated. The thickness of the top green moss layer had the strongest relationships with deeper soil temperatures, suggesting that the top layer had the most relevant role in regulating heat transfer into deeper soils. Further drying of the top green moss layer could better insulate the soil and prevent permafrost thawing, representing a negative feedback on climate warming, but damage or loss of the moss layer due to drought or fire could reduce its insulating effects and release carbon stored in the permafrost, representing a positive feedback to climate warming.

Large-scale wildfires are essential sources of black carbon (BC) and brown carbon (BrC), affecting aerosol-induced radiative forcing. This study investigated the impact of two wildfire plumes (Plume 1 and 2) transported to Moscow on the optical properties of BC and BrC during August 2022. During the wildfires, the total light absorption at 370 nm (b(abs_370nm)) increased 2.3-3.4 times relative to background (17.30 +/- 13.98 Mm(-)(1)), and the BrC contribution to total absorption increased from 14 % to 42-48 %. BrC was further partitioned into primary (BrCPri) and secondary (BrCSec) components. Biomass burning accounted for similar to 83-90 % of BrCPri during the wildfires. The b(abs_370nm) of BrCPri increased 5.6 times in Plume 1 and 11.5 times in Plume 2, due to the higher prevalence of peat combustion in Plume 2. b(abs_370nm) of BrCSec increased 8.3-9.6 times, driven by aqueous-phase processing, as evidenced by strong correlations between aerosol liquid water content and b(abs_370nm) of BrCSec. Daytime b(abs_370nm) of BrCSec increased 7.6 times in Plume 1 but only 3.6 times in Plume 2, due to more extensive photobleaching, as indicated by negative correlations with oxidant concentrations and longer transport times. The radiative forcing of BrCPri relative to BC increased 1.8 times in Plume 1 and Plume 2. In contrast, this increase for BrCSec was 3.4 times in Plume 1 but only 2.3 times in Plume 2, due to differences in chemical processes, which may result in higher uncertainty in its radiative forcing. Future work should prioritize elucidating both the emissions and atmospheric processes to better quantify wildfire-derived BrC and its radiative forcing.

Soil organic matter (SOM) stability in Arctic soils is a key factor influencing carbon sequestration and greenhouse gas emissions, particularly in the context of climate change. Despite numerous studies on carbon stocks in the Arctic, a significant knowledge gap remains regarding the mechanisms of SOM stabilization and their impact on the quantity and quality of SOM across different tundra vegetation types. The main aim of this study was to determine SOM characteristics in surface horizons of permafrost-affected soils covered with different tundra vegetation types (pioneer tundra, arctic meadow, moss tundra, and heath tundra) in the central part of Spitsbergen (Svalbard). Physical fractionation was used to separate SOM into POM (particulate organic matter) and MAOM (mineral-associated organic matter) fractions, while particle-size fractionation was applied to evaluate SOM distribution and composition in sand, silt, and clay fractions. The results indicate that in topsoils under heath tundra POM fractions dominate the carbon and nitrogen pools, whereas in pioneer tundra topsoils, the majority of the carbon and nitrogen are stored in MAOM fractions. Moreover, a substantial proportion of SOM is occluded within macro-and microaggregates. Furthermore, the results obtained from FTIR analysis revealed substantial differences in the chemical properties of individual soil fractions, both concerning the degree of occlusion in aggregates and across particle size fractions. This study provides clear evidence that tundra vegetation types significantly influence both the spatial distribution and chemical composition of SOM in the topsoils of central Spitsbergen.

The critical role of light-absorbing aerosol black carbon (BC) in modifying the Earth's atmosphere and climate system warrants detailed characterization of its microphysical properties. The present study examines the BC microphysical properties (size distributions and mixing state) and their impact on the light-absorption characteristics over a semi-urban tropical coastal location in Southern Peninsular India. The measurements of refractory BC (rBC) properties, carried out using the single particle soot photometer during 2018-2021, covering four distinct air mass conditions (Marine, Continental, Mixed-1, and Mixed-2), were used for this purpose. These were supported by measurements of non-refractory submicron particulate matter (NR-PM1) mass loadings and the core-shell Mie theory model for BC-containing particles. The results suggested that the BC particles exhibited varying sizes (mass median diameters from 0.181 +/- 0.079 mu m to 0.202 +/- 0.064 mu m) and relative coating thicknesses (RCT) (1.3-1.6) under distinct air mass conditions. These characteristics reflected varying source/sink strengths, aging processes of BC, and potential condensable coating material. The aerosol system during the Marine air mass period has lower BC (similar to 0.67 +/- 0.57 mu g m(-3)) and NR-PM1 (12.06 +/- 10.81 mu g m(-3)) mass concentrations, and the lowest RCT on BC (similar to 1.34 +/- 0.14). However, the other periods with continental influence depicted significant coatings on BC (mean RCT >1.5). The coatings on BC particles exhibited daytime enhancement, driven by photochemically produced condensable material, a contrasting diurnal pattern to that of other BC properties. Interestingly, the RCT on BC increased and/or remained invariant with increasing relative humidity (RH) until RH 85 %), indicating the potential role of secondary organics as coatings. The changes in the BC mixing state resulted in a significant alteration to its light-absorption properties. The mean light-absorption enhancement of BC (compared to uncoated BC) ranged from 1.36 +/- 0.14 for the Marine air mass periods to 1.58 +/- 0.15 for the Continental air mass periods, whereas the overall mass absorption cross-sections of BC varied between 7.91 +/- 0.91 to 9.03 +/- 0.84 m(2)/g at 550 nm. The key implication of this study is that changes to the BC mixing state, caused by multiple underlying processes unique to tropical atmospheric conditions, can lead to a significant enhancement in its light-absorption characteristics, which can lead to a notable increase in the positive radiative forcing of BC.

The thermal stability of permafrost, a foundation for engineering infrastructure in cold regions, is increasingly threatened by the dual stressors of climate change and anthropogenic disturbance. This study investigates the dynamics of the crushed rock revetted embankment at the Kunlun Mountain Section of the Qinghai-Tibet Railway, systematically investigating the coupled impacts of climate warming and engineering activities on permafrost thermal stability using borehole temperature monitoring data (2008-2024) and climatic parameter analysis. Results show that under climate-driven effects, the study area experienced an air temperature increase of 0.2 degrees C per decade over the 2015-2024. Concurrently, the mean annual air thawing degree-days (TDD) rose by 13.8 degrees C center dot d/a, leading to active-layer thickening at a rate of 3.8 cm center dot a- 1at natural ground sites. From 2008 to 2024, the active layer had thickened by 0.7-0.8 m. At the embankment toe (BH 5), the active-layer thickening rate (3.3 cm center dot a- 1) was 25 % lower than that at the natural ground borehole (3.8 cm center dot a- 1); correspondingly, the underlying permafrost temperature increase rate at the toe (0.3 degrees C per decade) was lower than that at the natural borehole (0.5-0.6 degrees C per decade). Permafrost warming rates decreased with depth. Shallow layers (above -2 m) were significantly influenced by climate, with warming rates of 0.3-0.6 degrees C per decade. In contrast, deep layers (below -10 m) showed warming rates converging with the background atmospheric temperature trend (0.2 degrees C per decade). Thermal regime disturbance was most pronounced at horizontal distances of 3.0-5.0 m from the embankment. Nevertheless, the crushed-rock revetment maintained a permafrost table 0.6 m shallower than that of natural ground, confirming its thermal diode effect (facilitating convective cooling in winter), which partially offset climate warming impacts. This study provides critical empirical data and validates the cooling mechanism of crushed-rock revetment, which is essential for predicting the long-term thermal stability and informing adaptive maintenance strategies for railway infrastructure in warming permafrost regions.

Climate warming has impacted the sustainability of freshwater supply in the global water tower unit (WTU) zone. The rainfall infiltration process, a key component of WTUs supply, is affected by freeze-thaw cycles, yet it remains uncertain whether it has undergone corresponding changes. We propose a temperature-mediated infiltration model considering changes in soil water holding, water potential, and hydraulic conductivity due to varying degrees of freezing under negative temperature. Using this model, we calculate the infiltration of 78 WTUs globally from 1980 to 2023. Our results indicate that global WTUs have a multi-year average infiltration of 26 similar to 2359 mm/year. Notably, WTUs in the key latitudinal zone (24 degrees S-42 degrees N) contribute 54 % of the total infiltration volume, showing expanding differences in infiltration characteristics compared to other regions. While rainfall primarily influences infiltration and infiltration capacity, soil temperature and initial soil water content also significantly impact these characteristics. Enhanced infiltration capacity promotes vegetation growth, though the relationship is not linear. Variations in infiltration characteristics threaten the water resource buffering and the stability of downstream living ecological water supply of WTUs. This study provides crucial references for the integrated management of water resources and ecological conservation amid changing infiltration characteristics.

Accurate soil thermal conductivity (STC) data and their spatiotemporal variability are critical for the accurate simulation of future changes in Arctic permafrost. However, in-situ measured STC data remain scarce in the Arctic permafrost region, and the STC parameterization schemes commonly used in current land surface process models (LSMs) fail to meet the actual needs of accurate simulation of hydrothermal processes in permafrost, leading to considerable errors in the simulation results of Arctic permafrost. This study used the XGBoost method to simulate the spatial-temporal variability of the STC in the upper 5 cm active layer of Arctic permafrost during thawing and freezing periods from 1980 to 2020. The findings indicated STC variations between the thawing and freezing periods across different years, with values ranging from-0.4 to 0.28 W & sdot;m-1 & sdot;K-1. The mean STC during the freezing period was higher than that during the thawing period. Tundra, forest, and barren land exhibited the greatest sensitivity of STC to freeze-thaw transitions. This is the first study to explore the long-term spatiotemporal variations of STC in Arctic permafrost, and these findings and datasets can provide useful support for future research on Arctic permafrost evolution simulations.

Current research predominantly emphasizes elemental carbon (EC) light absorption, while ignoring its relationship with aerosol hygroscopic scattering. In this study, concentrations and optical properties of aerosol components were measured during a full-year monitoring campaign at an urban site in Suzhou. Results from a multiple linear regression model suggested that secondary organic carbon was a primary contributor to high mass absorption efficiency of EC in summer. Through the estimation of aerosol scattering coefficients under both dry and ambient atmospheric conditions, it was found that hygroscopic growth accounted for more than 35.0 % of the total aerosol scattering coefficient. Hygroscopic growth of nitrate and sulfate enhanced their annual mean scattering contributions by 42.1 % and 45.2 %, respectively. A negative correlation between EC concentration and the hygroscopic growth factor (f(RH)) was observed under varying relative humidity (RH) conditions. Associated with the decrease in f(RH), reductions in PM2.5 scattering coefficients (14.0 f 2.2, 29.4 f 5.2, and 24.5 f 8.2 Mm-1) were linked to EC concentration increases of 0.37 f 0.1, 0.40 f 0.1, and 0.21 f 0.1 mu g/m3 under low, medium, and high RH conditions, respectively. An increase in EC concentration by 0.19-0.37 mu g/m3 elevated the PM2.5 absorption coefficient by 2.66-5.41 Mm-1, and reduced the scattering coefficient by 10.53-17.91 Mm-1. Collectively, increased EC concentrations reduced aerosol single scattering albedo (SSA), particularly under high RH conditions. This study reveals that EC not only reduces aerosol extinction coefficients but also shifts aerosol radiative forcing in a positive direction by suppressing hygroscopic scattering.