River-controlled permafrost dynamics are crucial for sediment transport, infrastructure stability, and carbon cycle, yet are not well understood under climate change. Leveraging remotely sensed datasets, in-situ hydrological observations, and physics-based models, we reveal overall warming and widening rivers across the Tibetan Plateau in recent decades, driving accelerated sub-river permafrost thaw. River temperature of a representative (Tuotuohe River) on the central Tibetan Plateau, has increased notably (0.39 degrees C/decade) from 1985 to 2017, facilitating heat transfer into the underlying permafrost via both convection and conduction. Consequently, the permafrost beneath rivers warms faster (0.37 degrees C-0.66 degrees C/decade) and has a similar to 0.5 m thicker active layer than non-inundated permafrost (0.17 degrees C-0.49 degrees C/decade). With increasing river discharge, the inundated area expands laterally along the riverbed (16.4 m/decade), further accelerating permafrost thaw for previously non-inundated bars. Under future warmer and wetter climate, the anticipated intensification of sub-river permafrost degradation will pose risks to riverine infrastructure and amplify permafrost carbon release.

Snow distribution has been altered over the past decades under global warming, with a significant reduction in duration and extent of snow cover and an increase in unprecedented snowstorms across large areas in cold regions. The altered snow conditions are likely to have immediate (in winter) and carry-over or legacy (which an extended effect might continue in the following spring, summer and autumn) impacts on soil processes and functioning, but a quantification of the legacy effect of snow coverage alternation is still lacking. Furthermore, studies investigating the effect of snow cover changes on soil respiration, soil carbon pools and microbial activity are increasing, but contrasting results of different studies makes it difficult to assess the overall effect of snow cover changes and the underlying mechanisms, thus a systematic and comprehensive meta-analysis is required. In this study, we synthesized the results from 60 papers based on field snow manipulation experiments and conducted a meta-analysis to evaluate immediate and prolonged effects on eight variables related to soil carbon dynamics and microbial activity to snow coverage alternation. Results showed that snow removal had no significant effect on soil respiration, but increased dissolved organic carbon (DOC) (11.5%) and fungal abundance (32.0%). By contrast, snow addition significantly increased soil respiration (16.3%) and microbial biomass carbon (MBC) (6.6%). Snow addition had immediate and prolonged impacts on soil carbon dynamics and microbial activity lasting from winter to the following autumn, whereas an effect of snow removal on total organic carbon (TOC) and DOC was detectable only in the following spring. Snow depth, ecosystem and soil types determined the extent of the impact of snow treatments on soil respiration, DOC, MBC and microbial biomass nitrogen (MBN). Our findings provide critical insights into understanding how changes in snow coverage affect soil respiration and microbial activity. We suggest future field-based experiments to enhance our understanding the effect of climate change on soil processes and functioning in the winter and the following seasons.

This study uses a new dataset on gauge locations and catchments to assess the impact of 21st-century climate change on the hydrology of 221 high-mountain catchments in Central Asia. A steady-state stochastic soil moisture water balance model was employed to project changes in runoff and evaporation for 2011-2040, 2041-2070, and 2071-2100, compared to the baseline period of 1979-2011. Baseline climate data were sourced from CHELSA V21 climatology, providing daily temperature and precipitation for each subcatchment. Future projections used bias-corrected outputs from four General Circulation Models under four pathways/scenarios (SSP1 RCP 2.6, SSP2 RCP 4.5, SSP3 RCP 7.0, SSP5 RCP 8.5). Global datasets informed soil parameter distribution, and glacier ablation data were integrated to refine discharge modeling and validated against long-term catchment discharge data. The atmospheric models predict an increase in median precipitation between 5.5% to 10.1% and a rise in median temperatures by 1.9 degrees C to 5.6 degrees C by the end of the 21st century, depending on the scenario and relative to the baseline. Hydrological model projections for this period indicate increases in actual evaporation between 7.3% to 17.4% and changes in discharge between + 1.1% to -2.7% for the SSP1 RCP 2.6 and SSP5 RCP 8.5 scenarios, respectively. Under the most extreme climate scenario (SSP5-8.5), discharge increases of 3.8% and 5.0% are anticipated during the first and second future periods, followed by a decrease of -2.7% in the third period. Significant glacier wastage is expected in lower-lying runoff zones, with overall discharge reductions in parts of the Tien Shan, including the Naryn catchment. Conversely, high-elevation areas in the Gissar-Alay and Pamir mountains are projected to experience discharge increases, driven by enhanced glacier ablation and delayed peak water, among other things. Shifts in precipitation patterns suggest more extreme but less frequent events, potentially altering the hydroclimate risk landscape in the region. Our findings highlight varied hydrological responses to climate change throughout high-mountain Central Asia. These insights inform strategies for effective and sustainable water management at the national and transboundary levels and help guide local stakeholders.

Driven by human activities and global climate change, the climate on the Qinghai-Xizang Plateau is experiencing a warming and humidifying trend. It significantly impacts the thermal-moisture dynamics in the active layer of the permafrost, which in turn affects the ecological environment of cold regions and the stability of cold region engineering. While the effect of air temperature on permafrost thaw has been well quantified, the processes and mechanisms behind the thermal-moisture response of the permafrost under the combined influence of increased rainfall and rising air temperature remain contentious and largely unknown. A coupled model was applied to quantify the impacts of increased rainfall, rising air temperature, and their compound effects on the thermal-moisture dynamics in the active layer, considering the sensible heat of rainwater in the ground surface energy balance and water balance process. The results indicate that the compound effect of warming and humidifying resulted in a significant increase in surface net radiation and evaporation latent heat, a more significant decrease in surface sensible heat, and a smaller impact of rainfall sensible heat, leading to an increase in surface soil heat flux. The compound effect of warming and humidifying leads to a significant increase in the liquid water flux with temperature gradient. The increase in liquid water flux due to the temperature gradient is larger than that of warming alone but smaller than the effect of humidifying alone. Warming and humidifying result in a smaller increase in soil moisture content during the warm season compared to rainfall increases alone. The thermal conductivity heat flux in the active layer increases significantly during the cold season but less than the effect of warming alone. The convective heat flux of liquid water flux increases noticeably during the warm season but less than the effect of rainfall increases alone. Increased rainfall significantly cools the soil during the warm season, while both warming and humidifying lead to a more pronounced warming effect on the soil during the cold season than during the warm season. An increase in the average annual temperature by 1.0 degrees C leads to a downward shift of the permafrost table by 10 cm, while an increase in rainfall by 100 mm causes an upward shift of the permafrost table by 8 cm. The combined effect of warming and humidifying results in a downward shift of the permafrost table by 6 cm. Under the influence of climate warming and humidifying, the cooling effect of increased rainfall on permafrost is relatively small, and the warming effect of increased temperature still dominates.

Satellite observations have shown widespread greening during the last few decades over the northern permafrost region, but the impact of vegetation greening on permafrost thermal dynamics remains poorly understood, hindering the understanding of permafrost-vegetation-climate feedbacks. Summer surface offset (SSO), defined as the difference between surface soil temperature and near-surface air temperature in summer (June-August), is often predicted as a function of surface thermal characteristics for permafrost modeling. Here we examined the impact of leaf area index (LAI), detected by satellite as a proxy to permafrost vegetation dynamics, on SSO variations from 2003 to 2021 across the northern permafrost region. We observed latitude- and biome-dependent patterns of SSO changes, with a pronounced increase in Siberian shrublands and a decrease in Tibetan grasslands. Based on partial correlation and sensitivity analyses, we found a strong LAI signal (similar to 30% of climatic signal) on SSO with varying elevation- and canopy height-dependent patterns. Positive correlations or sensitivities, that is, increases in LAI lead to higher SSO, were distributed in relatively cold and wet areas. Biophysical effects of permafrost greening on surface albedo, evapotranspiration, and soil moisture (SM) could link the connection between LAI and SSO. Increased LAI substantially reduced surface albedo and enhanced evapotranspiration, influenced energy redistribution, and further controlled interannual variability of SSO. We also found contrasting effects of LAI on surface SM, consequently leading to divergent impacts on SSO. The results offer a fresh perspective on how greening affects the thermal balance and dynamics of permafrost, which is enlightening for improved permafrost projections. Climate change has caused substantial vegetation growth that was detected by satellite observations (greening) over northern permafrost regions. However, the consequences or feedbacks of vegetation greening remain largely unknown, hindering the understanding of near-surface thermal dynamics and bringing considerable uncertainty in model projections. Here we aimed to decipher the biophysical impact of permafrost greening on the summer surface offset (SSO), which is an indicator of permafrost degradation. We found latitude- and biome-dependent patterns of SSO changes and divergent responses of SSO to greening. Increases in satellite-observed leaf area index lead to higher SSO in relatively cold and wet areas but lower SSO in warm-dry regions. Biophysical mechanisms associated with surface albedo, evapotranspiration, and SM can help explain various effects of greening on SSO. Our results highlight greening feedbacks on the thermal dynamics of permafrost with climate warming, calling for the improvement of current projections. Vegetation greening impacts the thermal dynamics of permafrost surface Biophysical effects of greening on surface offset could be related to surface albedo, evapotranspiration, and soil moisture

In the context of global warming, increasingly widespread and frequent freezing and thawing cycles (FTCs) will have profound effects on the biogeochemical cycling of soil carbon and nitrogen. FTCs can increase soil greenhouse gas (GHG) emissions by reducing the stability of soil aggregates, promoting the release of dissolved organic carbon, decreasing the number of microorganisms, inducing cell rupture, and releasing carbon and nitrogen nutrients for use by surviving microorganisms. However, the similarity and disparity of the mechanisms potentially contributing to changes in GHGs have not been systematically evaluated. The present study consolidates the most recent findings on the dynamics of soil carbon and nitrogen, as well as GHGs, in relation to FTCs. Additionally, it analyzes the impact of FTCs on soil GHGs in a systematic manner. In this study, particular emphasis is given to the following: (i) the reaction mechanism involved; (ii) variations in soil composition in different types of land (e.g., forest, peatland, farmland, and grassland); (iii) changes in soil structure in response to cycles of freezing temperatures; (iv) alterations in microbial biomass and community structure that may provide further insight into the fluctuations in GHGs after FTCs. The challenges identified included the extension of laboratory-scale research to ecosystem scales, the performance of in-depth investigation of the coupled effects of carbon, nitrogen, and water in the freeze-thaw process, and analysis of the effects of FTCs through the use of integrated research tools. The results of this study can provide a valuable point of reference for future experimental designs and scientific investigations and can also assist in the analysis of the attributes of GHG emissions from soil and the ecological consequences of the factors that influence these emissions in the context of global permafrost warming.

Understanding the dynamics of glaciers is essential for the knowledge of global sea-level rise, local freshwater resources in high mountain and arid regions, and the potential glacial hazards. In this paper, we present a two-dimensional thermomechanically coupled ice flow model named PoLIM (Polythermal Land Ice Model). The velocity solver of PoLIM is developed based on the Blatter-Pattyn approximation of Stokes flow. It uses an enthalpy formulation of the energy balance, an approach that is suitable for modeling the polythermal glaciers. PoLIM also includes a scheme for gravity-driven drainage of water in temperate ice, a subglacial hydrology model coupled with ice dynamics, and multiple basal sliding laws. The model has been verified by standard benchmark problems, including the ISMIP-HOM experiments, the enthalpy benchmark experiments, and the SHMIP experiments. PoLIM shows good performances and agrees well with these benchmark results, indicating its robust capability of simulating the thermomechanical behaviors of glaciers.

Absorbing aerosols and their impact on the Indian monsoon system is highly complex and demands more scientific understanding. Our study using a chemistry-coupled regional climate model (RegCM 4.5) with idealized experiments observed that natural and anthropogenic absorbing aerosols (i.e., dust and carbonaceous aerosols) reduce monsoon precipitation in a seasonal time scale. More than 1 mm day(-1) decline in mean summertime rainfall was observed over parts of the central Indian region and Indo-Gangetic plane for dust aerosol. A substantial reduction in the land-sea pressure gradient and lower tropospheric moisture distribution were found to control the observed modulation in rainfall. Near-surface wind circulation responded distinctly to natural (dust) and anthropogenic (carbonaceous) aerosols. The dust forcing weakened the monsoon trough by creating an anomalous anticyclonic circulation. The Northern Arabian Sea acted as a moisture source for the carbonaceous aerosol forcing. Intraseasonal rainfall over central India appeared to have a sharp reduction for dust forcing during early June, with a moderate increase for carbonaceous aerosols. Such quantification is essential for understanding the impact of aerosol forcing on regional climate change and the water cycle and has implications for emissions management and mitigation policies.

Resource depletion and climate changes due to human activities and excessive burning of fossil fuels are the driving forces to explore alternatives clean energy resources. The objective of this study was to investigate the potential of potato peel waste (PPW) at various temperatures T15 (15 degrees C), T25 (25 degrees C), and T35 (35 degrees C) in anaerobic digestion (AD) for biogas generation. The highest biogas and CH4 production (117 mL VS-g and 74 mL VS-g) was observed by applying 35 degrees C (T35) as compared with T25 (65 mL VS-g and 22 mL VS-g) on day 6. Changes in microbial diversity associated with different temperatures were also explored. The Shannon index of bacterial community was not significantly affected, while there was a positive correlation of archaeal community with the applied temperatures. The bacterial phyla Firmicutes were strongly affected by T35 (39%), whereas Lactobacillus was the dominant genera at T15 (27%). Methanobacterium and Methanosarcina, as archaeal genera, dominated in T35 temperature reactors. In brief, at T35, Proteiniphilum and Methanosarcina were positively correlated with volatile fatty acids (VFAs) concentration. Spearman correlation revealed dynamic interspecies interactions among bacterial and archaeal genera; facilitating the AD system. This study revealed that temperature variations can enhance the microbial community of the AD system, leading to increased biogas production. It is recommended for optimizing the AD of food wastes.

Freezing/thawing indices are important indicators of the dynamics of frozen ground on the Qinghai-Tibet Plateau (QTP), especially in areas with limited observations. Based on the numerical outputs of Community Land Surface Model version 4.5 (CLM4.5) from 1961 to 2010, this study compared the spatial and temporal variations between air freezing/thawing indices (2 m above the ground) and ground surface freezing/thawing indices in permafrost and seasonally frozen ground (SFG) across the QTP after presenting changes in frozen ground distribution in each decade in the context of warming and wetting. The results indicate that an area of 0.60 x 10(6) km(2) of permafrost in the QTP degraded to SFG in the 1960s-2000s, and the primary shrinkage period occurred in the 2000s. The air freezing index (AFI) and ground freezing index (GFI) decreased dramatically at rates of 71.00 & DEG;C & BULL;d/decade and 34.33 & DEG;C & BULL;d/decade from 1961 to 2010, respectively. In contrast, the air thawing index (ATI) and ground thawing index (GTI) increased strikingly, with values of 48.13 & DEG;C & BULL;d/decade and 40.37 & DEG;C & BULL;d/decade in the past five decades, respectively. Permafrost showed more pronounced changes in freezing/thawing indices since the 1990s compared to SFG. The changes in thermal regimes in frozen ground showed close relations to air warming until the late 1990s, especially in 1998, when the QTP underwent the most progressive warming. However, a sharp increase in the annual precipitation from 1998 began to play a more controlling role in thermal degradation in frozen ground than the air warming in the 2000s. Meanwhile, the following vegetation expansion hiatus further promotes the thermal instability of frozen ground in this highly wet period.