There is 78 % permafrost and seasonal frozen soil in the Yangtze River's Source Region (SRYR), which is situated in the middle of the Qinghai-Xizang Plateau. Three distinct scenarios were developed in the Soil and Water Assessment Tool (SWAT) to model the effects of land cover change (LCC) on various water balance components. Discharge and percolation of groundwater have decreased by mid-December. This demonstrates the seasonal contributions of subsurface water, which diminish when soil freezes. During winter, when surface water inputs are low, groundwater storage becomes even more critical to ensure water supply due to this periodic trend. An impermeable layer underneath the active layer thickness decreases GWQ and PERC in LCC + permafrost scenario. The water transport and storage phase reached a critical point in August when precipitation, permafrost thawing, and snowmelt caused LATQ to surge. To prevent waterlogging and save water for dry periods, it is necessary to control this peak flow phase. Hydrological processes, permafrost dynamics, and land cover changes in the SRYR are difficult, according to the data. These interactions enhance water circulation throughout the year, recharge of groundwater supplies, surface runoff, and lateral flow. For the region's water resource management to be effective in sustaining ecohydrology, ensuring appropriate water storage, and alleviating freshwater scarcity, these dynamics must be considered.

Accurately quantifying the impact of permafrost degradation and soil freeze-thaw cycles on hydrological processes while minimizing the reliance on observational data are challenging issues in hydrological modeling in cold regions. In this study, we developed a modular distributed hydro-thermal coupled hydrological model for cold regions (DHTC) that features a flexible structure. The DHTC model couples heat-water transport processes by employing the conduction-advection heat transport equation and Richard equation considering ice-water phase change. Additionally, the DHTC model integrates the influence of organic matter into the hydrothermal parameterization scheme and includes a subpermafrost module based on the flow duration curve analysis to estimate cold-season streamflow sustained by subpermafrost groundwater. Moreover, we incorporated energy consumption due to ice phase changes to the available energy, enhancing the accuracy of evaporation estimation in cold regions. A comprehensive evaluation of the DHTC model was conducted. At the point scale, the DHTC model accurately replicates daily soil temperature and moisture dynamics at various depths, achieving average R-2 of 0.98 and 0.87, and average RMSE of 0.61degree celsius and 0.03 m(3)m(-3), respectively. At the basin scale, DHTC outperformed (Daily: R-2 = 0.66, RMSE = 0.75 mm; Monthly: R-2 = 0.90, RMSE = 15.7 mm) the GLDAS/FLDAS Noah, GLDAS/VIC, and PML-V2 models in evapotranspiration simulation. The DHTC model also demonstrated reasonable performance in simulating daily (NSE = 0.70, KGE = 0.84), monthly (NSE = 0.86, KGE = 0.90), and multi-year monthly (NSE = 0.97, KGE = 0.93) streamflow in the Source Regions of Yangtze River. DHTC also successfully reproduced the snow depth in basin-averaged time series and spatial distributions (RMSE = 0.86 cm). The DHTC model provides a robust tool for exploring the interactions between permafrost and hydrological processes, and their responses to climate change.

Deformation and failure of the talus slope in the cold region significantly threaten engineered structures. Its driving mechanism of the deformation process is the most challenging issue. In this study, we try to explore these issues using tree ring characteristics. Fifty samples from 21 trees of Pinus densiflora growing on the talus slope in the Huanren area of Northeast China are tested to investigate the characteristics of tree rings and their relation to climate change. The deformation and its driving mechanism of this talus slope are then studied by combining the analysis of tree-ring width and mutation identification with the local meteorological data. The results present that the studied talus slope in Huanren has deformed to varying degrees at least 60 times since 1900. It is reasonable to speculate that the deformation mode of this slope is probably of a long-term and slow type. The local precipitation and seasonal temperature difference are the vital inducing factors of the mutation of tree-ring width and slope deformation. Repeated freezing and thawing are believed to be the driving factors of this talus slope in the cold region. A theoretical model is proposed to capture and predict the deformation of the talus slope. This work presents a new perspective and insight to reveal the deformation and its driving mechanism of similar talus slopes in the cold region. It is of great significance to practical engineering treatment and disaster prevention for this kind of cold region environment.

Climate warming is causing significant changes in the Arctic, leading to increased temperatures and permafrost instability. The active layer has been shown to be affected by climate change, where warmer ground surface temperatures result in progressive permafrost thaw and a deepening active layer. This study assessed the effects of thermal modeling parameters on permafrost ground response to climate warming using the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and TEMP/W software. We analyzed how variations in depth, water content, and soil type affect predictions of future active layer depths and settlement under various climate scenarios using the soil characteristics along Hudson Bay Railway corridor. The results indicate that, for finegrained soils, the depth of the model is a more significant parameter than for coarse-grained soils. The water content of all soil types is a critical factor in determining the time at which permafrost thaws and the depth at which the active layer is located, as higher water content leads to larger active layer changes and more settlement in most cases. Our findings have important implications for infrastructure and land use management in the Arctic region.

Permafrost degradation alters the flow rate, direction, and storage capacity of soil moisture, affecting ecohydrological effects and climate systems, and posing a potential threat to natural and human systems. The most widely distributed permafrost regions are coastal, high-latitudes and high-altitudes (mainly by the Qinghai-Tibet Plateau). Past studies have demonstrated that permafrost degradation in these regions lacks sorting out regional driving factors, assessing cascading effects on the hydrological environment and monitoring methods. To address this, we reviewed the historical research situation and major topics of permafrost degradation from 1990 to 2022. We analyzed the spatio-temporal dynamics and driving mechanism of permafrost degradation. Then, we comprehensively discussed the effects of permafrost degradation on the soil physical structure and hydraulic properties, soil microorganisms and local vegetation, soil evapotranspiration and stream runoff, and integrated ecohydrological effects. Permafrost field site data were then collected from existing findings and methods for direct or indirect monitoring of permafrost changes at different scales. These results revealed that the research on the hydrological effects of permafrost change was mainly centered on the soil. In addition, regional environmental factors driving permafrost degradation were inconsistent mainly in coastal regions influenced by sea level, high-latitude regions influenced by lightning and wildfire, and high-altitude regions influenced by topography. Permafrost degradation promoted horizontal and/or vertical hydrological connectivity, threatening the succession of high latitude vegetation communities and the transition from high altitude grassland to desert ecosystems, causing regional water imbalances would mitigate or amplify the ability of integrated ecohydrological benefits to cope with climate warming. The never-monitored permafrost area was 1.55x106 km2, but the limitations of using data for the same period remained a challenging task for soil moisture monitoring. Finally, future research should enhance the observation of driving factors at the monitoring site and combine remote sensing data, model simulations or numerical simulations, and isotope tracers to predict the future degradation state of deep permafrost effectively. It is expected that this review will guide further quantifying the driving mechanisms of permafrost degradation and the resulting cascading effects.

Rivers originating from the Tibetan Plateau (TP) provide water to more than 1 billion people living downstream. Almost 40% of the TP is currently underlain by permafrost, which serves as both an ice reserve and a flow barrier and is expected to degrade drastically in a warming climate. The hydrological impacts of permafrost thaw across the TP, however, remain poorly understood. Here, we quantify the permafrost change on the TP over 1980-2100 and evaluate its hydrological impacts using a physically-based cryospheric-hydrological model at a high spatial resolution. Using the ensemble mean of 38 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), the near-surface permafrost area and the total ground ice storage are projected to decrease by 86.4% and 61.6% during 2020-2100 under a high-emission scenario, respectively. The lowering of the permafrost table and removal of permafrost as a flow barrier would enhance infiltration and raise subsurface storage capacity. The diminished water supply from ground ice melt and enhanced subsurface storage capacity could jointly reduce annual runoff and lead to exacerbated regional water shortage when facing future droughts. If the most severe 10-year drought in the historical period occurs again in the future, the annual river runoff will further decrease by 9.7% and 11.3% compared with the historical dry period due to vanishing cryosphere in the source area of Yellow and Yangtze River. Our findings highlight the importance to get prepared for the additional water shortage risks caused by pervasive permafrost thaw in future water resources management across the TP.

This study diagnoses the impact of projected changes in climate and glacier cover on the hydrology of several natural flowing Bow River headwater basins in the Canadian Rockies: the Bow River at Lake Louise (-420.7 km2), the Pipestone River near Lake Louise (-304.2 km2), the Bow River at Banff (-2192.2 km2) all of which drain the high elevation, snowy, partially glaciated Central Range, and the Elbow River at Calgary (-1191.9 km2), which drains the drier Front Ranges and foothills, using models created using the modular, flexible, physically based Cold Regions Hydrological Modelling platform (CRHM). Hydrological models were constructed and parameterised in CRHM from local research results to include relevant streamflow generation processes for Canadian Rockies headwater basins, such as blowing snow, avalanching, snow interception and sublimation, energy budget snow and glacier melt, infiltration to frozen and unfrozen soils, hillslope sub-surface water redistribution, wetlands, lakes, evapotranspiration, groundwater flow, surface runoff and open channel flow. Surface layer outputs from Weather Research and Forecasting (WRF) model simulations for the current climate and for the late 21st century climate under a business-as-usual scenario, Representative Concentration Pathway 8.5 (RCP8.5) at 4-km resolution, were used to force model simulations to examine the climate change impact. A projected glacier cover under a business-as-usual scenario (RCP8.5) was incorporated to assess the impact of concomitant glacier cover decline. Uncalibrated model simulations for the current climate and glacier coverage showed useful predictions of snow accumulation, snowmelt, and streamflow when compared to surface obser-vations from 2000 to 2015. Under the RCP8.5 climate change scenario, the basins of the Bow River at Banff and Elbow River at Calgary will warm up by 4.7 and 4.5 degrees C respectively and receive 12% to 15% more precipitation annually, with both basins experiencing a greater proportion of precipitation as rainfall. Peak snow accumulation in Bow River Basin will slightly rise by 3 mm, whilst it will drop by 20 mm in Elbow River Basin, and annual snowmelt volume will increase by 43 mm in Bow River Basin but decrease by 55 mm in Elbow River Basin. Snowcovered periods will decline by 37 and 46 days in Bow and Elbow river basins respectively due to sup-pressed snow redistribution by wind and gravity and earlier melt. The shorter snowcovered period and warmer, wetter climate will increase evapotranspiration and glacier melt, if the glaciers were held constant, and decrease sublimation, lake levels, soil moisture and groundwater levels. The hydrological responses of the basins will differ despite similar climate changes because of differing biophysical characteristics, climates and hydrological processes generating runoff. Climate change with concomitant glacier decline is predicted to increase the peak discharge and mean annual water yield by 12.23 m3 s-1 (+11%) and 11% in the higher elevation basins of the Bow River but will decrease the mean annual peak discharge by 3.58 m3 s-1 (-9%) and increase the mean annual water yield by 18% in the lower elevation basin of the Elbow River. This shows complex and compensatory hydrological process responses to climate change with the reduced glacier contribution reducing the impact of higher precipitation in high elevation headwaters and drier soil conditions and lower spring snowpacks reducing peak discharges despite increased precipitation during spring runoff in the Front Range and foothills headwaters under a warmer climate.

Initially, cryohydrology was referred to as hydrology involving low temperatures, for example, the hydrological study of snow, ice, frozen ground, and cold water. This discipline broadened with the development of cryospheric science and now involves hydrological processes of various cryosphere elements systematically coupled with river basin hydrological processes. However, limited studies have introduced the characteristics and discipline connotations of cryohydrology from a perspective of cryospheric science. Here, we reviewed the evolution of the connotations of cryohydrology and analyzed its hydrological basis and discipline system. Three major conclusions were drawn. (1) Cryohydrology was developed based on traditional hydrology for a single element of the cryosphere and focuses on the hydrological functions of the cryosphere and its impact on the water cycle and water supply to other spheres. (2) The hydrological basis of cryohydrology can be summarized as water conservation, runoff recharge, and hydrological regulation. In detail, the water conservation function is primarily expressed as source of freshwater and cold and wet islands, the runoff recharge function is concerned with water supply, and the regulation function is effective at intra- and inter-annual scales. (3) The core research issues of cryohydrology are research methods, hydrological processes, watershed functions, and regional impact. The important characteristics of cryohydrology are frequent water phase transitions and high variability across spatial and temporal scales. Cryohydrology aims to deepen the understanding of the theoretical and cognitive levels of its mechanisms and processes, accurately quantify the hydrological functions of the basin, and promote understanding of the ecological and environmental impacts of the cryosphere.

Hydrological conditions in cold regions have been shown to be sensitive to climate change. However, a detailed understanding of how regional climate and basin landscape conditions independently influence the current hydrology and its climate sensitivity is currently lacking. This study, therefore, compares the climate sensitivity of the hydrology of two basins with contrasted landscape and meteorological characteristics typical of eastern Canada: a forested boreal climate basin (Montmorency) versus an agricultural hemiboreal climate basin (Aca-die). The physically based Cold Regions Hydrological Modelling (CRHM) platform was used to simulate the current and future hydrological processes. Both basin landscape and regional climate drove differences in hy-drological sensitivities to climate change. Projected peak SWE were highly sensitive to warming, particularly for milder baseline climate conditions and moderately influenced by differences in landscape conditions. Landscape conditions mediated a wide range of differing hydrological processes and streamflow responses to climate change. The effective precipitation was more sensitive to warming in the forested basin than in the agricultural one, due to reductions in forest canopy interception losses with warming. Under present climate, precipitation and discharge were found to be more synchronized in the greater relief and slopes of the forested basin, whereas under climate change, they are more synchronized in the agricultural basin due to reduced infiltration and storage capacities. Flow through and over agricultural soils translated the increase in water availability under a warmer and wetter climate into higher peak discharges, whereas the porous forest soils dampened the response of peak discharge to increased available water. These findings help diagnose the mechanisms controlling hy-drological response to climate change in cold regions forested and agricultural basins.

The Tibetan Plateau (TP), also known as the world's Third Pole, is underlain by frozen ground and is highly sensitive to climate change. However, it remains unclear how the variations in soil freeze-thaw could affect vegetation dynamics across the TP. In this study, we adopted the latest datasets for vegetation, climate and soil freeze-thaw in the past two decades to explore the possible impacts of changes in soil freeze-thaw on vegetation greenness and phenology on the TP. According to the satellite-based observations, the TP showed an overall greening trend during 2001-2020, and the growing season length increased significantly at a rate of 3.6 days/ 10a, mainly contributed by the advances of the start of the growing season (2.7 days/10a). Based on ridge regression and partial correlation analysis, air temperature and precipitation were found to be the major dominant factors of vegetation dynamics on the TP, and precipitation played a dominant role in the relatively warm-dry southwestern TP where vegetation browning and spring phenology delays were observed. In the relatively cold regions, earlier soil thaw onset generally facilitated spring phenology, and longer soil thaw duration tended to increase the growing season soil moisture content, which could in turn enhance vegetation greenness. In the relatively warm regions, however, earlier thaw onset and longer thaw duration could possibly exacerbate the growing season water stress and limit vegetation growth. The negative impacts were more evident in the regions with unstable and completely degraded permafrost according to the results in the source region of Yellow and Yangtze rivers. Our findings highlight the spatially varying role of soil freeze-thaw changes in vegetation dynamics, which have important implications for the carbon budget of the TP in a warming future climate as frozen ground continues to degrade.