Soil parameters form the foundation of hydrogeological research and are crucial for studying engineering construction and maintenance, climate change, and ecological environment effects in cold regions. However, the soil properties in the permafrost region of the Qinghai-Tibet Plateau (QTP) remain unclear. Hence, in this study, soil temperature (Ts), volumetric specific heat capacity (C), thermal conductivity (K), thermal diffusivity (D), soil water content (SWC), electric conductivity (EC), vertical (Kv) and horizontal (Kh) saturated hydraulic conductivity, bulk density (rho b), and soil texture near the Qinghai-Tibet Railway were measured, and their effects on the freeze-thaw process were evaluated. The results revealed a predominantly sandy loam soil texture, with Kh and Kv showing strong spatial variability, while the other parameters presented moderate spatial variability. Thermokarst lake had a limited influence on D, C, K, and rho b but significantly reduced Kh and Kv. Groundwater affected SWC, Ts, and EC. The model results showed that all parameters indicated small sensitivities to the maximum thawing depth (MTD), with MTD positively responding to all parameters except for Kv and porosity (rho p). Except for Kh and Kv, all parameters showed high sensitivities to the time from starting to complete freezing (TSCF). TSCF responded positively to C, rho p, and density (rho d) and negatively to K and Kh. This study expanded the quantification of soil properties in the QTP, which can help improve the accuracy of cryohydrogeologic models, thus guiding the construction and maintenance of infrastructure engineering.

Ground freeze-thaw processes have significant impacts on infiltration, runoff and evapotranspiration. However, there are still critical knowledge gaps in understanding of hydrological processes in permafrost regions, especially of the interactions among permafrost, ecology, and hydrology. In this study, an alpine permafrost basin on the northeastern Qinghai-Tibet Plateau was selected to conduct hydrological and meteorological observations. We analyzed the annual variations in runoff, precipitation, evapotranspiration, and changes in water storage, as well as the mechanisms for runoff generation in the basin from May 2014 to December 2015. The annual flow curve in the basin exhibited peaks both in spring and autumn floods. The high ratio of evapotranspiration to annual precipitation (>1.0) in the investigated wetland is mainly due to the considerably underestimated 'observed' precipitation caused by the wind-induced instrumental error and the neglect of snow sublimation. The stream flow from early May to late October probably came from the lateral discharge of subsurface flow in alpine wetlands. This study can provide data support and validation for hydrological model simulation and prediction, as well as water resource assessment, in the upper Yellow River Basin, especially for the headwater area. The results also provide case support for permafrost hydrology modeling in ungauged or poorly gauged watersheds in the High Mountain Asia.

The increase in temperatures and changing precipitation patterns resulting from climate change are accelerating the occurrence and development of landslides in cold regions, especially in permafrost environments. Although the boundary regions between permafrost and seasonally frozen ground are very sensitive to climate warming, slope failures and their kinematics remain barely characterized or understood in these regions. Here, we apply multisource remote sensing and field investigation to study the activity and kinematics of two adjacent landslides (hereafter referred to as twin landslides) along the Datong River in the Qilian Mountains of the Qinghai-Tibet Plateau. After failure, there is no obvious change in the area corresponding to the twin landslides. Based on InSAR measurements derived from ALOS PALSAR-1 and -2, we observe significant downslope movements of up to 15 mm/day within the twin landslides and up to 5 mm/day in their surrounding slopes. We show that the downslope movements exhibit distinct seasonality; during the late thaw and early freeze season, a mean velocity of about 4 mm/day is observed, while during the late freeze and early thaw season the downslope velocity is nearly inactive. The pronounced seasonality of downslope movements during both pre- and post-failure stages suggest that the occurrence and development of the twin landslide are strongly influenced by freeze-thaw processes. Based on meteorological data, we infer that the occurrence of twin landslides are related to extensive precipitation and warm winters. Based on risk assessment, InSAR measurements, and field investigation, we infer that new slope failure or collapse may occur in the near future, which will probably block the Datong River and cause catastrophic disasters. Our study provides new insight into the failure mechanisms of slopes at the boundaries of permafrost and seasonally frozen ground.

Permafrost is mostly warm and thermally unstable on the Tibetan Plateau (TP), particularly in some marginal areas, thereby being susceptible to degrade or even disappear under climate warming. The degradation of permafrost consequently leads to changes in hydrological cycles associated with seasonal freeze-thaw processes. In this study, we investigated seasonal hydrothermal processes of near-surface permafrost layers and their responses to rain events at two warm permafrost sites in the Headwater Area of the Yellow River, northeastern TP. Results demonstrated that water content in shallow active layers changed with infiltration of rainwater, whereas kept stable in the perennially frozen layer, which serves as an aquitard due to low hydraulic conductivity or even imperviousness. Accordingly, the supra-permafrost water acts as a seasonal aquifer in the thawing period and as a seasonal aquitard in the freezing period. Seasonal freeze-thaw processes in association with rain events correlate well with the recharge and discharge of the supra-permafrost water. Super-heavy precipitation (44 mm occurred on 2 July 2015) caused a sharp increase in soil water content and dramatic rises in soil temperatures by 0.3-0.5 degrees C at shallow depths and advancement thawing of the active layer by half a month. However, more summer precipitation amount tends to reduce the seasonal amplitude of soil temperatures, decrease mean annual soil temperatures and thawing indices and thin active layers. High salinity results in the long remaining of a large amount of unfrozen water around the bottom of the active layer. We conclude that extremely warm permafrost with T-ZAR (the temperature at the depth of zero annual amplitude) > 0.5 degrees C is likely percolated under heavy and super-heavy precipitation events, while hydrothermal processes around the permafrost table likely present three stages concerning TZAR of 0 degrees C.

The mechanisms of hydrological processes, biochemical cycles, and permafrost revolution, and the potential impacts of climate change on these, are still poorly quantified in alpine regions, partly due to a lack of understanding of soil water dynamics in the permafrost active layer. In this study, soil water in the active layer was monitored in-situ at nine sites, including wet meadow (WM), alpine meadow (AM), alpine steppe (AS), transitional area-steppe (TA-S), transitional area-meadow (TA-M), bare land (BL), extremely degraded wet meadow (EDWM), alpine steppe on south-facing slope (ASSF), and alpine meadow on north-facing slope (AMNF) regions. These sites are located in the hinterland of the Qinghai-Tibet Plateau (QTP). Ground-ice distributions and isotope variations under different alpine ecosystems were also examined. The results demonstrate that soil water content was low at 0.5-m depth and high at the surface and at 1.0-m depth in the soil profiles from the TA-S, BL, EDWM, ASSF, and AMNF sites. However, denser vegetation coverage masked the effects of the freeze thaw processes, which leading soil water content increased gradually with soil depth. Moreover, rainfall infiltration for recharging soil water in the lower layers was hampered due to the buffering action of mattic epipedons and the existence of clayed layers. Additionally, preferential flow often occurred in the degraded alpine meadows, which supplied deeper soil water. The Pearson correlation coefficients between soil water in the deeper layers and ground-ice were above 0.67 (significance < 0.05), suggesting that deep soil water had a stronger effect on the formation of ground-ice near the permafrost table than soil water at the surface and middle root layers. Furthermore, results from the analysis of isotopic tracers suggest that precipitation directly recharged more ground-ice near permafrost table at the EDWM, ASSF, and AWNF sites, but less so at the WM, AM, AS, and BL sites, due to greater evapotranspiration and land cover. These results provide insights into the effect future climate warming can have on ecological succession and regional hydrological processes.

Accurate quantification of the distribution and characteristics of frozen soil is critical for evaluating the impacts of climate change on the ecological and hydrological systems in high-latitude and-altitude regions, such as the Tibetan Plateau (TP). However, field observations have been limited by the harsh climate and complex terrain on the plateau, which greatly restricts our ability to predict the existence of and variations in frozen soils, especially at the regional scale. Here, we present a study relying solely on satellite data to drive process-based simulation of soil freeze-thaw processes. Modifications are made to an existing process-based model (Geomorphology-Based Eco-Hydrological Model, GBEHM) such that the model is fully adaptable to remote sensing inputs. The developed model fed with a combination of MODIS, TRMM and AIRX3STD satellite products is applied in the upper Yellow River Basin (coverage of similar to 2.54 x 10(5) km(2)) in the northeast TP and validated against field observations of freezing and thawing front depths (D-ft) and soil temperature (T-soil) at 54 China Meteorological Administration (CMA) stations, as well as frozen-ground types at 22 boreholes. Results indicate that the developed model performs reasonably well in simulating D-ft (R-2 = 0.69; mean bias = -0.03 m) and T-soil (station averaged R-2 and mean bias range between 0.90-0.96 and -0.51 similar to -0.14 degrees C at eight observational depths, respectively), and outperforms the original GBEHM forced with ground-measured meteorological variables. The frozen-ground types are also (in general) accurately identified by the satellite-based approach, except for a few permafrost boreholes located near the permafrost boundary regions. Additionally, we also demonstrate the importance of considering dynamic soil water content in frozen soil simulation: We find that a static-soil-moisture assumption (as used in previous studies) would lead to biased soil temperature estimates by > 0.5 degrees C. Our study demonstrates the value of using satellite data in frozen-soil simulation over complex landscapes, potentially leading to a greater understanding of soil freeze-thaw processes at the regional scale.