No abstract

Freezing and thawing of soil have a significant impact on the thermal‐hydrological processes in cold regions. Freezing point and unfrozen water content are key variables characterizing the freezing and thawing of soil. The testing results show that unfrozen water content is independent of initial water content in nonsaline silt, based on which a unified model for a soil freezing characteristic curve (SFCC) is presented. The SFCC describes the relationship between unfrozen water content and temperature for variably‐saturated saline soils. It is also demonstrated that the SFCC can describe the variation of soil freezing point with respect to water content and salt concentration. The SFCC model is validated by comparing the experimental data to the calculated result for unfrozen water content and freezing point in a variety of conditions. When the initial water content varies in saline soil, the SFCC changes with constant initial salt concentration, but it remains unchanged with constant gravimetric salt content. The SFCC model can be adopted in the simulation of thermal‐hydrological processes in arid and saline lands and coastal regions. Finally, an example of thermal‐hydrological processes was simulated with the new SFCC model to show the application of the presented model.

Due to environmental disturbances such as local human activity and global warming, melting of massive ground ice has resulted in thermokarst ponds, which are extensively distributed in the Qinghai-Tibet Plateau (QTP). Besides the global warming, the thermokarst pond, as a major heat source, speeds up the moisture change and degradation of its surrounding permafrost. To analyze the long-term coupled moisture-heat process near a representative nonpenetrative thermokarst pond in a permafrost region, abundant temperature data over multiple years at different depths and horizontal distances from the center of the thermokarst pond have been collected at a field experimental station in QTP. A numerical model is built to analyze this thermokarst pond. The temperature and moisture processes of surrounding permafrost are simulated by this model and compared with measured temperature data. Our results show that if the rate of air temperature rise is 0.048°C/yr, which refers to a 2.4°C temperature rise over 50 years, the thawing fronts underneath the thermokarst pond move downward at a linear rate of 0.18 m/yr and the permafrost beneath the pond center would disappear after the year of 2281. Beyond that time, the impact range of the pond on the natural ground increases to about 50 m in horizontal direction. So a dish-shape thawing zone occurs around the thermokarst pond. Simultaneously, the moisture state is greatly changed in 2281 and becomes completely different from that in 2013. All of these would inevitably deteriorate the ecological and environmental system in QTP.

No abstract