# Effects of Cyclical Climate Change on Water Temperature Characteristics of Permafrost Slopes
## 3 Results and Discussion
### Long-Term Water Temperature Characteristics  
Figure 5 reflects the temperature change characteristics of the slope top and different depths (1 m, 2 m) and the foundation center, reflecting the hydrothermal coupling thermodynamic response mechanism of the soil under long-term freeze-thaw cycles. The temperature of shallow-layer soil shows significant periodic fluctuations, and the fluctuation amplitude gradually decreases with the increase in depth, accompanied by a certain phase-lag phenomenon. This characteristic indicates that the shallow-layer soil is more significantly affected by seasonal freeze-thaw cycles. Frequent temperature fluctuations lead to the alternating freezing and thawing of soil pore water, thereby affecting the soil's hydrothermal balance and structural stability. In comparison, the temperature change amplitude of the foundation center is significantly reduced, showing higher thermal stability. Due to the thermal diffusion effect, deep-layer soil has an obvious buffering effect from external temperature fluctuations, thereby weakening the impact of freeze-thaw cycles on the soil. This thermal diffusion effect is closely related to the soil's thermal conductivity coefficient, heat capacity, and depth, further revealing the complexity of soil hydrothermal conduction. Figure 6 shows the long-term dynamic change law of soil water content with time at different locations, reflecting the significant influence of climate change on soil water migration. The water content in the figure shows obvious periodic fluctuations [with a period of about one year], and there are significant differences in fluctuation amplitudes and phases [12]. Among them, the water content at the top of the slope has the largest fluctuation amplitude, with the lowest value close to 0.08% and the highest value exceeding 0.28%, indicating that the top of the slope is exposed to climate conditions (such as precipitation and evaporation) and is the location with the most drastic water changes. The fluctuation amplitudes of water content at 1 m and 2 m below the top of the slope gradually decrease with the increase in depth, and there is an obvious phase lag, reflecting the influence of soil permeability and hydrodynamic effects on the process of water permeating from the surface to the deep layer. In comparison, the fluctuation amplitude of water content at the center of the foundation is the smallest, about 0.26-0.30%, and the water change is relatively stable, which may be controlled by the groundwater level and lower permeability. The large  
Figure 5: Slope and foundation temperature variation. amplitude fluctuations in the slope area indicate that it is more sensitive to environmental changes and may become a potential instability factor [12], while the relatively stable water content at the center of the foundation provides safe foundation conditions. In addition, the depth-lag effect of the fluctuations further reveals the time-response characteristics of water migration. Therefore, the accumulation of moisture at the slope toe during both freezing and thawing stages poses a critical risk of collapse. These findings directly inform engineering practices: the real-time monitoring of pore water content at depths of \(-\)2-0 m could serve as an early warning indicator for instability and provide a dynamic assessment of seasonal risks, essential for infrastructure design in permafrost regions. In summary, the hydrothermal coupling mechanism plays a central role in the soil freeze-thaw cycle. It drives the phase change and migration of water through temperature changes, thereby affecting the thermodynamic properties and structural stability of the soil. Shallow-layer soil is directly affected by external climate conditions, with significant temperature fluctuations, resulting in the frequent freezing and thawing of pore water, triggering water migration and soil expansion and contraction, thus exacerbating soil instability.