## 1 Introduction  
Frozen soils formed under low-temperature conditions significantly influence regional ecosystems, hydrological processes, and infrastructure development [1, 2]. The Qinghai-Tibet Plateau hosts extensive frozen soil deposits and, as one of the most climate-sensitive spheres, its frozen soils are experiencing pronounced degradation under the current context of global warming [3, 4]. In particular, the dynamic variations in the thickness of the frozen layer, freezing depth, and moisture migration in seasonally frozen soils directly govern the coupled hydrothermal processes of shallow geotechnical materials, and exhibit high sensitivity to surface soil structure, moisture redistribution, and root-zone activity, thereby affecting vegetation growth. In addition, infrastructure such as roads, pipelines, and site foundations in the region are susceptible to disturbance and damage caused by freeze-thaw deformation and water content fluctuations [5, 6]. Consequently, in-depth investigation of the freezing characteristics and spatiotemporal evolution of frozen soils in the Qinghai-Tibet Plateau is vital for ensuring ecological security and the stable operation of regional infrastructure [7; 8]. In recent years, electrical resistivity tomography (ERT) technology has demonstrated significant potential in identifying frozen soil distribution and monitoring moisture dynamics due to its non-destructive nature, high resolution, and capability for large-scale detection. This technique is particularly suitable for the plateau's remote and geologically complex areas with restricted access and challenging conditions. However, the practical application of ERT in monitoring frozen soils on the Qinghai-Tibet Plateau remains limited. This limitation is attributed to the complex geological and harsh climatic conditions that strongly affect detection accuracy, as well as incomplete understanding of the electrical response mechanisms and freezing processes of frozen soils, which results in inaccurate estimation of unfrozen water content [9; 10; 11]. During the freeze-thaw evolution of frozen soils, the phase-change behavior of pore water plays a dominant role. In particular, the state and content of unfrozen water govern key soil properties such as thermal conductivity, electrical response, and mechanical strength. Compared to frozen water, unfrozen water exhibits higher polarity and conductivity, and its distribution determines the continuity of electrical conduction pathways in soil, serving as a primary factor controlling resistivity variations [12; 13]. Nevertheless, due to the combined influences of temperature, initial water content, and pore structure, the quantitative relationship between unfrozen water content and resistivity is complex and remains unresolved [14; 15]. The interference mechanisms affecting geophysical monitoring results are not yet clearly elucidated, thus hindering the widespread application of resistivity methods in frozen soil environments [16; 17; 18; 19]. In contrast, traditional research on frozen soils has predominantly focused on the thermophysical processes and mechanical characteristics of frozen soils, emphasizing issues such as thermal equilibrium below the freezing point and stress redistribution. Investigations into the spatial distribution of frozen soils have frequently relied on integrated geophysical methods and comparative analyses of the resolution and sensitivity of different techniques [20; 21]. For instance, [PERSON] et al. (2017) [22] employed ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) in the vicinity of Barrow, Minnesota, USA, to determine the thickness of the active layer, snow depth, and frozen soil features in support of parameterizing soil freeze-thaw dynamic models. Their study demonstrated that the combination of these methods significantly improved the accuracy in detecting the heterogeneity of frozen soils. Similarly, [PERSON] et al.