Spatial Variability and Drivers of Preferential Flow Under Influence of Snowpack-freeze-thaw Cycles

The freeze-thaw process is crucial for forming soil macropore structure to promote movement of water and salt downward by preferential flow in seasonally frozen regions. However, the freeze-thaw process of soil is hindered by the snowpack, and the effects of the snowpack on the soil macropore structure and its implications on the formation of preferential flow are not well understood. This study collected soil samples from Da’an City, Northeast China, on July 15 and 16, 2022, and conducted an indoor soil column snowpack-freeze-thaw tracing experiment on October 10 to 30, 2022, to reveal the impact of snowpack and freeze-thaw cycles on the formation of preferential flow. The experiments were carried out with three levels of initial moisture content (IMC) of the soil column, the times of freeze-thaw cycles (T-FTC), and the snowpack thickness (SPT). Results show that increases in both IMC and SPT decreased the max infiltration depth (MID) of preferential flow. Greater T-FTC increased the MID and non-uniformity of the wet front trace and promoted the creation of preferential flow. The T-FTC and IMC both increased the overall variability of preferential flow, but this variability decreased with greater SPT. The length index (LI) had the most significant impact on the preferential flow index (PFI) with an entropy weight of 0.2340, while the height difference of the multifractal spectrum (Δf(α)) had the most negligible impact with a weight of 0.0753. Finally, results of redundancy analysis (RDA) and structural equation model (SEM) show that multifractal characteristic indicators have a much stronger ability to reflect the degree of preferential flow than developmental characteristic indicators. The T-FTC was the most important factor driving the formation of preferential flow in snowpack-freeze-thaw cycles. Therefore, conducting research on preferential flow in cold and arid regions is greatly significant for the utilization of regional water resources and the improvement of soil ecological environments.