Experimental analysis and formula development for natural soil water infiltration processes in cold region freeze-thaw environments

Infiltration is a vital component of the water cycle, governing the runoff generation and concentration processes. A more accurate description of the infiltration process is essential to improve hydrological modeling and facilitate effective water management strategies. In cold regions, soil water infiltration process is affected by freeze-thaw cycle and more crucial due to its sensitivity to global warming. Current infiltration models are developed for stable, temperate conditions and constant soil properties, which contrast sharply with the thermal and hydraulic conditions in freeze-thaw environments. Based on the widely used infiltration Horton equation, this study proposed a Horton-RCCC (Research Center for Climate Change) formula specifically designed for the freeze-thaw environment in cold regions, which are achieved by several steps as follows. A large-size undisturbed soil sampling and restoration method to enable laboratory simulation of soil freeze-thaw processes. The soil freeze-thaw state is described using the ratio of current freeze-thaw depth to maximum freeze-thaw depth. The calculation equations for soil water initial infiltration rate and stable infiltration rate are developed, shifting from the traditional approach of using a single parameter set for entire watersheds and improving distributed characterization of soil infiltration capacity under varying underlying surface conditions. The Horton-RCCC formula is calibrated and validated in permafrost and seasonally frozen ground regions. In complete thawing stage, the Horton-RCCC formula demonstrates comparable accuracy with that of Horton equation on a condition of zero slope, and shows its advantage to calculation infiltration under sloped conditions. In freeze-thaw period, the Horton-RCCC formula effectively addresses the dynamics of underlying surface infiltration conditions, and shows a significant improvement in accuracy. This formula breaks away from the conventional research paradigm of directly applying infiltration formulas for temperate conditions, could stimulate improvements in hydrological modeling, water resource management and climate change adaptation in cold regions. • f 0 and f c were significantly and negatively correlated with γ and FVC . • As the slope increased from 0° to 30°, the cumulative soil infiltration decreased in a negative exponential trend. • The ratio of freeze-thaw front depth to maximum freezing depth solves the continuity problem of infiltration equations between different freeze-thaw periods. • The Horton-RCCC equation can be applied to fit the entire freeze-thaw process.