Local Controls on the Development of Percolation Features After a Rain-on-Snow Event in a Southern Taiga Snowpack

Abstract. Rain-on-snow (ROS) events can rapidly introduce liquid water into cold snowpacks. However, direct field observations of preferential-flow structure development under such conditions remain limited. In this study, we document the formation of percolation columns and linear flow pathways after a ROS event in a cold, predominantly fine-grained snowpack in the southern taiga. We combine meteorological observations, snow-pit measurements, stratigraphic descriptions, density and snow-water-equivalent (SWE) measurements, and low-cost photogrammetric mapping to examine how local surface conditions influenced the spatial organization of preferential flow.

The same ROS event produced contrasting flow structures over short distances. In the floodplain meadow, percolation features developed mainly in inter-tussock depressions and formed relatively large funnels with the highest areal coverage. In the more homogeneous field site, features were more numerous but smaller, while in the birch forest they were sparse and clustered, mainly in canopy gaps. On the slope (~25°), liquid water was routed into elongated, downslope flow pathways rather than discrete vertical columns. At the meadow and field sites, snow within percolation columns was denser and stored more SWE than the surrounding snow occupying the same volume, indicating localized water accumulation and refreezing.

These results show that rain-induced infiltration in cold snowpacks can be reorganized at sub-meter scales by microtopography, vegetation, slope, and snow stratigraphy. Percolation columns and associated ice structures therefore represent important small-scale heterogeneities that can affect meltwater storage, refreezing, drainage pathways, causing challenges in snowpack modelling, and the interpretation of microwave remote-sensing signals.