Drivers of Flow Channel Formation on the Snow Surface: Rain Versus Meltwater—A Case Study in the Austrian Alps

Flow channels on the snow surface are a common phenomenon frequently reported by field observers. The interpretation of those field observations and an understanding of the underlying physical processes are important for forecasting routines and models of avalanche warning, hydrological, or meteorological services. Flow channels on the snow surface are typically associated with rain-on-snow (ROS) events and are often interpreted as an indicator of the approximate snowfall level. However, recent field observations of flow channels on the snow surface without significant liquid precipitation in the Austrian Alps challenge the assumption that ROS events are the sole cause of flow channel formation. In this study, we quantitatively compare liquid water input into the snowpack from melt processes to the amount of rain during a documented flow channel formation event. Using a combination of field observations, energy balance calculations and model simulations, we demonstrate that, in our case study, meltwater was the predominant driver of flow channel formation. Our results indicate that more than 97 % of the total liquid water input originated from melt, while rain contributed only roughly 2 %. These findings highlight the need for a revised interpretation of flow channel formation, suggesting that meltwater-driven flow channels may be more significant than previously assumed.