Separations of meltwater discharge in a snowpack by artificial rain-on-snow experiments

In temperate regions, snow and its meltwater constitute primary freshwater resources and snowmelt isotopes offer valuable insights into understanding the snowmelt processes including the timing and contribution of snowmelt to the soil and watershed in spring. Assessing the storage and movement of liquid water within natural snowpacks, a previously unquantified aspect, holds significance for predicting natural hazards and managing water resources for agricultural purposes and ecosystem health. The escalating occurrence of rain-on-snow (ROS) events, attributed to winter warming, has the potential to trigger natural hazards and surface runoff into major river systems in temperate climate regions. End member mixing calculations (EMMC) based on isotopic and chemical tracers were employed to quantify the proportions of rainwater, meltwater, and pore water within the snowpack discharge. In this study, artificial rain-on-snow experiments involving conservative anions and stable water isotopes were conducted at the surface of snowpack to differentiate each component (rainwater, pore water, and snowmelt) within the discharge collected at the bottom of the snowpack. Pore water content exhibited a shift from 1.1 ± 1.1% (± 1σ, N = 23) after the initial artificial ROS event to 2.8 ± 1.2% (± 1σ, N = 19) following the spray in our experiment. Based on the EMMC, the contributions of rainfall, pore water, and snowmelt to the meltwater discharge were 2,620.2 L (63.3%), 829.0 L (20.0%), and 687.4 L (16.6%), respectively. Notably, contrary to prior studies, our experimental results suggest that rainwater reached the bottom through multiple rapid flow channels before matrix flow occurred. This experimental approach provides additional insights into the dynamics of water percolation in snowpacks during rain-on-snow events.