2017 Volume 47 Issue 2 Pages 119-126
Rain-on-snow (ROS) events cause severe snowmelt hazards such as river flooding, snow avalanches, slope failure, landslides, etc. ROS event studies have been increasing since 2000. Snowmelt energy balance studies show that the amount of advective energy carried by rainfall is usually small, and substantial contributions are made by turbulent heat transfer. However, snow melting does not occur entirely due to turbulent transfers, as radiative or ground heat transfers are also important depending on the site and period. The principal energy for melting snow during ROS events depends on the rainfall amount, meteorological and snowpack conditions, and the watershed characteristics. Moreover, the percolating process of rain water through the snowpack and the runoff characteristics of the outflow from the snowpack bottom are poorly understood. Artificial rain sprinkling experiments have been performed at some snowy sites, but the methods used in these experiments differed. In Moshiri of northern Hokkaido, Japan, a total artificial rainfall of 120 mm sprinkled over the 1.12 m deep snowpack over 207 minutes. The water that flowed out from the bottom of the snowpack was 67% event water and 33% pre-event water. This result indicates that the rain and snowmelt water percolation process during ROS events is remarkably different from the process that occurs during typical snow melting on sunny days.
