Research papersIsotopic tracing of the outflow during artificial rain-on-snow event

- An intensive rain-on-snow event was simulated on a ripe coarse grain snow cover.
- The deuterium concentrations in the rain water and in the outflow were estimated.
- The hydrograph separation based on deuterium concentrations was computed.
- Rainwater pushes-out the non-rainwater and then contributes to the outflow.
- The point scale allows investigation of dynamics of individual hydrograph components.

The frequency of rain-on-snow (ROS) occurrence is increasing and this natural phenomenon is beginning to play an important role in temperate climate regions. Present knowledge of outflow generation mechanisms and rainwater dynamics during ROS is still insufficient. The study introduces a combined method of artificial ROS, isotopic tracing and energy balance to partition the event rainwater and the pre-event non-rainwater in the outflow. A rainfall simulator and water enriched with deuterium were used for identifying event rainwater and pre-event non-rainwater during an ROS event.The ROS experiment was conducted in the Krkonoše Mountains in the Czech Republic. An experimental snow block consisting of ripe and isothermal snow was sprayed with deuterium enriched water. The outflow from the snowpack was continuously monitored to gain quantitative and qualitative information about outflow water. The isotopic deuterium content was further analysed from the samples by means of laser spectroscopy in order to separate the hydrograph components. The deuterium content was also analysed from the snow samples gathered before and after the experiment to identify the retention of event rainwater in the snowpack.Isotopic hydrograph separation revealed that although high rain intensity was applied, the event rainwater represented one half (52.7%) of the total outflow volume. The ripe snowpack retained about one third of the rainwater input (33.6%). Significant changes in the outflowing water quality can therefore be expected during ROS events. This experiment also shows that rainwater during ROS firstly pushes-out the non-rainwater and then contributes to the outflow. These results show that the presented technique allows us to gain sufficient information about rainwater dynamics during ROS.