Abstract
Abstract. The mechanisms of rainwater propagation and runoff generation during rain-on-snow (ROS) events are still insufficiently known. Understanding storage and transport of liquid water in natural snowpacks is crucial, especially for forecasting of natural hazards such as floods and wet snow avalanches. In this study, propagation of rainwater through snow was investigated by sprinkling experiments with deuterium-enriched water and applying an alternative hydrograph separation technique on samples collected from the snowpack runoff. This allowed us to quantify the contribution of rainwater, snowmelt and initial liquid water released from the snowpack. Four field experiments were carried out during winter 2015 in the vicinity of Davos, Switzerland. Blocks of natural snow were isolated from the surrounding snowpack to inhibit lateral exchange of water and were exposed to artificial rainfall using deuterium-enriched water. The experiments were composed of four 30 min periods of sprinkling, separated by three 30 min breaks. The snowpack runoff was continuously gauged and sampled periodically for the deuterium signature. At the onset of each experiment antecedent liquid water was first pushed out by the sprinkling water. Hydrographs showed four pronounced peaks corresponding to the four sprinkling bursts. The contribution of rainwater to snowpack runoff consistently increased over the course of the experiment but never exceeded 86 %. An experiment conducted on a non-ripe snowpack suggested the development of preferential flow paths that allowed rainwater to efficiently propagate through the snowpack limiting the time for mass exchange processes to take effect. In contrast, experiments conducted on ripe isothermal snowpack showed a slower response behaviour and resulted in a total runoff volume which consisted of less than 50 % of the rain input.
Highlights
Rain-on-snow (ROS) events are a natural phenomenon which has been in the focus of hydrological research in the past decades, because of their high potential to cause natural hazards
The three snow blocks in Ex. 2–4 consisted of snow with similar conditions which included characteristics such as isothermal, well ripened with bulk densities above 400 kg m−3 and containing considerable initial liquid water
The most notable benefit of our approach is seen in an increased accuracy of the mass balance estimates
Summary
Rain-on-snow (ROS) events are a natural phenomenon which has been in the focus of hydrological research in the past decades, because of their high potential to cause natural hazards. ROS events have initiated severe floods in the past in many European countries such as Germany (HND Bayern, 2011; Sui and Koehler, 2001), Switzerland (Badoux et al, 2013; Rössler et al, 2014) and the Czech Republic (Cekal et al, 2011), as well as in North America (Ferguson, 2000; Kattelmann, 1997; Marks et al, 1998; McCabe et al, 2007; Pomeroy et al, 2016). In addition to natural hazards, ROS events are relevant from a geochemical point of view. Rainwater affects the transport of ions (Jones et al, 1989) and solutes (Feng et al, 2001; Harrington and Bales, 1998; Lee et al, 2008; Waldner et al, 2004) through snow which affects the pH and chemical compositions of adjacent streams (Casson et al, 2014; Dozier et al, 1989; MacLean et al, 1995).
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