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Analysis of main controls of runoff events in the Sumava Mts. caused by rain-on-snow
Šťovíček, Vít ; Jeníček, Michal (advisor) ; Juras, Roman (referee)
Rain-on-snow (ROS) events are hydrometeorological phenomena when a sufficient combination of rainfall and snowmelt can generate floods, snow avalanches or landslides. As average air temperature gradually increases, the trend of ROS events occurring earlier in spring and at higher altitudes can be expected to continue. Snowmelt during ROS events is controlled by the snowpack energy balance and is influenced by several factors, especially meteorological conditions, and initial conditions of the snowpack. The calculations were made using data from four automatic stations in the Šumava Mountains, namely the Vydra river basin. Based on these data and pre-defined threshold conditions, 105 ROS events were selected. Resulting components of the energy balance, climatic, snow and outflow characteristics were mutually correlated, and their influence on ROS events was determined. The analyses showed that during ROS events, the most important source of energy for melting were turbulent fluxes, i.e., latent, and especially sensible heats. According to the monthly averages, they accounted, at almost all observed stations, for at least 40% (and up to 60% in December), of the total energy available for snow melting. Another important energy flux was shortwave radiation, whose fraction increased with the progress of...
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Changes in snowfall fraction in cold season and their impact on spring runoff in selected mountain catchments
Blšťák, Adam ; Jeníček, Michal (advisor) ; Juras, Roman (referee)
The precipitation falling as rain or snow has different impact on regional water resources and their annual distribution. Shift from solid to liquid form of precipitation following the increase of the surface air temperatures could be important because such change could influence the timing of spring runoff and cause water scarcity in summer. In this study, the spatial and temporal variations of ratio of snowfall to total precipitation (Sf), mean air temperature, day of year of melt-out and winter and spring runoff is analysed. Data were examined for 11 meteorological and 6 hydrological stations in the mountains catchment in Czechia for November-April 1965-2014. Data were analyzed using the Mann-Kendall trend test. Major results show that Sf has been decreasing strongly throughout the whole examined area, with the strongest decrease in the foothill area of the northern mountains of Czechia. Stronger decrease is observed in lower elevations, at the stations with meant air temperature close to melt temperature. Strongest decrease was observed in March and the weakest decrease was observed in December and April, The significant decreases in Sf are associated with large increase in mean winter air temperatures. Due to the increasing mean air temperature in the cold season, the total rainfall is...
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Effect of snowpack on runoff generation during rain on snow event.
Juras, Roman ; Máca, Petr (advisor) ; Ladislav , Ladislav (referee)
During a winter season, when snow covers the watershed, the frequency of rain-on-snow (ROS) events is still raising. ROS can cause severe natural hazards like floods or wet avalanches. Prediction of ROS effects is linked to better understanding of snowpack runoff dynamics and its composition. Deploying rainfall simulation together with hydrological tracers was tested as a convenient tool for this purpose. Overall 18 sprinkling experiments were conducted on snow featuring different initial conditions in mountainous regions over middle and western Europe.
Dye tracer brilliant blue (FCF) was used for flow regime determination, because it enables to visualise preferential paths and layers interface. Snowpack runoff composition was assessed by hydrograph separation method, which provided appropriate results with acceptable uncertainty. It was not possible to use concurrently these two techniques because of technical reasons, however it would extend our gained knowledge. Snowmelt water amount in the snowpack runoff was estimated by energy balance (EB) equation, which is very efficient but quality inputs demanding. This was also the reason, why EB was deployed within only single experiment.
Timing of snowpack runoff onset decrease mainly with the rain intensity. Initial snowpack properties like bulk density or wetness are less important for time of runoff generation compared to the rain intensity. On the other het when same rain intensity was applied, non-ripe snowpack featuring less bulk density created runoff faster than the ripe snowpack featuring higher bulk density. Snowpack runoff magnitude mainly depends on the snowpack initial saturation. Ripe snowpack with higher saturation enabled to generate higher cumulative runoff where contributed by max 50 %. In contrary, rainwater travelled through the non-ripe snowpack relatively fast and contributed runoff by approx. 80 %.
Runoff prediction was tested by deploying Richards equation included in SNOWPACK model. The model was modified using a dual-domain approach to better simulate snowpack runoff under preferential flow conditions. Presented approach demonstrated an improvement in all simulated aspects compared to the more traditional method when only matrix flow is considered.
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