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Long-term changes in winter and spring runoff in mountain catchments in Czechia
Klinkovská, Simona ; Jeníček, Michal (advisor) ; Vlach, Vojtěch (referee)
Climate changes occurring on Earth influence most of the natural processes. This also includes snow storages which have been decreasing in many mountain regions over the last decades. Besides increasing air temperature, changes in snowfall fraction, snow storages and snowpack duration also occur. For snow dominated mountain catchments, runoff timing from snowmelt is essential. Due to air temperature increase, runoff occurs earlier. Additionally, evapotranspiration increases as well. This thesis summarizes current knowledge regarding snowpack and runoff changes in mountain catchments. It further analyzes changes in 14 Czech mountain catchments over a 50-year period (1965-2014) using a Mann-Kendall trend test which identifies trends in selected time series. The trend analysis was followed by quantification of trends using Sen's slope estimator. The results showed that the day of 50% of total annual runoff occurred earlier in all catchments. Increased winter runoff was found in the Krkonoše catchments. Significant and extensive negative trends were detected in May for most of the catchments. There were almost no significant trends detected in the Beskydy catchments. Key words: snow, snowmelt runoff, trends, climate changes
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Snow drought and its importance for runoff in the context of changes in climatic and snow characteristics
Hlavatý, Vojtěch ; Jeníček, Michal (advisor) ; Nedělčev, Ondřej (referee)
Snow drought, defined as a lack of snow accumulation, is one of the consequences of increasing air temperature, which has a considerable impact on the runoff generation as it provides a substantial part of water supplies in the warm season. However, the attention to snow drought has been paid mainly to North America. Therefore, this work aimed to evaluate the current state of research on this topic and to analyze data from the Churáňov station in the Šumava Mountains. Long-term trends in climatic and snow characteristics in the period 1966-2017 were described using linear regression and Mann-Kendall test and relationships between them were examined by correlation coefficients. Consequently, the occurrences of snow drought were classified using different approaches. According to the results, the main cause of interannual changes in snow storage in the Šumava Mountains was the increasing mean cold season air temperature, causing a decrease in snowfall and thus a reduction in the maximum snow water equivalent, which can be intensified by a decrease in cold season precipitation. This was also indicated by the frequency of different types of snow drought, especially an increase in warm snow-poor seasons, which, considering the predicted climate change, highlighted the importance of this phenomenon....
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Snowmelt runoff during rain-on-snow events in the Ptačí brook basin calculated using stable water isotopes
Valdhansová, Klára ; Jeníček, Michal (advisor) ; Šípek, Václav (referee)
Rain-on-snow events represent one of the basic mechanisms causing floods. Rain falling on the snow cover causes enhanced melting and the resulting runoff often exceeds the runoff caused by rain. During the winter seasons 2018 and 2019, water samples from the stream, snowpack and precipitation were repeatedly taken in the the Ptačí Brook catchment in the Šumava mountains, and the concentrations of 2 H and 18 O were measured in the laboratory. Based on the observed isotope ratios 18 O/16 O and 2 H/1 H in combination with other variables measured in the catchment, the two ROS events from 2019 were reconstructed. The ratio of heavy isotopes increased in the snowpack due to ROS events. Using the end member mixing equation, a hydrograph separation was performed for both investigated events. For the first event, it was not possible to clearly separate groundwater from rainfall, and thus the range of snow in the total runoff was determined by its separation from rainfall and subsequent separation from groundwater. The second event examined was separated directly into three components: rainfall, groundwater and snow. According to the analyses, the total runoff during ROS events in both cases was mostly formed by event water (a combination of rainfall and melt water). The melting water from the snow cover...
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Long-term changes in snow depth and snow water equivalent at selected mountain stations in Czechia
Kožíšek, Matěj ; Jeníček, Michal (advisor) ; Nedělčev, Ondřej (referee)
Long-term changes in snow depth and snow water equivalent at selected mountain stations in Czechia This bachelor's thesis deals with the topic of long-term changes of snow cover in the peripheral mountain ranges in the Czech Republic. The first part is a research of foreign and czech literature dealing with changes in the parameters of snow cover depending on climate change and the consequences of these changes on various components of nature. The second part of the work consists of the analysis of climatic data from stations located in the peripheral mountains of the Czech Republic in the period of hydrological years 1980-2014. The mountains included in this research include Šumava (Churáňov, Lenora and Husinec), Jizera Mountains (Bedřichov and Desná), Krkonoše (Harrachov), Orlické Mountains (Deštné and Rokytnice v O. h.) and Moravskoslezské Beskydy (Lysá hora). The statistical Mann-Kendall test is used to evaluate trends. Changes in snow cover have a significant impact on the functioning of many landscape processes and on the life of the population in terms of future water availability and recreation.
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Main controls affecting the occurrence and extremity of rain-on-snow events in the Ptačí potok basin in the Šumava Mts.
Paulusová, Barbora ; Jeníček, Michal (advisor) ; Hotový, Ondřej (referee)
Rain-on-snow events (ROS) are natural phenomena that have the potential to cause serious floods, wet avalanches and slushflows. Due to climate change the spatial distribution and intensity of ROS events is changing. Accordingly, ROS events become more frequent in high-elevation areas as well as in high latitudes, whereas their occurrence at low-elevation and low latitudes is less common. The behaviour of a snow coverduringrainfallandmechanismsofrainwaterpropagationthroughthesnowpackarestill poorly understood. A frequency and correlation analysis of ROS events in the Ptačí potok basin in the Šumava Mts. was conducted. The selected characteristics of the events were calculated from measured climate and streamflow data (2015-2019) and then analysed to examine the influence of individual characteristics on the development of ROS events. Results indicate a significant correlation between the amount of precipitation and the resulting outflow, as well as the influence of other snow and rain characteristics was shown. The time lag of outflow was mainly influenced by snow density. In order to evaluate the impact of climate change on ROS events, climate time series were analysed for the period 1961-2017 and a significant increasing trend in winter air temperature and decreasing trend in snow depth were...
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Potential of watercourses restoration measures as a tool for water retention in the floodplain
Zelíková, Nikol ; Matoušková, Milada (advisor) ; Jeníček, Michal (referee)
The object of this thesis is the evaluation of the restoration potential of small hydraulic structures for increasing water retention in river floodplain by using 2D HEC-RAS hydraulic model. A former millrace of the Rožnovská Bečva River was used for the design of restoration measures. The restoration proposal consists of partial modification of the current millrace and new close-to-nature watercourse in the agricultural floodplain. Restoration proposal also includes changes in land use, which consist of grassing and afforestation. The input data used for the hydraulic model are digital terrain model (5G) by ČÚZK, surface roughness parameter and mean hourly discharge data of 1997 (Q100) and 2007 (Q5) flood events provided by CHMI. The results of the hydraulic simulations point to the positive effect of proposed restoration measures especially in the change of flooded volumes (3x higher) and flooded areas (2x higher). The results indicate that restoration measures lead to the flooding from the newly designed watercourse that precedes the flooding from the Rožnovská Bečva River. This brings the possibility of more frequent occurrence of inundation events favourable for water retention in the river floodplain. Keywords: retention, floodplain, restoration, hydraulic structures, Rožnovská Bečva River,...
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Spatial snow distribution in locality with diverse forest structure in the Sumava Mountains
Švejdová, Klára ; Jeníček, Michal (advisor) ; Šípek, Václav (referee)
Snowpack is strongly influenced by several environmental factors. Besides meteorological and topographical conditions, vegetation structure plays an important role. The aim of this bachelor thesis was to assess how the canopy structure affects snow distribution. The snow depth and snow water equivalent (SWE) were measured in a selected location situated in the Kvildský potok basin in the Šumava Moutains during the winter season 2019. Canopy structure was described using Leaf Area Index (LAI) obtained from hemispherical images of the area. The degree-day method was used to calculate melt factors. The influence of vegetation was examined by using the correlation and regression analyses. Snow depth and SWE was significantly lower in forest sites than in the open area and in the forest disturbed by the bark beetle (Ips typographus). The influence of canopy structure was highest during snow accumulation and its importance decreased with time. The SWE variability was largest for last measurement during the melt phase. Melt factor calculated for period between last two field measurements was 2.3 mm∙řC-1 ∙d- 1 .
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Variability in shortwave and longwave radiation in plots with different forest structure in the Sumava Mts. during snowmelt
Míka, Dominik ; Jeníček, Michal (advisor) ; Hotový, Ondřej (referee)
The bachelor thesis analyzed the variability in shortwave and longwave radiation at three locations with different canopy structure in the Ptaci brook basin in the Sumava Mts. The canopy structure was quantified by Leaf Are Index calculated from hemispherical images of the canopy. The shortwave and the longwave radiation were measured by radiometer at all locations. In the healthy forest, the average transmittance of the shortwave radiation was 6,5 % and did not change between individual study years. On the contrary, the transmittance of shortwave radiation increased in the damaged forest during study period. The transmittance relatively increased with increasing incoming shortwave radiation. The net longwave radiation was influenced by several factors which included not only the effect of the canopy structure but also transmittance of incoming longwave radiation and the total magnitude of the incoming solar radiation. The net longwave radiation was positive in the healthy forest, negative in the open area and changing from positive to negative in the damaged forest. The differences in the net longwave radiation lead to different dynamic of snowmelt. The net longwave radiation was correlated with incoming shortwave radiation (r = 0.68) in the healthy forest. The net longwave radiation gradually...
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Snow cover detection from webcam images
Fišer, Jan ; Brodský, Lukáš (advisor) ; Jeníček, Michal (referee)
This thesis deals with the possibility of using webcams as a source of spatial data for snow occurrence. The aim of this study is to propose a suitable method of snow cover detection from web camera images. From a sample of 6 webcams of the Czech Hydrometeorological Institute (CHMI) the snow cover is detected by pixel classification methods. The effect of training file size on the accuracy of classification is examined and the overall accuracy achieved by the SVM method was shown to be 97.46%. This study also aims to propose a system for determining the proportion of snow-covered areas. The algorithm consists of several sub-steps: filtering and registration of images, detection of snow, introduction of a coordinate system, calculation of the size of the surveyed area and the proportion of snow-covered area. The designed model can be used for automatic processing of images for various webcams. The melting curves of the snow cover are generated from the obtained daily values of the snow covered area. The results are validated using data from selected CHMI stations. The proposed and parameterized model confirms the possibility of successful use of webcams as a complement to ground measurement of meteorological stations and for the validation of remote sensing products.
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