National Repository of Grey Literature 67 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
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 .
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...
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.
Melt rates calculation with respect to meteorological conditions
Šťovíček, Vít ; Jeníček, Michal (advisor) ; Hotový, Ondřej (referee)
Meteorological conditions are an important factor affecting the speed of snowmelt. Their impacts have been changing accroding to physical-geographical factors such as elevation, slope of the terrain, slope orientation and vegetation, affecting energy balance of the snowpack. The calculations were made using data from four automatic stations in the Šumava Mountains, namely the Vydra river-basin. These stations measure individual meteorological aspect and snow properties. Based on these data and pre-defined conditions, 136 melting events were selected. The melt factors were calculated based on degree-day approach. Similarly, the melt rates were calculated from the snow water equivalent decrease and snowmelt event duration for each snowmelt event. The correlation and regression analyzes were used to determine the effect of each meteorological factor on the snowmelt speed. The analyses proved the highest dependence of the snowmelt speed on the precipitation amount (the value of the Spearman's rank correlation coefficient rs reached 0.54 for the melt factor and 0.68 for melt rate). There is more substantial difference in the effects of meteorological conditions if we compare the winter season from November to February and the spring snowmelt season from March to May, while the highest snowmelt...
Impact of climate change on runoff in montane catchments of Central Europe
Lörinc, Michal ; Langhammer, Jakub (advisor) ; Jeníček, Michal (referee)
The diploma thesis "Impact of climate change on runoff in montane catchments of Central Europe" aims to assess published scientific literature on the subject and to develop projections of changes in study catchments of Upper Vydra in Czechia and Kokra in Slovenia. The thesis contains a review of selected theoretical knowledge on climate change impacts, evaluates existing methodology of impact studies and presents projection results for two study catchments in its practical part. Those were acquired using a multi-step methodology by using climate model projections, bias correction methods, usage of hydrological model and analysis of variance. Among the main conclusions is the anticipated continuation of changes in seasonal runoff, decrease of summer runoff and increase in winter runoff, as well as changes in drought characteristics. The analysis of variance revealed a substantial influence of cliamte models on the achieved results, however selection of emission scenario plays a major role as well. It is apparent that the selected catchments do and will react to climate change differently, however both can be considered to be sensitive to these changes. Kľúčové slová: climate change, hydrological cycle, montane catchments, HBV Light, ANOVA
Using ultrasonic snow depth data to minimaze the error in winter precipitaton measurements
Peňáz, Štěpán ; Jeníček, Michal (advisor) ; Šípek, Václav (referee)
Winter precipitation measurement is more problematic in terms of accuracy than measurement of rainfall precipitation that occur during the rest of the year. The results of rainfall measurements during the winter are significantly influenced by wind, both during the accumulation itself and subsequent redistribution of the snow cover. The aim of this work is to analyze automatically measured data from a heated tipping bucket, ultrasonic snow depth sensor for snow measurement and sensors for measuring snow water equivalent, which aims to determine the dependence of the density of new snow on temperature or humidity and consequently to derive the relation that will serve to refine the quantum estimation of winter precipitation. Based on the correlation and regression analysis of the data, the direct dependence between the density of the new snow and air humidity has not been proven, but the dependence between the density of the new snow and the air temperature has already been proven, though not very significant (Spearman's rank corelation rs = 0.39), this dependence explains approximately 9 % of data variability. The resulting calculated snowfall values in the winter seasons of 2016 and 2017 indicate that the heated tipping bucket has underestimated the amount of precipitation by 50% (2016) and 59%...
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...
Snowpack energy balance in forest environment: spatial and temporal variability of shortwave and longwave radiation
Hotový, Ondřej ; Jeníček, Michal (advisor) ; Matějka, Ondřej (referee)
Snowpack energy balance in forest environment: spatial and temporal variability of shortwave and longwave radiation Assessment of the role of forest on snowmelt processes and snowpack attributes contributes to the accuracy of spring floods forecasting. An importance of the coniferous forest consists in change of the snowpack energy balance. Forest reduces the total amount of solar radiation, however trees cause emitting of longwave radiation, both factors are fundamentally reflected in time of snowmelt in forest environment. Master thesis focuses on temporal and spatial variability of shortwave and longwave radiation depending on the structures of vegetation cover. Individual site types were defined as an open area, a forest affected by the bark beetle (Ips typographus) and a healthy coniferous forest, based on the hemispheric images of vegetation and its Leaf Area Index (LAI). Moreover, repeated manual measurements of the snow depth and snow water equivalent (SWE) were done in plots during winter period 2016/2017 in the Ptačí Brook catchment in the Šumava Mountains, and an analysis of shortwave and longwave radiation data the radiometers in plots was performed. Radiation fluxes in different plots were described in daily and seasonal scale, including the calculation of total heat from shortwave and...
Climate change impacts on snow storages and spring runoff in the Vydra river basin
Cuřín, Vojtěch ; Jeníček, Michal (advisor) ; Šípek, Václav (referee)
Climate change impacts on snow storages and spring runoff in the Vydra river basin Abstract As a result of increasing air temperature, the fraction of precipitation falling as snow decreases. This affects snow cover indicators including snow cover duration, snow cover extent and the amount of water that accumulates in snow cover during winter. These changes further propagate through local runoff process and alter winter and spring runoff. The impacts of air temperature warming of 1℃, 2℃ and 3℃ on the above-mentioned indicators were simulated using a conceptual catchment runoff model HBV-light. Multi- criteria calibration, based on functions describing the goodness of fit of simulated runoff and snow water equivalent (SWE) values was performed. The temperature change scenarios were derived using the delta-change method from reference dataset 1980-2014. The indicator changes were evaluated for 5 elevation belts of the catchment as well as for the catchment as a whole, so that the observed alternations of snow cover indicators could be related to the modelled alternations of runoff. The changes in snow cover characteristics based on these simulations include a decrease of snowfall fraction, shortened snow season, decrease in average and maximal SWE values, and the shift of the average day of year of SWEmax to...

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1 Jeníček, M.
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