Český hydrometeorologický ústav, pobočka Praha, Na Šabatce 17, 143 06 Praha 4-Komořany a Ústav aplikací matematiky a výpočetní techniky Přírodovědecké fakulty Univerzity Karlovy, Albertov 6, 128 43 Praha 2, Česká republika.The main aim of this work is to evaluate the development of rainfall-runoff regime in selected river basins of the Šumava Mountains (Bohemian Forest), the Jeseníky Mountains and the Krušné Mountains (Ore Mountains) in the last 50 years. Besides the identification of inhomogeneity in time series of mean discharges, rainfall amounts, temperature and snow cover data, the work deals with an analysis of trends using annual and monthly data. Different methodological tools for identification of changes and trends in hydro-climatic time series have been introduced in this study, especially different methods of statistic testing and an application of Mann-Kendall seasonal test. The results have been compared not only from the point of view of the methods applied here, but as well from the viewpoint of geographical difference of the mentioned areas. Hlavním cílem předložené studie je zhodnotit vývoj srážko-odtokového režimu ve vybraných povodích v oblasti Šumavy, Jeseníků a Krušných hor za posledních 50 let. Vedle zjišťování nehomogenit v časových řadách průměrných průtokových, srážkových, ale i teplotních a sněhových dat se práce zabývá analýzou trendů na úrovni ročních hodnot a jednotlivých měsíců. V práci jsou představeny různé metodické nástroje ke sledování změn a trendů v hydroklimatologických řadách, zejména různé metody statistického testování a aplikace Mann-Kendallova sezónního testu. Výsledky jsou porovnány nejen z hlediska použitých metod, ale i geografické rozdílnosti sledovaných území.

The main aim of our research project was to determine the extent to which the outflow can be influenced by human interventions in three selected water basins in the Šumava Mountains (Black Forest) and its foothills. The rainfall-runoff analyses using both the single-mass and double-mass curves over the period of hydrologic observations were taken as a preliminary methodology. Standard statistical testing methods Wilcoxon and Mann-Kendall non-parametric tests were applied to detect the trends. Besides mean discharge, precipitation, snow and air temperature trends, analysis of land cover change and human impact on the river network and development of drainage areas were also carried out. The greatest deviations were widely observed in the period between the second half of the 1970s and the first half of the 1980s. The whole system came slowly back to its initial condition in the early 1990s. The runoff trend deviation was related to natural and human factors, mainly to current climatic changes, river network modification and changes of land cover.

Many water authorities face the challenge to comply with WFD criteria. Overview survey methods are faster and more economic compared to more intensive field surveys. This work tests the quality of both approaches, with a focus on the hydromorphological status assessment. First, WFD criteria and descriptions for hydromorphological quality components and monitoring demands are summarized. A practical assessment of hydromorphological features follows, performed in German and Czech sub-catchments of the Elbe River. Three different methods of stream habitat survey were applied, two German field and overview survey standards by LAWA (Weisseritz basin), and a new Czech field survey method EcoRivHab (Rolava basin). Comparability of results and suitability to fulfil the WFD and CEN standard requirements were tested. Results show that the field and overview survey methods are non-interchangeable and irreplaceable. The overview method provides good results when conditions of large areas need to be evaluated but results seem to overestimate the true quality of the aquatic ecosystem. The field survey methods provide more accurate information. Both field survey methods (LAWA and EcoRivHab) offer good results on hydromorphological river characteristics, evaluated by a point system. Both methods are powerful in evaluating riparian belts and floodplain hydromorphology. The relative added effort of field mapping is overcompensated by the quality of the outputs, which are fully compatible with the aims of the WFD.

This study investigates changes in seasonal runoff and low flows related to changes in snow and climate variables in mountainous catchments in Central Europe. The period 1966-2012 was used to assess trends in climate and streamflow characteristics using a modified Mann-Kendall test. Droughts were classified into nine classes according to key snow and climate drivers. The results showed an increase in air temperature, decrease in snowfall fraction and snow depth, and changes in precipitation. This resulted in increased winter runoff and decreased late spring runoff due to earlier snowmelt, especially at elevations from 1000 to 1500 m a.s.l. Most of the hydrological droughts were connected to either low air temperatures and precipitation during winter or high winter air temperatures which caused belowaverage snow storages. Our findings show that, besides precipitation and air temperature, snow plays an important role in summer streamflow and drought occurrence in selected mountainous catchments.

In the context of the ongoing climate warming in Europe, the seasonality and magnitudes of low flows and streamflow droughts are expected to change in the future. Increasing temperature and evaporation rates, stagnating precipitation amounts and decreasing snow cover will probably further intensify the summer streamflow deficits. This study analyzed the long-term variability and seasonality of low flows and streamflow droughts in fifteen headwater catchments of three regions within Central Europe. To quantify the changes in the low flow regime of selected catchments during the 1968–2019 period, we applied the R package lfstat for computing the seasonality ratio (SR), the seasonality index (SI), mean annual minima, as well as for the detection of streamflow drought events along with deficit volumes. Trend analysis of summer minimum discharges was performed using the Mann–Kendall test. Our results showed a substantial increase in the proportion of summer low flows during the analyzed period, accompanied with an apparent shift in the average date of low flow occurrence towards the start of the year. The most pronounced seasonality shifts were found predominantly in catchments with the mean altitude 800–1000 m.a.s.l. in all study regions. In contrast, the regime of low flows in catchments with terrain above 1000 m.a.s.l. remained nearly stable throughout the 1968–2019 period. Moreover, the analysis of mean summer minimum discharges indicated a much-diversified pattern in behavior of long-term trends than it might have been expected. The findings of this study may help identify the potentially most vulnerable near-natural headwater catchments facing worsening summer water scarcity.