Jan Pekar

Comenius University Bratislava · Department of Applied Mathematics and Statistics

The man activity in the basin affects the water temperature in the increasingly higher levels (construction of water reservoirs, construction of thermal and nuclear power plants or drainage of waste water to streams). In this paper, we focused our attention on the evaluation of the impact of anthropogenic activity to increase the thermal load of th...

Histograms of air temperature with a bimodal shape are commonly observed in many regions of the world. In this study, we investigate the causes of bimodality in the histograms of daily temperature series (minimum, average, and maximum) for selected climatological stations in Slovakia. Our findings suggest that in the Central European region, the bi...

The aim of the study is to analyse changes and predict the course of mean monthly water temperatures of the Danube River at various locations for the future. The first part of the study involves conducting a statistical analysis of the annual and monthly average air temperatures, water temperatures, and discharges along the Danube River. The study...

Climate change is presently a widely discussed subject in relation to alterations in water storage capacity and the components of the hydrological balance within catchment areas. This research study was directed at two main objectives: 1. The indirect estimation of long-term mean annual runoff using an empirical model; 2. The determination of chang...

This study aimed at the analysis and modelling of the groundwater temperature at the water table in different regions of Slovakia. In the first part, the analysis of the long-term trends of air and soil/ground temperature to a depth of 10 m is presented. The average annual soil/groundwater temperatures at different depths were the same but lower th...

The occurrence of extreme floods in several river basins of the countries of Central and Eastern Europe over the last thirty years has drawn the attention of the public (as well as the competent authorities) to the problems of flood protection. Although the development and operational use of non-structural measures (such as flood forecasting and wa...

After a dry spring, in June 2020 several intense storms occurred at the headwaters of the small basins of the Muráň and Zdychava rivers in the territory of the Muránska planina National Park (Slaná River basin, Slovakia). In the first part of the study– according to a hydrological survey made by the authors after the flash flood – the peak discharg...

The long-term runoff variability is identified to consist of the selected large rivers with long-term data series in the Danube River Basin. The rivers were selected in different regions of the Danube River Basin and have a large basin area (Danube: Bratislava gauge with 131,338 km2; Tisza: Senta with 141,715 km2; and Sava: Sremska Mitrovica with 8...

One of the basic problems of the flood hydrology was (and still is) the solution of the relationship between peak discharges of the flood waves and probability of their return period. The assessment of the design values along the Danube channel is more complicated due to application of different estimation methods of design values in particular cou...

In the present study, we focused on the statistical analysis of changes in the characteristics of the minimum, average annual, and maximum discharge series of the Danube River at Ceatal Izmail water gauge. We have processed the series of annual average discharges during the whole water stage observation period 1840–2015, as well as the average dail...

The extent (determined by the repellency indices RI and RIc) and persistence (determined by the water drop penetration time, WDPT) of soil water repellency (SWR) induced by pines were assessed in vastly different geographic regions. The actual SWR characteristics were estimated in situ in clay loam soil at Ciavolo, Italy (CiF), sandy soil at Culbin...

The aim of the paper is to study spatial and temporal changes in the magnitude, duration and frequency of high flows in the Danube basin. A hydrological series of the mean daily discharges from 20 gauging stations (operated minimally since 1930) were used for the analysis of changes in the daily discharges. The high flow events were classified into...

The problem of understand natural processes as factors that restrict, limit or even jeopardize the interests of human society is currently of great concern. The natural transformation of flood waves is increasingly affected and disturbed by artificial interventions in river basins. The Danube River basin is an area of high economic and water manage...

The soil water repellency index, R, is calculated from the ethanol sorptivity, Se, and water sorptivity, Sw, using an equation: R = 1.95 Se/Sw. In the older method, Se and Sw were measured in pairwise arrangements to reduce the influence of spatial heterogeneity of soil properties, and one value of R only was calculated from one pair of Se and Sw m...

The aim of this paper is to investigate the statistical aspects of multiannual variability of precipitation at the Hurbanovo station, Slovakia, over 140 years (1872-2011). We compare the long-term variability of annual precipitation for Hurbanovo (Slovakia), Brno (Czech Republic), Vienna (Austria), and Mosonmagyarovar (Hungary) stations using autoc...

Changes in runoff parameters are very important for Slovakia, where stream-flow discharges, being supplied by precipitation and groundwater runoff, are preferentially influenced by climatic conditions. Therefore, teleconnections between runoff parameters, climate parameters and global atmospheric drivers such as North Atlantic Oscillation, Southern...

Study is devoted to the long term basin water balance analysis of the Bela River up to the Podbanske gauge, and to the simulation of the monthly runoff and to estimation of its individual components in the monthly time step, during the 60 years period: 1945/46-2004/05.

In the first part of the paper the long-term trends of the water temperature are analysed of the high mountain river Belá, and the lowland river Morava. The stations were selected to cover wide range of elevations. The trends were studied on 50-year data series by Mann-Kendal test. The long-term mean annual water temperature of the Belá river was 4...

In this paper we focused on the history of floods and extreme flood frequency analysis of the upper Danube River at Bratislava. Firstly, we briefly describe the flood marks found on the Danube River in the region of Bratislava, Slovakia, and provide an account of the floods’ consequences. Secondly, we analyzed the annual maximum discharge series fo...

Estimating Flash Flood Peak Discharge in Gidra and Parná Basin: Case Study for the 7-8 June 2011 Flood We analyzed the runoff and its temporal distribution during the catastrophic flood events on river Gidra (32.9 km ² ) and Parná (37.86 km ² ) of the 7th June 2011. The catchments are located in the Small Carpathian Mountains, western Slovakia. Dir...

Biological processes in surface waters appreciably depend on temperature of water. This paper summarizes our investigations of water temperature in the Bela River. The Bela River is a mountainous stream not influenced by direct human activities, draining the headwaters of the Vah River basin in the Tatra National Park (TANAP), Slovakia. Our primary...

A long-term hydrological and water chemistry research was conducted in three experimental microbasins differing in land cover: (1) a purely agricultural fertilized microbasin, (2) a forested microbasin dominated by Carpinus betulus (European hornbeam), and (3) a forested microbasin dominated by Picea abies (L.) (Norway spruce). The dissolved inorga...

This paper is a statistical analysis and long-term prognosis of monthly flows of the Danube River at Bratislava. Analysis of the mean annual and monthly flows implies that, while the annual flow regime of the Danube oscillates around its long-term average, its monthly flows undergo a significant and probably permanent changes, attributable to the e...

One of the requirements imposed by the Water Framework Directive (WFD, 2000/60/EC) is to analyze and predict how quality of surface waters will evolve in the future. In assessing the development of a stream’s pollution one must consider all sources of pollution and understand how water quality evolves over time. Flow and water temperature regime of...

It is widely acknowledged that global warming will result in an increased extremality of hydrological phenomena. As for streamflow it is anticipated that duration of low-flow conditions and flood frequency will both increase. Approving this hypothesis by statistically evaluating daily runoff characteristics depends on the availability of long and h...

Several hypotheses claim that more extremes in climatic and hydrologic phenomena are anticipated. In order to verify such hypotheses it is inevitable to examine the past periods by thoroughly analyzing historical data. In the present study, the annual maximum runoff volumes with t-day durations were calculated for a 130-year series of mean daily di...

This paper aims to reveal the annual regime, time series, and long-term water temperature trends of the Danube River at Bratislava, Slovakia, between the years 1926 and 2005. First, the main factors affecting the river's water temperature were identified. Using multiple regression techniques, an empirical relationship is derived between monthly wat...

Evaluation of climate change impacts upon the natural processes is one of the possible methods for verifying hypotheses about the increase of extremes in the observed climatic and hydrologic data series. It relates, of course, to the thorough and detailed analysis of data from the historical observation sets. Trying such evaluations of the statisti...

One of the requirements imposed by the Water Framework Directive 2000/60/EC is to analyze and predict long-term evolution of surface water quality parameters. During a 20-year period (1987-2006), concentrations of nutrients were studied in three model microbasins of the experimental Mostenik basin (Institute of Hydrology) in Central Slovakia: 1. Ry...

The aim of the paper is to analyze a possible teleconnection of Quasi-Biennial Oscillation (QBO), Southern Oscillation (SO), North Atlantic Oscillation (NAO), and Arctic Oscillation (AO) phenomena with long-term streamflow fluctuation of the Bela River (1895–2004) and Cierny Hron River (1931–2004) (central Slovakia). Homogeneity, long-term trends,...

In this study, applying the historical stage-discharge rating curve, the average daily stages of the Danube River measured at the Bratislava gauging station over the historical period 1876–1890 were used to obtain average daily flows. In the second part, the reconstructed 130-year series of average daily Danube flows was subject to a sta-tistical a...

The influence of the number of the water samples on classifying surface water into water quality classes with regard to nitrate was determined. The characteristic values c90 (percentile 90%) of the nitrate nitrogen concentrations were computed according to following three ways:–from the monthly time series of nitrate nitrogen concentrations monitor...

The long-term trends of yearly discharge time series and runoff variability at seven stations along the River Danube are identified. The results of statistical analysis of discharge time series indicate the period around the year 1860 was the driest decade in central and eastern Europe since 1840. In these years, the mean annual air temperature in...

In this paper the occurrence of dry and wet periods for 18 major European rivers during the period 1850-1997 is analysed. Annual discharge series were standardized for three regions: West/Central Europe, East Europe and North Europe, and for the whole of Europe. The statistical analysis of these series did not confirm any long-term increase or decr...

In the first part of this study, a flood wave transformation analysis for the largest historical floods in the Danube River reach Kienstock–Bratislava was carried out. For the simulation of the historical (1899 and 1954) flood propagation, the nonlinear river model NLN-Danube (calibrated on the recent river reach conditions) was used. It was shown...

This paper assesses the vulnerability to erosion of the soils in the upper Torysa catchment down to the planned drinking water reservoir at Tichy Potok (Slovakia). Experimental observations in the Torysa catchment, together with the outputs of the AGricultural Non-Point Source pollution model (AGNPS), have been used to select optimal sites for smal...

The aim of the paper is to analyse a possible teleconnection of AO (Artic Oscillation), SO (Southern Oscillation), PDO (Pacific Decade Oscillation), NAO (North Atlantic Oscillation) and QBO (Quasi Biennial Oscillation) phenomena with long-term streamflow fluctuation in Hron River basin (Central Slovakia). The spectral analysis shows that for the se...

The procedure for identification of the long-term trends in the individual water quality determinands in surface water is described in the study. The methodology is based on requirements of the Directive 2000/60/EC and the existing water quality data in the database of the Slovak Hydrometeorological Institute. The methodology gives guidance for est...

The annual discharge time series of selected large rivers in the world were tested for wet and dry periods. The 28–29-years cycle, as well as 20–22-years cycle of extremes occurrence were identified. From the trend analysis it follows that the hydrological characteristics of the rivers must be stated at least for one 28-year period. If we want to i...

The paper deals with the following subjects: 1. Statistical evaluation of rain-, surface-, and groundwater quality data in the Small Carpathian region. 2. Analysis of chemical regime of surface water in this region. 3. Analysis of interaction between surface- and groundwater in Trnavka brook catchment. The analysis was based on the data monitored b...

In the first part of this paper, the impact of forestry, agriculture and urban activities on the quality of surface water is analysed. Daily data from 15 forest and agricultural experimental catchments of the Institute of Hydrology, Slovak Academy of Sciences are used. It is shown, that the nitrate concentrations in surface water have decreased in...

In the paper, a two-step method of three-component hydrograph separations is proposed. Sulfates are used as tracers to enable the separation of the stream runoff hydrograph into three components: rain, soil and groundwater. Both, stream water and rain water were sampled. The sulfate concentrations in soil water and groundwater were determined from...

Uses a modified three-dimensional equation for turbulent dispersion in a model of water pollution dispersal in an open channel. Describes field studies on the Ondava river to investigate the current velocities and cross sectional mixing of phosphates, nitrates and sulphates just downstream of the confluence of the Ondava with tributaries. The model...

An algorithm for solving the special boundary value problem for the ordinary differential equation of the second order on interval [0, ∞) is proposed. Results obtained by numerical experiments are also given.

We construct and test an algorithm for solving a three-point boundary value problem which is from the class of such algorithms as the one described for the two-point boundary value problem by R. P. Tewarson and N. S. Huslak [BIT 23, 382-387 (1983; Zbl 0577.65067)]. The exact formulation of the problem and the used notation are given in §2. The prop...

It is generally supposed that the global warming will result in increasing of the hydrological phenomena extremality. In case of discharges it is expected that both low flows duration and flood frequency will increase. Approval of this hypothesis by statistical evaluation of the daily runoff characteristics depends on availability of high quality h...

The paper deals with the analysis of the long-term trends and possibilities of the long-term flow forecast of the rivers in the Danube River basin using the winter North-Atlantic Oscillation Index. The value of the winter NAO index in year 2010 (average of the months December 2009 – March 2010) was extraordinary low, only –2.85. The statistical ana...

1. vyd Rozmn

1. vyd Rozmn

In recent years the issue of the natural hydrological and meteorological time series fluctuation has been discussed more and more intensively. As the series of measured hydrological and climatological data become longer and easier worldwide accessible it is possible to deal with a large amount of historical data in their complexity. Handling these...