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 than the annual average air temperature by about 0.8 °C. The long-term trend analysis of the air temperature and soil temperature at a depth of up to 10 m in Slovakia showed that the air and soil/ground water temperature have risen by 0.6 and 0.5 °C, respectively, per decade over the past 30 years. The second part of the study aimed at modelling the daily groundwater temperatures at depths of 0.6–15 m below the surface. The simple groundwater temperature model was constructed based on a one-dimensional differential Fourier heat conduction equation. The given model can be used to estimate future groundwater temperature trends using regional air temperature projections calculated for different greenhouse gas emission scenarios.

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 autocorrelation and spectral analysis methods. From the long-term point of view, there is no consistent trend in the annual precipitation; only a multiannual variability has been detected. Consequently we identify changes in the distribution of annual maximum daily precipitation for Hurbanovo during different periods for winter-spring and summer-autumn seasons using histograms, empirical exceedance curves, and frequency curves of daily precipitation. Next, we calculate the periods of days without precipitation exceeding 29 days between 1872 and 2011. The longest period of days without precipitation was 83 days in 1947. The statistical analysis does not confirm our initial hypothesis that neither high daily precipitation (over 51.2 mm per day) nor long dry periods (more than 50 days without precipitation) would occur more frequently nowadays. We assume that the decrease in annual precipitation over the period 1942–2011 (compared to 1872–1941) is caused by the less frequent occurrence of daily precipitation between 0.4 and 25.6 mm.

This study integrates 90 years of hydrometeorological observations (1930/31–2019/20) with end-century projections (2080–2099) to evaluate climate-driven changes in the water balance of the Nitra River basin (2094 km²), Slovakia. Despite a modest 2–3% increase in annual precipitation from 1930/31–1959/60 to 1990/91–2019/20, mean annual runoff declined from 229 mm to 201 mm (≈−12%), primarily due to enhanced evapotranspiration stemming from a +1.08 °C basin-wide temperature increase. An empirical regression from 90 hydrological years shows that +100 mm in precipitation boosts runoff by ≈41 mm, while +1 °C in temperature reduces it by ≈13 mm. The BILAN monthly water balance model was calibrated for 1930/31–2019/20 to decompose runoff components. Over the 90-year period, the modeled annual runoff averaged 222 mm, comprising a 112 mm baseflow (50.4%), a 91 mm interflow (41.0%), and a 19 mm direct runoff (8.6%), underscoring the key role of groundwater and subsurface flows in sustaining streamflow. In the second part of our study, the monthly water balance model BILAN was recalibrated for 1995–2014 to simulate future runoff under three CMIP6 Shared Socioeconomic Pathways. Under the sustainability pathway SSP1-1.9 (+0.88 °C; +1.1% precipitation), annual runoff decreases by 8.9%. The middle-of-the-road scenario SSP2-4.5 (+2.6 °C; +3.1% precipitation) projects a 17.5% decline in annual runoff, with particularly severe reductions in autumn months (September −32.3%, October −35.8%, December −40.4%). The high-emission pathway SSP5-8.5 (+5.1 °C; +0.4% precipitation) yields the most dramatic impact with a 35.2% decrease in annual runoff and summer deficits exceeding 45%. These results underline the extreme sensitivity of a mid-sized Central European basin to temperature-driven evapotranspiration and the critical importance of emission mitigation, emphasizing the urgent need for adaptive water management strategies, including new storage infrastructure to address both winter floods and intensifying summer droughts.

In the last decade (2011-2020), Slovakia has experienced a significant decrease in flows in most river basins. The aim of this study is to statistically analyse the changes in the hydrological regime of selected Slovak streams based on observations over a 90-year period (1931-2020), using measured average daily discharges. Several regions in Europe, particularly in the Mediterranean area, including Spain, Italy, and Greece, have been affected by significantly dry years. The occurrence of dry years is not unusual, as extreme droughts have also occurred in the Danube River basin in the past, such as in 1863, 1921, 1947, 1992-93, and 2003. Our goal is to analyse changes in the low flow regime of rivers in Slovakia, which have long observation records. Understanding the low flow regime is one of the inputs for determining hydro-ecological limits, which is essential for maintaining and achieving good ecological status of surface waters. Several flow and non-flow characteristics were evaluated when assessing hydrological drought. Flow characteristics include: minimum average daily flows (in monthly or annual steps, over the entire period), M-day flows (the exceedance curve of average daily flows), minimum monthly and annual flows, and T-year minimum flows. Non-flow characteristics evaluated include changes in the timing of dry periods (date of occurrence), the number of low flow days, the longest drought episode, and the deficit volumes. Individual flow characteristics were calculated from the series of average daily flows. The trend analysis showed that in the given sub-catchments there is a decrease in the T-year minimum flows, as well as a decrease in the basic runoff. The comparison of the 100-year minimum specific runoff with the values of the specific base runoff shows that the 100-year minimum runoff can be up to ca. 4 times lower than the estimated specific base runoff in an extremely dry year. AcknowledgementThis work was supported by the project VEGA No. 2/0015/23 “Comprehensive analysis of the quantity and quality of water regime development in streams and their mutual dependence in selected Slovak basins”, and by the project APVV No. 20-0374 “Regional detection, attribution and projection of impacts of climate variability and climate change on runoff regimes in Slovakia”

Each year, we witness the devastating effects of floods in Central Europe and worldwide. In September 2024, a flood wave passed through the Danube in Bratislava with a discharge of approximately 9,400 m3s-1. Over the past 20 years, two floods in Bratislava have reached peak discharges exceeding 10,000 m3s-1 – in August 2002 and June 2013. A comparison of flood waves since 1991 indicates a slight increase in extreme peak discharges in Bratislava and Nagymaros, along with a significant rise in peak water levels of the Danube. The first part of this paper describes the gauging stations along the Danube in Bratislava / Devín. It presents a series of maximum annual discharges (Qmax) from 1876 to 2024, supplemented by historical flood records dating back to 1501. The second part focuses on the statistical analysis of average and maximum annual discharges from the gauging stations in Bratislava and Nagymaros. The third part compares the September 2024 flood with the September flood of 1899. Finally, the paper discusses possible reasons for the rise in water levels in the Bratislava – Nagymaros section over the past 100 years. The main factors contributing to these trends are as follows: i) In the past, the Danube naturally meandered and regularly flooded adjacent areas, which facilitated greater flood wave transformation and reduced water velocity. ii) Historically, breaches in flood protection levees helped mitigate flood risks in cities. For instance, during the 1787 flood, the Viennese Road (a flood protection levee) was breached in six places over a total length of 600 meters, preventing the flooding of Bratislava. Similar levee breaches occurred around Bratislava in 1897, 1899, 1954, and 1965. iii) The Danube riverbed is gradually silting up, which affects flow dynamics and peak water levels.