Water Gauging Stations Research Articles

Effect of Teleconnection Patterns on the Formation of Potential Ecological Flow Variables in Lowland Rivers

Climate is probably the most important factor affecting river discharge and flow dynamics. Low flows in rivers during the warm period cause stress to aquatic ecosystems and pose a challenge to sustainable water management. Previous research has shown that the average minimum discharge of the 30 driest continuous days, known as Q30, is a suitable measure for ecological flow estimation in Lithuania. This study aims to examine whether large-scale atmospheric processes, so-called teleconnections, can have an impact on Q30 during the warm period. Hydrological data for 1961–2020 from 25 water gauging stations were used to search for hydrological response signals with five selected climate indices (NAO, SCA, POL, EA/WR, and EA). Pearson correlation and Wilcoxon–Mann–Whitney test approaches were applied. The results suggested that the EA/WR and NAO had the strongest influence on Q30 in the studied region during the warm period. The positive phases of the indices tended to cause a greater decrease in Q30 values due to the prevailing easterly edge of the anticyclonic circulation over the studied region determined by the EA/WR and NAO indices, while the negative phases of the mentioned indices caused an increase and greater dispersion of Q30.

Evaluating indicators of hydrologic alteration to demonstrate the impact of open-pit lignite mining on the flow regimes of small and medium-sized rivers

Our study provides a retrospective evaluation of the perturbances of the opencast mining on the small river. Based on a standard 'before-after-control-impact' approach, we assess the impact of disturbances on aquatic ecosystems. For this purpose, we used IHA (Index of Hydrological Alteration) statistics to fully quantify the impact of open-pit mine on flow regimes of small-to-medium-size rivers. The analysis results in flow data captured in the 33 parameters of the range variability approach (RVA) and five ecological flow components (EFC). This approach helped us comprehensively evaluate the alteration in the flow regime in areas of open-pit mining on the example of the Noteć River, a typical lowland river. We conclude that the level integrated hydrologic alterations to this river under the influence of the groundwater depression cone and water from the mine dewatering are high, as assessed by the RVA and EFC methods. Specifically, this work uses the IHA framework to verify the necessity of including a specific group of indicators. Our analysis shows that for the post-impact period on the investigated river, the functioning of the river ecosystem was degraded. One of the EFC components completely disappeared at both water gauge stations. There were also profound hydrologic alterations, such as increased frequency or duration of “extreme low flows” at one station; at the second station, “high flow pulses” occurred more frequently. More than 65 % of the altered parameters in five IHA groups were modified drastically. In the river section affected by the groundwater depression cone, both the minimum and maximum flows decreased by 20 % to 55 %. In the section where water from the mine dewatering is fed in, the minimum flows changed by + 170 to + 230 %. The use of the IHA tool provides an opportunity for environmental flow restoration of water conditions in degraded post-mining areas.

URBAN ENVIRONMENTAL FLOOD SUSCEPTIBILITY USING A MULTI-LAYERED NEURAL NETWORK MODEL FROM SATELLITE IMAGERY SOURCES

<p>Recently, there has been a rise in research based on data-driven based machine learning models to address the issue of processing speed posed by various physiological simulations. The majority of studies, however, have concentrated on creating models for particular water sources, drainage systems, and gauge stations area. Therefore, unless further data is supplied and the models are subsequently trained, their outcomes cannot be effectively applied to different scenarios. With its excellent spatio-temporal accuracy range with the advanced analytics, the forthcoming Global Navigations Satellite Systems (GNSSs) technology offers a novel method for the monitoring of flood disasters in dynamic manner. This study recommends a Multi-layered Neural Network (MNN) for flood monitoring, which combines a Convolutional Neural Networking (CNN) along with a backward propagation based (BP) learning network. The CNN component is used to obtain the abstracted features from full delay doppler maping images. The BP section is provided with GNSSs characteristics, such as reflection of surface with power range, and also the vegetation attributes from the Soil Moistening Active Passives (SMAP) satellite source data. In comparison to physiologically based models, the results shown that the CNN-oriented system makes accurate predictions on "unseen" areas of catchment with a substantially shorter processing time. The obtained results imply that, with respect to accuracy of prediction, the patch-enabled option is superior to the resizing-based option. Additionally, every experiment has demonstrated that the forecast of flow speed is more precise than the prognosis of water depth, indicating that the water deposition is more complex to information about global level elevations than the flow speed with velocity.</p>

Effects of the Time Period Length on the Determination of Long-Term Mean Annual Discharge

Currently, the 40-year-long reference period 1961–2000 is used in Slovakia for systematic assessment of the hydrological regime. The World Meteorological Organization recommends unifying the climatic normal 1991–2020 with a reference period for hydrological characteristics for the purpose of climate change research. We have analyzed changes in the long-term mean annual discharges at 113 water-gauging stations over different time periods. Considering the history of the reference periods used in Slovakia, we have focused on the analysis of the 10, 20, 30, 40, and 50-year-long moving averages of the long-term mean annual discharges in the period 1961–2020 in comparison with the 1961–2000 reference period and the whole selected and analyzed period. The deviations of the annual flow rates for the area of Slovakia and river sub-basins have been analyzed. The results indicate that the new reference period to be used in Slovakia should include the time period after the year 2000. To determine its precise length, a more detailed analysis is needed.

Patterns of Recent Changes in Channel Morphology and Flows in the Upper and Middle Odra River

Our research introduces the river regulation effects on three sections of the upper and middle Odra River (south-western Poland), with differently channelized parts. In the upper and lower reaches, the river was straightened, narrowed, and trained with groins, whereas in the middle section, it was also impounded by numerous barrages. The discharge duration (DD) and water stage duration (WSD) curves for water-gauge stations from these river sections were analyzed to recognize changes in river flows and channel morphology since the mid-20th century. This analysis is supplemented by an examination of repeated surveys of the gauge cross sections of the river, annual precipitation totals in its catchment, and their relationship to the variation of the North Atlantic Oscillation (NAO) index. Our findings provide new hydrological insights for the region. The three river sections exhibited different patterns of the adjustment of the channel morphology to the river channelization: upper section was typified by channel incision, middle section by channel stability, and lower section by channel incision in its upper part and vertical stability of the channel bed in the lower part. Barrages in the middle section stabilized water stages in a wide range of hydrological conditions. Annual precipitation totals and river run-off did not change systematically over the study period. The variation in precipitation totals was inversely related to annual values of the NAO index. The study confirms the usefulness of DD/WSD curves to analyze changes in river run-off and the vertical position of the channel bed.

The drought characteristics and their changes in selected water-gauging stations in Slovakia in the period 2001–2020 compared to the reference period 1961–2000

The drought characteristics and their changes in selected water-gauging stations in Slovakia in the period 2001–2020 compared to the reference period 1961–2000

Changes in Selected Low-Flow Characteristics in the 2001–2015 Period Compared to the 1961–2000 Reference Period in Slovakia

This research is focused on the assessment of drought on surface watercourses in Slovakia. Low-flow characteristics and their changes in the 2001–2015 period in comparison with the 1961–2000 reference period were evaluated at selected representative water-gauging stations. Two different methods were used to calculate the flow duration curves (FDCs): the standard method, based on mean daily discharge data series for the whole evaluated period in descending order, and the alternative method, based on first calculating the values of FDCs for each year of the assessed period and then averaging the corresponding percentile values. The changes were evaluated for selected percentiles of the FDCs (330-, 355-, and 364-day discharge). The number of days with the mean daily flow below the set limits and the seasonality of their occurrence were assessed. The results show significant changes in cases of both methods in the compared time periods, while differences in individual regions of Slovakia were also found. The weakness of the standard method is in allowing the values of the smallest quantiles to be influenced by a small number of long-lasting drought episodes. The alternative method eliminates the aforementioned shortcoming and could be used to determine the ecological flows in Slovakia.

Identification of Hydrological Droughts in Lithuanian Rivers

Globally, hydrological droughts are most commonly identified based on various indices calculated from water flow values. However, the water flow rate is calculated from a flow rate curve that needs to be updated constantly, so it takes a long time to resolve its true value. For this reason, the possibility of identifying a hydrological drought on the basis of hourly and prompt treated water levels seems much more attractive. 8 water gauging stations (WGS) operating along 7 important rivers and covering the hydrological areas of visas in the Lithuanian region were selected for the study. In this study, a modified SPI function of the R programming language SPEI package (traditionally used to calculate the standardized precipitation index, SPI) was applied for the streamflow drought index (SDI) calculations. Given how it was applied to the SDI calculation, just like the baseline data, this was the ten-day mean water flow and then the water level. The suitability of water level data for SDI calculations was assessed by analyzing the relationships between SWLI (Standartized Water Level Index) calculated from water level data and SDI calculated from water flow information. SWLI and SDI in all 8 WGS are closely interconnected. It was found that the possibility of recurrence of droughts of different severity identified by both methods is significantly influenced by the profile of the river bed in a specific section. In areas where riverbanks have steeper slopes, the SWLI and SDI similarly describes the water situation and the recurrence of droughts. It is believed that a modified SDI methodology (SWLI), which is based on water level data, may become a good alternative in our country for identifying hydrological droughts. Keywords: Lithuanian rivers, hydrological drought, identification of droughts, water level, SDI, SWLI.

Calculating the characteristics of flash floods on small rivers in the Mountainous Crimea

The maximal surface runoff from territory of the Crimean Mountains is represented as a runoff of small rivers that flow through the western and eastern part of the northern slope and from the southern coast. The materials from 54 water gauging stations (WGS) were used to characterize the maximum runoff during rain and meltwater-rain floods on the rivers in the Crimean Mountains. A modified reduction structure of a calculation formula was used for valuation of the maximal runoff of different origin flash flood for rivers at the Mountainous Crimea. The main parameters of the proposed model are summarized as dependencies on the average height of the catchments and generalized in the form of a map. It is also possible to use the second variant of the suggested method taking into account the factor of underlying surface is introduced. Comparison of the calculated values of maximal runoff shows good convergence with both the initial information, and the largest values in the observation period.

Detecting Patterns of Changes in River Water Temperature in Poland

The study determined water temperature trends of rivers in Poland in the period 1971–2015, and also their spatial and temporal patterns. The analysis covered daily water temperature of 53 rivers recorded at 94 water gauge stations and air temperature at 43 meteorological stations. Average monthly, annual, seasonal and maximum annual tendencies of temperature change were calculated using the Mann–Kendall (M–K) test. Regional patterns of water temperature change were determined on the basis of Ward’s hierarchical grouping for 16 correlation coefficients of average annual water temperature in successive 30-year sub-periods of the multi-annual period of 1971–2015. Moreover, regularities in monthly temperature trends in the annual cycle were identified using 12 monthly values obtained from the M–K Z test. The majority of average annual air and water temperature series demonstrate statistically significant positive trends. In three seasons: spring, summer and autumn, upward tendencies of temperature were detected at 70%–90% of the investigated water gauges. In 82% of the analysed rivers, similarity to the tendencies of change of monthly air temperature was concluded, with the climatic factor being recognised as of decisive importance for the changes in water thermal characteristics of the majority of rivers in Poland. In the winter months, positive trends of temperature were considerably weaker and in general statistically insignificant. On a regional scale, rivers with a quasi-natural thermal regime experienced temperature increases from April to November. In the other cases, different directions of change in river water temperature (RWT) were attributed to various forms of human impact. It was also found that for the majority of rivers the average annual water temperature in the analysed 30-year sub-periods displayed upward trends, statistically significant or close to the significance threshold. Stronger trends were observed in the periods after 1980, while a different nature of water temperature change was detected only in a couple of mountainous rivers or rivers transformed by human impact. In the beginning of the analysed period (1971–2015), the average annual water temperature of these rivers displayed positive and statistically significant trends, while after 1980 the trends were negative. The detected regularities and spatial patterns of water temperature change in rivers with a quasi-natural regime revealed a strong influence of climate on the modification of their thermal regime features. Rivers characterised by a clearly different nature of temperature change, both in terms of the direction of the tendencies observed and their statistical significance, were distinguished by alterations of water thermal characteristics caused by human activity. The results obtained may be useful in optimising the management of aquatic ecosystems, for which water temperature is a significant indicator of the ongoing environmental changes.

Sezonowe zróżnicowanie temperatury wody na przykładzie wybranych rzek nizinnych Mazowsza = Seasonal differentiation of water temperature on the example of lowland Mazovian rivers

Thermal regime has a critical impact on the lotic environment, as maximum temperature determines the boundaries of the occurrence of aquatic species, seasonal and diurnal water temperature variations affect their bioenergetics, while the timing of specific water temperature values during the year is important in the context of spawning and migrations. However, despite the great importance of water temperature studies in the context of environmental management and fisheries, as well as the development of accurate measurement techniques, such investigations have received relatively limited attention in Poland. The current study attempted to examine the seasonal differentiation of water temperature in lowland rivers. For this purpose, water temperature was recorded from the 1st of May 2015 to the 30th of April 2019 with a temporal resolution of 30-minutes. Digital temperature reorders used to make the measurements were distributed across six sites in Jeziorka, Świder and Utrata catchments located on the Mazovian Lowland and the Southern Podlachia Lowland near Warsaw. The hydrometeorological background of the water temperature monitoring was determined on the basis of data from the Warszawa-Okęcie station and water gauging stations. On the basis of the measurement data, mean, maximum, and minimum monthly water temperatures were calculated and presented on the background of the appropriate air temperature data, while statistical distribution of the 30-minute water temperature, aggregated in a monthly timescale, was presented on the box and whiskers plots. The Ward method was used to group months similar in terms of their thermal conditions, while the Pearson correlation coefficient was applied to evaluate the strength of the relationship between water and air temperature. The results indicate that the seasonal course of water temperature follows the course of air temperature, with the highest mean monthly water temperatures recorded in July, while the lowest in January. Statistical distribution analysis of water temperature in individual months and its grouping by the Ward method allowed to identify two periods characterized by relatively stable thermal conditions and two periods of dynamic changes of water temperature. In contrast to the maximum values of water temperature, which were observed in the summer as a result of intensive solar radiation and low streamflow rates, the greatest variability of water temperature, as indicated by reference to mean daily range and standard deviation, was found in the spring months, i.e. in April and May, while the lowest in winter, from December to February. The relationship between daily mean water temperature and air temperature, established with the use of the Pearson correlation coefficient on a monthly basis, was clearly stronger during the spring increase and the autumn fall of the water temperature, which can be linked with greater vulnerability to atmospheric heat fluxes. A definitely weaker relationship was found in the winter and summer months, when greater importance can be attached to other drivers of stream temperature, like the presence of ice cover, cloudiness, riparian shading, and groundwater inflows.

Temporal variation of water discharges in the lower course of the Danube River across the area from Reni to Izmail under the influence of natural and anthropogenic factors

The Danube River mouth is a main source for fresh water used for water supply and irrigation purposes in the arid southern part of Ukraine. In addition, the water of the mouth is used for filling the Danube Lakes. Climate change and numerous social and economic factors reduce the area and the water level of the Danube Lakes and increase their salinity. Under these circumstances the water exchange between the Danube River and the lakes is a very important process which allows maintenance of the water–salt balance of the latter. Such water exchange massively depends on the Danube River regime. The paper presents research of temporal variation of typical water discharges in the lower course of the Danube River associated with assessment of natural and anthropogenic factors affecting river runoff fluctuations. Time series of annual average water discharge at the water gauging stations of such cities as Reni and Izmail were considered uniform for the selected periods. They cover the period of conventionally natural river runoff regime (1840–1920), the period of the least altered river runoff regime (1921–1960) and the most altered river runoff regime under a heavy anthropogenic influence (1961–1989). The analysis of the impact of climate changes on the river runoff allowed introduction of a new, modern period of the Danube River hydrological regime (1990–2015). It is established that the series of maximum and minimum water discharges are characterized by the lack of their uniformity from the beginning of the period of initial influence of hydraulic engineering structures on the hydrological regime (since 1961). The analysis of the aggregate multi-year series (1840–2015) of average annual, maximum and minimum water discharges of the Danube River across its length from Reni to Izmail showed the presence of positive trends. At the same time the period of climatic changes (after 1989) is characterized by a less intensive growth of maximum water discharges. The research resulted in establishing the periodicity and synchronism of water discharge fluctuations in the lower course of the Danube River from Reni to Izmail within the territory of Ukraine. In particular, the study showed for the first time that from the 2000s onwards the redistribution of river runoff between the Danube River branches led to unsynchronization of minimum river runoff in different parts of the Danube Delta. The research shows that comprehensive analysis of the Danube River hydrological regime under modern climatic conditions is required to ensure efficient engineering regulation of the Danube Lakes filling pattern. Such regulation, in its turn, will ensure that the water supply and irrigation purposes are achieved.

Spatial development of hydrological droughts in lake catchments

Abstract In river-lake systems, reservoirs significantly affect the formation of water resources in the catchment by reducing the maximum flows and floods as well as increasing the low flows. In lake catchments, the pace of hydrological drought progression is usually slow. However, this phenomenon can be very extreme and destructive for water balance structure as a result of the very slow renewal rate of catchment resources. An estimation of hydrological drought development was conducted in the Biebrza river catchment (6,900 km2) on the basis of a daily discharge series for 18 water-gauge stations in the period 1982–2014. The number and location of the gauges allowed reliable results of the spatial pattern of drought to be obtained. The main objective of the research was the construction and assessment of the applicability of indicators which are estimators of drought spatial progression. Comparative analysis of four proposed indices led to two of them being recommended. These characteristics estimate the direction of drought development according to the stream network hierarchy, location of sub-catchments and the direction of river basin area increase. As a result, determinants of the spatial development of hydrological drought as well as its importance in the hydrographical structure were identified. Furthermore, the intensity of drought was evaluated and all investigated indices were applied to a time series analysis.

Relationship between Water Temperature of Polish Rivers and Large-Scale Atmospheric Circulation

The objective of the paper consisted in determining the effect of macroscale types of NAO, AO, EA, EAWR, SCAND, and AMO atmospheric circulation on changes in water temperature in Polish rivers. The study has made use of a broad body of hydrometeorological materials covering daily water temperature values for 96 water gauge stations located on 53 rivers and air temperature values for 43 meteorological stations. Percentage shares of positive and negative coefficients of correlation of annual, seasonal, and monthly circulation type indices with air and river water temperature were determined, demonstrating the character of teleconnection. Determinations were made of water temperature deviations in positive and negative phases of the analyzed indices from average values from the years 1971–2015, and their statistical significance ascertained. Research has shown that relations between the temperature of river waters in Poland and macroscale circulation types are not strong, however they are noticeable, sometimes even statistically significant, and both temporally and spatially diverse. NAO, AO, EA, and AMO indices are characterized by a generally positive correlation with temperature, whereas SCAND and EWAR indices are characterized by a negative correlation. Research showed a varying impact of types of atmospheric circulation, with their effectiveness increasing in the winter season. The strongest impact on temperature was observed for the positive and negative NAO and AO phases, when deviations of water temperature from average values are correspondingly higher (up to 1.0 °C) and lower (by a maximum of 1.5 °C), and also for the positive and negative SCAND phases, when water temperature are correspondingly lower (by a maximum of 0.8 °C) and higher (by 1.2 °C) than average values. The strongest impact on water temperature in summer, mainly in July, was observed for AMO. The results point to the complexity of processes determining the thermal regime of rivers and to the possibility of additional factors—both regional and local—exerting an influence on their temporal and spatial variability.

Photogrammetric reconstruction of changes in vertical river position using archival aerial photos: case study of the Czarny Dunajec River, Polish Carpathians

Rivers of the Polish Carpathians incised deeply during the twentieth century, but detailed information about the timing and amount of incision of their channels exists only for water-gauge cross sections. Applicability of photogrammetric extraction of digital elevation models (DEMs) from archival aerial photos for reconstructing changes in vertical river position was verified in the study of a 3-km reach of the Czarny Dunajec River. DEMs extracted from a few sets of archival aerial photos from the years 1964–1994 together with recent orthophotos and DEMs were used in the analysis. Measurements taken in river cross sections spaced at 100-m intervals indicated that on average the lowest point of the channel bed lowered between 1964 and 2009 by 1.74 ± 0.17 m, low-flow water surface by 1.57 ± 0.07 m, active river channel by 1.54 ± 0.12 m and the belt of river migration by 1.03 ± 0.15 m. However, the change in vertical river position during the years 1964–2009 varied greatly along the reach, with the elevation of low-flow water surface lowered by up to 3.61 ± 0.07 m in the upper part of the reach and increased by up to 1.34 ± 0.07 m in its lower part. Combining the information about changes in vertical river position and the width of river migration belt yielded data about the change in sediment volume in the reach, with an average annual loss of sediment amounting to 256 ± 37 m3 per 100-m channel segment. The study indicated that DEMs generated from archival aerial photos can be a useful tool in analysing recent vertical channel changes outside water-gauge stations.

Hydrological characteristics of lakes in the eastern part of the Broknes Peninsula, Larsemann Hills, East Antarctica

Broknes Peninsula (the area of the Progress station, Larsemann Hills, Princess Elisabeth Land, East Antarctica) is characterized by the presence of well developed hydrographic network consisting of reservoirs located not only in the bedrock, but also inside the glacier thickness and on its surface. As a rule, most of them are dammed by natural snowice weirs, which are often destroyed during the Antarctic summer. As a result of this process, glacial water outburst may occur. In the course of the summer season of the 63‑th Russian Antarctic Expedition (RAE) intensive hydrological field observations were carried out for identification and comprehensive investigation of potentially outburstprone reservoirs located in close proximity to Russian and foreign stations and field bases (area of the Progress station and the field base Law-Racovita). The works included: the organization of temporary pile and depth-stick water gauge stations, mapping positions of the shoreline of lakes (reservoirs), bathymetric surveys of them, as well as field hydro-chemical express analyses. Based on the results of the level measurement, it was found that most of the lakes of the oasis are characterized by a sharp drop in the height of the water surface level associated with the breakthroughs. In particular, the authors witnessed the breakthrough of the Discussion Lake, which occurred on January 22, 2018. This resulted in decrease of the water level by 0.95 m. Based on the data of the bathymetric surveys, the morphometric (hydrometric) characteristics of the lakes were calculated and detailed grids (regular net of rectangular matrices, in the nodes of which some effective values of the mapped values are located) were formed for the following numerical modeling of hypothetical and real breakthroughs of water bodies and construction of estimated hydrographs.

A comparison of three parameter estimation methods of the gamma distribution of annual maximum low flow duration and deficit in the Upper Vistula catchment (Poland)

Based on 30-year 24-hour flow sequences at 69 water gauging stations in the Upper Vistula catchment, it was determined that the probability distributions of the low flow duration and its maximum annual deficit can be described by the gamma distribution with the estimated parameters by the methods: MOM, the method of moments, LMOM, the method of linear moments, and MLE, the method of maximum likelihood. The stationarity of the time series was tested by the Mann-Kendall correlation using the Hamed and Rao variance correction. The low flows were defined by the SPA method, with the limit flowQ70%. The quality of the match was tested by the Anderson-Darling goodness of fit test. This test allowed accepting the gamma distribution in all analysed cases, regardless of the method used to estimate the distribution parameters, since thepv(p-values) values were greater than 5% (over 18% forTmaxand 7.5% forVmax). The highestpvvalues for individual water gauging stations, as well as the highest 90%TmaxandVmaxquantiles were noted using LMOM to estimate the gamma distribution parameters. The highest 90%TmaxandVmaxquantiles were observed in the uppermost part of the studied area.

Prediction of fish catch in the Danube River based on long-term variability in environmental parameters and catch statistics

The effects of physical factors on fish catch in the Serbian part of the Danube River were studied for period of six decades. The data on total catch for the Danube River from river kilometre 845 to river kilometre 1433 were collected from Statistical Office of the Republic of Serbia, while water level and water temperature data were collected from 16 water gauge stations along the investigated part of the Danube River for the period 1948–2009. Cross-correlation functions have been used to analyse the functional connection between Danube water level, water temperature and fish catch while ARMA model which combines cyclic (deterministic) and random (stochastic) components of the analysed sequences was used for the forecasts. The cross-correlation function showed negative correlation between water level and temperature as well as between water temperature and catch and positive correlation between water level and catch. The Danube water level and catch were coherent at the periods of 2.06, 4.13, 6.2, 10.33, 20.66years, while the cross correlation function between these time series did not show phase lag. The results of reconstruction and forecast of water level, temperature, and catch of fish in the Danube River, obtained by summing the cyclic and stochastic components, was used for the forecast till 2029. In 2016, seven years after, the initial forecasts were made, validity of the model was checked by obtaining data for water temperature, water level and fish catch in the Danube River for the period 2010–2015. Model gave the best prediction for water temperature; average standard error was 1.6 times higher for predicted value than for model value while for fish catch and water level they were 1.96 and 4.97, respectively. Methods used in this work could be powerful tool for prediction of fish catch and serve as the basis for better fisheries management.

Insight into variability of spring and flash flood events in Lithuania

In this research, variability of spring (from 1 March to 30 May) and flash (from 1 June to 30 November) floods in rivers of different regions was analysed. The territory of Lithuania is divided into three regions according to hydrological regime of the rivers: Western, Central, and Southeastern. The maximum river discharge data of spring and flash floods [a total of 31 water gauging stations (WGS)] were analysed. Comparison of the data of four periods (1922–2013, 1941–2013, 1961–2013, and 1991–2013) with the data of the reference period (1961–1990) was performed. Analysis included the longest discharge data set of the Nemunas River at Smalininkai WGS (1812–2013) as well. Mixed patterns of flood changes in Lithuanian rivers were detected. The analysis of flood discharges of the Nemunas River indicated that both spring and flash floods in Lithuania were getting smaller.

Freely available mean daily discharge series from Czechia: what can be inferred from them?

Most hydrometeorological data from Czechia are still provided for a fee. This especially applies to time series with a finer step than monthly. The fact that the data must be paid with respect to an expert’s appraisement and that the proper licence agreement ratification has to be performed causes a considerable delay in the data transfer to potential customers, unfortunately including scientists as well. Naturally, this time-consuming process is unpleasant to the experts on both sides. Due to a substantial rise of university students’ requests for data, the Czech Hydrometeorological Institute’s hydrologists launched a website from which long mean daily discharge series representing ten selected water-gauging stations can be downloaded. Besides other assessments, the series may play an important role when studying climate change impacts on water resources in Czechia. Therefore, the objective here was to extract from these series some preliminary information on long-term changes such as abrupt and gradual trends caused either by the construction of reservoirs or by climate variability itself. The main tool used was nonparametric trend analysis. Mainly different months were of interest so as to determine if there have been recorded some changes in seasonality. The results may be easily expanded by students.