Changing climate both increases and decreases European river floods

Climate change has led to concerns about increasing river floods resulting from the greater water-holding capacity of a warmer atmosphere. These concerns are reinforced by evidence of increasing economic losses associated with flooding in many parts of the world, including Europe. Any changes in river floods would have lasting implications for the design of flood protection measures and flood risk zoning. However, existing studies have been unable to identify a consistent continental-scale climatic-change signal in flood discharge observations in Europe, because of the limited spatial coverage and number of hydrometric stations. Here we demonstrate clear regional patterns of both increases and decreases in observed river flood discharges in the past five decades in Europe, which are manifestations of a changing climate. Our results—arising from the most complete database of European flooding so far—suggest that: increasing autumn and winter rainfall has resulted in increasing floods in northwestern Europe; decreasing precipitation and increasing evaporation have led to decreasing floods in medium and large catchments in southern Europe; and decreasing snow cover and snowmelt, resulting from warmer temperatures, have led to decreasing floods in eastern Europe. Regional flood discharge trends in Europe range from an increase of about 11 per cent per decade to a decrease of 23 per cent. Notwithstanding the spatial and temporal heterogeneity of the observational record, the flood changes identified here are broadly consistent with climate model projections for the next century, suggesting that climate-driven changes are already happening and supporting calls for the consideration of climate change in flood risk management

Megafloods in Europe can be anticipated from observations in hydrologically similar catchments

Megafloods that far exceed previously observed records often take citizens and experts by surprise, resulting in extremely severe damage and loss of life. Existing methods based on local and regional information rarely go beyond national borders and cannot predict these floods well because of limited data on megafloods, and because flood generation processes of extremes differ from those of smaller, more frequently observed events. Here we analyse river discharge observations from over 8,000 gauging stations across Europe and show that recent megafloods could have been anticipated from those previously observed in other places in Europe. Almost all observed megafloods (95.5%) fall within the envelope values estimated from previous floods in other similar places on the continent, implying that local surprises are not surprising at the continental scale. This holds also for older events, indicating that megafloods have not changed much in time relative to their spatial variability. The underlying concept of the study is that catchments with similar flood generation processes produce similar outliers. It is thus essential to transcend national boundaries and learn from other places across the continent to avoid surprises and save lives

Estimation of the long-term cyclical fluctuations of snow-rain floods in the Danube basin within Ukraine

Floods are a periodic natural phenomenon, often accompanied by negative consequences for the local population and the economy as a whole. Therefore, knowledge of the trends of maximum flow have great practical importance, because it is the basis for planning and designing various hydraulic structures, hydrological forecasting, the mapping of flood risk, etc. In this paper, we analysed the long-term cyclical fluctuations of the maximum flow of snow-rain floods of the Danube basin within Ukraine (5 large rivers, 14 medium and 5 small). The database includes time series (34 gauging stations) of the maximum discharges of the cold period from the beginning of the observations up to 2015. The methodological approaches (developed by Gorbachova) are based on the use of hydro-genetic methods − namely the mass curve, the residual mass curve, and combined graphs. The presented results illustrate that the longterm fluctuations of the maximum flow of snow-rain floods are synchronous at all study gauging stations in the Danube basin within Ukraine, but these fluctuations are not always in the synchronous phase. We found that the maximum flow of snow-rain floods in the Danube basin within Ukraine have four types of long-term fluctuations, each with a different cycle duration

Changes in extreme temperature indices at the Ukrainian Antarctic Akademik Vernadsky station, 1951-2020

In the late 20th century, warming on the Antarctic Peninsula was most pronounced compared to other parts of Antarctica. However, air temperature showed a significant variability, which has become especially evident in recent decades. Thus, the investigation of air temperature trends on the Antarctic Peninsula is important. This study examines the extreme air temperature at the Ukrainian Antarctic Akademik Vernadsky station, located on Galindez Island, Argentine Islands Archipelago, near the Antarctic Peninsula. For 1951 to 2020, based on the daily air temperature data, the temporal trends of extreme air temperature were analyzed, using 11 extreme temperature indices. Based on linear trend analysis and the Mann-Kendall trend test, the TXn, TNn, TN90p, and TN90p indices showed an upward trend, whereas theFD0, ID0, TN10p, TX10p, and DTR indices showed a downward trend. Among them, annually, FD0, ID0, and TN10p significantly decreased by –0.427 days, –0.452 days, and -0.465%, respectively, whereas TXn and TNn increased by 0.164℃ and 0.201℃, respectively. The indices TXx and TNn showed no statistically significant trends. The average annual difference between TX and TN (index DTR) showed a nonsignificant decreasing trend at –0.029℃ year-1 . Thus, for the period of 1951-2020, the Ukrainian Antarctic Akademik Vernadsky station was subjected to warming

Trends and fluctuations of river ice regimes in the Prypiat Basin, within Ukraine

Information about the formation, destruction, and duration of river ice regimes is especially important for hydropower, shipping, fisheries, etc. Research into modern trends in river ice regimes and their spatial and temporal fluctuations is essential, especially in a changing climate. This study examines the trends and fluctuations of air temperature and ice regimes based on series of observations in the Prypiat River basin within Ukraine. Air temperature data from 17 meteorological stations and ice data from 29 water gauges were analyzed. A complex analytical approach involving statistical and graphical methods was employed. The Mann-Kendall statistical test, mass curve, residual mass curve, and combined graphs were used in the study. In the Prypiat River basin within Ukraine, observations of mean monthly air temperature, ice occurrence, freeze-up, and their duration are homogeneous (quasi-homogeneous) and stationary (quasi-stationary). The quasi-homogeneous and quasi-stationary characteristics are explained by the presence in the observation series of only increasing and decreasing phases of long-term cyclical fluctuations, which are incomplete. The trends of air temperature and ice regime correspond strongly, indicating the defining role of air temperature in the formation of ice occurrence and freeze-up. Since the end of the 1990s, the warming phase of air temperature in the autumn-winter period determines the appearance of ice and freeze-up later in the year. In March, the warming trend in air temperature, which began after 1988, determines the freezeup, break-up, and disappearance of ice earlier in the year. Thus, the duration of ice and freeze-up on the rivers has decreased

Application of the commensurability method for long-term forecasting of the highest summer floods on the Danube River at Bratislava

This paper reports the use of the commensurability method for long-term forecasting of the highest summer floods on the Danube River at Bratislava. Bratislava is the capital of the Slovak Republic, as well as its major administrative and industrial centre. In the past, Bratislava has suffered from dangerous floods. The highest floods have occurred most frequently in the summer. Consequently, long-term forecasting of summer floods on the Danube River at Bratislava has important scientific and practical significance. We used the dates of the highest summer floods for the period 1876-2018, as well as historical information about the highest summer floods that occurred before the beginning of regular hydrometric observations. The commensurability method supports prediction of various natural phenomena, including floods and other dangerous events. It is characterized by the simplicity of the calculations and minimum needs for input information. Four methods of forecasting were used: (1) the calculated value of commensurability; (2) the two-dimensional and three-dimensional graphs of commensurability; (3) the time intervals between floods that have occurred in the past; and (4) the number of commensurability equations with three components. The results indicate that the highest summer floods are likely to occur on the Danube at Bratislava in 2020, 2025, and 2030

Fluctuations of Winter Floods in Small Austrian and Ukrainian Catchments

Studying the changes in extreme river runoff induced by climate change is of utmost importance, as the variability of floods directly affects life and human activities. This study examines the fluctuations and persistence of winter floods in 14 catchments in the Rika River Basin (Ukraine) and ten catchments in the Steyr River Basin (Austria). The catchments represent typical hydrological regimes in the Danube River region. The fluctuations and persistence of floods are analyzed by the hydro-genetic method and a seasonality analysis for the period 1951–2015. The results show a much more pronounced fluctuation pattern in the upper Rika catchments than in the upper Steyr catchments. This pattern indicates an increase in winter flood magnitudes between the mid-1960s and the 1990s, followed by a decrease until recently. The flood seasonality shows a large inter-annual variability in both regions. The most significant winter floods tend to occur in November and December. The winter flood fluctuations are compared with changes in associated climate characteristics, i.e., seven-day maximum precipitation, a melt index, and annual maximum snow depth. The seasonality of these characteristics has a strong inter-annual variability and only partly explains the winter flood fluctuations

Monthly stream temperatures along the Danube River: Statistical analysis and predictive modelling with incremental climate change scenarios

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 examines long-term trends, changes in the trends, and multiannual variability in the time series. The second part of the study focuses on simulating the average monthly water temperatures using Seasonal Autoregressive Integrated Moving Average (SARIMA) models and nonlinear regression models (NonL), based on two RCP based incremental mean monthly air temperature scenarios. To assess the impact of future climate on stream temperatures, the historical long-term average of the monthly water temperature (1990–2020) was compared with scenarios S1 (2041–2070) and S2 (2071–2100). The simulation results from the two stochastic models, the SARIMA and NonL, showed that in scenario S1, the Danube River’s average monthly water temperature is projected to increase by 0.81/0.82°C (Passau), 0.55/0.71°C (Bratislava), and 0.68/0.56°C (Reni). In scenario S2, the models predict higher increases: 2.83/2.50°C (Passau), 2.06/2.46°C (Bratislava), and 2.52/1.90°C (Reni). Overall, the SARIMA model proved to be more stable and effective in simulating the increase in monthly water temperatures in the Danube River

Megafloods in Europe can be anticipated from observations in hydrologically similar catchments

Megafoods that far exceed previously observed records often take citizensand experts by surprise, resulting in extremely severe damage and loss oflife. Existing methods based on local and regional information rarely gobeyond national borders and cannot predict these foods well because oflimited data on megafoods, and because food generation processes ofextremes difer from those of smaller, more frequently observed events.Here we analyse river discharge observations from over 8,000 gaugingstations across Europe and show that recent megafoods could have beenanticipated from those previously observed in other places in Europe.Almost all observed megafoods (95.5%) fall within the envelope valuesestimated from previous foods in other similar places on the continent,implying that local surprises are not surprising at the continental scale. Thisholds also for older events, indicating that megafoods have not changedmuch in time relative to their spatial variability. The underlying conceptof the study is that catchments with similar food generation processesproduce similar outliers. It is thus essential to transcend national boundariesand learn from other places across the continent to avoid surprises andsave lives.</p

Megafloods in Europe can be anticipated from observations in hydrologically similar catchments

Megafloods that far exceed previously observed records often take citizens and experts by surprise, resulting in extremely severe damage and loss of life. Existing methods based on local and regional information rarely go beyond national borders and cannot predict these floods well because of limited data on megafloods, and because flood generation processes of extremes differ from those of smaller, more frequently observed events. Here we analyse river discharge observations from over 8,000 gauging stations across Europe and show that recent megafloods could have been anticipated from those previously observed in other places in Europe. Almost all observed megafloods (95.5%) fall within the envelope values estimated from previous floods in other similar places on the continent, implying that local surprises are not surprising at the continental scale. This holds also for older events, indicating that megafloods have not changed much in time relative to their spatial variability. The underlying concept of the study is that catchments with similar flood generation processes produce similar outliers. It is thus essential to transcend national boundaries and learn from other places across the continent to avoid surprises and save lives