A natural hazard is a naturally occurring extreme event that has a negative effect on people and society or the environment. Natural hazards may have severe implications for human life and can potentially generate economic losses and damage ecosystems. A better understanding of their major causes, probability of occurrence, and consequences enables society to be better prepared to save human lives as well as to invest in adaptation options. Natural hazards related to climate change are identified as one of the Grand Challenges in the Baltic Sea region. Here, we summarize existing knowledge about extreme events in the Baltic Sea region with a focus on the past 200 years as well as on future climate scenarios. The events considered here are the major hydro-meteorological events in the region and include wind storms, extreme waves, high and low sea levels, ice ridging, heavy precipitation, sea-effect snowfall, river floods, heat waves, ice seasons, and drought. We also address some ecological extremes and the implications of extreme events for society (phytoplankton blooms, forest fires, coastal flooding, offshore infrastructure, and shipping). Significant knowledge gaps are identified, including the response of large-scale atmospheric circulation to climate change and also concerning specific events, for example, the occurrence of marine heat waves and small-scale variability in precipitation. Suggestions for future research include the further development of high-resolution Earth system models and the potential use of methodologies for data analysis (statistical methods and machine learning). With respect to the expected impacts of climate change, changes are expected for sea level, extreme precipitation, heat waves and phytoplankton blooms (increase), and cold spells and severe ice winters (decrease). For some extremes (drying, river flooding, and extreme waves), the change depends on the area and time period studied.

Regional studies of precipitation changes over Europe show that its eastern part is characterized by small changes in annual precipitation and insignificant aridity trends compared to central and southern Europe. However, a frequency analysis over the past 30 years showed statistically significant increasing dryness trends in eastern Europe and an increase in the occurrence of extremely high rainfall as well as prolonged no-rain intervals during the warm season. The largest increase in aridity was observed in the western and central parts of Belarus. During 1990–2020, the frequency of dry periods doubled in all river basins along the Black, Caspian, and Baltic Sea water divide areas of eastern Europe. From 1970 to 1990, there were high streamflow rates during the winter low-flow season. Consequently, over the past 50 years, in spring, we observed here a continued decrease in maximal discharges across all river basins. In summer, we detected a statistically significant increase in the number of days with anticyclonic weather over eastern Europe, a decrease in rainfall duration by 15–20%, an increase in daily precipitation maxima by 20–30%, and an increase in the number of days with a low relative humidity by 1–4 days per decade.

The study presents an assessment of the recent and projected changes of the middle and upper Western Dvina River runoff and regional climate during the 20th and 21st centuries. For this assessment, we used historical runoff data, the output of EURO-CORDEX consortium calculations for scenarios RCP4.5 and RCP8.5, and hydrological model “Hydrograph.” Analysis of monthly runoff data for the 1945–2015 period revealed positive trends for each of the five months from December to April. These trends are statistically significant at the 0.05 level. No significant trends were found for other months. Significant negative trends were established for spring flood peak discharges (from −69 to −88 m³ s^–1 per 10 years). Usually, maximum discharges are observed during spring floods. Minimum discharges during winter low-water period were increased by 6 m³ s^–1 per 10 years. The annual runoff trend was statistically significant only at the Polotsk gauging station (9.5 m³ s⁻¹ per 10 years). To the end of the current century over the study region, estimates of projected meteorological parameters (air temperature and precipitation) show positive tendencies of air temperature (from 2.4°C to 4.7°C depending on scenario) and precipitation (up to 15 to 30 mm). Changes of seasonal and annual temperature and precipitation vary depending on the models and scenarios used. The strongest changes were noticed for the RCP8.5 scenario. The greatest changes within each scenario were revealed for the winter and spring seasons. It is projected that during the 2021–2100 period according to both RCP scenarios, annual discharges will not change in the upper part of the Western Dvina River Basin and increase by 10–12% in its lower part. The maximum spring flood discharges in both RCP scenarios are expected to decrease by 25%. The minimum runoff of winter low-flow period is expected to increase by up to 60 to 90% above the present long-term mean values.

We studied long-term fluctuations of streamflow and occurrence of extreme phenomena on the rivers of Belarus during the post-World War II period. It was found that formation of annual runoff within the nation has no constant tendencies and varies from year to year. At the same time, analysis of intra-annual distribution of streamflow reveals significant changes since the 1970s, first of all, increase of winter and decrease of spring streamflow. As a result, the frequency of extreme floods has decreased. These changes in water regime are associated with climatic anomalies (increase of the surface air temperatures) caused by large-scale alterations in atmospheric circulation, specifically in trajectories of cyclones. During the last two decades, the frequency of Atlantic and southern cyclones has changed and caused decreasing of cold season storms and extreme phenomena on the rivers.

The study presents the pattern of climatic changes in the region of the Belarusian Polesje in current period and shows peculiarities of agricultural conditions on drained peat bogs during last decades. Also the climatic projections in the study region are presented with emphasize on agricultural indices. The climate changes in the region are synchronized with a global climate warming, and expressed more significant on the natural than drained areas. But at the same time a severe and extreme conditions for vegetation growth are more evident on the drained peat bogs. The precipitation sums exceeding have been noticed in the eastern part of the Belarusian Polesje in comparison with western part. The amelioration, deforestation and decrease of underlying surface roughness have led to wind speed growth and decrease of precipitation. The observed climate change tendencies will be kept in the current century. The growth of air temperature will continue, the largest deviations of the air temperature will be noticed in winter season. The deviations of minimal temperature will exceed deviations of maximal and mean temperature. The precipitation wills growth, but deviations will be heterogeneous during the current century. The largest growth of precipitation will be observed in winter season due to the rainfall of moderate intensity increase. But in the same time the duration of the drought periods will increase in summer.