Wind waves play an important role in the climate system, modulating the energy exchange between the ocean and the atmosphere and effecting ocean mixing. However, existing ship-based observational networks of wind waves are still sparse, limiting therefore the possibilities of validating satellite missions and model simulations. In this paper we present data collected on three research cruises in the North Atlantic and Arctic in 2020 and 2021 and the SeaVision system for measuring wind wave characteristics over the open ocean with a standard marine navigation X-band radar. Simultaneously with the SeaVision wind wave characteristic measurements, we also collected data from the Spotter wave buoy at the same locations, and we ran the WaveWatch III model in a very high-resolution configuration over the observational domain. SeaVision measurements were validated against co-located Spotter wave buoy data and intercompared with the output of WaveWatch III simulations. Observations of the wind waves with the navigation X-band radar were found to be in good agreement with buoy data and model simulations with the best match for the wave propagation directions. Supporting datasets consist of significant wave heights, wave directions, wave periods and wave energy frequency spectra derived from both SeaVision and the Spotter buoy. All supporting data are available through the PANGAEA repository – https://doi.org/10.1594/PANGAEA.939620 (Gavrikov et al., 2021). The dataset can be further used for validation of satellite missions and regional wave model experiments. Our study shows the potential of ship navigation X-band radars (when assembled with SeaVision or similar systems) for the development of a new near-global observational network providing a much larger number of wind wave observations compared to e.g. Voluntary Observing Ship (VOS) data and research vessel campaigns.

The numerical model simulations of storm activity in the White, Baltic andBarentsSeaswere analyzed for the period from 1979 to2015. Inthis paper the storm number of these seas was calculated. The connections of wind wave climate with indecies of large-scale atmospheric circulation such as NAO, AO and SCAND were estimated. Also, the future changes of wind wave climate were analysed.

Changes in rivers ice regime features and the climatic resources of the winter period were examined for the territory of Russia northward from 60° N. Datasets from 220 gauging stations for the period from 1960 to 2014 have been used in the study both with the results of numerical experiments carried out using climate models in the framework of the international project CMIP5. A change in the duration of the ice phenomena period, the ice cover period and the maximum thickness of ice on the rivers for the scenario RCP 8.5 by the end of the 21st century for a spatial grid with a distance between the nodes of 1.75x1.75 degrees in latitude and longitude has been estimated. We elaborated series of the maps. Main features of the ice regime changes are consistent with the expected changes in the duration of the cold season and the accumulated negative air temperatures. The significant changes are expected for the rivers of the Kola Peninsula and the lower reaches of the rivers Northern Dvina and Pechora, whereas the lowest changes - for the center of Eastern Siberia.

ABSTRACTInterannual variability and long‐term changes of summer temperature extremes and hot spells in Moscow during 1949–2012 are investigated using air temperature station data, the National Centres for Environmental Prediction/the National Centre for Atmospheric Research (NCEP/NCAR) reanalysis and the Climatic Research Unit (CRU) data sets. Significant interdecadal changes in different characteristics of the temperature extremes are revealed. It is shown that summertime warming detected in the Moscow region in recent decades is not solely due to an increase in the number of hot days, but also due to a decrease in the number of cold days. Statistically significant positive (negative) trends in the number of anomalously hot (cold) days since the mid 1970s are detected. Respective trend values are 5%/decade–1 for the positive trends and −6%/decade–1 for the negative trends. We find that in 1981–2012 the number of summer seasons with extremely hot days has doubled with respect to earlier period (1949–1980). However, we do not find statistically significant trend‐like changes in the duration of the hot events in Moscow. A chronology of temperature extremes in Moscow has been constructed. This can be used as a diagnostic tool allowing the detection of extremes. Typical regional sea level pressure patterns associated with air temperature extremes in Moscow are defined and briefly described.

Inundatios on the Black Sea coast of Krasnodar krai between 1945 and 2013 have been analyzed. The main genetic types of inundations on the coast have been identified. The specific features and regularities of inundation wave transformation along the rivers and over time have been studied. Seasonal and maximal runoff of Black Sea rivers has been analyzed over a long-term period. Regularities in the variations of the number of inundatios and their characteristics over the coastal area have been revealed both at the annual and long-term scales. Quantitative estimates are given to the hazard and damage to the population and economic activity due to inundations in the valleys of Black Sea rivers.

The inundation situations on the Black Sea coast of the Krasnodar territory for the period from 1945 until 2013 were analysed and the main types of inundations at the coast are described. Synoptic factors of the formation of extreme precipitation and rainfall floods, features and regularities of the downstream flood wave transformation in the rivers are also studied. Therefore, assessments of seasonal and maximum flow of the Black Sea coast rivers for the period of hydrometric measurements were done. Regularities of change of the occurrence of inundations and their characteristics on the coastal terrain were analysed, for a year and on a perennial timescale. Most catastrophic and exceptional inundations arise in the summer and in early autumn. Small inundations during the remaining year reflect the seasonal distribution of river flow and floods in the Black Sea rivers. Extensive and sometimes extreme precipitation dominates the river flow regimes. The seasonal distribution of small and moderately dangerous inundations reflects, on average, a water regime of two groups of rivers of the coast – to the north and to the south of the Tuapse River. To the north of the Tuapse River, floods prevail from November until March (up to 70 % of observed floods took place in this period) as a result of precipitation and winter snowmelt during frequent thaw periods. In winter, high waters often overlap to form a multi-peak high water of 2–3 weeks' duration. In the summer and in early autumn we observe a steady low flow. The total amount of runoff increases both in a southeast direction, and with the altitude of the river basins. Interannual variability of mean annual runoff, as well as maximum runoff, on the contrary decreases in the southern direction and with an increasing area of the river basins. The coastal high waters of the rivers of the Sochi part of the coast are typical at any time of the year, but more often floods in the cold season result from incessant rain, and thawing snow. Annually up to 25 floods have been observed. The principal reason of such distribution is the increase of extreme rainfall in the warm season. Orographic features of the coast and detailed features of rainfall only cover a small number of local river basins and a limited area. The geographical correlation of individual rainfall and subsequent floods ceases to be statistically significant for distances over 40–60 km. The annual flow cycle is mainly determined by two seasons, winter/spring and summer, with strong and weak flows, respectively; almost 71 % of all catastrophic and exceptional inundations took place in July–August (71 %) and in October–November (29 %). The characteristic features of dangerous floods are their rapid formation and propagation, a significant increase of water level (up to 5–7 m and more) and the multiple increase of water discharges in comparison with low flow period. Analysis of the interannual changes of the number of inundations at the Black Sea coast of the Krasnodar territory has shown some increase of the number of inundations in the period from the early 1970s until the early years of the twenty-first century. Quantitative assessments of risk, hazard and damage for the population and economic activities from accidental inundations in the valleys of the Black Sea coast rivers show that economic and social losses from inundations at the Black Sea coast of the Krasnodar territory are some of the highest in the Russian Federation. The basic conclusion from recent inundations is the need to consider not only the lower reaches and mouths of the Black Sea coast rivers where the main part of the social and economic development of the coast is concentrated, but also whole river basins and catchments. Further, an analysis of the efficiency of the measures applied at the coast to mitigate inundations and their after-effects is provided.

The low-frequency sea level spectrum in the Baltic Sea has been analysed based on long-term time series of sea level data (15–124 yr) from three tide gauge stations in the Baltic Sea and two stations in the North Sea. The principal periodicities detected in the spectrum are seasonal and tidal oscillations including the pole tide with a period of about 14 months. Cross-spectral analysis has been applied to estimate the frequency response of sea level oscillations in the Baltic Sea relative to the North Sea. It is demonstrated that the basic factor in the formation of the low-frequency sea level spectrum in the Baltic Sea is the barotropic water exchange through the Danish straits. The limited throughput of these straits plays the role of a natural low-pass filter for the sea level variations: high-frequency sea level variations from the North Sea are effectively damped, while the low-frequency signal can pass through into the Baltic Sea almost undisturbed. A simple model of the barotropic water exchange used in the study allows us to estimate the parameters of the filter. It is shown that the cutoff frequency is about 0.014 cpd (74 d period): the energy of sea level oscillations at this frequency is reduced by one half after their penetration into the Baltic Sea. This study contributes to quantifying extreme sea level events in the Baltic Sea in height and time to improve their predictability.

The spectrum of low-frequency sea level variations was analyzed on the basis of long-term (15–124 years) time series of sea-level data from three tide gauge stations in the Baltic Sea and two stations in the North Sea. The principal periodicities revealed in the spectrum are seasonal as well as the tidal oscillations including the pole tide with a period of about 14 months. The response function of the Baltic Sea level to variations in the North Sea level is calculated using a cross spectral analysis. It is shown that the barotropic water exchange through the Danish Straits is a basic factor in the formation of the low-frequency sea level spectrum in the Baltic Sea. The limited throughput of these straits plays the role of a natural low-pass filter for the sea level variations: high frequency sea level variations from the North Sea are effectively damped, while the low frequency signal can pass through into the Baltic Sea almost undisturbed. The simple model of the barotropic water exchange used in the study enables us to estimate the parameters of this filter. It is shown that the cutoff frequency is about 0.014 cpd (a period of 74 days): the energy of the sea level oscillations at this frequency is reduced by one half after their penetration into the Baltic Sea.

The paper presents examples of the change in snow avalanches and debris flows activity due to the anthropogenic pressure on vegetation and relief. The changes in dynamical characteristics of selected snow avalanches and debris flows due to the anthropogenic activity are quantified. The conclusion is made that the anthropogenic effects on the snow avalanches and debris flows activity are more pronounced than the possible effects of the climate change. The necessity is expressed on the unavoidable changes of the natural environment as the result of a construction and of use of the constructed infrastructure to be account for in corresponding planning of the protection measures.

The SWAN spectral wave model was realized for the White and Barents seas, as well as for the northern part of theAtlantic. A new irregular grid was used for calculation with 1° interval for the Atlantic, 0.5° for the Barents Sea and 0.2° for theWhite Sea. The input wind data were the NCEP CFSR reanalysis data of high resolution (about 0.3°). The results of numerical experiments made it possible to estimate the influence of swell originating from theNorthern Atlanticon the White and Barents seas, thus contributing to the solution of the problem of open boundaries while simulating wave processes in the seas. In the process of three numerical experiments the wind field over the White and Barents seas was «switched off» in order to isolate the influence of swell originating from the Northern Atlantic. The impact doesn’t exceed0.25 mwithin the White Sea, while it is above5 mfor theBarents Sea. The height of swell coming from the Barents Sea into the White Seais about1 m. The results provide for the estimation of possible errors in the process of wave simulation for the White and Barents seas under the situation of open boundaries and in the absence of waves coming from theNorthern Atlantic. The accuracy of simulation was verified by comparing the results with remote sensing data about wave heights. Correlation of results with the data of satellite altimetry and the WaveWatch3 model showed that in general both models simulate near-real wave heights. The simulated wave height values are 2–3 m above the satellite data, mainly because the averaged remote sensing data represent a largely smoothed wave field. During storms with the waves higher than 6–7 m the swell from the Northern Atlantic has the period of 15–16 s and to the central part of theBarents Seathe peak period changes for 18 s.

In this study we describe the wind wave fields in the Black Sea. The general aims of the work were the estimation of statistical wave parameters and the assessment of interannual and seasonal wave parameter variability. The domain of this study was the entire Black Sea. Wave parameters were calculated by means of the SWAN wave model on a 5 × 5 km rectangular grid. Initial conditions (wind speed and direction) for the period between 1949 and 2010 were derived from the NCEP/NCAR reanalysis. According to our calculations the average significant wave height on the Black Sea does not exceed 0.7 m. Areas of most significant heavy sea are the southwestern and the northeastern parts of the sea as expressed in the spatial distribution of significant wave heights, wave lengths and periods. Besides, long-term annual variations of wave parameters were estimated. Thus, linear trends of the annual total duration of storms and of their quantity are nearly stable over the hindcast period. However, an intensification of storm activity is observed in the 1960s–1970s.

Debris flows are the most frequent and disastrous natural hazards among other exogenic processes at the Black Sea coastal region of the North Caucasus. Numerous debris flow releases are reported every year between Novorossiysk and Krasnaya Polyana. The debris flows bring economic losses, and sometimes loss of human lives. Quantification of the economic, individual and collective debris flows risk is based on their spatial distribution, repeatability, debris flows’ regime, as well as economical and social characteristics of the territory accounted for. Estimation of the individual debris flow risk shows that the level of such risk corresponds to “allowable” and “acceptable” degrees [Vorob’ev, 2005] - less than 3,3 × 10-6. The maximal values of the economic debris flow risk are estimated in the Adler region - more than 1 mln. rub. per year.

The comprehensive World Ocean Circulation Experiment (WOCE) survey of physical and biogeochemical observations, conducted between 1990 and 1998, was unprecedented in spatial coverage, accuracy, and types of measurements. WOCE data represent the “state of the oceans” during the 1990s, providing a baseline for changes that have been observed subsequently through repeats of selected WOCE sections via the Global Ocean Ship‐Based Hydrographic Investigations Program (GO‐SHIP; http://www.go‐ship.org ).

Methods and results of social vulnerability and risk assessment are presented in the article. It is explored if modified methodology of the United Nations University (World risk index) can be used on different scale levels: regional, municipal and settlement. It was estimated that, despite the low value of the World risk index for Russia, southern coastal and mountain regions have high values of the risk index for hydrological phenomena because of higher frequency of the hazardous events, higher population density, and high social vulnerability. The Krasnodar region (in the south-western part of Russia) was chosen for a detailed analysis. A municipal risk index was developed, and municipal districts in the Kuban rivermouth were identified as territories with the highest risk. For verification of the index results, the percentage of vulnerable people was estimated based on opinion polls. The results can be used in further risk calculation for other hazardous phenomena.

Atlantic Multidecadal Oscillation (AMO), associated with variations in oceanic heat transport in the North Atlantic and the Atlantic sector of the Arctic, influences appreciably the climate of the Northern Hemisphere (NH). From the 1970s to early 2000s, there was a growth in the AMO index, coinciding with the trend of global warming. To estimate the AMO contribution to the NH seasonal temperature changes, we analyzed the numerical experiments with the atmospheric general circulation model (ECHAM5) coupled to the thermodynamic model of the upper mixed ocean layer using anomalous ocean heat convergence fluxes associated with the AMO. As part of the research, we studied the relative contribution of anomalous heat fluxes in the Atlantic and the Arctic. It is shown that AMO can explain about 40% of the observed winter and summer temperature changes over the last three decades. The vertical structure of the AMO-related temperature changes has also much in common with empirical estimates. In particular, the model reproduces the Arctic amplification with maximum temperature trends near the surface at high NH latitudes. AMO in the model leads to more probable anomalously cold temperature regimes in February on the territory of Russia, despite the rise of the mean February temperature. Also, we indicated more a probable development of anomalously hot Julys, particularly in European Russia. It is shown that an important contribution to the seasonal variations comes from anomalous heat fluxes in the Arctic, which are generally disregarded when the effect of North Atlantic Multidecadal Oscillation in the Northern Atlantic is modeled. The results obtained indicate an important role of AMO in the formation of weather and climate anomalies.

Characteristics of Northern Hemisphere extratropical cyclone activity were compared for five concurrent reanalyses: the NCEP-U.S. Department of Energy (DOE) reanalysis (herein NCEP-DOE), the Japanese 25-year Reanalysis Project (JRA-25), the ECMWF Interim Re-Analysis (ERA-Interim), the National Aeronautics and Space Administration's Modern-Era Retrospective Analysis for Research and Applications (NASA-MERRA), and the NCEP Climate Forecast System Reanalysis (NCEP-CFSR), for the period 1979-2010 using a single cyclone tracking algorithm. The total number of cyclones, ranging from 1400 to more than 1800 yr(-1), was found to depend strongly on the spatial resolution of the respective reanalysis. The largest cyclone population was identified using NASA-MERRA data, which also showed the highest occurrence of very deep cyclones. Of the reanalyses, two (NCEP-DOE and ERA-Interim) are associated with statistically significant positive trends in the total number of cyclones from 1% to 2% decade(-1). These trends result from moderate and shallow cyclones contributing to approximately 90% of the total cyclone count on average. The number of very deep cyclones (<960 hPa) in the North Atlantic increased in most reanalyses until 1990 and then declined during the last decade. In the North Pacific, the number of these events reached a peak in 2000 and then decreased during the last decade. The winter pattern is characterized by robust trends in cyclone numbers, with an enhancement of the North Atlantic storm track and a weakening of the North Pacific subtropical storm track. In the summer, there is a robust intensification of the Mediterranean storm track and a decrease in counts over the North Atlantic. Interannual variability and decadal-scale variations of the cyclone counts are highly correlated among the reanalyses, with the greatest agreement in moderate and deep cyclones.