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Processes of formation and melting of snow cover in large cities remain poorly studied, for example, one of those is Nizhny Novgorod, the largest city in the Volga River basin. Using the relationship between the amount of precipitation, falling over the cold season, and the snow storage, formed on the whole territory of the city, that was built taking account of the influence of thaws, a continuous series of values of the snow water equivalent (snow storage) for the time of the snowmelt beginning was restored for the period 1965– 2019. Thaws were taken into account through the use of the sums of positive air temperatures for the cold period, calculated for each individual year of observation. During the period under consideration, the maximum snow storage occurred in 2011, while the minimum – in 1998; and it was close to the average value in 1973. Field snow-measuring surveys in the city and its environs, carried out in 2020, showed that the classical notion of the snow-storm transport is not true in the urban landscapes rather than in the environs. The use of the results of field snow surveys performed in different parts of the city in 2021, as well as the statistical characteristics of the above series of snow storage values, allowed estimating the distribution of the snow water equivalent in catchments of six small rivers in the city Nizhny Novgorod. The assessment is detailed for different types of urban landscapes and for years of different snow conditions, including the extreme ones.

In framework of the project «The Earth system Models – Snow Models Intercomparison Project» (ESMSnowMIP), calculations of snow storages were carried out on ten experimental sites organized for longterm monitoring of the snow cover variability in various regions of the globe. The calculation method is based on the physical and mathematical description of heat and moisture exchange processes occurring within the system «ground water – soil – vegetation cover/snow cover – surface layer of the atmosphere», and it is implemented in the form of the model of interaction between the land surface and the atmosphere (SWAP). The model was developed at the Institute of water problems (IWP) of Russian Academy of Sciences. The model makes possible to calculate components of water and heat balances and different characteristics of the hydrological regime of terrestrial ecosystems and river basins having different spatial scales and located in different natural conditions. Good quality of reproduction of the snow storages variability on all considered sites is reached that allows consideration of the SWAP model as one of the best models of the snow cover formation. Thus, the SWAP model has a sufficiently optimal degree of complexity of the algorithm for reproducing the dynamics of snow cover, which is necessary and sufficient in global and regional hydrological models describing formation of the water balance of the land in the cold regions of the planet, and can be used to create scenario forecasts of snow dynamics (as the important part of the cryosphere). This conclusion is verified by the results of using the SWAP model to reproduce long-term variability of snow storages in basins of the River Lena and the River Ob (with its tributary Irtysh) which are the two largest rivers of the Russian Federation. The calculated and measured characteristics of snow cover dynamics for these basins are shown to be in good agreement.

In 1966-2010, snow surveys were simultaneously performed in forests and fields on the Russian plain territory. This made it possible to analyze characteristics of snow storages on fields and in forests as well as a dynamics of them under the present-day climate changes. Data of 81 weather stations located on the territory were used. According to data of these stations for the period 2001–2010 we obtained the following estimates for the maximal snow storage values, on average: for 20 stations located on the European territory of Russia to the north of 60° N –167 mmin forests and 162 on fields; for 44 stations to the south of 60° N – 118 and116 mm, respectively; for 10 stations in the south of West Siberia – 125 and107 mm; and for 7 stations in the East Siberia – 64 and70 mm. As one can see the last region is characterized by the opposite relation between forest and field conditions. Comparison of these values with similar data for the period 1966-2000 demonstrated that maximal snow storages decreased in forests by 7% but in fields they increased by 2%. The ratio of the maximum snow storage in the forest to their value in the field (i.e. a coefficient of snow reserve) for the periods 1981–1990, 1991–2000, and 2001–2010 are 1.15; 1.11 and 1.03, respectively. One of the reasons for the equalization of snow storage in forest and field may be changes of intensity and duration of snowstorms. In the calendar winters of 2001-2010, the average number of observations at weather stations with wind speeds over 10 m/s decreased relative to 1966-2010: in the European part of Russia by factor of 8.9 times, and in Western and Eastern Siberia – by 2.0 and 1.9 times, respectively. In the European part ofRussia, the number of observation periods when wind speed from 6 to 10 m/s was observed decreased by 1.9 times.

The paper presents characteristics of a snow cover observed on the Lagonaky high plateau (the Western Caucasus) in the interfluve of the rivers Belaya and Pshekha along two snow-measuring courses. The period of observations is 1973–2015, and the altitude interval is 460–2020 m. The characteristics measured are the following: depths of snow cover, the snow density, and temperature of different snow layers in the test pits. The stratigraphy of the snow thickness is described. In different years, observations did show changes in the depths which felt within a wide range of values from a few centimeters up to 5–6 m at the same points. The observations allowed determination of dates of snow appearance (setting-up of snow cover) as well as the disappearance in different parts of the Lagonaky high plateau. Durations of the snow cover in different altitudinal belts were also determined. By the end of March the snow cover disappears to altitudes of 700 m, and after 20th of April the slopes become free of snow to 1000 m. The snow cover duration in the low-altitude zone (500–1000 m) is 70–80 days, while in the middle altitudes (1,000–1,500 m) it is 130 days. In the highlands (above 2000 m), the snow cover lasts for 215 days. It must be emphasized that during the last five years the duration of snow cover has changed significantly. Materials of snow surveys showed that snow depths and water contents (water equivalents of snow cover) significantly differ from year to year. In seasons 1975/76, 1978/79, 19861/87, 1989/90 the winters were extremely snowy, while winters in 1976/77, 1979/80, 1983/84, 1990/91, 2013–2015 had small amount of snow. According to data of distant snow-measuring sticks, the maximum values of the snow depth (610 cm) have been recorded in March of 1976 near the tourist shelter Fisht (1596 м). Significant changes in the distribution of snow cover in recent years were probably related to the global climate changes.

Using of the Chang model for calculation of the snow water equivalent on the basis of measurements of the Earth thermo-microwave radiation by means of scanning polarimeters (SMMR, SSM/I, AMSR-E) from board of orbital satellites does not allow obtaining the accuracy needed hydrological purposes. Low accuracy of the calculations is caused by both simplified character of the mathematical model, and due to significant influence of the surface characteristics (relief, vegetation and complex structure of snow thickness) upon the microwave radiation propagation. This work was aimed at finding a way to increase accuracy of calculations of the snow water equivalent on the Russian Federation territory with its different climate conditions by means of application the neural network approach for processing of results of the passive microwave scanning of the Earth surface. Feed-forward multi-layer artificial neural network was trained by back-propagation algorithm using SSM/I data and results of snow water equivalent in situ measurements obtained at 117 meteorological stations during the period from January 1st, 1988 till December 31st, 1988. Validation was performed using data from the same sources collected during 7 years (1992–1998). Results of performed numerical experiments and obtained values of rootmean-square error (σ = 24.9 мм; r = 0.39±0,01) allow coming to conclusion that the best estimation of water equivalent of a snow cover is provided by artificial neural network using as the input data a set of the SSM/I channels 19.35, 37.0, 85.5 GHz of horizontal and vertical polarizations with meteorological data differentiated by types of the snow survey route.It is shown that low correlation coefficients (

Character of spatial and long-term variability of snow cover is specified for the period 1966–2006. Long-term decrease of snow storage in November and December and absence of changes in January and March are revealed. The standard deviation for regional spatial distribution changes according to changes of snow storage. Long-term changes of the area with displays of the large snowiness (Sср + δs < Si< Sср + 2δs) and extremely large snowiness (Si>> Sср + 2δs) are estimated. The territories where large and extremely large snowiness are displayed does not exceed 12% from the total area, it is not very perilously for economic activity. Long-term changes of the area with displays by the large and extremely large snowiness correspond to long-term changes of snow storage. The area with simultaneous display of extremely large snowiness, extremely large sums of precipitation and extremely low air temperature is small and does not vary year by year. Hence, concurrence of extreme parameters dispositions also cannot be considered dangerous.

Local and regional differences in the snow formation were studied in different landscapes of the central part of the East European Plain – within reserves in the Moscow and Tver’ regions (south-north direction); the study period is the winter 2011/12. The observed increase of snow storage in 1.3–1.5 times in the direction south-north is connected, apparently. The difference in the five-day appearance of snow cover maximum is related to differences in regional winter air temperature. Throughout the snow depth and snow storage in spruce are smaller than in deciduous forest – in the ratio of 0.81 in south area and 0.93 in north area; in spruce the large part of solid precipitation is intercepted by the crowns pine trees. Snow stratigraphy at south areas has four layers, six layers at the north area are more variable in snow density and snow storage. Perhaps, gravitational conversion is more noticeable due to larger snow depth. Snow density and snow storage at the open areas are more heterogeneous than in the forest. This is due to sharp fluctuations in air temperature, wind transport and compaction of snow, evaporation from the snow surface. The stratigraphy of snow also reflects the history of winter changes of air temperature and snow accumulation. Common feature for reserves at south and north is the availability of layers with maximum snow storage in the middle of the snow thickness, which were formed during the air temperature drops to the lowest seasonal values in period with increase of snow depth to maximum. Formation of depth hoar in snow thickness are touched everywhere the bottom and middle layers, respectively, it was formed both before and during the period with minimal air temperature. Thus, the results of experimental studies confirm the significance of the differences of individual components of the landscape setting. Analytical conclusions are largely qualitative in nature due to the lack to date of initial information, and therefore to continue experimental studies is expected.

Statistical parameters and tendencies of the long-term changes in snow cover characteristics of forest-steppe in Fore-Baykal region were evaluated according to the observational data obtained at meteorological stations by means of permanent snow stake as well as using snow survey in the field and in the forest for the long-term period 1961–2000. Duration of snow cover decreases. The snow depth according to the permanent snow stake increases. The observed values of snow survey show that in the field without any significant changes in the snow depth manifest itself the local effect of water supply reduction in the snow cover. The largest rates of decrease of snow depth and snow storage has experienced in the forest. The maximum snow density decreases both in the field and in forest.

The paper deals with study of snowiness and estimation of modern tendencies of its changes in the area of Krasnaya Polyana in the West Caucasus. Olympic Games will take place here in February, 2014. The paper is based on the data of meteorological stations Krasnaya Polyana (567 m), Achishho (1880 m) and snow surveys along the Mzymta River valley (0–2500 m). Period under study characterized by winters with different snowiness. This difference is analyzed due to their changes in altitude levels. During two last decades, the noticeable reduction of snowiness occurred in the investigated district. The dependence between snowy winters and periods of cold temperatures is identified. In seasons of anomaly high and low snowiness the difference of snow depth can reach 5 m (Achishho). In places of Olympic ski lower stations (Gornaya Karussel, Gasprom, Rosa-Hutor) the temperature of cold period runs from −1,6 ºC up to 4,9 ºC, and the periodicity of winters with positive temperatures is 86% on this level. Parameters of winter conditions are given in the paper, and we can consider them as a paradox of Krasnaya Polyana winters