The objective of the study is to evaluate and analyze the modern data on water resources and their use in the region, which is a relevant problem. It is shown that in terms of renewable water resources per inhabitant, the Republic of Crimea and the city of Sevastopol are in the worst position in the Russian Federation. An assessment of changes in the volume of water withdrawal and the structure of water consumption in 2014-2021 is provided. The damage to river runoff due to the water withdrawal from surface and underground sources and the water resource utilization factor are calculated for the main rivers of the Crimean Peninsula. It has been revealed that most of the studied river basins are characterized by a high or very high load on water resources.

The calculation of runoff from natural and urbanized landscapes is based on hydrological characteristics and information on the surface condition of catchments – forestation, ploughing, urbanization, and so on. While the condition of a watershed can be assessed using various cartographic sources, remote sensing methods, digital models, etc., to determine runoff characteristics, it is necessary to implement different procedures for generalizing monitoring data depending on the hydrometeorological study of the territory. Methods. Engineering methods of hydrological computation are well known and standardized. However, when determining the characteristics of pollutant washoff, the need arises for detailed assessments, which can be addressed through mathematical modeling of runoff. In this case, it is essential to have methods for assigning characteristics of rainfall events or snowmelt runoff that can be used to calculate events of a given probability (such as runoff layers and maximum rain flood and spring flood discharges). Such methods may be developed based on specialized approaches to the analysis of observational data, demonstrated by the example of spring flood and rain flood calculation in the Kazanka River basin. Results. The method was implemented on the example of modeling of runoff formation from the Kazanka River watershed. The values for rain flood and spring flood runoff layers were calculated. A design rainfall hyetograph was proposed, and other parameters necessary for the subsequent calculation of wash-off and soil erosion were determined.

The problem of long-range probabilistic forecasting of the salinity in the Sea of Azov is considered. Due to the disturbed freshwater balance of the sea, which is caused by both increasing irrevocable withdrawals and the climate change in the Don and Kuban river basins and in the interfluve of the Don and the Kuban, the water salinity in the sea has increased in recent decades. To analyze current processes and to assess the future regime of salinity of the sea, it is proposed to use a simulation model based on the known balance ratios and probabilistic projections of the main processes (factors). The developed scheme of probabilistic forecasting makes it possible to take into account projected changes in the freshwater inflow (the volumes of withdrawal and inter-basin runoff transfer) in a simple form and to evaluate their effect.

In 2013, a catastrophic flood occurred on the Amur River, caused by heavy rainfall throughout almost the entire basin. The floodplains of Blagoveshchensk, Khabarovsk, and Komsomolsk-on-Amur were flooded. Similar hydrological phenomena on the Amur occurred earlier (1954, 1972, and 1984), but they did not lead to catastrophic flooding. In the proposed manuscript, the authors investigated three issues: the causes of the 2013 flood, advanced hydrological forecast, and measures to prevent catastrophic flooding. For research, a hydrodynamic model of the Amur River section from Blagoveshchensk to the mouth was developed. Based on the analysis of model calculations, it was shown that some flood problems arose due to the construction of hydraulic structures in recent years (protective dams, bridges, and embankments) and a medium-term forecast scheme proposed.

Emergencies in recent years caused by floods make us to think about the sufficiency and adequacy of the preventive technical measures taken to protect territories from flooding. In the current conditions, the emphasis should shift from the fight against natural hydrological processes to a set of measures aimed at eliminating the causes of flood-caused damage increasing.

This article considers the possibility of using probabilistic models to analyze the maximal flow discharges of rivers in order to obtain reliable calculated statistical characteristics for basins with poorly studied hydrological features. The research was performed by the example of Cisbaikalia, which is characterized by a flood regime of river flow. It is found that floods in the study area most often occur in summer (July−August), are associated with the climatic characteristics of the region, and are often destructive. The analysis of the maximal flow of rivers is based on data from the Roshydromet observation network. The series of maximal water discharges are checked for homogeneity and, in general, no disturbances in the steady state of runoff caused by climate changes are detected. A generalized distribution of extremes is proposed as the main probabilistic model; it is recommended to determine its parameters on the basis of the group analysis. The integrated approach has been applied for the first time; it combines conventional methods of hydrological calculations, which are most often used to refine the characteristics obtained for the runoff in the zone of extreme values: the apparatus for truncation of distributions; joint analysis of data; a reduction formula with the reduction of the drain modulus value not only to the area of 200 km 2 , but also to the mean height of basins in the region; and the frequency probability method for estimation of obtained results. These methods are recommended by regulatory documents for discharge calculations and are most often individually used. The comprehensive approach described by the authors enables us to take into account the features of the runoff formation in the zone of extreme values and obtain more accurate values of characteristic quantiles of a given probability of excess for use in design on poorly studied rivers of the region.

A probabilistic model of the sums of extreme precipitation was developed for heavy showers covering large areas in the Baikal region. The spatial correlation functions of precipitation fields over one day and the entire rain period were studied. Data on the Iya River basin were used to evaluate the errors in estimating the mean values over a specified contour of extreme precipitation. Errors in the interpolation of precipitation estimates for the Baikal region were evaluated in the absence of observation data with estimation of the errors of the obtained values by Drozdov–Shepelevskii formulas. These errors amounted to about 10–15% and more. The specific features of precipitation field structures were studied with the use of their expansion in series in natural orthogonal functions for one day and over a rain period for different samples: for the entire combination of cases and for samples containing 10 and 30 maximal precipitation totals for each weather station, i.e., for extreme events. It was found that, if the observation data are limited to a range of maximal values, the structure of precipitation fields is simplified and the first 4–5 decomposition components are enough for its description. The obtained results are of importance for forecast problems and for the construction of simulation models of precipitation fields for further use in deterministic runoff simulation.

The article presents an overview of the main hydrological and water management tasks and problems that have arisen in recent decades on the Lower Volga because of the construction and operation of the Volga-Kama cascade of reservoirs, anthropogenic changes in runoff as a result of economic activity, and the consequences of poorly predictable climatic changes. It is shown that the hydrological regime in the lower reaches of the Volga River has undergone significant changes, both as a result of regulation of runoff by reservoirs and due to climatic changes. The observed changes in flow fluctuations have led to serious changes in the aquatic environment and the entire ecosystem of the river. A number of negative consequences were predicted during the development of reservoir cascade projects, and the construction and operation processes were accompanied by the implementation of a set of compensatory measures of a fisheries’ nature. Nevertheless, the functioning of a complex water management system and insufficient attention to environmental problems led to the emergence of new environmental, technical, and scientific problems that required an integrated approach for their solution, and the effectiveness of the planned measures turned out to be insufficient. The study of the consequences of seasonal regulation of runoff by reservoirs, changes in the estimates of water resources, the involvement of new methods of studying the hydrological system, including multi-arm channels, and the analysis of anthropogenic-altered river sections allowed to obtain new results but at the same time to formulate a block of unresolved scientific problems. Among such problems, there is a need to solve such engineering and hydrological tasks as increasing the feasibility of forecasts of inflow to reservoirs, long-term forecasting of long-term fluctuations in runoff under conditions of ongoing climate change, obtaining up-to-date estimates of negative processes—deformation of riverbeds under anthropogenic impact. The latter is very important for the downstream of the Volgograd Hydroelectric Power Station. In terms of predicting the behavior of the ecosystems of the Lower Volga, with an assessment of their stability, further development of methods for assessing permissible impacts, the development of monitoring systems for their condition is required. The management of the Volga-Kama cascade of reservoirs is a complex scientific and technical task. Today, this management is carried out on the basis of dispatching rules dating back more than a dozen years. It is shown that modern management should be based on a coordinated system of priorities, including environmental criteria. The required optimization formulation of the task of finding optimal cascade control can be based, for example, on the search for a compromise solution at the level of agreement of the parties. A set of environmental and water management problems unsolvable for decades has been formed in the northern part of the Volga-Akhtuba floodplain as well as in the zone of the Western-subtidal ilmens (system of lakes in the Volga River Delta). To solve these problems, new methods of studying ecological systems under severe anthropogenic stress and appropriate engineering approaches that allow a comprehensive approach to achieving sustainable water resources management are considered. The problem of poorly predictable fluctuations in the level of the Caspian Sea and the problem of water resource management in the region in conditions of conflicting interests of users are touched upon. The main measures are discussed, whose implementation will mitigate the consequences of flow regulation for the ecosystem of the Lower Volga. Among the important system principles, the need for a basin approach is noted, which involves, at a minimum, the development of a General Scheme for the Use of Water Resources of the Volga River.

When managing water resources in order to provide water to consumers, a number of consequences arise related to the violation of the hydrological regime due to the regulation of flow by reservoirs. The second factor is possible climate change. These changes can negatively (or positively) affect the functioning of aquatic ecosystems. To reduce the impact on the environment, it is necessary to determine the nature and indicators of changes in the hydrological regime, calculate quantitative estimates of these indicators and ranges of acceptable values, and develop release rules that ensure compliance with these ranges with a given probability. To manage the water resources of the Volga and Kama Rivers, the main ecological task is to flood the floodplain meadows, to maintain the conditions of natural reproduction of fish on the Lower Volga, including the Volga River delta and the Volga–Akhtuba floodplain. In addition, it is necessary to meet with sufficient reliability the requirements of energy in the summer–autumn and winter low-water periods and water transport during the navigation period. The task of optimal management is to find such solutions in years of different water content that ensure the well-being of the main water users with a given probability and do not disturb the Lower Volga ecosystem. This article presents the research of the water resources state of the water resource system of the Volga and Kama river basins. A statistical analysis of the hydrological series of the observed inflow for 1916–2020 was performed, and the inflow change point (1979) was found by the Bayesian method of estimation. A statistically significant difference between the average inflow values of two series (1916–1978, 1979–2020) was proved using a two-sample Student’s test. The seasonal parameters of the reliability curves were calculated based on the three-parameter Kritsky and Menkel distribution. For these two series, water resource optimization calculations (using Excel Solver) were performed, and the reliability of fulfilling the requirements of water users was determined; for the series 1916–1978, an alternative solution was found in favor of fisheries, and an analysis of the results was also performed. The methodology used in the research allows finding trade-off solutions in the favor of different water users (ecology, agriculture and fisheries, water supply, hydropower, navigation, etc.) and is based on the use of multi-criteria optimization methods and the trade-offs theory. As a result of the research, new knowledge was obtained about the hydrological situation in the basin of the Volga–Kama reservoir cascade in connection with climate change.

This paper discusses the formation of level regimes in lakes located in arid parts of Central Asia. Water resource formation specifics in the studied region include the presence of runoff formation and dispersal zones in river basins. When rivers leave mountainous areas, the dispersal of runoff occurs due to seepage losses from river channels and the remaining waters fill drainless depressions, thus forming enclosed or terminal lakes. Water levels in such lakes depend entirely on water content fluctuations in rivers, and their sizes fluctuate in a wide range, up to completely drying up. Factors determining the hydrological regimes of terminal lakes whose catchment basins are located in the Russian Federation, Mongolia, and the People’s Republic of China are examined. Approaches to the stochastic modeling of water balance components in lakes and probabilistic forecasts of their long-term water level fluctuations are presented. Using the examples of the Torey Lakes (the Russian Federation) and lakes located in the Heihe River basin (the People’s Republic of China), the level regime formation and its probabilistic forecasting are described, including situations involving severe anthropogenic impacts.

An important trend of modern development is the concentration of population in urban agglomerations, where a specific meso- and micro-climate is created under conditions of dramatically transformed natural landscapes. In the present paper, the long-term statistical analysis of intense rainfalls and annual daily precipitation maxima was carried out based on the Moscow region weather stations timeseries for the period of 1966-2021. An increase in the variability of intense precipitation over the Moscow region corresponding to the formation of significant floods was revealed in some years. The COSMO-CLM model simulated extreme precipitation for the basin of the Setun' River (190 km2), the largest right-bank tributary of the Moskva River within the Moscow city, which was recorded over Moscow in May 2020 and June 2021. Maximum precipitation was registered over the Setun' River basin during 45-90 minutes and induced rainfall floods that exceeded the spring flood by two times. The estimated basin travel time was 6-8 hours. Rainfalls form a multistep hydrograph inheriting the shower precipitation structure on small rivers.

— The article presents a digital decision support technique for deriving compromise rules for the water level management of Lake Baikal and the Angara River cascade of reservoirs. The proposed technique is based on interactive Pareto front visualization, which helps users find an efficient compromise between conflicting demands and validating the decision resulting from the compromise. The compromise cascade management rule developed using the technique satisfies all key demands and can be used as reference for developing state directives concerning management of water resources of the Angara River basin.

The determination of errors in the runoff probability distribution parameters when estimating them on a heterogeneous sample is considered. For the case that allows using composite curves (or a mixture of distributions), some expressions for errors of the estimates of the mean and the variation coefficient are proposed. It has been found that accounting of the sample heterogeneity based on a probabilistic model of the time series, which allows its examination in the form of two stationary sections without accounting the averaged autocorrelation, magnifies the error of the mean value estimate. It is shown that the overestimation of the first autocorrelation coefficient assessed on the entire series without taking into account inhomogeneity should be considered.

Aim. Assess the change in the hydrological regime of the Torey Lakes based on a probabilistic forecast of the parameters of the water balance of these reservoirs, taking into account anthropogenic influence. Material and Methods. The study used materials from the state observation network of Roshydromet, Earth remote sensing data, research materials from scientific organisations and other sources of information that are in the public domain. Methods of statistical data analysis, mathematical modeling, hydrological calculations, including the water balance method and methods of processing and decoding satellite information were used. Results. With the implementation of the planned water management project, accompanied by additional non‐returnable water consumption in Mongolia, the consequences for the water regime of the Torey Lakes can be significant, especially in the low‐water phase of the water cycle, when the level decrease in the Barun‐Torey Lake will average 70 cm and in Zun‐ Torey – 80 cm. Through this project, the faster drying of the lakes, on average 2–3 years earlier, will be avoided. Conclusions. The ecological systems of the Dauria region are characterized by a process of cyclic succession and are mainly adapted to the contemporary climatic moisture cycle. For these ecosystems, any changes in external factors are fundamentally important, since they can lead to the irreversibility of natural processes. Based on the results obtained in this study, it is possible to conduct a comprehensive analysis of the anthropogenic impact on the state of the Torey Lakes and nearby ecosystems.

The management of the water management complex is based on the analysis of a large number of processes developing in systems that are techno-natural in nature, on the one hand, and in complex socio-economic systems affecting the whole society as a whole, on the other. The management methods implemented in practice today are based mainly on the analysis of the functioning of individual parts (individual processes) of the system, ideas about the processes under consideration are often not consistent, especially when it comes to technical and social systems. Regulatory management methods, including technical regulation, are considered separately. Socio-economic processes at different levels of temporal and spatial organization are investigated and predicted independently. At the same time, of course, regulatory legal knowledge is taken into account, but resource restrictions may fall out or be ignored, society is immune to instructions and recommendations lowered from above, legal nihilism takes place, the problem of qualification of decision-makers arises, etc.Certain possibilities for analyzing such situations are provided by risk theory methods. The purpose of the article is to analyze the risks arising at various stages of justifying water management measures, from design to strategies for the development of the industry as a whole. In particular, traditional methods of engineering calculations are considered, which ensure a given level of reliability of the designed water construction facilities in relation to hazardous impacts (loads), which are based on the concept of design probabilities. This approach provides a normative level of reliability, but does not guarantee the economic optimality of decisions made, is insufficient to implement the social functions of measures and structures, and is difficult to analyze environmental problems. Obtaining quantitative estimates of the parameters of structures and measures, carried out on the basis of probabilistic approaches, should be based at least on taking into account the possible consequences of decisions taken, as well as on damage assessments expressed in the form of relevant risks.

This article discusses the main methodological problems in determining water levels during the implementation of current standard regulations that define the flood zones in offshore territories of rivers and water reservoirs. A new approach is proposed to determine the maximum water levels on the Baikal coast and in the downstream of the Irkutsk Hydropower Plant.

The article deals with the problem of determining the calculated hydrological characteristics in conditions of the runoff time series homogeneity (stationary state) violation. Methods for processing heterogeneous samples, accepted in engineering hydrology, are applied to the case of the series stationary state violation as a result of climatic changes. In practice, such a problem is solved by the method of compound curves and involves the construction of one-dimensional distribution laws for parts of a heterogeneous sample. The paper summarizes the existing approaches based on Bayesian estimation and forecasting algorithms.

Changes in the spatial structure of runoff fields in the Don River basin due to the revealed non-stationarity of the hydrological regime are investigated. It is shown that the spatial correlation of the spring flood runoff layers, winter and summer-autumn low runoff, as well as snow storage have changed significantly. The chaotic pattern of the spatial correlation was gained, as a result of which the fields of the studied runoff characteristics became heterogeneous and anisotropic.

The effect of climate changes on the water resources and the functioning of water supply system in Moscow region is considered. The data on the inflow into the main part of the water management system in the region, i.e., the Moskvoretsko-Vazuzskaya Hydroengineering System (MVHS), are analyzed. The results of simulation have shown that, against the background of the recent changes in the character of inflow into the MVHS system reservoirs, the management of the water supply system as a whole can be considered more efficient than before 1978. In the case of the Vazuzskaya Hydroengineering System as a component of MVHS, the efficiency characteristics have not improved. The analysis of changes in the operation characteristics showed that they are to be taken into account in the management strategy for the entire MVHS system.

Th e transboundary Russian-Chinese Lake Khanka is characterized by a complex and poorly predictable hydrological regime with long-term cyclic fl uctuations of the level. Th e last rise of the level, which began after 2000 year, turned out to be anomalous in the entire history of observations and caused severe fl ooding of the coastal territories of the Russian part of the basin with related intensifi cation of erosion processes, impact on ecosystems, etc. Th e main factors aff ecting the hydrological regime of the lake are climatic changes in the region and anthropogenic impact on the water resources observed in the Khanka Lake catchment area because of the development of irrigated agriculture, especially in the Chinese part of the basin. Th e reduction in the capacity of the Sungacha River due to the deposition of sediment in the source of the riverbed make current state of the lake’s water regime worse.