This study investigates the transformation of river runoff and its sensitivity to changes in large-scale atmospheric circulation in the Zhaiyk–Caspian water management basin during the period of 1951–2023. The analysis is based on hydrometeorological observations data, the Vangengeim–Girs classification of macro-circulation patterns, and the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indices. Correlation analysis, the Mann–Kendall test, Sen’s slope estimator, and the Pettitt test were applied to identify trends, structural shifts, and the spatial coherence of hydroclimatic changes. The results show that interannual variability in river runoff is characterized by a degree of spatial coherence, with correlation coefficients between annual streamflow records at most gauging stations reaching up to 0.95. It is demonstrated that the most pronounced changes in the hydrological regime occur during the cold season and are expressed in a statistically significant increase in winter runoff, while no significant long-term trend in annual runoff is observed. Structural shifts in winter runoff are predominantly associated with the late 1990s, whereas changes in the temperature regime are detected earlier and exhibit spatial coherence. The findings indicate that the contemporary transformation of river runoff is primarily driven by rising air temperatures and the associated intra-annual redistribution of flow.

Water dynamics and nutrients are widely recognized as the main triggers of phytoplankton blooms. These factors may control the stability of marine ecosystems. Penzhina Bay and the Shelikhov Gulf are famous for their high tidal dynamics in comparison with the basins of the World Ocean and for being the feeding places of Bowhead whales. Here, we study the dynamics and thermohaline structure of water; nutrients; isotopic signatures of δ15N–NO3− and δ18O–NO3−; as well as chlorophyll a in Penzhina Bay, the Shelikhov Gulf, and the Penzhina River to understand the features of an ecosystem with intense tidal dynamics in the subpolar region. This work is based on data obtained in three cruises of the R/V “Akademik Oparin” in the period from 2023 to 2025, with speed boat observations in the Penzhina River from May to October, including the flooding peak in June. The observations covered cases with tides from 7 to 13.4 m in height. The interaction between tides and river runoff was observed to supply dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) from the sea and dissolved silicate (DSi) from the river. The “white nights” in July, combined with the increased supply of nutrients, are good conditions for phytoplankton blooms, and as a result, the concentration of chlorophyll a in the study area was observed to be up to 39 µg/L. High primary production supports the food chain, and this is probably the main reason why Bowhead whales come to feed in the summer. The DIN/DIP ratio indicates DIN as a limiting factor in most of Penzhina Bay and throughout the Shelikhov Gulf. At the same time, the DSi/DIP ratio at a significant distance from the mouth of the Penzhina River is close to 0, indicating unfavorable conditions for diatoms. The DSi limit can cause the blooming of dinoflagellates, which sometimes occurs in this region.

Abstract. Part of Mediterranean Sea variability is forced and paced by external drivers (e.g. atmosphere, river runoffs, Atlantic inflow), while the other part has a random phase and spontaneously emerges due to chaotic intrinsic variability (CIV). This study quantifies across time scales the imprints of both variability components on the surface and zonal overturning circulations within the basin, from a 39-year 30-member ensemble ocean 1/12° simulation. We find that most of sea surface height (SSH) variance is intrinsic over 17 % of the basin, in particular in the southern Ionian and Levantine basins, and most notably in the Algerian basin where CIV explains 80 % of the SSH variance at periods greater than 4 months. In contrast, 75 % of the interannual-to-decadal SSH variance of the North Ionian Gyre circulation is paced by the atmosphere, suggesting an external triggering of the Adriatic-Ionian Bimodal Oscillating System (BiOS) reversal. CIV exerts a larger influence on the Rhodes, Bonifacio, and Alboran gyre circulations. Fluctuations of the density-coordinate zonal overturning circulation (ZOCσ) and of associated transports are mostly paced by the forcing over the basin. However, CIV tends to explain a larger fraction of these transports variance in the intermediate and bottom layers near deep convection sites, in particular in the Levantine basin where this fraction exceeds 50 % between 27 and 30° E at submonthly periods, 30 % at subannual periods, and 20 % at longer periods (reaching 20 years locally). This partly random character of the multi-scale Mediterranean variability has implications for evaluating model simulations and designing long-term observation systems, which are finally discussed.

For the rivers of the Don basin, the Hydrometeorological Center of Russia has developed a methodology for daily short-term and medium-term forecasting of water discharges and levels. Average daily discharges and water levels are forecasted throughout the year with a lead time of 1 to 10 days based on the hydrograph extrapolation method, which takes into account their values for the date of the forecast issue and for the five previous days. To assess the parameters of the forecast scheme, hydrological observation data for each river gauge are used. The method yields quite satisfactory results and can be used within the framework of an automated system for preparing and issuing forecasts in order to provide necessary forecast information for operational decisions on the use of water resources of the Don basin’s rivers and the protection of the population from dangerous floods.

Isotopic parameters of runoff in the Mizhirgi Glacier basin during the mid-ablation period were studied, and the isotopic and hydrochemical characteristics of runoff components—melting ice on the glacier tongue, snow from avalanche snowfields, glacial ice, and snow cover in the accumulation area—were determined. A four-component runoff analysis based on two isotopic (δ18O, d-exc) markers and TDS demonstrated the feasibility of studying the melting structure in a high-mountain glacier basin. This approach is based on the differences in deuterium excess of the snow cover formed during the winter and summer seasons in the glacier accumulation area of the Bezengi basin.

Geosystem–hydrological studies encompass a wide range of methods within the geographic–hydrological field. For analyzing the formation of surface runoff on the southern coast of Lake Baikal, the basin concept, as well as landscape–hydrological and structural–hydrographic approaches, is applied. The primary spatial unit of analysis is the river basin, considered together with the landscape structure and the parameters of the hydrographic network. This study is aimed at determining the landscape and hydrographic conditions and features of the formation of surface runoff in the area. As a result, runoff-forming, runoff-regulating, transit, and accumulation landscape complexes are identified; areas of runoff formation, transit, and accumulation are identified; and the territory is zoned according to the conditions and magnitude of runoff formation. This study is primarily of fundamental importance, aimed at identifying patterns in the structure of river systems that determine runoff areas and which are expressed in the orographic and landscape features of the basin. The practical significance of the calculations lies in the indicative assessment of possible runoff, primarily in the mountainous part of river basins, under conditions of uneven distribution of the standard observation network sections and their insufficient duration. The identification of runoff formation areas and assessment of potential runoff from these areas can be used to develop recommendations for rational planning and use of basin lands, as well as to prevent the occurrence of negative natural consequences.

This paper presents the results of studies on intra-annual runoff changes in the Ile River basin based on data from gauging stations up to 2021. Changes in climatic characteristics that determine runoff formation in the mountainous and foothill areas of the river catchment have led to alterations in the water regime of the watercourses. The analysis of the temporal and spatial patterns of river flow formation in the basin, as well as its distribution by seasons and months, is essential for solving applied water management problems and assessing the risks of hazardous hydrological phenomena, such as high floods and low water levels. The statistical analysis of annual and monthly river runoff fluctuations enabled the identification of relatively homogeneous estimation periods during stationary observations under varying climatic conditions. The obtained characteristics of annual and intra-annual river runoff in the Ile River basin for the modern period provide insights into changes in average monthly water discharge and, more broadly, runoff volume during different phases of the water regime. In the future, these characteristics are expected to guide the design of hydraulic structures and the rational use of surface runoff in this intensively developing region of Kazakhstan.

Abstract The California Undercurrent is a dominant flow feature and has large impacts on regional ecosystems off the west coast of Canada. So far there is limited knowledge on their interannual transport variations. In this paper a high‐resolution ocean circulation model in the northeast Pacific has been established to investigate seasonal and interannual transport variability in the California Undercurrent off Vancouver Island (VI) over 1993–2020. The model forcing includes winds, heat flux, ocean tides, and river runoffs. The model monthly temperature, salinity, and currents are in good agreement with observations at two long‐term monitoring site off West VI. Seasonally the California Undercurrent transport increases from spring to fall and decreases in winter. Interannually the transport anomalies of the California Undercurrent are positively correlated with the inflow through the model southern boundary off Oregon and with the Oceanic Niño Index. It is argued that the interannual changes of the California Undercurrent off VI are likely associated with the sea level variability off South California propagating poleward, providing the poleward longshore pressure gradient along the upper continental slope. El Niño enhances the California Undercurrent mainly due to the equatorial coastal sea level variation propagating poleward.

The ice cover variability of the Kara and Laptev seas in 1978–2022 and the effect of river runoff fluctuations on the ice processes in the seas are studied. A significant decrease in sea ice extent is detected for the analyzed seas. It is found that the influence of river runoff on the interannual variability of the sea ice extent increased in 2004–2022. An increase in the average annual sea ice extent was observed in the Kara Sea at a high water content of the Yenisei River and in the Laptev Sea at a high water content of the Lena River. The Ob River runoff affected the ice processes in the Kara Sea less than the Yenisei runoff. In the Kara Sea, there was a faster growth of sea ice in autumn and its delayed melting in spring during years with a high water content of the Yenisei. An increase in the Ob runoff caused a trend toward faster ice growth in autumn, but did not significantly affect ice cover melting in spring. The high water content of the Lena was associated both with the accelerated sea ice growth in the Laptev Sea in autumn and with its delayed melting in spring.

Abstract Kongsfjorden is located in West Spitsbergen, Svalbard archipelago. Its hydrography is influenced by the West Spitsbergen Current (WSC) transporting warm and saline Atlantic Water (AW) toward the Arctic basin. We assessed changes in fjord water properties over two decades (1999–2020) using summer hydrographic surveys performed by the Norwegian Polar Institute in the fjord, the adjacent shelf, and open ocean regions. The heat content (HC) and salinity within the fjord have increased driven by a larger inflow of AW. These trends are consistent with observations in neighboring Isfjorden but not mirrored in the properties of the WSC over the same timeframe. Therefore, hydrographic changes in these two fjords can be attributed to larger AW intrusions rather than variations in the upstream WSC properties. We hypothesize that the increased HC in Kongsfjorden is driven by shifts in the synoptic wind patterns and larger glacier meltwater release enhancing fjord shelf exchanges. Idealized modeling experiments revealed that although these modifications contribute by increasing the fjord's HC, they explain only a small portion of the observed changes, suggesting that the availability of Atlantic Water on the shelf is the dominant factor.

The article presents the results of the analysis of spatiotemporal patterns of long-term river runoff dynamics in the Ural River basin. We note the absence of statistically significant or unidirectional trends, due to the transformations of the intra-annual runoff distribution within the basin under study. Climate-induced changes in the river water availability are confirmed by the in-phase character of runoff fluctuations in most rivers of the Ural River basin. Five phases of runoff change have been distinguished in the study basin for 1938–2022, characterized by different duration and intensity.

The south of Eastern Siberia is a territory with contrasting natural conditions, including hydrological ones, with diverse factors of water regime formation and anthropogenic impacts on water bodies. Extreme hydrological processes whose formation is governed, in particular, by peak river runoff are typical of the region. An attention is focused on landscape hydrological and structural hydrographic research methods, analysis of the water regime formation conditions, determination of the peak river runoff parameters on the territory, and consequences of the negative impact of high river runoff on the population life. The zoning of the water-bearing capacity of the Iya River basin is carried out.

Debit banjir rencana merupakan debit maksimum yang digunakan sebagai dasar dalam perencanaan infrastruktur air seperti bendungan, jembatan, dan saluran drainase. Penelitian ini menganalisis debit banjir rencana pada suatu daerah aliran sungai (DAS) di Indonesia dengan luas 1111,69 km² untuk mendukung perencanaan bendung pada pembangkit listrik run-off river. Perhitungan debit banjir dilakukan berdasarkan data curah hujan dari stasiun penakar menggunakan metode Hidrograf Satuan Sintetik (HSS) Nakayasu. Analisis hidrologi diawali dengan perhitungan hujan rata-rata menggunakan metode Poligon Thiessen, distribusi frekuensi dianalisis dengan metode Log Pearson III yang diuji dengan metode chi-square, serta analisis probabilitas dan periode ulang hujan dilakukan menggunakan metode Mononobe. Nilai koefisien pengaliran ditentukan berdasarkan data penggunaan lahan untuk memperoleh curah hujan efektif. Hasil perhitungan menunjukkan bahwa debit banjir rencana untuk periode ulang 2, 5, 10, 25, 50, 100, dan 200 tahun berturut-turut adalah 935,138 m³/s, 1112,585 m³/s, 1201,498 m³/s, 1291,535 m³/s, 1346,449 m³/s, 1393,253 m³/s, dan 1433,899 m³/s. Hasil penelitian ini dapat digunakan sebagai dasar perencanaan bendung dan pengelolaan sumber daya air di DAS tersebut.

Data on the effect of the Chernaya River runoff on the estuarine coast during floods of various genesis were obtained based on long-term (1991–2023) and operational (2024) information from the Shelf Hydrophysics Department of Marine Hydrophysical Institute of the Russian Academy of Sciences. It was found that floods of natural and anthropogenic origin had the greatest impact on the surface water layer of the Sevastopol Bay under the conditions of regulation of river runoff by the Chernaya River reservoir. For example, an emergency discharge into the lower reaches of the reservoir in January 2024 caused the desalination of the surface water layer of a significant part of the estuarine coast up to 2–17 ‰, a phenomenon not observed in field studies over the past 30 years. During this flood, water from the adjacent part of the Black Sea with a salinity of 18–20 ‰ entered the western part of Sevastopol Bay. In the frontal zone, the horizontal gradients of water salinity reached 2–6 ‰ per km. In addition, that flood caused geomorphological changes at the estuary section of the river, flooding of adjacent areas, necessitating significant funds to mitigate adverse effects on the environment, population and economy. A comparative analysis of the average long-term salinity distribution at the surface water layer of the estuarine coast, performed taking into account the natural cyclicity of hydrometeorological characteristics, reveals a trend of increasing salinity аof the coastal water area of Sevastopol, and the analysis of salinity anomalies indicates its dependence on freshwater discharges from the Chernaya River reservoir. На основе многолетней (1991–2023 гг.) и оперативной (2024 г.) информации Отдела гидрофизики шельфа МГИ РАН получены данные о влиянии стока р. Черной на устьевое взморье в период паводков различного генезиса. Установлено, что наибольшее влияние на поверхностный слой воды Севастопольской бухты, в условиях регулирования речного стока Чернореченским водохранилищем, оказывали паводки природно-антропогенного происхожде-ния. Например, аварийный сброс в нижний бьеф водохранилища в январе 2024 г., вызвал распреснение поверхностного слоя воды значительной части устьевого взморья до 2–17 ‰, что в последние 30 лет по натурным наблюдениям не отмечалось. В период этого паводка в западную часть Севастопольской бухты поступала вода из прилегающей части Черного моря соленостью 18–20 ‰. Во фронтальной зоне горизонтальные градиенты солености воды достигали 2–6 ‰ на км. Кроме того, рассматриваемый паводок вызвал геоморфологические изменения устьевого участка реки, затопление прилегающих территорий, что потребовало значительных средств для ликвидации негативных последствий его влияния на среду, население и хозяйство. Сравнительный анализ средних многолетних распределений солености поверхностного слоя воды устьевого взморья, выполненный с учетом природной цикличности гидрометеорологических характеристик, свидетельствует о наметившемся осолонении прибрежной акватории г. Севастополя, а анализ аномалий солености – об её зависимости от сбросов пресной воды из Чернореченского водохранилища.

Volterra series was applied to river runoff phenomena to model the input-output nonlinear relation between rainfall and runoff of rivers. The application results were reported in “Electrical Engineering in Japan” (vol. 98, 101). In the report, good results from modeling and simulation were shown, meanwhile unfavorable results were also shown in some cases depending on modeling condition.

Attribution Analysis of Interannual Variability and Long-Term Trends in the Yellow River Runoff Across the Jiziwan Region During 1960–2022

River Runoff Modeling Under Conditions of Limited Data Availability

Water runoff components were evaluated for experimental river basins in the Mountain Crimea based on a two-tracer mixing model with three recharge sources. The identified recharge sources for river runoff in karstified catchments were found to include: epikarstic waters, soil-slope waters, and baseflow waters, circulating at the contact with underlying impermeable rocks. Epikarstic waters account for a considerable portion of the runoff of small rivers. Their proportions in the outlet sections increase during floods and steadily increase with an increase in water discharge, obeying logarithmic relationships. The proportions of baseflow water decrease compared with those of epikarstic waters.

A three-component mixing model with the use of geochemical tracers was adapted to experimental basins of karst aquifer systems in the Mountain Crimea. As a result, the following stable recharge sources were identified: epikarstic water, forming mostly in the near-surface fractured and weathered zone of karstifying rocks; surface–slope water with different formation mechanisms; base flow karstic water, including a mixture of groundwater in the aeration zone of karst massifs below epikarst and phreatic water, forming the low-water part of runoff hydrograph. Epikarstic water contributes much to the runoff of karst aquifer systems (>30%). Close empirical relationships were identified between the proportions and water discharges at the outlet sections.

Abstract A wave–current coupled numerical model with 3D radiation stress formalism is used to study baroclinic effects, specifically stratification and baroclinic pressure gradient force (BcPGF), on wind-wave-driven flows, separated as vertically sheared flows and vertically homogeneous flows. Numerical experiments are conducted under ideal offshore winds of 8 m s−1. Results show that stratification enhances the two-layer structure of the wave-driven sheared flow, while BcPGF has minimal impact. Stratification and BcPGF have limited influence on the direction of the wave-driven depth-averaged circulation, but they can enhance the total circulation by promoting the upper one. In the upper layer where form drag dominates, the competition between the vertical form drag divergence (FDD) and turbulent stress divergence (TSD) plays a critical role in shaping the wave-driven flow. Stratification reduces vertical eddy viscosity Km, suppressing the growth of TSD associated with the vertical shear of velocity, which facilitates the FDD driving the upper outflow. Likewise, stratification can enhance the effect of FDD curl on the upper horizontal circulation by limiting the growth of TSD curl related to the vertical shear of vorticity. Additionally, low Km reinforces geostrophic effect and therefore enhances the lateral circulation. Baroclinic torque contributes to reducing the vertical variation of vorticity and the growth of TSD curl, indirectly improving the effectiveness of FDD curl in driving the upper circulation. Stratification undergoes fortnightly adjustments due to the spring–neap cycle, leading to the synchronized variation in the strength of wave-driven flow, particularly its vertically sheared component. During neap tides with weak tidal forcing and well-developed stratification, wave-driven sheared flow, horizontal circulation, and lateral circulation are stronger. Significance Statement The aim of this study is to enhance our comprehension of the impact of baroclinic processes on wind-wave-driven flows in wind-dominated regimes. During summer, wave-driven flows exhibit noticeable vertical shearing, which differ from those observed in winter. This is particularly important because during summer, river runoffs generate strong stratification and introduce large quantities of terrigenous materials into coastal oceans. Consequently, wave-driven flows may play a crucial role in bay-shelf exchange, which has been given in few studies. Our findings highlight the influence of baroclinic processes on turbulent stress divergence, which can enhance wave-driven flows, both the vertically sheared and the vertically homogeneous components, especially during neap tides.