Significant alterations in the hydrological regimes of major Arctic basins, evidenced by earlier freshet timing and increased winter runoff, have been extensively documented. However, the response of streamflow in small catchments (<1000 km(2)), characterized by minimal or even absent winter discharge, to climate change remains poorly understood. In the Shestakovka River Basin (170 km(2)), located in the continuous permafrost zone of the middle Lena River, the number of days with river flow increased by 16 between 1951 and 2022. The average annual runoff was approximately 24.2 mm and increased significantly by 1.4 mm/decade from 1951 to 2022, with the highest rate in spring (1.2 mm/decade), followed by autumn (0.2 mm/decade). Notably, precipitation did not exhibit significant changes, indicating that other indirect factors may have contributed to these hydrological shifts. By incorporating the thawing-freezing index (TIFI) into the Budyko framework, it becomes evident that enhanced permafrost thaw, driven by rising temperatures, is a key factor contributing to these changes. Isotope analysis further indicated a shift in river runoff from spring nival runoff to suprapermafrost groundwater runoff during summer and autumn. This shift is consistent with enhanced hydrological connectivity through taliks (perennially thawed ground in a permafrost environment), which may facilitate the transfer of shallow suprapermafrost groundwater to the river network. The occurrence of aufeis further supports the presence of seasonal suprapermafrost groundwater discharge. Understanding these hydrologic changes in small, high-latitude catchments is essential for predicting Arctic river discharge in response to climate warming.

Rapid climate warming and intensified human activities are causing profound alterations in terrestrial hydrological systems. Understanding shifts in hydrological regimes and the underlying mechanisms driving these changes is crucial for effective water resource management, watershed planning, and flood disaster mitigation. This study examines the hydrological regimes of the Heilongjiang-Amur River Basin, a transboundary river basin characterized by extensive permafrost distribution in northeastern Asia, by analyzing long-term daily meteorological (temperature, precipitation, evaporation) and hydrological data from the Komsomolsk, Khabarovsk, and Bogorodskoye stations. Missing daily runoff data were reconstructed using three machine learning methods: Convolutional Neural Networks (CNN), Long Short-Term Memory Networks (LSTM), and Convolutional Long Short-Term Memory Networks (CNN-LSTM). Trend analysis, abrupt change detection, and regression techniques revealed significant warming and increased actual evapotranspiration in the basin from 1950 to 2022, whereas precipitation and snow water equivalent showed no significant trends. Climate warming is significantly altering hydrological regimes by changing precipitation patterns and accelerating permafrost thaw. At the Komsomolsk station, an increase of 1 mm in annual precipitation resulted in a 0.48 mm rise in annual runoff depth, while a 1 °C rise in temperature led to an increase of 1.65 mm in annual runoff depth. Although annual runoff exhibited no significant long-term trend, low-flow runoff demonstrated substantial increases, primarily driven by temperature and precipitation. These findings provide critical insights into the hydrological responses of permafrost-dominated river basins to climate change, offering a scientific basis for sustainable water resource management and strategies to mitigate climate-induced hydrological risks.

The article presents the results of instrumental measurements of stem sap flow with the use of sap-flowmeters in the trunks of white fir (Abies nephrolepis), the analysis of the main factors of the process of moisture transport in tree trunks, and the results of modeling hourly series of xylem flow rates. The analysis of factors was made with the use of the method of principal components, and the reproduction of individual series of xylem consumption was based on a multiple linear regression model. The evaluated volume of the transported moisture flux in fir trees over the vegetation period in 2020 varied from 1720 to 5620 L, depending on tree diameter, and the mean daily velocity of stem sap flow in the xylem varied from 0.3 to 1.0 cm/h. Regression analysis was used to find the optimal structure of the empirical model, which includes two predictors—air temperature and humidity. The empirical coefficients of regression equations were determined for each tree based on calibration samples. The results of testing on long enough test samples showed that the model series of xylem discharge on a complete sample (from May to October) for three test trees out of four are close to the measured values: the coefficient of correlation is 0.79–0.88, Nash–Sutcliffe coefficient is 0.62–0.85. The simulation efficiency improves significantly when samples for individual months are used: the correlation coefficient is 0.87‒0.94, the Nash–Sutcliffe coefficient is 0.73‒0.97.

Using remote methods and materials for meteorological observations, climate changes and the area of 36 thermokarst lakes located in the Anadyr lowland in Chukotka over a 65-year period were analyzed. More than 20 lakes were studied by field methods. With an increase in the average annual air temperature by 1.8°C and an increase in the amount of annual precipitation by 135 mm, the total area of the lakes mirror decreased by 24%. Cryogenic processes have had a significant impact on the decrease in the water quantity of lakes. Thermal erosion in drainage channels has led to multiple discharges of water in abnormally warm years. The heaving of permafrost in the coastal zone affected the reduction of the lake catchment area. If the trends of climate change continue, further drainage of large lakes and an increase in the number of small sag pond is expected in the next 25 years.

Water quality degradation and eutrophication of lakes are global ecological and environmental concerns, especially shallow lakes. This study collected hydrochemical data from 2935 samples of the Chinese part of Xingkai (Khanka) Lake, based on 40 published papers spanning the period from 2001 to 2023. Using the water quality index (WQI), improved geo-accumulation index (Igeo), and redundancy analysis (RDA), we analyzed the overall contamination characteristics of the water environment in Xingkai Lake. Additionally, we explored the impact of climate change and human activities on the lake’s water quality. The results showed that the annual WQI for Xingkai Lake ranged from 47.3 to 72, with a general downward trend, indicating improving water quality. Notably, the average WQI in May and total nitrogen (TN) content decreased significantly, signaling further improvement in water quality. The average concentration of TN in sediments was 1401.3 mg/kg, reflecting mild contamination. The Igeo values for the heavy metals Hg and Cr were greater than 1, indicating moderate contamination, while the Igeo values for Cd and Pb were between 0 and 1, which is in the range of uncontaminated to moderately contaminated. Land use and climate change (average annual temperature and annual precipitation) were key factors influencing water quality, with cumulative explanatory ratios of 67.3% and 50.1%. This study utilized land-use change as a metric for human activities, highlighting the potential impacts of climate change and human activities on the water quality of Xingkai Lake. It offers vital insights for the sustainable management of Xingkai Lake and provides valuable references into the management of similar transboundary lakes.

ABSTRACTClimatic and environmental change is leading to increased frequency and intensity of permafrost degradation processes; however, our knowledge of their mechanisms and rate is still limited. We examined structure of deposits, surface topography, and weather conditions during the initiation of a thermo‐erosion gully in eastern Siberia and monitored its changes between 2020 and 2022. The initiation of the gully was caused by a combination of processes: (1) the catchment area of the gully was artificially increased several decades ago as a result of the interception of runoff by the winter road; (2) ice‐wedge degradation led to surface runoff concentration above the gully head, while a large volume of ground ice remained in other parts of the slope, and frost cracking continued; (3) the entry of water into frost cracks formed underground tunnels; and (4) high air temperatures and heavy rainfall immediately before the gully appearance resulted in the expansion of the tunnels and collapse of their roof. In 2 years, the volume of the gully reached 1000 m3; at least 40% of that volume consists of ground ice. The gully development did not significantly change the water chemistry due to significant water freshening caused by melting of ground ice.

The effect of time aggregation (1, 3, 6, 12, and 24 h) of input data on the efficiency and parameter values of the conceptual HBV model was studied based on special field observations, carried out on four small experimental catchments (3.1–26.3 km2) in the basin of the Pravaya Sokolovka R. (Verkhneussuriiskii gage, upper Ussuri R., southern Primorskii Krai) in 2012–2022. It was shown that a decrease in the calculation step leads to a gradual decrease in the simulation quality, calculated with the use of Nash–Sutcliff coefficient. The model demonstrates high efficiency in calculating the hydrographs of high floods for all examined catchment areas, but does not reproduce diurnal variations of water discharges (0.1–1.0 mm layer) during low-water season. The model proportions of runoff genetic components, at which the system gradually passes to the predominance of some genetic component, do not depend on the calculation step and have relatively constant values. At the same time, an increase in the calculation time step also leads to a successive increase of the model water discharges, expressed in mm of layer thickness, by a factor of about 2. The regularities in the variations of the parameters in the block describing the formation and transformation of HBV, as well as maximal measured precipitation totals at changes in the time step for rains ≥30 mm/day can be well approximated by power relationships with exponents 0.3–0.6. It was supposed that for high-intensity rains, the dependence of maximal precipitation amounts on the aggregation time interval can have an effect on the values of parameters of HBV-type models.

Приведены результаты инструментальных измерений стволового сокодвижения с помощью датчиков сокодвижения ("sap-flowmeters") в стволах пихты белокорой (Abies nephrolepis), анализ основных факторов процесса транспорта влаги в стволах деревьев и результаты моделирования часовых серий расходов ксилемного потока. Анализ факторов выполнен методом главных компонент, а воспроизведение индивидуальных серий ксилемного расхода – на основе модели множественной линейной регрессии. Оцененный объем транспортируемого потока влаги в экземплярах пихты в 2020 г. за вегетационный период в зависимости от диаметра дерева составил от 1720 до 5620 л, а среднесуточные скорости сокодвижения в ксилеме – от 0.3 до 1.0 см/ч. На основе регрессионного анализа установлена оптимальная структура эмпирической модели, которая включает в себя два предиктора – температуру и влажность воздуха. По калибровочным выборкам для каждого дерева определены эмпирические коэффициенты регрессионных уравнений. Результаты проверки на достаточно длинных тестируемых выборках показали, что модельные серии ксилемного расхода по полной выборке (с мая по октябрь) для трех экспериментальных деревьев из четырех достаточно близки к измеренным: коэффициент корреляции составляет 0.79–0.88, коэффициент Нэша–Сатклиффа – 0.62–0.85. Качество моделирования существенно улучшается в случае использования выборок по отдельным месяцам: коэффициент корреляции – 0.87–0.94, коэффициент Нэша–Сатклиффа – 0.73–0.97.

Изотопный состав природной воды отражает ее приуроченность к различным звеньям гидрологического цикла, изменяясь в процессе фазовых переходов (испарения, транспирации, конденсации, замерзания, оттаивания), а также при взаимодействии воды с водовмещающими средами (горными породами, почвами, воздушными массами, биотой). В статье впервые на основе детальных натурных исследований, выполненных в период с 2013 по 2016 год в экспериментальных малых горных речных бассейнах, анализируется внутригодовая и межгодовая динамика содержания изотопов 2Н и 18О в основных географических типах вод, циркулирующих в летне-осенний период в типичных речных бассейнах горной страны Сихотэ-Алинь (Приморский край Российской Федерации). Показано, что для малых речных бассейнов вблизи морского побережья характерен более тяжелый изотопный состав дождевых, речных и почвенных вод. Обосновывается предварительный вывод о том, что в относительно влажные годы воды континентальных горных районов Приморья по изотопному составу в среднем легче в сравнении с районами побережья приблизительно в 1,5 раза. Для речных водосборов, расположенных прибрежно-морских районах, почвенные воды и воды устойчивых приповерхностных склоновых потоков в изотопном отношении почти неразличимы, тогда как для континентальных водосборов почвенные воды близки по содержанию 18О и 2Н к речным водам, а воды склоновых потоков отличаются чуть более легким, чем речные воды, изотопным составом. В целом близкие значения природных изотопов в почвенных и речных водах обоих районов подтверждают полученные ранее с помощью природных химических трассеров выводы о в целом преобладающей доли склоновых вод – почвенных вод и вод приповерхностных склоновых потоков – в питании малых горных рек Сихотэ-Алиня и, соответственно, относительно невысокий объем подземного питания и низкие значения доли дождевых вод в речном стоке.

This study is focused on the comparison of streamflow composition simulated with three well-known rainfall–runoff (RR) models (ECOMAG, HBV, SWAT) against hydrograph decomposition evaluated with End-Member Mixing Analysis (EMMA). In situ observations at two small mountain testbed catchments located in the south of Pacific Russia are used. All applied RR models and EMMA analysis demonstrate that two neighboring catchments disagree significantly on the mutual dynamics of the runoff sources. The RR models' benchmark test is based on proximity to EMMA hydrograph composition. Different aggregation intervals (season, month, and pentad) were applied to find a reasonable generalization period ensuring the clarity of results. ECOMAG is most conformable to EMMA outcome; HBV reflects flood events well enough; SWAT exhibits distinctive behavior compared to the other models. It is shown that, along with standard efficiency criteria of simulated and observed runoff proximity, EMMA analysis might provide useful auxiliary information for the validation of modelling results.

Эрозионные процессы играют важную роль в выносе продуктов разрушения мерзлых пород. С целью выявления темпов и механизмов эрозионных процессов в условиях деградации мерзлых пород были типизированы формы флювиального рельефа малых водосборов в предгорьях Хараулахского хребта, охарактеризована их морфология, условия образования и динамика за 2019-2022 гг. Наиболее динамичны формы рельефа, связанные с вытаиванием жильных льдов: термокарстовые ложбины стока, рытвины и эрозионно-термокарстовые овраги. Термоэрозионные овраги, формирующиеся в отложениях без жильных льдов, растут при аномально высоких паводках, а в остальное время их борта медленно оползают под действием снежников. В верховьях малых рек происходит аккумуляция наносов, вынесенных из оврагов и рытвин. Русла рек и ручьев начальных порядков стабильны, что характерно и для других районов криолитозоны. Различия в динамике разных типов эрозионных форм можно объяснить усилением теплового, а не механического воздействия водных потоков на мерзлые отложения, которое наблюдается в условиях повышения температур воздуха при стабильном количестве осадков на севере Якутии. Erosion plays an important role in removing permafrost degradation products. In order to identify the rates and mechanisms of erosion in degrading permafrost, fluvial landforms in small catchments at the foothills of the Kharaulakh Range were typified, and their morphology, formation conditions, and dynamics for 2019-2022 were characterized. The most dynamic landforms associated with melting ice wedges were thermokarst runoff troughs (water tracks), rills, and thermoerosional gullies. Thermoerosional gullies forming in sediments without wedged ice grow upon very high floods; in the rest of the time, their sides slowly slide down under the action of snowfields. Sediments from gullies and rills are deposited in the upper reaches of small rivers. The channels of small rivers are relatively stable, which is also typical of other permafrost regions. Differences in the dynamics of erosional landforms can be explained by an increase in the thermal rather than mechanical impact of water on frozen deposits, which is observed with the rise in air temperature against the background of relatively stable precipitation in the north of Yakutia.

The problems of biodiversity reduction and degradation of river ecosystems in the Russian Far East require urgent solutions. This is especially important for areas of intensive development and urbanized territories that are located in the areas of the strongest anthropogenic impact. In order to understand the processes taking place in such ecosystems, an adequate assessment of their ecological state is necessary, based on reliable methods of integrated assessment adapted to regional conditions. To this end, a long-term scientifi c project «Development of methods for a comprehensive assessment of the ecological state of East Russian streams and rivers under anthropogenic infl uence» was initiated. The Muravyov- Amursky Peninsula, on which the Vladivostok urban agglomeration is located, was chosen as a model territory.

The results of long-term field studies on small catchments in the upper reaches of the Ussuri River (Primorskii krai, Pacific Russia) are presented. By virtue of modern means of observation, a unique dataset was obtained to record effectively the complicated runoff formation process in small low-mountain river basins. Geochemical and hydrological modeling were used jointly to describe the catchment dynamics, and genetic components of the river flow were assessed to study more thoroughly the runoff processes and to evaluate the runoff modeling accuracy factors.

Изотопный состав природной воды отражает ее приуроченность к различным звеньям гидрологического цикла, изменяясь в процессе фазовых переходов (испарения, транспирации, конденсации, замерзания, оттаивания), а также при взаимодействии воды с водовмещающими средами (горными породами, почвами, воздушными массами, биотой). В статье впервые на основе детальных натурных исследований, выполненных в период с 2013 по 2016 год в экспериментальных малых горных речных бассейнах, анализируется внутригодовая и межгодовая динамика содержания изотопов 2Н и 18О в основных географических типах вод, циркулирующих в летне-осенний период в типичных речных бассейнах горной страны Сихотэ-Алинь (Приморский край Российской Федерации). Показано, что для малых речных бассейнов вблизи морского побережья характерен более тяжелый изотопный состав дождевых, речных и почвенных вод. Обосновывается предварительный вывод о том, что в относительно влажные годы воды континентальных горных районов Приморья по изотопному составу в среднем легче в сравнении с районами побережья приблизительно в 1,5 раза. Для речных водосборов, расположенных прибрежно-морских районах, почвенные воды и воды устойчивых приповерхностных склоновых потоков в изотопном отношении почти неразличимы, тогда как для континентальных водосборов почвенные воды близки по содержанию 18О и 2Н к речным водам, а воды склоновых потоков отличаются чуть более легким, чем речные воды, изотопным составом. В целом близкие значения природных изотопов в почвенных и речных водах обоих районов подтверждают полученные ранее с помощью природных химических трассеров выводы о в целом преобладающей доли склоновых вод – почвенных вод и вод приповерхностных склоновых потоков – в питании малых горных рек Сихотэ-Алиня и, соответственно, относительно невысокий объем подземного питания и низкие значения доли дождевых вод в речном стоке. The isotopic composition of natural water reflects its confinement to various links of the hydrological cycle, changing during phase transitions (evaporation, transpiration, condensation, freezing, thawing), as well as during the interaction of water with water-containing media (rocks, soils, air masses, biota, etc.). In the article, for the first time based on detailed field studies in the testbed small mountain river basins in 2013–2016, the intra-annual and inter-annual dynamics of the 2H and 18O isotopes in the main geographical types of water circulating in warm period in typical river basins of the mountainous country of Sikhote-Alin (Primorsky Krai, Russian Federation) are analyzed. We show that rain, river and soil waters at the catchments near the seacoast have a heavier isotopic composition. A preliminary conclusion is substantiated that in relatively humid years, the waters of the continental mountainous regions of Primorye are, on average, lighter in isotopic composition than those in the coastal regions by about 1.5 times. For coastal-marine river catchments, soil water and water of near-surface slope flows are almost indistinguishable in isotope ratio, while for continental catchments, soil water are close in 18O and 2H to river water, and slope water differ in a slightly lighter isotopic composition. In general, close values of natural isotopes in soil and river water of the both studied areas confirm the conclusion obtained with natural chemical tracers about the prevailing total share of slope water – soil water and water of near-surface slope flows – in the feeding of small mountain rivers in the Sikhote-Alin mountains and, accordingly, relatively low groundwater recharge and low values of the share of rainwater in river flow.

The article considers the theory, methods, and some results of four-year field studies of the processes of runoff formation on a small freezing experimental river catchment in a continuous thick (400 m) permafrost zone (the Republic of Sakha (Yakutia)) based on data on natural water chemistry. The analyzed problems include the seasonal and daily dynamics of river flow in the warm season, the concentrations of some dissolved substances in different types of water, as well as the role of channel widenings, supra-permafrost water, and aufeises in flow formation. Various types of relationships between water discharges and the concentrations of some dissolved substances are described under varying hydrothermal conditions. The role of nonfreezing lake-like channel widenings (bochags) in the regulation of freshet flow of water and dissolved matter is evaluated. The efficiency of the automated digital registration of the level, temperature, and specific electric conductance of water with a high time resolution at hydrological gages is discussed, especially, as applied to the rapid processes in a river.

The article gives the results of generalization of a short-time expedition hydrological–hydrochemical survey in an arctic river basin in the northeastern part of Chaunskaya Lowland in the northern Chukotka, carried out in July 2020. At a scale of a small Yanranaivaam River basin, the structure of water masses was analyzed, and the catchments of individual tributaries with intense development of cryogenic processes were identified; these processes have an effect on water chemistry, in particular, in a higher concentration of hydrocarbonate ions, dissolved ferrum, and dissolved organic carbon. Two-tracer mixing model was used to identify and evaluate the contributions of water sources and their spatial relationships at the moment of survey. The main river water sources are atmospheric waters (mostly snowmelt water), slope soil water of the seasonally thawed layer (STL), and melt water of bald-mountain ice. The dominating water source in the catchments of the middle and upper parts of the basin is atmospheric water (67–78%), and that in the catchments of the lower part of the basin is STL soil water (59–64%). River recharge by meltwater of bald-mountain ice is typical of the entire basin, and at the moment of survey it accounted for 10–14% of the total.

The specific features of the parameterization and verification of FCM model were analyzed, and the data published before, as well as new results of the authors’ field observations, are systematized. The parameterization algorithms and the results of model testing in different regions with the predominance of rain floods in river regime are described. The basis and empirical confirmation of some principal hypotheses of FCM are discussed and the so-called effect of basin buffer storage is considered. This most vivid manifestation of the nonlinearity of the extreme runoff formation is, though a rare, but principally important phenomenon in the formation of extraordinary rain floods.

The article analyses landscape factors that determine the runoff of small Arctic and Subarctic rivers in the far northeast of Asia. The paper considers hydrography, structure of permafrost landscapes and their hydro-chemical characteristics, and the spatial dynamics of low-water runoff in the basins of the Ugolnaya-Dionisiya and Yanranayvaam rivers. It has been established that sustainable water intake depends on the ratio of land-scapes generating and depositing the permafrost runoff, namely Arctic char gravelly shrub tundra, lowland tussock tundra and hummock swamps. The low-water runoff of 20-50 l/km2·sec is typical for the sources of rivers, where seasonal char ice melts in the slope deposits and condensation waters are formed. Melt water of sea-sonal intra-surface soil ice on the gentle slopes of tundra hummocks provides specific runoff of 10-20 l/km2·sec. Upland and lowland marshes deposit above-frozen waters, and their runoff is less than 10 l/km2ˑsec. Using the example of two catchment basins, it is shown that the decrease in precipitation in the north of Chukotka is almost completely compensated by the formation of condensation waters. At the same time, inground seasonal infiltration soil ice is replaced in Arctic landscapes by infiltration-condensation char ice, and its melt water makes up for the loss of surface runoff.

It is known that atmospheric pressure surges affect the discharge of underground water sources in large artesian basins. In southern latitudes, the groundwater tables change insignificantly following the diurnal variations of atmospheric pressure. There is no information on the influence of rapid changes in atmospheric pressure on the position of the surface of the suprapermafrost waters and river flow in the Arctic region. The study of the diurnal course of the level of underground suprapermafrost and surface waters was carried out to identify the links of river flow with atmospheric phenomena and cryogenic processes. It was found that the daily atmospheric pressure drop with an amplitude of 1.2 kPa in the area of the small Ugolnaya-Dionisia river, located in the Anadyr lowland in Chukotka, led to a simultaneous decrease and then an increase in the level of suprapermafrost underground and surface river basin waters by 2.5-7.8 cm. This corresponds to a short-term decrease and then an increase in the river water discharge by more than 3.5 times. To clarify the factors that determine the mechanism of the influence of atmospheric pressure on the water level and river flow, a consideration of the hydrophysical properties of aquifer-containing peat soils was carried out. Compression tests revealed that the elasticity of the peat soils horizon remains within the range of 0-15 kPa, which contributes to a dynamic change in porosity even with a slight change in the external load. This means that the atmospheric pressure changes during weather development are sufficient to modify the water capacity of peat soils and deposit them, and then discharge a part of the suprapermafrost flow. The discovered pressure impact in the tundra soils of the permafrost zone is a unique mechanism for providing plants with moisture during droughts and reducing the risk of tundra fires. As part of the further study of the pressure impact, it is planned to conduct laboratory experiments to determine the quantitative parameters of the change in the peat soils moisture capacity under pressure drops in the atmosphere. Mathematical modeling of the capillary moisture capacity of peat soils will be performed under conditions of ambient load changes. The results of experiments and theoretical studies are assumed to be useful for predicting the flow of bogged-up river basins, design of reclamation, and irrigation of areas of peat soils distribution.