Spring Flood Research Articles

Meteorologically-Related Factors Leading to the 2008, 2018, and 2019 Major Spring Floods in the Transboundary Saint John River (Wolastoq) Basin

Abstract The flood-prone Saint John River (SJR, Wolastoq), which lies within a drainage basin of 55,110 km2, flows a length of 673 km from its source in northern Maine, United States to its mouth in southern New Brunswick, Canada. Major industries in the basin include forestry, agriculture, and hydroelectric power. During the 1991–2020 reference period, the SJR basin (SJRB) experienced major spring flood events in 2008, 2018, and 2019. As part of the Saint John River Experiment on Cold Season Storms, the objective of this research is to characterize and contrast these three major spring floods events. Given the floods all occurred during spring, the hypothesis being tested is that rapid snowmelt alone is the dominant driver of flooding in the SJR basin (SJRB). There were commonalities and differences regarding the contributing factors of the three flood years. When averaged across the upper basin, they showed consistency in terms of positive winter and spring total precipitation anomalies, positive snow water equivalent anomalies, and steep increases in April cumulative runoff. Rain-on-snow events were a prominent feature of all three flood years. However, differences between flood years were also evident, including inconsistencies with respect to ice jams and high tides. Certain factors were present in only one or two of the three flood years, including positive total precipitation anomalies in spring, positive heavy liquid precipitation anomalies in spring, positive heavy solid precipitation anomalies in winter, and positive temperature anomalies in spring. The dominant factor contributing to peak water levels was rapid snowmelt.

Mobilization of porewater Pb and Zn in response to seasonal wetting and drying within contaminated floodplains.

The mobility and bioavailability of metal contaminants such as lead (Pb) and zinc (Zn) is impacted by their interactions with other sediment constituents such as iron (Fe), sulfur (S), and organic matter, which depend on sediment redox conditions. Understanding the role that water level fluctuations have on redox conditions and subsequent impacts on metal mobility is critical for predicting impacts of increased wetting and drying cycles resulting from climate-related changes or management actions. This study measured the sediment-porewater partitioning of Pb and Zn in the Coeur d'Alene River basin downstream of the Bunker Hill Superfund Site under both flooded and seasonally dry conditions. The results show that both time of year and hydrology are important when considering metal exposure risks in contaminated floodplains. For Pb, seasonal spring flooding appears to mobilize dissolved Pb in both seasonally inundated and permanently inundated areas due to increases in sediment-derived Pb that undergo desorption processes from suspended Fe and DOC. For Zn, oxygenation of floodplain sediments in the fall drives elevated dissolved Zn year-round due to limited ZnS precipitation. Wetting-drying cycles had a significant impact on Zn mobility, which could be exacerbated by climate-driven hydrological changes or floodplain management actions.

Geostatistical Model Development and Assessment of Tidal Stream Energy Resources: A Case Study of Indus Delta, Pakistan

In this paper, an approach is applied by using the Geographical Information System for the development of geostatistical models to assess available tidal stream energy resources of the Indus Delta Creek system. The mean spring tidal current of twelve different locations in the Indus Delta Creek system (Pakistan) is utilized to develop geostatistical models for the prediction of tidal currents at different locations where no data was available. Models are validated and an investigation of prediction error is carried out to select the best model. For the prediction of tidal stream data, various models are collated namely (i) Circular (ii) K-Bessel (iii) Stable, and (iv) Exponential. These models show the range of mean spring ebb current between 1.9 m/s and 2.12 m/s and the range of mean spring flood current between 1.4 m/s and 1.65 m/s. The stable model for mean spring flood current and circular model for mean spring ebb current agreed with the observed ones. Furthermore, the tidal kinetic power density model and bathymetry model are also developed for the selection of potential sites within the study area. Based on results achieved from geostatistical and bathymetry models; deployment of the suitable turbine at the study area is proposed and generation of 2754.7 MW electric power is estimated.

Influencing Factors and Ecological Risks of Organochlorine Pesticide Adsorption in Surface Sediments of Qingshui River

ABSTRACT Taking the first-level tributary of Ningxia section of the Yellow River (Qingshui River) as the study area, surface sediment samples were collected during the seasons in 2018. The distribution characteristics, pollution levels, possible sources, influencing factors, and ecological risks of organochloride pesticides (OCPs) in the surface sediments were studied. The detected mean amounts were n.d. ~10.640 (1.474) ng·g−1, and the detection rate was 80.95%. The content (mean values) of Hexachlorocyclohexanes (HCHs), Endosulfan, Chlordane, and Dichlorodiphenyltrichloroethane (DDT) with higher detection amounts and detection rates were n.d. ~0.949 (0.153), n.d. ~1.973 (0.331), n.d. ~0.271 (0.052), and n.d. ~10.583 (0.819) ng·g−1, respectively. The total OCP amounts were detected in Changshantou and Liwang research sections, which have surrounding farmlands and low water flow. The total organic carbon plays a vital role in the residue and distribution of β-HCH and Dieldrin. In a high-salinity environment, the lower-layer sediments had higher adsorption efficiencies for DDT and γ-HCH and the HCH content decreased with the increase in pH. The total nitrogen and phosphorus in sediments were among the controlling factors affecting the distribution of Endosulfan II and p,p’-DDT, respectively, but their effects on Dieldrin only appeared in the spring flood season. Further, a functional model was established with respect to the adsorption amount of various OCPs and the influencing factors. The component analysis results showed that OCPs primarily originated from historical residues; however, only small amounts of Lindane, Dicofol, Endosulfan, and Chlordane compounds have been observed recently in the local environment. Using the low-effect interval and median method for potential ecological risk assessment, Endosulfan was noted to have potential ecological risks, mainly distributed in the middle and lower reaches of the river. The reasons for the potential harm require attention and further research.

Microplastic accumulation in one-year freshwater ice: A four-year monitoring study reveals winter dynamics of microplastics

Microplastic research has reached a point where microplastics (MPs) have been found in virtually every environment studied. However, MP studies of freshwater ice are scarce, and the winter dynamics of MPs are less understood. Measuring MPs from one-year freshwater ice samples can aid understanding seasonal MP fluxes in freshwater systems. In this study we explored the same four sites close to urban/suburban areas over four subsequent years. We collected a total of 48 ice samples across all the years and sites with an average sample volume of 2.9 to 5.0 L of liquid water. In addition, we sampled an annually laminated section of bottom sediments representing these four years in seasonal resolution. MP concentrations varied considerably between years and samples, being 1–44 MPs/L in all the ice samples. The MPs found in ice were small with a mean (± average) size of 142 ± 177 μm. In total, 9 different polymer types were identified: the most common types being polypropylene, polyethylene and polyethylene terephthalate. We found that MPs accumulate to one-year freshwater ice, because the MP concentrations found from ice are one to two orders of magnitude higher than concentrations from surfaces waters in the same area. This further confirms that ice acts as a temporal repository for MPs in the aquatic freshwater systems. Our study also indicates that the properties of MPs were relatively similar in all sites around the city. The accumulation of MPs in sediments was highest during the spring flood periods, when MPs were released from the ice and snow at the catchment area of the sediment samples. We highlight the importance of monitoring to collect representative MP data from various environmental compartments.

Diversity of Macroinvertebrate Communities Following Abnormal Spring Flooding of Denton Creek, Denton County, Texas

Diversity of Macroinvertebrate Communities Following Abnormal Spring Flooding of Denton Creek, Denton County, Texas

River restoration effects on dispersal and the development of riparian seed bank: do poor seed banks limit restoration of boreal riparian zones?

In boreal streams, restoration after channelization typically consists of increasing instream geomorphic complexity with no other active restoration measures (e.g. planting) as it mainly targets fish. Unsurprisingly, this restoration fails to restore riparian vegetation within the time frames needed to meet biodiversity goals. To understand the potential role of dispersal and seed banks in the poor restoration results, we compared deposition patterns from a seed release experiment conducted during spring flood and summer low flow conditions to seed bank‐ and vegetation composition. The experiment was conducted across seven boreal streams, each differing in time since restoration (0–22 years). We found that seed deposition increased due to low flow and local flow obstruction, suggesting the importance of instream boulders. Locations where there was a high deposition likelihood in our seed release experiment had higher Shannon diversity compared to locations with a low seed deposition likelihood. Riparian vegetation composition is related to flow obstruction, while seed bank species composition is correlated to spring flood seed deposition. In general, the sampled riparian seed banks contained few seeds and species. We therefore conclude that (1) restoration of hydrogeomorphic complexity (especially instream boulders) can enhance seed deposition with some effects on species composition of the vegetation and seed bank diversity, and (2) the importance of these generally species poor seed banks for the return of species after restoration boreal streams is questionable. Other (active) methods or more time may therefore be needed to meet biodiversity goals within riparian vegetation restoration.

Prediction of long-term future runoff under multi-source data assessment in a typical basin of the Yangtze River

Study regionThree Typical Basins of the Yangtze River (YRB), China Study focusMeteorological factors, such as precipitation, are key drivers of the hydrological system and critical inputs in hydrological modeling, and accurate meteorological data are essential to simulate hydrological processes. This study compares and evaluates the CN05.1, CMFD, and ERA5-L and meteorological forcing datasets in three typical basins of the Yangtze River and predicts the future runoff changes in the basin based on CMIP6 data. New hydrological insights for the regionThis study indicated that (1) the CN05.1 data exhibit the best applicability on the interannual and intra-annual scales in YRB, while ERA5-Land performs better in the upper reaches, and CMFD is more suitable for the middle and lower reaches. (2) Future runoff is projected to initially decrease and then increase, with the inflection and inflections points of runoff occurring earlier in the ssp585 scenario compared to the ssp245. The risk of spring flooding is increasing in CS and JZ river basin, and the risk of flooding is decreasing in the FH River Basin as the flood peaks are earlier. (3) Significant trend changes are anticipated in the future, with climate change contributing over 90 % of the runoff changes in the CS, while human factors will increasingly influence the JZ and FH basins.

Changes in water regime in the high-mountain region of the Terek River (North Caucasus) in connection with climate change and degradation of glaciation

In this study, we adapted the ECOMAG model of the runoff formation for analysis of the Terek River basin using comprehensive hydrometeorological information as well as data on soils, landscape, and glaciation. To take account of regional characteristics of the glaciation, the additional ice module was used with the model. This improvement has resulted in a satisfactory agreement between the modeled runoff hydrographs and the observed ones. In our simulations we used the updated glacier cover predictions from the- global glaciological model GloGEMflowdebris together with regional climate projections from the CORDEX experiment to determine possible future changes in the Terek River flow in the 21st century. The results show that the runoff will change between −2% and +5% according to the RCP2.6 scenario, and from −8% to +14% in the RCP8.5 scenario. The directedness of the runoff changes in particular subbasins of the River will essentially depend on the altitude position of the snow and glacier feeding zones, that is responsible for the intensity of their degradation. Thus, in the RCP8.5 scenario, the flow of the Chegem River will begin to decrease significantly in the second half of the 21st century. In contrast, the predicted increasing of the runoff in Malka and Baksan rivers, which are primarily fed by meltwater from glaciers and snow on Elbrus and other high-mountain zones, is expected to be continued until the end of the century. But this increase may be caused only by a growth of a part of the snowmelt feeding due to greater winter precipitation. The model estimates confirm the present-day observed trends within the intra-annual runoff distribution, demonstrating the earlier start of the spring flood, a decrease in summer runoff volumes and then its increase in the autumn months. The results of the research may be used for more efficient management of water resources in the North Caucasus in the future, including electricity generation and water supply.

Ecosystem engineering at the regional scale—Beaver impact on floodplain pondscapes

Currently, global climate change has led to alterations in river discharge. In Eastern and Southern Europe, decreasing spring flood levels are observed, leading to drying and overgrowth of floodplain water bodies, especially in semiarid regions. Under such conditions, the scale of influence of the ecosystem engineer, the Eurasian beaver, which is often considered one of the tools for wetland restoration, is of interest. The aim of this study was to analyze beaver digging activity on a regional scale by estimating beaver abundance and occurrence patterns in floodplain pondscapes of the upper Khoper River and by quantifying changes in the morphometric parameters of water bodies due to the impact of this species. During the field survey and remote GIS analysis, 80 water bodies were surveyed. The results of the field study revealed that 67 % of the water bodies were inhabited by beavers, 21 % of which were inhabited by large families. Only 5.6 % of the water bodies had no traces of beaver activity. Approximately 30 % of all the water bodies under study were significantly altered, and 10–13 % were almost completely excavated by beavers. The remote sensing analyses revealed that beavers digging increased the area of the water bodies by an average of 40 %, the perimeter of the water bodies by an average of 60 %, and the shoreline development (complexity) by 60 %. In total, beaver-created structures occupied 0.05 km2 in the floodplain of the upper reaches of the river, and their total length reached 30.5 km. The main factor influencing beaver digging activity was the drying of water bodies; the values of morphometric parameters altered or created by beavers increased significantly at large differences in the maximum and minimum water levels. Our results highlight the importance of ecosystem engineering activities at the regional scale in the face of climate change and provide insight into the possibility of considering beaver digging activities as an inspiration for the development of nature-based strategies.

Internal tidal dynamics and associated processes at highly supercritical slopes in Banda Sea: Lessons from the oceanic island of Ambon, eastern Indonesia

Interactions between the deep sea and steep-sloping oceanic islands generate physical processes with potential impacts on sediment resuspension and ocean productivity. While studies have been conducted in the open oceans, those focusing on oceanic islands of the deep Banda Sea in eastern Indonesia are lacking. Here, we present the first observational evidence of vertical mechanisms (i.e. internal tidal reflection, internal hydraulic jumps) at the highly supercritical slope in outer Ambon Bay (OAB) in Ambon Island – an oceanic island in the Banda Sea. A 23-h CTD yoyo experiment combined with ADCP measurements conducted during spring flood and ebb tides demonstrated tidally-varying vertical temperature, salinity and density profiles. During spring flood tide, incoming internal tides were reflected by OAB's highly supercritical slope back to the deep sea with isopycnals and isotherms showing sharp downward plunges (downward vertical velocity = 6.5–8.3 × 10−3 m/s), and the internal tidal amplitude reaching 90–110 m. The reflection during flood tide caused seaward overturning flow at deeper depths despite the prevailing landward flow at the upper layers. During spring ebb tide, internal hydraulic jumps (upward vertical velocity = 6.1–6.48 × 10−3 m/s) occurred to rebound the downward plunges of isopycnals and isotherms as flood tide relaxed with the observed amplitude of internal tides of 90 m. We also observed weakened seaward ebb flow during the isothermal uplifting (when hydraulic jumps occurred), and subsequent intensified landward flow at the end of spring ebb tide indicating strong upslope flow when isotherms reached the maximum shoaling depths. Taken together, the observed vertical mechanisms indicate the conservation of energy at the highly supercritical slope of OAB evident by the comparable vertical velocities. An embedded turbidity-chlorophyll profiler in the CTD reveals that internal tidal activities at the highly supercritical slopes OAB may induce bottom nepheloid layers, and influence ocean productivity by regulating the vertical distribution of phytoplankton biomass.

Differential Spatiotemporal Patterns of Major Ions and Dissolved Organic Carbon Variations from Non-Permafrost to Permafrost Arctic Basins: Insights from the Severnaya Dvina, Pechora and Taz Rivers

The Arctic river basins, among the most sensitive regions to climate warming, are experiencing rapid temperature rise and permafrost thawing that profoundly affect their hydrological and hydrochemical systems. However, our understanding of chemical export from Arctic basins to oceans remains limited due to scarce data, particularly in permafrost-dominated regions. This study examines the spatiotemporal variations and seasonal dynamics of major ions (Na+, K+, Mg2+, Ca2+, Cl−, SO42−) and dissolved organic carbon (DOC) concentrations across three river basins with varying permafrost extents: the Severnaya Dvina (2006–2008, 2012–2014), the Pechora (2016–2019) and the Taz Rivers (2016–2020). All the data were sourced from published Chemical Geological researches and were taken from Mendeley and PANGAEA datasets. Our results showed that DOC concentrations ranged from 1.75 to 26.40 mg/L, with the Severnaya Dvina River exhibiting the highest levels of DOC concentrations, alongside significantly elevated ion concentrations compared to the other two basins. A positive correlation was observed between DOC concentrations and river discharge, with peaks during the spring flood and summer baseflow due to leaching processes. The Severnaya Dvina and Pechora Rivers exhibited the highest DOC values during the spring flood, reaching 26.40 mg/L and 8.07 mg/L, respectively. In contrast, the Taz River had the highest runoff during the spring flood season, but the DOC concentration reached its highest value of 11.69 mg/L in the summer. Specifically, a 1% increase in river discharge corresponded to a 1.25% rise in DOC concentrations in the Severnaya Dvina River and a 1.04% increase in the Pechora River, while there was no significant correlation between runoff and DOC concentrations in the Taz River. Major ion concentrations demonstrated a negative correlation with river discharge, remaining relatively high during winter low-flow period. A robust power-law relationship between river discharge and concentration of DOC and major ions was observed, with distinct variations across the three river basins depending on permafrost extent. The Pechora and Taz Rivers, characterized by extensive permafrost, exhibited increasing trends in river discharge and DOC concentrations, accompanied by decreasing major ion concentrations, whereas the non-permafrost-dominated Severnaya Dvina River basin showed the opposite pattern. The Taz River, with the most extensive permafrost, also displayed a delayed DOC peak and more complex seasonal ion concentration patterns. These findings highlight the importance of varying permafrost extents and their implications for water quality and environmental protection in these vulnerable regions.

Establishing perennial strips in a cultivated floodplain for habitat restoration: monitoring over 4 years and success drivers

Floodplains, one of the most biologically diverse and productive ecosystems, are under threat from intensive crop production. Implementing perennial strips alongside agricultural ditches and streams could reduce negative impacts of intensive agriculture and restore wildlife habitats in cultivated floodplains. To successfully set up perennial strips, it is important to understand the parameters that drive their establishment. Here we assessed the establishment success of reed canarygrass (RCG; Phalaris arundinacea) strips in the lake Saint Pierre (LSP) floodplain, Québec, Canada by monitoring RCG biomass and vegetation height over 4 years and identify the factors driving its establishment. A total of 26 RCG strips across six municipalities of LSP were monitored. Biomass and vegetation height of RCG increased over time to reach an average of 5048 kg/ha in year 4 and 104 cm in year 3 in established strips. The RCG established successfully in 62% of surveyed plots and three environmental parameters explained 61% of this success. Establishment of RCG was most successful when a first rain came right after seeding (<3 days). High clay content and low elevation were associated with establishment failures. Overall, our results highlight the ability of RCG strips to restore dense perennial vegetation cover in cultivated floodplain, thereby providing suitable habitat for fish spawning during spring floods. This study provides significant insight into the drivers of establishment of perennial grass strips in highly constrained cultivated areas such as floodplains.

НЕКОТОРЫЕ МОМЕНТЫ СОВЕРШЕНСТВОВАНИЯ ПРОГНОЗИРОВАНИЯ ОБЪЕМА ПОЛОВОДЬЯ В УСЛОВИЯХ ОГРАНИЧЕННЫХ ГИДРОМЕТЕОРОЛОГИЧЕСКИХ ДАННЫХ

The article deals with methods of improving the forecasting of the volume of spring flood runoff. The main objects of the study are the Oba, Ulbi and Dresvyanka rivers, which are lateral tributaries of the Shulba reservoir. These rivers belong to the type of rivers with spring-summer flooding and extended flow for more than 2...3 months. The aim of the study is to develop a methodology for flow forecasting based on the relationship between snow accumulation and river flow in spring and summer periods. The results of the study of hydrological and meteorological factors affecting runoff formation are presented, and equations for forecasting runoff during spring and summer floods and its duration are derived. The obtained multiple regression equations demonstrated high accuracy in modelling flood volumes, with correlation coefficients between observed and predicted data ranging from 0,79 to 0,91. According to S/σ calculations, the results obtained indicate good reproducibility of the observed flood volumes, with values ranging from 0,46 to 0,53.

Effects of polluted groundwater on chum salmon (Oncorhynchus keta) survival and body size

This study reports the effect of spatial variation in hyporheic water, partially influenced by urban-polluted groundwater, on the early life stage of chum salmon (Oncorhynchus keta) in the Toyohira River, Northern Japan. We hypothesized that increased groundwater influence would reduce the survival rate and body size of O. keta due to the combined effects (i.e., growth retardation effects) of chemical toxicants, low dissolved oxygen (DO), and high winter temperatures. Experimental tests were conducted in field and laboratory conditions to address the difficulties associated with field observations of fry emergence during snowmelt floods in spring and to examine the independent effects of water pollution in groundwater in relation to temperature and DO. Artificially fertilized eyed eggs, alevins, and fry of O. keta were monitored for several months with varying exposure to groundwater from winter to early spring. We noted that groundwater affected the fish by reducing their size and weight by >10% and by increasing their mortality in both tests. Moreover, independent effects of water pollution were identified in the swim-up fry stage in laboratory experiments, along with growth-retarding effects from warmer groundwater temperatures. Not all factorial combinations of potentially confounding factors were tested rigorously, and the specific toxicants are unidentified, leaving questions about how groundwater pollution affects Salmonidae fish. Immediate concerns regarding the current water quality (including DO) of hyporheic water associated with groundwater influence are low because no detrimental effects on survival were detected in the field. Nevertheless, spawning grounds formed in areas with high exposures to polluted groundwater require continuous management attention due to potential risks associated with low DO levels. Additionally, pollution-induced growth patterns could pose a risk of size- or weight-dependent mortality at the swim-up fry stage and in early juveniles.

Материковый сток в Кандалакшский залив Белого моря с Карельского берега в теплый сезон года (с конца весеннего паводка до осеннего половодья

In order to determine the flow of fresh water from the Karelian coast in the warm season, in 2018–2023. Seasonal observations of water flow were carried out in watercourses flowing into the Chupa, Medvezhya, Kiv, Keret and Letnyaya bays of the Kandalaksha Bay of the White Sea. In rivers and streams, changes in water flow per day were studied, starting from the end of the spring flood to the end of the autumn flood. It was revealed that river water flow in the warm season of the year from this part of the Karelian coast does not exceed 750 million m3, and stream flow – 60 million m3. Seasonal water flow has two maximums (end of May–first ten days of June and end of September–mid-October) separated by a summer low-water period. Despite the length of the summer low-water period, its share in the total seasonal runoff does not exceed 40 % (on average 34±1 %). Over the course of 6 years, the volume of stream flow in this part of the Karelian coast increased on average by 2–3 % per year, and river flow by 1–2 % per year. Two years with a low total seasonal runoff (2018 and 2022) and two years with an increased total seasonal runoff (2021 and 2023) are distinguished. The data obtained indicate that freshwater runoff from the Karelian coast to the waters of the White Sea is subject to cyclical nature with a slight increase in the total volume of continental runoff.

Spatial Variation of Changes in Extreme Discharge Seasonality Across the Northeastern United States

ABSTRACTThe Northeast United States exhibits significant spatial heterogeneity in flood seasonality, with spring snowmelt‐driven floods historically dominating northern areas, while other regions show more varied flood seasonality. While it is well documented that since 1996 there has been a marked increase in extreme precipitation across this region, the response of flood seasonality to these changes in extreme precipitation and the spatial distribution of these effects remain uncertain. Here we show that, historically, snowmelt‐dominated northern regions were relatively insensitive to changes in extreme precipitation. However, with climate warming, the dominance of snowmelt floods is decreasing and thus the extreme flood regimes in northern regions are increasingly susceptible to changes in extreme precipitation. While extreme precipitation increased everywhere in the Northeastern United States in 1996, it has since returned to near pre‐1996 levels in the coastal north while remaining elevated in the inland north. Thus, the inland north region has and continues to experience the greatest changes in extreme flooding seasonality, including a substantial rise in floods outside the historical spring flood season, particularly in smaller watersheds. Further analysis reveals that while early winter floods are increasingly common, the magnitude of cold season floods (Nov‐May) have remained unchanged over time. In contrast, warm season floods (June‐Oct), historically less significant, are now increasing in both frequency and magnitude in the inland north. Our results highlight that treating the entire Northeast as a uniform hydroclimatic region conceals significant regional variations in extreme discharge trends and, more generally, climate warming will likely increase the sensitivity of historically snowmelt dominated watersheds to extreme precipitation. Understanding this spatial variability in increased extreme precipitation and increased sensitivity to extreme precipitation is crucial for enhancing disaster preparedness and refining water management strategies in affected regions.

Water budgets in an arid and alpine permafrost basin: Observations from the High Mountain Asia

Ground freeze‒thaw processes have significant impacts on infiltration, runoff and evapotranspiration. However, there are still critical knowledge gaps in understanding of hydrological processes in permafrost regions, especially of the interactions among permafrost, ecology, and hydrology. In this study, an alpine permafrost basin on the northeastern Qinghai‒Tibet Plateau was selected to conduct hydrological and meteorological observations. We analyzed the annual variations in runoff, precipitation, evapotranspiration, and changes in water storage, as well as the mechanisms for runoff generation in the basin from May 2014 to December 2015. The annual flow curve in the basin exhibited peaks both in spring and autumn floods. The high ratio of evapotranspiration to annual precipitation (>1.0) in the investigated wetland is mainly due to the considerably underestimated ‘observed’ precipitation caused by the wind-induced instrumental error and the neglect of snow sublimation. The stream flow from early May to late October probably came from the lateral discharge of subsurface flow in alpine wetlands. This study can provide data support and validation for hydrological model simulation and prediction, as well as water resource assessment, in the upper Yellow River Basin, especially for the headwater area. The results also provide case support for permafrost hydrology modeling in ungauged or poorly gauged watersheds in the High Mountain Asia.

Changes in the air temperature regime across the Dniester River basin at the beginning of the 21st century

The relevance of the chosen topic is based on the goals and objectives of the Water Strategy of Ukraine until 2050 that provides for promotion of studies on the impact of climate change on the water content of Ukrainian rivers. The Dniester River is a transboundary river. It supplies water to Moldova and several regions of Ukraine. Predicting possible changes in the Dniester River's runoff due to global warming will help our society adapt to new climate conditions and take preventive measures. The research of the mountainous part of the watershed is of particular importance, as it is the area of runoff formation. Warming can change contribution of the snow component to the river's feed pattern and affect the total river flow. The object of the study: changes in air temperature due to global warming. The subject of the study: assessment of changes in the temperature regime within the Dniester watershed and impact of such changes on formation of its mountainous part's runoff. The study is aimed at assessing the changes in the air temperature regime within the Dniester River watershed at the beginning of the 21st century and assessing the impact of warming during winter season on formation of mountain rivers' spring floods. The main research methods include the method of difference integral curves and the method of regression analysis. The research materials include average monthly and annual air temperatures at 13 meteorological stations located within the Dniester watershed for the period of 1947-2021. The research indicated that the Dniester watershed is subject to warming. Statistically significant changes in air temperature began in 1988. Fluctuations in average annual air temperatures occur synchronously. Positive statistically significant trends over the entire observation period (1947-2021) were found for average annual air temperatures, average monthly temperatures of both warm and cold periods, and for the winter season. When considering two measurement periods (before 1989 and after), it was found that no statistically significant trends were observed before 1989. They were formed after 1989. It was also discovered that mountainous watersheds of the Ukrainian Carpathians respond to warming by forming negative trends in the fluctuations of average monthly runoff of spring floods.

Carbon emission from the Lower Ob River floodplain during spring flood

Carbon emission from Arctic rivers constitutes a positive feedback between the climate warming and C cycle. However, in case of rivers with extensive floodplains, the impacts of temporary water bodies and secondary channels on CO2 exchange with atmosphere, compared to the main stem and tributaries, remain strongly understudied. In order to quantify the relative role of various water bodies of the Arctic river basin in the C cycle, the hydrochemical variables and greenhouse gases GHG concentrations and fluxes were measured within the floodplain of the largest Arctic River, Ob, in its low reaches located in the permafrost zone. These included the main stem, secondary channels, tributaries and floodplain lakes sampled over a 900 km north-south transect (25,736 km2 of the main stem and adjacent floodplain area; 7893 km2 water surface) during peak of spring flood (May 2023). In addition to main stem and tributaries, providing less than a half of overall C flux, floodplain lakes and secondary channels acted as important factor of C emission from the floodplain water surfaces. Multi-parametric statistical treatment of the data suggested two main processes of C emission from the Ob River floodplain waters: terrestrial organic matter-rich flooded wetlands (fens) provided elevated pCO2, whereas the sites of possible groundwater discharge in the secondary channels decreased the CO2 fluxes due to more alkaline environments, rich in labile metals and anionic elements.Based on available high-resolution Landsat-8 images, which matched the period of field work, it was found that the total water coverage of the floodplain during spring 2023 was 30 % of overall territory, compared to 18 % during the baseflow. Based on chamber-measured CO2 fluxes (1.56 ± 0.47 g C-CO2 m−2 d−1), overall CO2 emissions during 2 months of the spring flood from the entire Lower Ob River floodplain water surfaces including the main stem amounted to 0.73 ± 0.25 Tg C. Diffuse CH4 flux represented <1 % of total C flux. The main stem of the Ob River accounted for 34 % and 18 % of CO2 and CH4 emissions, respectively, whereas the floodplain lakes provided 59 % and 50 % of CO2 and CH4 emission, respectively. Considering that the low reaches of the Ob River represent >70 % of total river basin floodplain, and that during some years, the entire floodplain can be covered by water, emissions from the river – if assessed solely from summer (July–August) measurements – can be at least 3 times underestimated. It is therefore important to account for extended water surface during high water levels on Arctic rivers when assessing global riverine C emissions.