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• River water quality tends to deteriorate during droughts and heatwaves. • Water quality data are analysed at 314,046 locations worldwide. • Climate type, land use and wastewater treatment affect water quality responses under extremes. Droughts and heatwaves have a major impact on river water quality worldwide. However, previous studies of river water quality under these climate extremes are limited to a small number of river basins and regions, mainly located in North America, Europe or Australia. In this study, we estimate the large-scale effects of droughts, heatwaves and compound drought-heatwave events on river water quality for a total of 314,046 water quality monitoring stations worldwide over the period 1980–2021. We focus on 16 water quality constituents grouped into physical (e.g., temperature, salinity), chemical (e.g., pharmaceuticals, pesticides) and biological constituents (e.g., biochemical oxygen demand, faecal coliform). Further, we analyse the response of each constituent to droughts and heatwaves in relation to climate type, land use and level of wastewater treatment. We find a general deterioration in river water quality under droughts and heatwaves globally for most rivers and water quality constituents considered. For example, there is on average a 27 % increase in river water temperature, 17 % decrease in dissolved oxygen and 24 % increase in salinity under droughts and heatwaves. In addition, we find that climate type, land use and level of wastewater treatment have a significant effect on the magnitude of response in each water quality constituent during these extreme events. The median increase in river water temperature under compound drought-heatwaves is strongly driven by climate zone with higher warming rates at the polar climate zone (+4.5 °C) compared to the tropical zone (+2.1 °C). Increases in salinity under droughts are on average two times larger in irrigated regions compared to non-irrigated regions. The concentrations of nutrients (P and N) in rivers can either increase or decrease under droughts, depending on the nutrient form (dissolved vs. particulate) and land use (urban vs. rural). Higher levels of wastewater treatment contributed to a greater decrease in pathogenic concentrations under droughts and heatwaves (as indicated by faecal coliform). Pharmaceuticals show mixed responses mainly depending on the persistence of the constituent in surface waters, with for instance declines in diclofenac concentrations under droughts and heatwaves due to increased decay under higher water temperatures. The results of this study provide a broader understanding of how droughts and heatwaves affect river water quality compared to previous local and regional-scale analyses. In addition, this study could form the basis for large-scale modelling of river water quality under droughts and heatwaves. [ABSTRACT FROM AUTHOR]

• A framework developed for investigating cumulative impact of damming on water. • Tibetan damming having serious downstream impact but limited to local scale. • Runoff increase under warmer climate most likely offsetting damming impact. • This framework can be applicable for various anthropogenic impact analysis. Damming is one of the major methods that human being secure reliable freshwater. It can change flow magnitude and regime along a river, particularly for Transboundary Rivers shared by multiple jurisdictions. This study develops a coupled framework to assess both the current and future cumulative impacts of damming on downstream water availability for data-sparse regions like the Tibetan Plateau. The framework is applied to the Brahmaputra River Basin (BRB), where dam developments on the Tibetan Plateau are highly concerned. The results show that, despite being part of the 'Asian water tower', the Yarlung Tsangpo River (YTR) contributes just 15–16% to Brahmaputra streamflow, for 48% of its contributing area. We found that the maximum impact due to five recently constructed dams in YTR suggests about 8–11% reduction of mean annual streamflow at outlet of Brahmaputra River. The impacts of damming would be largely offset by runoff increases under the climate scenarios projected by 28 CMIP5 model outputs from RCP4.5 median-level emission scenarios and 29 CMIP5 model outputs from RCP8.5 high-level emission scenarios for the period of 2049 to 2075, compared to the historical period of 1979 to 2005. Our results suggest that it is necessary to use our framework or a similar one to comprehensively evaluate the maximum possible damming impact across the Transboundary Rivers. [ABSTRACT FROM AUTHOR]

Throughout the western United States, researchers have started documenting a trend toward earlier runoff, lower in-stream flows, and warmer-than-average water temperatures. These 'drought-like' stream conditions often lead to negative ecological, economic, and social consequences. To gain a deeper understanding of these emerging impacts, we focused our investigation on the Yellowstone River, which experienced a major drought event in 2016. This drought lead to an outbreak of Proliferative Kidney Disease that killed approximately 10,000 fish and resulted in an emergency closure of 294.5 km of the river for 15 days. We conducted semi-structured, in-depth interviews with outfitters, guides, government researchers, and state fisheries biologists/managers working within the Yellowstone River watershed. Our work was guided by three objectives: 1) to determine if people perceive changes in the runoff cycle; 2) to identify the impacts of changing runoff; and 3) if impacts are occurring, to document what adaptations strategies are being used to address them. In our discussions, respondents described an earlier runoff, shorter and more intense runoff, and more interannual variability in runoff. The impacts respondents associated with these changes were: 1) increased uncertainty in yearly planning and fishing quality; 2) altered fishing quality; 3) changes in species distributions; 4) disease outbreaks; and 5) imposed fishing restrictions. Respondents also described the following adaptations to mitigate impacts: 1) altering catch-and-release practices; 2) temporally shifting trips; 3) spatially shifting trips; 4) drought anticipation; and 5) targeting warm water species. [ABSTRACT FROM AUTHOR]

The influences of natural and anthropogenic factors on temporal changes in sediment load of the main Baikal rivers (Upper Angara River and Barguzin River) were analyzed through the relationship between hydro-climatic parameters (air temperature, precipitation, water discharge and sediment load) and their variation tendencies for the periods of 1945–2014, 1945–1975 and 1976–2014. Mann–Kendall test, abrupt change test were employed to analyze the hydro-climatic data. The results indicated that the air temperature increased on 1.0–1.1 °C in the watersheds over the warming period (1976–2014), and the precipitation had an insignificant decreasing trend in this period, and the reduction was −2.6% and −4.9%. The statistically insignificant increasing in water discharge was 4.2% and 1.3% in the Upper Angara and Barguzin over the period 1976–2014, respectively. Meanwhile, there was a strong decrease in sediment load of −66% and −70%. The abrupt decrease the sediment load in the Upper Angara since the mid-1970s was caused by the combination of human activities in river basin and changes of natural processes. In the Barguzin basin, the significant anthropogenic impact against the background the changes of natural processes in the mid-1980s was began. In the Upper Angara, the period of rapid decline of sediment load from 1976 to 1984 continued, in the Barguzin – from 1976 to 1991, after that, the other regime of sediment load had established. In recent decades, the actual sediment load supply from the Upper Angara and Barguzin into Lake Baikal are 92 × 103 t y−1 and 27 × 103 t y−1 or 22% and 18% of the 1945–1975, respectively. [ABSTRACT FROM AUTHOR]

Reconstructing the Plio-Pleistocene sedimentary history of the Yellow Sea, is important for understanding the long-term influence of the Yellow River (Huanghe) and/or Yangtze River (Changjiang) on the Asian marginal seas and to further constrain any links between river development, regional paleoenvironmental change, tectonic deformation and/or global climate change. Here we present the first high-resolution clay mineral record combined with Sr-Nd isotopic compositions from a 300-m long sediment core recovered in the western South Yellow Sea. Our study suggests that large-scale transgression in the Yellow Sea occurred after ∼0.8 Ma, possibly related to tectonic subsidence of eastern China coast and the Min-Zhe Uplift. In contrast, the sedimentary environment of Bohai and Yellow Seas was mainly dominated by fluvial/lacustrine deposits at 3.5–0.8 Ma. Provenance analysis suggests a major change in sediment provenance from the Yangtze River to the Yellow River at ∼0.8 Ma, which corresponds to the timing of the final integration of the Yellow River in its present form. At the same time the major channels of the Yangtze River migrated from the South Yellow Sea to the modern Yangtze River delta due to the subsidence of east China coast. The consistence in timing of the provenance transition and large-scale regional marine transgression suggests that tectonic deformation, rather than climate change, is the first-order control on the evolution of the Yellow and Yangtze Rivers and sedimentary environmental change in the Bohai and Yellow Seas. • A major change in sediment provenance in South Yellow Sea from the Yangtze River to Yellow River occurred at 0.8 Ma. • Large-scale transgression in the Yellow Sea began at 0.8 Ma, possibly related to subsidence of the Min-Zhe Uplift. • Tectonic deformation, rather than climate change, is the major control on the evolution of the Yellow and Yangtze Rivers. [ABSTRACT FROM AUTHOR]

This study evaluates the future change in hydropower potential and sustainability of the Tibetan Plateau (TP) in 21st century under climate change, using the Lancang River hydropower base (LRHB) in the upper Mekong basin (UMB) as a case study. Future climate projections simulated by five different global climate models (GCMs) individually and the variable infiltration capacity (VIC) distributed hydrological model coupled with a reservoir model are used to project the future hydropower outputs. Results present a generally ideal prospect for hydropower development in the UMB, as most GCMs illustrate overall increasing hydropower outputs of the plants along with the increasing reservoir inflow. The sustainability of the hydropower is also improved in most GCMs, with generally higher reliability and lower vulnerability; however, due to the large impact of increased climate variability, some GCMs show poorer sustainability for the hydropower plants in the future scenarios, even though its overall hydropower outputs are increased. Therefore, the negative influence of the increased variability of some passive GCM projections still indicates the risks for hydropower development in the TP and thus requires consideration. This study is expected to provide reference for further hydropower planning and development over the TP under climate change. • First assessment of future hydropower changes in the Tibetan Plateau (TP) is presented. • Overall increased hydropower output is found for the upper Mekong basin. • Increased sustainability is commonly found except for some Global Climate Model (GCM) projection cases. • The risk in hydropower induced by increased climate variability in TP should not be ignored. [ABSTRACT FROM AUTHOR]

Strategic studies of gravel deposits, in particular using heavy-mineral analyses, have thrown light on the important unresolved question as to the timing of the initiation of the Yellow River drainage through the Sanmen Gorge, which linked the headwaters of that system in the Fenwei Basin and further upstream with the North China Plain and the Pacific Ocean in the east. Survey of the Sanmen Gorge reach revealed previously unrecognized gravel levels: a higher fifth terrace (T5) and a gravel that formed on a high-level planation surface that is preserved on the flanks of the gorge, below the Xiaoshan upland. This high-level gravel differs markedly from the Yellow River terraces, with a lack of material from the upstream catchment, and would appear to represent a small fluvial catchment that developed in the area during the formation of the planation surface, before the Sanmen Gorge was excavated. Comparison was also made with basin-fill gravels from the endorheic fluvio-lacustrine system that existed immediately upstream of the gorge, and was captured by the Yellow River when the latter was cut, and with the modern bedload gravel of the Yellow River in this reach. The former contains significant quantities of unstable hornblende, which implies more local derivation for the endorheic system, whereas the modern bedload resembles the terrace gravels in showing compositional maturity and long-distance transport from upstream within the catchment. The work reinforces a minimum age of 1.2 Ma for the formation of the Sanmen Gorge. • The gravel layer accumulated on the planation surface along the eastern front of the Xiaoshan represents a local river. • The local river sediments are different from the typical Yellow River gravels and the upper Sanmen Formation. • The Sanmen paleolake within the Fenwei basin was finally disrupted by the westward capture of this local river. • The Sanmen Gorge was excavated by the local river through the Xiaoshan separating the Fenwei basin and North China Plain. • The Yellow River integration may be attributed to the remarkable climatic fluctuation starting in the Mid-Pleistocene. [ABSTRACT FROM AUTHOR]

The relationship between climate changes and human responses has been hotly debated. This paper expands this topic by reviewing and presenting case studies in the middle and lower Yellow River, Henan and Shandong provinces. We first review the paleoenvironmental data of both regions and then use the Sanyangzhuang site, Henan, and the Chengziya and Jiaojia sites, Shandong, as examples of human activities and sedimentary histories. Comparisons between the paleoenvironmental and archaeological data reveal that the changes in human occupation at these sites did not occur synchronously with climatic and paleoenvironmental changes. On the one hand, human activities were influenced by extreme climate-related events such as floods. However, humans also show great resilience by returning to the same sites or continuing cultivation at the same sites. Changes in temperature and precipitation did not result in settlement abandonments. On the other hand, human activities ceased to exist in periods of land and climate stabilities. With their increasing capacity to modify landscapes through time, human decisions and activities become equally important as climate change. [ABSTRACT FROM AUTHOR]

In many different societies around the world, people transitioned from slash-and-burn agriculture to an intensive mode of agricultural production. However, why agriculture was increasingly intensified by early farmers remains less understood. This study investigates the driving forces of agricultural intensification from an environmental perspective. Based on our fieldwork at the Sanyangzhuang site and previous paleoclimatic studies, we reconstruct the depositional processes and climatic changes at Sanyangzhuang and its surrounding area between 5000 yr BP and 2000 yr BP. Data suggest that farmers in the lower reaches of the Yellow River were confronted with increasingly severe Yellow River flooding and drier and colder climate during this time period. The environmental changes increase risks of crop failure and famine, disrupt the equilibrium of the social system and induce a process that brings about initial agricultural intensification. This environmental pressure is aggravated by social/political factors and results in the further development of agricultural intensification. [ABSTRACT FROM AUTHOR]

• Nonlinear methods determine positions of watersheds on the pluvial-nival continuum. • Nival systems have low embedding dimensions; pluvial systems have higher dimensions. • Embedding dimension influenced by basin characteristic and streamflow statistics. • Nonlinear methods useful for diagnosis of streamflow generating process changes. The nonlinear dynamics of streamflow time series from 667 reference hydrometric stations in North America spanning the pluvial-nival hydrological continuum are explored using minimum embedding dimensions as determined by False Nearest Neighbor (FNN) methods. Simulations using synthetic time series demonstrate that snowmelt dominated time series have lower embedding dimensions than those that are rainfall dominated, and that mixtures of the two processes result in a nearly linear change in the embedding dimension. The majority of the reference hydrometric stations drop below a 1% threshold at a dimension less than 30, showing a high degree of natural complexity in the signals ranging from annual snowmelt to weather-driven pseudo-stochastic systems. A less restrictive threshold, 5% is suggested to be more appropriate for streamflow time series. Time series smoothing impacts the embedding dimension and over-smoothing results in incorrect reductions of embedding dimensions. The relationship of the embedding dimensions to watershed and statistical properties of streamflow record showed the lowest embedding dimensions are restricted to large drainage areas, high elevations, and large mean annual flows and variance, high autocorrelations, and large fractions of the records with only small changes in magnitude. Times series that have a large proportion of consecutive days of equal streamflow typically result in higher embedding dimensions. Mapping of the embedding dimension shows spatial patterns related to the streamflow generating processes and geographical features. The use of embedding dimension resolved different dynamics across the hydrological continuum for rainfall to snowmelt over many climate zones. Changes in the embedding dimension might indicate process changes related to climate variability and change. [ABSTRACT FROM AUTHOR]

Abstract This study provides new data on the evolution of the landscape in south-western Amazonia during the Holocene and the impact of climate change and fluvial dynamics on the region's ecosystems. South-western Amazonia is covered by an extensive seasonally flooded savannah, known as the Llanos de Moxos. Severe drought during the southern hemisphere winter, followed by months of permanent waterlogging, means that forests only grow on the most elevated parts of the landscape, mostly river and paleoriver levees and crevasse splays. Paleoclimate reconstructions from surrounding areas show that a shift to wetter conditions at around 4 kyr BP caused an increase in forest cover. However, the impact that this change in climate had on the landscape of the Llanos de Moxos is unknown. Published lacustrine archives from the area only cover the last 2 kyr. Here we present new data from the analysis of paleosols located along a 300 km transect across the central Llanos. The analyses of stable carbon isotopes, from 36 paleosols, and biogenic silica, from 29 paleosols, show that the patchwork of forests and savannahs that we see today was established after the 4 kyr BP climate change. During the dry period between 8 and 4 kyr BP, most of the central Llanos de Moxos, nowadays covered with seasonally flooded savannah, were covered by Cerrado -like savannah in the west and by forest in the east. However, results also suggest that, at both regional and local scales, vegetation cover has been influenced by changes in topography resulting from the region's river dynamics. Highlights • We reconstructed Holocene landcover changes in SW Amazonia. • Changes in vegetation are reconstructed from biogenic silica and δ13C of paleosols. • From 8 to 4 kyr BP the Llanos de Moxos were covered with forest and Cerrado veg. • The modern savannah was established after 4 kyr BP. [ABSTRACT FROM AUTHOR]

Abstract The Yangtze (Changjiang) mega-delta, China, has a high risk of coastal erosion owing to the recent high rate of relative sea-level rise and reduced sediment supply. The study of the Holocene evolution of the delta can provide information about its response to rapid sea-level rise and changes in sediment supply caused by climate or human activity, although this has yet to be fully explored because of the lack of integrated studies using age-constrained sedimentary records. Here we document stratigraphic architecture and morphological changes over the last 11,700 years and estimate the amount of sediment trapped in the delta region on a millennial scale using a dataset of 344 sediment cores, 658 radiocarbon and 28 optically stimulated luminescence (OSL) ages (of which we obtained 64 cores, 345 radiocarbon and 28 OSL ages, and the others we sourced from the literature). Using this dataset we present the temporal and spatial morphodynamic evolution of the entire Yangtze River mouth from its early Holocene transgressive estuary to a mid- to late-Holocene regressive delta, making it possible to produce a quantitative and sequential analysis of sediment deposition. A destructive phase of the river mouth region was identified at 10 to 8 cal. kyr BP, including significant coastal erosion of tidal flats and troughs within the estuary and of tidal ridge-and-trough topography offshore; these resulted from the reshaping of the river mouth morphology caused by rapid sea-level rise at that time. As a result, the rate of sediment trapping at the river mouth declined from an average of 224 Mt yr−1 at 11.7–10 cal. kyr BP to 137 Mt yr−1 between 10 and 8 cal. kyr BP. Since delta initiation 8000 years ago, a retreat of the subaqueous delta occurred and the sediment trapping rate declined from 151 Mt yr−1 at 8–6 cal. kyr BP to 99–113 Mt yr−1 between 6 and 2 cal. kyr BP, caused by the reduction in sediment supply linked to summer monsoon weakening ~6000 years ago. In the last 2000 years the sediment trapping rate has increased to 162 Mt yr−1 due to intensified human activity. The present-day level of sedimentation in delta (49 Mt yr−1 in 2003–2011), after the completion of the Three Gorges Dam, is far lower than the 'natural' range in the Holocene. We thus infer a potential for system regime shift in terms of coastal erosion and a transition to a new equilibrium in delta morphology in the near future. [ABSTRACT FROM AUTHOR]

The biogeochemical sulfur cycle is intimately linked to the cycles of carbon, iron, and oxygen, and plays an important role in global climate via weathering reactions and aerosols. However, many aspects of the modern budget of the global sulfur cycle are not fully understood. We present new δ 34 S measurements on sulfate from more than 160 river samples from different geographical and climatic regions—more than 46% of the world's freshwater flux to the ocean is accounted for in this estimate of the global riverine sulfur isotope budget. These measurements include major rivers and their tributaries, as well as time series, and are combined with previously published data to estimate the modern flux-weighted global riverine δ 34 S as 4.4 ± 4.5‰ (V-CDT), and 4.8 ± 4.9‰ when the most polluted rivers are excluded. The sulfur isotope data, when combined with major anion and cation concentrations, allow us to tease apart the relative contributions of different processes to the modern riverine sulfur budget, resulting in new estimates of the flux of riverine sulfate due to the oxidative weathering of pyrites (1.3 ± 0.2 Tmol S/y) and the weathering of sedimentary sulfate minerals (1.5 ± 0.2 Tmol S/y). These data indicate that previous estimates of the global oxidative weathering of pyrite have been too low by a factor of two. As pyrite oxidation coupled to carbonate weathering can act as a source of CO 2 to the atmosphere, this global pyrite weathering budget implies that the global CO 2 weathering sink is overestimated. Furthermore, the large range of sulfur isotope ratios in modern rivers indicates that secular changes in the lithologies exposed to weathering through time could play a major role in driving past variations in the δ 34 S value of seawater. [ABSTRACT FROM AUTHOR]

The interactions between water, sediment and biology in fluvial systems are complex and driven by multiple forcing mechanisms across a range of spatial and temporal scales. In a changing climate, some meteorological drivers are expected to become more extreme with, for example, more prolonged droughts or more frequent flooding. Such environmental changes will potentially have significant consequences for the human populations and ecosystems that are dependent on riverscapes, but our understanding of fluvial system response to external drivers remains incomplete. As a consequence, many of the predictions of the effects of climate change have a large uncertainty that hampers effective management of fluvial environments. Amongst the array of methodological approaches available to scientists and engineers charged with improving that understanding, is physical modelling. Here, we review the role of physical modelling for understanding both biotic and abiotic processes and their interactions in fluvial systems. The approaches currently employed for scaling and representing fluvial processes in physical models are explored, from 1:1 experiments that reproduce processes at real-time or time scales of 10 −1 -10 0 years, to analogue models that compress spatial scales to simulate processes over time scales exceeding 10 2 –10 3  years. An important gap in existing capabilities identified in this study is the representation of fluvial systems over time scales relevant for managing the immediate impacts of global climatic change; 10 1 – 10 2  years, the representation of variable forcing (e.g. storms), and the representation of biological processes. Research to fill this knowledge gap is proposed, including examples of how the time scale of study in directly scaled models could be extended and the time scale of landscape models could be compressed in the future, through the use of lightweight sediments, and innovative approaches for representing vegetation and biostabilisation in fluvial environments at condensed time scales, such as small-scale vegetation, plastic plants and polymers. It is argued that by improving physical modelling capabilities and coupling physical and numerical models, it should be possible to improve understanding of the complex interactions and processes induced by variable forcing within fluvial systems over a broader range of time scales. This will enable policymakers and environmental managers to help reduce and mitigate the risks associated with the impacts of climate change in rivers. [ABSTRACT FROM AUTHOR]

Modelling river temperature at the catchment scale is needed to understand how aquatic communities may adapt to current and projected climate change. In small and medium rivers, riparian vegetation can greatly reduce maximum water temperature by providing shade. It is thus important that river temperature models are able to correctly characterise the impact of this riparian shading. In this study, we describe the use of a spatially-explicit method using LiDAR-derived data for computing the riparian shading on direct and diffuse solar radiation. The resulting data are used in the T-NET one-dimensional stream temperature model to simulate water temperature from August 2007 to July 2014 for 270 km of the Loir River, an indirect tributary of the Loire River (France). Validation is achieved with 4 temperature monitoring stations spread along the Loir River. The vegetation characterised with the LiDAR approach provides a cooling effect on maximum daily temperature ( T max ) ranging from 3.0 °C (upstream) to 1.3 °C (downstream) in late August 2009. Compared to two other riparian shading routines that are less computationally-intensive, the use of our LiDAR-based methodology improves the bias of T max simulated by the T-NET model by 0.62 °C on average between April and September. However, difference between the shading routines reaches up to 2 °C (monthly average) at the upstream-most station. Standard deviation of errors on T max is not improved. Computing the impact of riparian vegetation at the hourly timescale using reach-averaged parameters provides results close to the LiDAR-based approach, as long as it is supplied with accurate vegetation cover data. Improving the quality of riparian vegetation data should therefore be a priority to increase the accuracy of stream temperature modelling at the regional scale. [ABSTRACT FROM AUTHOR]

The Southwest Coastal people of Bangladesh have introduced Tidal River Management (TRM) as an environmentally acceptable water resource management practice based on their indigenous knowledge of water logging of low lying coastal land. TRM helps to address problems resulting from different anthropogenic and structural development activities, and it has been successful in helping coastal communities to adapt to climate change and rising sea level vulnerability by forming new land in Tidal Basins. Hence, it is essential to measure sustainability impacts of TRM from the environmental, socio-economic and institutional perspectives. Therefore, firstly, the study identifies sustainability indicators of TRM considering ecosystem services and secondly, develops an inclusive conceptual framework to understand the important impacts of each indicator at various spatial and temporal scales. The conceptual framework is followed by the construction of a Sustainability Index of Tidal River Management (SITRM). It has advantages over the Ramsar Convention framework (2007) and the World Meteorological Organization (WMO) framework (2012) to measure water sustainability as it includes a sustainable model to project future vulnerability of the community, river and Tidal Basin, emphasizing on climate change issues. It also involves trade-offs analysis, livelihood analysis and SWOT (Strengths, Weaknesses, Opportunities and Threats) analysis for a complete impact assessment to enable decision-makers to focus on those services most likely to be of risks and weaknesses or opportunities and strengths for the sustainability of TRM. Moreover, the framework is a useful guide for policymakers in identifying the sustainability impacts of TRM so that they can choose best coping strategies for coastal people to effectively deal with adverse effects of water-logging and undesired climatic events as well as environmental and socio-economic changes in coastal areas. [ABSTRACT FROM AUTHOR]

Recent observations indicate that over the last decades, climate change has increasingly influenced the frequency, intensity and duration of extreme climatic and hydrologic events. The main aim of this study is to determine the hydrologic response, especially the flood evolution, of the Lena River in Eastern Siberia to ongoing climate change. Draining the coldest region of the Northern Hemisphere, the Lena River is impacted by global warming, which is particularly pronounced in periglacial areas characterized by deep and continuous permafrost. We document the hydrologic variability of the Middle Lena River, first by characterizing trend and stationarity of monthly discharges. Second, we analyze on the basis of the peak over threshold method (POT) the temporal evolution of intensity and duration of three discharge classes: bar-full discharge, bank-full discharge and large floods. Finally, we also determined the dates of the flood beginning and of the flood peak. Data on mean monthly discharge and flood peaks are available since 1936 and daily discharges since 1954. Our results provide evidence for a net hydrologic change with an increase in the intensity and duration of floods in the two decades ending in 2012. The frequency of high floods is unprecedented, and small floods no longer occur. The tail of the temporal distribution of the flood peak is also changing. More frequent early floods are occurring in spring with secondary flood peaks in summer, the latest probably represents the most striking change. Furthermore, the changes have been accelerating since 2004. Finally, two islands were instrumented (2008–2012) in order to study the flooding dynamics with a better precision. [ABSTRACT FROM AUTHOR]

There is now widespread awareness of the impact of anthropogenic influences on extreme floods (and droughts) and thus an increasing need for methods to account for such influences when estimating a frequency distribution. We introduce a parsimonious approach to nonstationary flood frequency analysis (NFFA) based on a bivariate regression equation which describes the relationship between annual maximum floods, x , and an exogenous variable which may explain the nonstationary behavior of x . The conditional mean, variance and skewness of both x and y  = ln ( x ) are derived, and combined with numerous common probability distributions including the lognormal, generalized extreme value and log Pearson type III models, resulting in a very simple and general approach to NFFA. Our approach offers several advantages over existing approaches including: parsimony, ease of use, graphical display, prediction intervals, and opportunities for uncertainty analysis. We introduce nonstationary probability plots and document how such plots can be used to assess the improved goodness of fit associated with a NFFA. [ABSTRACT FROM AUTHOR]

Coverage of in situ observations to monitor surface waters is insufficient on the global scale, and decreasing across the globe. Satellite altimetry has become an increasingly important monitoring technology for continental surface waters. The ESA CryoSat-2 altimetry mission, launched in 2010, has two novel features. (i) The radar altimeter instrument on board of CryoSat-2 is operated in three modes; two of them reduce the altimeter footprint by using Delay-Doppler processing. (ii) CryoSat-2 is placed on a distinct orbit with a repeat cycle of 369 days, leading to a drifting ground track pattern. The drifting ground track pattern challenges many common methods of processing satellite altimetry data over rivers. This study evaluates the observation error of CryoSat-2 water level observations over the Po River, Italy, against in situ observations. The average RMSE between CryoSat-2 and in situ observations was found to be 0.38 meters. CryoSat-2 was also shown to be useful for channel roughness calibration in a hydrodynamic model of the Po River. The small across-track distance of CryoSat-2 means that observations are distributed almost continuously along the river. This allowed resolving channel roughness with higher spatial resolution than possible with in situ or virtual station altimetry data. Despite the Po River being extensively monitored, CryoSat-2 still provides added value thanks to its unique spatio-temporal sampling pattern. [ABSTRACT FROM AUTHOR]

Changes in Atlantic Meridional Overturning Circulation (AMOC) strength exert a major influence on global atmospheric circulation patterns. However, the pacing and mechanisms of low-latitude responses to high-latitude forcing are insufficiently constrained so far. To elucidate the interaction of atmospheric and oceanic forcing in tropical South America during periods of major AMOC reductions (Heinrich Stadial 1 and the Younger Dryas) we generated a high-resolution foraminiferal multi-proxy record from off the Orinoco River based on Ba/Ca and Mg/Ca ratios, as well as stable isotope measurements. The data clearly indicate a three-phased structure of HS1 based on the reconfiguration of ocean currents in the tropical Atlantic Ocean. The initial phase (HS1a) is characterized by a diminished North Brazil Current, a southward displacement of the ITCZ, and moist conditions dominating northeastern Brazil. During subsequent HS1b, the NBC was even more diminished or yet reversed and the ITCZ shifted to its southernmost position. Hence, dryer conditions prevailed in northern South America, while eastern Brazil experienced maximally wet conditions. During the final stage, HS1c, conditions are similar to HS1a. The YD represents a smaller amplitude version of HS1 with a southward-shifted ITCZ. Our findings imply that the low-latitude continental climate response to high-latitude forcing is mediated by reconfigurations of surface ocean currents in low latitudes. Our new records demonstrate the extreme sensitivity of the terrestrial realm in tropical South America to abrupt perturbations in oceanic circulation during periods of unstable climate conditions. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are expected to become more frequent in freshwaters globally due to eutrophication and climate change effects. However, our knowledge about cyanobacterial biogeography in the subtropics, particularly in lotic ecosystems, is still very limited and the relationship of blooms to temperature and precipitation remains unclear. We took advantage of a comprehensive database of field data compiled over several years (1997 to 2015) to compare cyanobacteria biomass and distribution between lentic and lotic subtropical freshwaters (36 ecosystems, 30°–35°S) and to investigate the role of water temperature and precipitation as significant predictors in eutrophic ecosystems. A filamentous Nostocales, Dolichospermum ( Anabaena ), was the most widely distributed and frequent genus in the region of the study, followed by the colonial Microcystis , supporting observations of a global latitudinal pattern. Similar total cyanobacteria biovolumes (TCB) were found in lentic and lotic ecosystems, but the proportion of Dolichospermum was higher in lotic ecosystems. Using generalized linear models (GLMs), we found that temperature and rainfall explained 27% of the variation in TCB in lotic ecosystems, while temperature explained 19 and 28% of Dolichospermum and Microcystis biovolume, respectively. In lentic ecosystems, accumulated rainfall explained 34% of the variation of Microcystis biovolume while temperature explained 64%. Our results imply that the increase in extreme meteorological events and temperature predicted by climate models will promote increasingly severe cyanobacterial blooms in eutrophic subtropical freshwaters. Our analysis provides new information about the occurrence of bloom-forming cyanobacteria for southeastern South America and thus fills an important knowledge gap for subtropical freshwaters. [ABSTRACT FROM AUTHOR]

Context Understanding natural temporal changes in Mediterranean rivers with contrasting flow regimes in relation to those of temperate rivers may prove helpful in predicting effects of climate change on aquatic biodiversity. Goal We aimed to compare temporal variability in taxonomic and trait compositions of nearly natural rivers in two climatic regions with varying flow regimes to address the effects of future climate changes on aquatic biodiversity in reference conditions. Methods We analysed taxonomic and biological trait compositions using the Foucard multivariate method to compare within-site temporal variability levels and the evolution of within-date spatial variability patterns. In addition, we assessed the effects of temporal variability levels on taxonomic and functional diversity and on community specialization. Results Our results reveal (i) highly fluctuating environments of the Mediterranean region, particularly in intermittent rivers, which lead to higher levels of temporal variability in both taxonomic and trait compositions of benthic invertebrate assemblages, with marked synchrony in Mediterranean streams linked to contrasting flow characteristics; (ii) higher degrees of taxonomic richness associated with higher levels of functional diversity in Mediterranean rivers relative to temperate rivers, (iii) higher temporal stability for functional diversity and trait compositions of benthic invertebrate assemblages than for taxonomic richness and compositions; and (iv) a recovery of all diversity metrics following drying events in intermittent sites. Conclusion This study offers insight into a rarely addressed question concerning the temporal variability of trait compositions in benthic invertebrate assemblages among rivers differing in terms of flow regimes. It suggests that temperate rivers will experience higher levels of temporal variability in terms of taxonomic and trait compositions under future climatic change scenarios, even in sites that will remain perennial, resulting in higher levels of taxonomic and functional diversity. This lack of temporal stability in least-disturbed situations should be taken into account when developing bioassessment tools based on reference conditions. [ABSTRACT FROM AUTHOR]

Episodic acidification during snowmelt is a natural phenomenon that can be intensified by acidic deposition from heavy industry. In Canada's oil sands region, acid deposition is estimated to be as much as 5% of the Canadian total and large tracks of northeastern Alberta are considered acid-sensitive because of extensive peatland habitats with poorly weathered soils. To identify the frequency, duration and severity of acidification episodes during snowmelt (the predominant hydrological period for delivery of priority pollutants from atmospheric oil sands emissions to surface waters), a 25-year record (1989 to 2014) of automated water quality data (pH, temperature, conductivity) was assembled for 3 rivers along with a shorter record (2012–2014) for another 2 rivers. Acidic episodes (pH < 7, ANC < 0) were recorded during 39% of all 83 snowmelt events. The severity (duration x magnitude) of episodic acidification increased exponentially over the study period (r 2 = 0.56, P < 0.01) and was strongly correlated ( P < 0.01) with increasing maximum air temperature and weakly correlated with regional land development ( P = 0.06). Concentrations of aluminum and 11 priority pollutants (Sb, As, Be, Cd, Cr, Cu, Pb, Se, Ag, Tl and Zn) were greatest ( P < 0.01) during low (< 6.5) pH episodes, particularly when coincident with high discharge, such that aluminum and copper concentrations were at times high enough to pose a risk to juvenile rainbow trout ( Oncorhynchus mykiss ). Although low pH (pH < 6.5) was observed during only 8% of 32 acidification episodes, when present, low pH typically lasted 10 days. Episodic surface water acidification during snowmelt, and its potential effects on aquatic biota, is therefore an important consideration in the design of long-term monitoring of these typically alkaline (pH = 7.72 ± 0.05) rivers. [ABSTRACT FROM AUTHOR]

River headwaters, in spite of their importance for habitats and water supply, are often inadequately studied and managed. This study discusses the effects of the hydrogeological system and climatic variations on the environment of Monte Fumaiolo (Central Italy), which corresponds to the headwaters of the rivers Tiber, Savio and Marecchia. The area is a key system for supplying drinking-water and is also the habitat of amphibians such as the endemic and endangered Bombina pachypus and other amphibian species. Ongoing climate change is affecting the area: during the last 30 years, five prolonged droughts have occurred, against only one in the preceding 40 years. On all time-scales, there is a decrease in rainfall during the recharge period and an increase of temperature: these trends correspond to a decrease in water yield of about 12% over the last 30 years. The hydrologic system of the study area is composed of one basic aquifer and a few perched aquifers feeding springs. Their resilience to drought depends on their geological setting: study of some depletion curves helped us to understand the geological setting of the various types, and two promising sites for the habitat preservation of amphibians were identified. Study results indicate new approaches to the study and management of the environment and its water supply, which could be useful in similar areas. [ABSTRACT FROM AUTHOR]

Water-borne pathogen contamination from untreated sewage effluent and runoff from farms is a serious threat to the use of river water for drinking and commercial purposes, such as downstream estuarine shellfish industries. In this study, the impact of climate change and land-use change on the presence of faecal indicator bacteria in freshwater was evaluated, through the use of a recently-developed catchment-scale pathogen model. The River Conwy in Wales has been used as a case-study, because of the large presence of livestock in the catchment and the importance of the shellfish harvesting activities in its estuary. The INCA-Pathogens catchment model has been calibrated through the use of a Monte-Carlo-based technique, based on faecal indicator bacteria measurements, and then driven by an ensemble of climate projections obtained from the HadRM3-PPE model (Future Flow Climate) plus four land-use scenarios (current land use, managed ecosystem, abandonment and agricultural intensification). The results show that climate change is not expected to have a very large impact on average river flow, although it might alter its seasonality. The abundance of faecal indicator bacteria is expected to decrease in response to climate change, especially during the summer months, due to reduced precipitation, causing reduced runoff, and increased temperature, which enhances the bacterial die-off processes. Land-use change can also have a potentially large impact on pathogens. The “managed ecosystems” scenario proposed in this study can cause a reduction of 15% in average water faecal indicator bacteria and up to 30% in the 90th percentile of water faecal indicator bacteria, mainly due to the conversion of pasture land into grassland and the expansion of forest land. This study provides an example of how to assess the impacts of human interventions on the landscape, and what may be the extent of their effects, for other catchments where the human use of the natural resources in the uplands can jeopardise the use of natural resources downstream. [ABSTRACT FROM AUTHOR]

Surface water bodies (lakes, reservoirs, and rivers) are key components of the water cycle and are important water resources. Water level and storage vary greatly under the impacts of climate change and human activities. Due to sparse in-situ monitoring networks, a comprehensive national-scale monitoring dataset of surface water bodies in China is not available. Over the last two decades, satellite altimetry has been used successfully for inland water monitoring. Here, we use CryoSat-2 radar altimetry to monitor water level variations of large lakes, reservoirs and rivers across China and demonstrate its potential to complement available in-situ monitoring datasets for the country. In this study, over 1000 lakes and reservoirs, and 6 large rivers are investigated. The results show that surface water varied greatly over the past 6 years, e.g. in the Tibetan Plateau, the Junggar Basin, the Northeast China Plain, and the central Yangtze River basin. Estimated changes in volume indicate that surface water variation contributes significantly to terrestrial storage variation, especially in the Qaidam Basin and the Tibetan Plateau. CryoSat-2 is capable of measuring regional-scale river level at high spatial resolution and competitive accuracy as demonstrated by comparison with available in-situ gauging data. The results are encouraging with RMSE values ranging from 0.24 to 0.35 m for the Heilongjiang-Amur River, 0.22 to 0.6 m for the Yellow River and 0.22 to 0.5 m for the Songhua River. Comparatively, accuracy is much lower over the Yangtze and Pearl Rivers (RMSE ~ 2.6 m and ~ 3.3 m), probably due to intensive inland waterway navigation. CryoSat-2 shows great potential for monitoring surface water at national scale in China. [ABSTRACT FROM AUTHOR]

The Nalinggele River, located in the northern Qinghai-Tibetan Plateau, is the largest river originating from the northern slope of the eastern Kunlun Mountains and flowing into the enclosed Qaidam Basin. Controversy exists whether the formation of its terraces reflects the history of the plateau uplift, or climate changes, or both. The salt lakes in the enclosed Qaidam Basin fed by this river bear an unusual world-class enrichment of lithium and boron elements, which are critical resources for regional economy. The concentration of lithium is one of the highest found in brine resource in the world, and sourced from the upstream water of the river. The chronology of the river terraces is essential to understand the plateau uplift history, the regional climate change, the evolution of the terminal salt lakes, and the process of enrichment of the valuable elements. However, the age constraint for the terraces of the rivers in the east Kunlun Mountains is still limited and debated, and no dating work has been reported yet for terraces of the Nalinggele River. Five terraces were identified in this river. In this study, the terraces were dated using quartz optically stimulated luminescence (OSL) dating. The results indicate that the OSL ages (∼7.5 ka, ∼9.9 ka, ∼11.3 ka, and ∼13.1 ka) of the four terraces (T1, T2, T3, and T4) are consistent with geomorphic relationship, and that they formed since ∼13.1 ka and were probably triggered by climatic change rather than by the plateau uplift. The sediment of T5 is too coarse to collect OSL samples and not dated. Based on our dating we confirm the previous view that the lithium concentration in the terminal salt lakes should have initiated since 15–13 ka. We further propose that the formation of salt lakes and the enrichment of their resources in the Qaidam Basin should have occurred mainly in interglacial periods (e.g. the Holocene), a warm and humid period, not as previously thought to be in the glacial periods, a dry and cold period, and that during the glacial periods the basin was mainly under wind erosion. [ABSTRACT FROM AUTHOR]

Non-perennial rivers and streams (NPRS) cover > 50% of the global river network. They are particularly predominant in Mediterranean Europe as a result of dry climate conditions, climate change and land use development. Historically, both scientists and policy makers underestimated the importance of NRPS for nature and humans alike, mainly because they have been considered as systems of low ecological and economic value. During the past decades, diminishing water resources have increased the spatial and temporal extent of artificial NPRS as well as their exposure to multiple stressors, which threatening their ecological integrity, biodiversity and ecosystem services. In this paper, we provide a comprehensive overview of the structural and functional characteristics of NPRS in the European Mediterranean, and discuss gaps and problems in their management, concerning their typology, ecological assessment, legislative and policy protection, and incorporation in River Basin Management Plans. Because NPRS comprise highly unstable ecosystems, with strong and often unpredictable temporal and spatial variability – at least as far as it is possible to assess – we outline the future research needs required to better understand, manage and conserve them as highly valuable and sensitive ecosystems. Efficient collaborative activities among multidisciplinary research groups aiming to create innovative knowledge, water managers and policy makers are urgently needed in order to establish an appropriate methodological and legislative background. The incorporation of NPRS in EU-Med River Basin Management Plans in combination with the application of ecological flows is a first step towards enhancing NPRS management and conservation in order to effectively safeguard these highly valuable albeit threatened ecosystems. [ABSTRACT FROM AUTHOR]

Riverine systems act as important aquatic conduits for carbon transportation between atmospheric, terrestrial and oceanic pools, yet the magnitude of these exports remain poorly constrained. Interconnected creek and river sites (n = 28) were sampled on a quarterly basis in three subcatchments of the subtropical Richmond River Catchment (Australia) to investigate spatial and temporal dynamics of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), carbon dioxide (CO 2 ), methane (CH 4 ), and carbon stable isotope ratios (δ 13 C). The study site is an area of high interest due to potential unconventional gas (coal seam gas or coal bed methane) development. DIC exports were driven by groundwater discharge with a small contribution by in situ DOC remineralization. The DIC exports showed seasonal differences ranging from 0.10 to 0.27 mmol m − 2 catchment d − 1 (annual average 0.17 mmol m − 2 catchment d − 1 ) and peaked during winter when surface water discharge was highest. DOC exports (sourced from terrestrial organic matter) had an annual average 0.07 mmol m − 2 catchment d − 1 and were 1 to 2 orders of magnitude higher during winter compared to spring and summer. CO 2 evasion rates (annual average of 347 mmol m − 2 water area d − 1 ) were ~ 2.5 fold higher during winter compared to spring. Methane was always supersaturated (0.19 to 62.13 μM), resulting from groundwater discharge and stream-bed methanogenesis. Methane evasion was highly variable across the seasons with an annual average of 3.05 mmol m − 2 water area d − 1 . During drier conditions, stable isotopes implied enhanced CH 4 oxidation. Overall, carbon losses from the catchment were dominated by CO 2 evasion (60%) followed by DIC exports (30%), DOC exports (9%) and CH 4 evasion (< 1%). Our results demonstrated broad catchment scale spatial and temporal variability in carbon dynamics, and that groundwater discharge and rain events controlled carbon exports. [ABSTRACT FROM AUTHOR]

Palaeo–hydrological and sedimentary investigations were carried out in the Longmenxia Gorge of the middle Yihe River. Five bedsets of flood slackwater deposits (SWD) were found interbedded into Holocene aeolian loess–soil profiles in the river bank at the Longmenxia site. They were identified as the deposits of the suspended sediment load during the extreme flood events of the Holocene. The minimum flood peak discharges were estimated to be 12, 300–15, 300 m 3 /s using the slope–area method. These are about twice the largest gauged record (7180 m 3 /s) that has occurred since 1937. These flood events occurred at 3100–3000 a B.P., 1800–1700 a B.P., 700–550 a B.P. and 350–250 a B.P., as dated by optically stimulated luminescence (OSL) in combination with stratigraphic correlation, to which may be added the recorded events of the 223 and 1761 CE floods. These were associated with Holocene monsoonal shifts and abrupt climatic events. This research not only provides palaeoflood discharge estimates on the middle Yihe River, but also provides important data for understanding interactions between regional hydro–climatic systems and global climate change in humid and semi–humid monsoonal regions, such as China. [ABSTRACT FROM AUTHOR]

Topographic and climatic changes are the main causes of abrupt flooding in tropical areas. It is the need to find out exact causes and effects of these changes. Numerical modeling techniques plays a vital role for such studies due to their use of hydrological parameters which are strongly linked with topographic changes. In this review, some of the widely used models utilizing hydrological and river modeling parameters and their estimation in data sparse region are discussed. Shortcomings of 1D and 2D numerical models and the possible improvements over these models through 3D modeling are also discussed. It is found that the HEC-RAS and FLO 2D model are best in terms of economical and accurate flood analysis for river and floodplain modeling respectively. Limitations of FLO 2D in floodplain modeling mainly such as floodplain elevation differences and its vertical roughness in grids were found which can be improve through 3D model. Therefore, 3D model was found to be more suitable than 1D and 2D models in terms of vertical accuracy in grid cells. It was also found that 3D models for open channel flows already developed recently but not for floodplain. Hence, it was suggested that a 3D model for floodplain should be developed by considering all hydrological and high resolution topographic parameter's models, discussed in this review, to enhance the findings of causes and effects of flooding. [ABSTRACT FROM AUTHOR]

Researchers often examine hydro-climatological processes via Global Circulation Model (GCM) and hydrological model, which have been shown to benefit water resources management and prediction, especially at the basin scale. In this study, the Soil and Water Assessment Tool (SWAT) and Statistical Downscaling Method (SDSM) were integrated and applied to estimate streamflows in the Xin River Basin, China, based on climate change scenarios downscaled from different GCMs (BCC-CSM1.1, CanESM2, and NorESM1-M) under three Representative Concentration Pathways (RCPs). Results confirmed that the calibrated SWAT model accurately depicts hydrological processes features at daily, monthly, and yearly scales. Three GCMs based on the calibrated SDSM showed that temperature is continually increasing in the region, however, future precipitation is highly complex and uncertain; there were significant differences among various GCM RCP scenarios. The average of the precipitation in three models showed slight and steady increase trends under RCP2.6 and RCP4.5, but a significant increase under the RCP8.5 scenario. The ensemble average of streamflow in GCMs demonstrated that many RCPs significantly decrease from May to June but increase from August to September relative to the baseline period. The ensemble mean of the multi-GCM indicated that future streamflows under RCP2.6 and RCP4.5 scenarios will be closer to the current streamflow volume. Many RCPs also revealed a significant increase in monthly streamflow dispersion coefficient in October, reflecting a tendency for drought and flood events in that month. The BCC-CSM1.1 and NorESM1-M models showed that streamflows are higher than the baseline with median probability in the future. The low monthly streamflow (10th percentile) processes for each GCM were altogether similar to the baseline, whereas the high monthly streamflows (90th percentile) showed various levels of disparity compared to the baseline. [ABSTRACT FROM AUTHOR]

River concentrations of suspended sediment and particulate contaminants, such as trace metals, increase sharply during ice breakup, with potentially detrimental ecological impacts that may be complicated by changing climatic conditions. To enhance the very limited knowledge on this issue, comprehensive data have been collected on the Saint John River (SJR). During breakup, the suspended sediment concentration (SSC) was found to rise gradually, crest, and decline, roughly in step with the runoff, but occasionally spiked to extremely high peaks. The latter ranged from 4.2 to 6.5 times the runoff-generated peak concentrations (RPCs), which ranged from 35 to 150 mg/L. Peak RPCs and individual-event sediment loads generally increased with flow discharge. The sediment spikes were invariably associated with waves resulting from releases of upstream ice jams and with the ensuing ice runs. Concentration–discharge graphs exhibited pronounced clockwise hysteresis, indicative of sediment supply constraints. This feature is more prominent in high-runoff events and typically associated with a lag of 1–3 days between peak concentration and peak discharge, which arrives later. Prediction of SSC via sediment-rating curves is hopeless, but such curves can be helpful in computing loads associated with individual events using a modified approach that terminates load computation 3 days after the arrival of peak discharge. The bulk of the sediment load is delivered on the rising limb of the hydrograph and is likely to be missed in routine sediment monitoring programs. Practical steps to capture this information are suggested. Increases in SJR spring flows during recent decades are projected to continue under a warming climate, resulting in considerable increases of SSCs and loads by the end of this century. [ABSTRACT FROM AUTHOR]

Freshwater stream systems are under immense pressure from various anthropogenic impacts, including climate change. Stream systems are increasingly being altered by changes to the magnitude, timing, frequency, and duration of their thermal regimes, which will have profound impacts on the life-history dynamics of resident biota within their home range. Although temperature regimes have a significant influence on the biology of instream fauna, large spatio-temporal temperature datasets are often reduced to a single metric at discrete locations and used to describe the thermal regime of a system; potentially leading to a significant loss of information crucial to stream management. Models are often used to extrapolate these metrics to unsampled locations, but it is unclear whether predicting actual daily temperatures or an aggregated metric of the temperature regime best describes the complexity of the thermal regime. We fit spatial statistical stream-network models (SSNMs), random forest and non-spatial linear models to stream temperature data from the Upper Condamine River in QLD, Australia and used them to semi-continuously predict metrics describing the magnitude, duration, and frequency of the thermal regime through space and time. We compared both daily and aggregated temperature metrics and found that SSNMs always had more predictive ability than the random forest models, but both models outperformed the non-spatial linear model. For metrics describing thermal magnitude and duration, aggregated predictions were most accurate, while metrics describing the frequency of heating events were better represented by metrics based on daily predictions generated using a SSNM. A more comprehensive representation of the spatio-temporal thermal regime allows researchers to explore new spatio-temporally explicit questions about the thermal regime. It also provides the information needed to generate a suite of ecologically meaningful metrics capturing multiple aspects of the thermal regime, which will increase our scientific understanding of how organisms respond to thermal cues and provide much-needed information for more effective management actions. [ABSTRACT FROM AUTHOR]

Daily temperature data from 1960 to 2013 and field-observed phenology data were used to investigate the spatiotemporal changes in thermal growing season and their relationship with the response of alpine grassland to climate variability in the Three-Rivers Headwater Region (TRHR) during the recent decades. We found a significant extension of the thermal growing season by 8.3 d per decade ( p < 0.01) between 1986 and 2013 due to the combination of earlier start (tGSS; −4.1 d per decade, p < 0.01) and delayed end (tGSE; 4.2 d per decade, p < 0.01) of the thermal growing season. However, earlier tGSS and delayed tGSE were weakened between 2000 and 2013, compared to that between 1986 and 1999, in association with changes in seasonal temperature. Our results also suggested that earlier start of actual growing season (aGSS) was associated with the increasing winter and spring temperature; while the end of actual growing season (aGSE) was triggered by summer temperature and precipitation; and earlier and delayed of aGSE were associated with the increasing summer temperature and precipitation, respectively. Additionally, earlier tGSS was associated with an earlier aGSS response to increased temperature, while delayed tGSE was associated with earlier aGSE. Thus, the actual growing season possibly move forward rather than extended in length, in contrast to the extension of the thermal growing season due to the ongoing warming. [ABSTRACT FROM AUTHOR]

The on- and off-site effects of soil erosion in many environments are well known, but there is still limited understanding of the soil loss fluxes in downstream direction due, among other factors, to scarce and poor quality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scales and (ii) interpret the results in terms of processes involved and the controlling factors, was conducted in Thukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km 2 ), subcatchment (1.20 km 2 ), catchment (9.75 km 2 ), sub-basin (253 km 2 ) and basin (29,038 km 2 ), were used in addition to fifteen (1 m 2 ) microplots and ten (10 m 2 ) plots on five locations within the microcatchment. The results showed 19% decrease of unit-area runoff (q) from 3.1 L m −2 day −1 at microplot to 2.5 L m −2 day −1 at plot scale followed by steeper (56%) decrease at microcatchment scale. The q decreased in downstream direction to very low level (q ≤ 0.26 L m −2 day −1 ). The changes in q were accompanied by initial 1% increase of soil loss (SL) from 18.8 g m −2 day −1 at microplot to 19.1 g m −2 day −1 at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m −2 day −1 at microcatchment scale, followed by further decrease in downstream direction. The decrease of q with spatial scale was attributed to infiltration losses, while initial increase of SL signified greater competence of sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution of the soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet. Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisation of gullies are recommended. [ABSTRACT FROM AUTHOR]

The geomorphic development of Japanese mountains and rivers during the Quaternary is the result of tectonic effects, sea-level change and climate change. The majority of the Japanese archipelago is being uplifted, with its mountains rising at rates ranging from 0.1 to 7 mm/y, as calculated by the mean altitudes of mountains under the assumption that they are in equilibrium between uplift and erosion. Filltop terraces built by climate-controlled accumulation of gravel are distributed throughout central and northern Japan. These terrace surfaces formed during glacial periods, and their surface ages are progressively younger upstream. This phenomenon was caused by sea-level lowering. These fluvial terraces are keys to reconstruction of geomorphic and topographic changes in Japanese mountain. Yonekura et al. classified the 61 mountainous areas of Japan into seven types, from the steepest type I to the gentlest type VII, on the basis of a steepness metric incorporating mountain heights, a steepness along the longitudinal and transverse profiles of ridges, and the heights of ridges relative to the valley floors. Half of Japanese mountains (types I to III) are in a state of equilibrium between uplift and erosion. Slowly rising or young mountains (types V to VII) have preserved uplifted peneplains on their tops and are not in the state of equilibrium. A proposed classification of river morphology into upper, middle and lower reaches, combined with the seven types classification of mountain morphology offers insight into the Quaternary development of Japanese landforms. The lower reaches of rivers in Japan are defined as lower area in elevation than the aggradation limit of sea level change. Terraces here are controlled by sea-level change. The middle reaches are defined as the part between point AL and the upstream limit of river terraces. Several terraces of older to younger ages are formed in middle reaches, indicating that the middle reaches are also uplifting. Sea level acts as the base level of erosion in the lower and middle reaches. River terraces are not formed in the upper reaches. Down-cutting for terrace emergence ceased at the LR, suggesting that the LR is stable. The upper reaches are defined by the LR point, which acts as a local base level of erosion. [ABSTRACT FROM AUTHOR]

The ecological state of the Baltic Sea and the inland waters has raised interest in reducing nutrient loads from anthropogenic sources. In this study our main aim was to estimate the trends in agricultural nitrogen and phosphorus fluxes and to explain them by large scale changes in land use and climate. We used long-term monitoring data of discharge and nutrient concentrations of seven small catchments and 20 river basins. In the analysis we used two regression based models to calculate nutrient fluxes and to make source apportionment, and Mann-Kendall statistics to study trends in nutrient concentrations and climatic variables. Annual mean temperature increased at six meteorological stations out of the 16 stations included in the study. There was a statistically significant increase in temperature in late summer/early autumn at 14 stations. There were no trends in annual mean runoff in any of the river basins but there was a decrease in runoff in spring or early summer in 15 and an increase in mid-winter runoff in 13 river basins. There was an increasing trend in the nitrogen concentrations and a decreasing trend in the phosphorus concentrations. The flow normalized nitrogen flux to the Baltic Sea increased steadily until the mid 2000s and has decreased by 20% from that time until 2012. The flow normalized phosphorus flux has steadily decreased from early 1990s to 2012. The specific agricultural nitrogen loading value was 1340 kg km −2 yr −1 and the phosphorus loading value 83 kg km −2 yr −1 . Clearing of new fields explained 50% of the increase in the nitrogen flux to the Baltic Sea between the periods 1995–1999 and 2000–2006. September mean temperature explained 15–30% of the variance in the nitrogen concentrations in the small catchments and 53% of that in the large river basins. Changes in field area or climate did not explain changes in the phosphorus fluxes. [ABSTRACT FROM AUTHOR]

A major challenge in the biological monitoring of stream ecosystems in protected wilderness areas is discerning whether temporal changes in community structure are significantly outside of a reference condition that represents natural or acceptable annual variation in population cycles. Otherwise sites could erroneously be classified as impaired. Long-term datasets are essential for understanding these trends, to ascertain whether any changes in community structure significantly beyond the reference condition are permanent shifts or with time move back to within previous limits. To this end, we searched for long-term (>8 years) quantitative data sets of macroinvertebrate communities in wadeable rivers collected by similar methods and time of year in protected wilderness areas with minimal anthropogenic disturbance. Four geographic areas with datasets that met these criteria in the USA were identified, namely: McLaughlin Nature Reserve in California (1 stream), Great Smoky Mountains National Park in Tennesse-North Carolina (14 streams), Wind River Wilderness Areas in Wyoming (3 streams) and Denali National Park and Preserve in Alaska (6 streams). Two statistical approaches were applied: Taxonomic Distinctness (TD) to describe changes in diversity over time and non-metric multidimensional scaling (MDS) to describe changes over time in community persistence (Jaccards Index) and community stability (Bray–Curtis Index). Control charts were used to determine if years in MDS plots were significantly outside a reference condition. For Hunting Creek, TD showed three years outside natural variation which could be attributed to severe hydrological events but years outside the natural-variation funnel at sites in other geographical areas were inconsistent and could not be explained by environmental variables. TD identified simulated severe pollutant events which caused the removal of entire invertebrate assemblages but not simulated water temperature shifts. Within a region, both MDS analyses typically identified similar years as exceeding reference condition variation, illustrating the utility of the approach for identifying wider spatial scale effects that influence more than one stream. MDS responded to both simulated water temperature stress and a pollutant event, and generally outlying years on MDS plots could be explained by environmental variables, particularly higher precipitation. Multivariate control charts successfully identified whether shifts in community structure identified by MDS were significant and whether the shift represented a press disturbance (long-term change) or a pulse disturbance. We consider a combination of TD and MDS with control charts to be a potentially powerful tool for determining years significantly outside of a reference condition variation. [ABSTRACT FROM AUTHOR]

The delivery of organic carbon (C) from rivers to the coastal ocean via estuaries is recognized as an important component of the global C budget however, smaller river systems are often overlooked and modern flux estimates are not very different from historical estimates. Here, the seasonal (wet vs. dry) concentration and fluxes of dissolved organic C (DOC) were measured in five small sub-tropical rivers that drain into the Tampa Bay (FL, USA) estuary. DOC distributions were highly variable among riverine, mesohaline, and marine end-member samples in all river catchments and no significant differences were observed among or between DOC concentrations with respect to river catchment, season, or year of sampling. In general, DOC mixed non-conservatively during the wet seasons, and conservatively during the dry seasons, with the estuarine reaches of each river serving as a sink of DOC. Fluxes were strongly tied to discharge irrespective of season, and the estuaries removed 15–65% of DOC prior to export to coastal Bay and Gulf of Mexico waters. DOC concentrations were similar to others reported for low-elevation sub-tropical rivers, and a combination of elevation, residence time, and climate appear to control the abundance and variability of DOC in sub-tropical vs. tropical river systems. The characterization of DOC in small, sub-tropical rivers, which share characteristics with both their temperate and tropical counterparts, is critical for quantitatively constraining the importance of these systems in local-to-regional scale ocean C budgets. In addition to geomorphic properties, the role of past, present, and future land cover and other environmental change in small coastal rivers also exerts control on the quantity and flux of DOC in these systems. [ABSTRACT FROM AUTHOR]

The pollen diagram from the Kobyle Jezioro raised bog, situated in the source area of the Tanew River in the Roztocze region, covers the whole Neoholocene. The deposit thickness (about 3.5 m) has permitted high resolution pollen, peat (including macrofossils) and lithology analyses. Vegetational and palaeoenvironmental changes in this part of the Roztocze were recorded in pollen spectra and organic deposits. Palynological evidence shows the typical Neoholocene succession, which corresponds with the phenomena described from central Europe: from mixed deciduous forests at the decline of the climatic optimum, through hornbeam- and beech-dominated forests to pine forests. Peat accumulation in the Kobyle Jezioro peat-bog started during increased climatic humidity at the beginning of the Subboreal, and originally a fen peat was formed. Raised bog peat layers make up the uppermost 80 cm of the deposit. Within the fen deposits can be found layers of transitional peat, indicating short-term episodes of water deficiency in the early Subboreal phase (short-term climatic dryness) and towards its end (drainage of the bog resulting from the lowering of the groundwater table in the source area of the Tanew River). The growth of the raised bog started at the beginning of the climate deterioration in the Little Ice Age, and the unstable climatic conditions are reflected in the numerous periodical mineral (aeolian) material supplies in the developing ombrogenic bog. The accumulation of the younger section of transitional and raised peats during the Little Ice Age reflects the local hydrological changes in the source area of the Tanew River. [ABSTRACT FROM AUTHOR]

We studied a newly formed spit in the Baram River mouth in Eastern Malaysia and evaluated the effects of climatic conditions and human interference over the last four decades (1974–2014). The development of a spit during a decade (1998–2008) and its maximum expansion over the period 2005–2010 is related to the erosion associated with deforestation and land use changes in the upstream region. The downstream transportation of the heavy sediment load occurred during the events of higher precipitation and flash floods. The recent spit was identified for the first time as a mud flat post the flash flooding of January 2005. It extended towards the south west of the river mouth till 2010 (six fold increase in area from 2005 to 0.29 km 2 ) and gradually disintegrated over the next 3 years. Depositional feature of coarse sediments and organic debris is clearly supported by the alternating thick layers in the top 25 cm of the three core samples (C1–C3) collected from the region. The non-existence of finer particles clearly indicates the supremacy of long shore currents in the region carrying away the fines to deeper regions. Gradual disappearance of the sand barrier post 2011 is due to the reduction in the amount of sediment load as a result of reduction in recent rainfall activity, land use/land cover changes mainly as reforestation, strengthening of palm plantation (controlling soil erosion in the river banks) in the upstream region. The dominant NW wind direction during the major part of the year is also one of the factors for the shift in depositional sequence and it is helped by the long shore currents which lead to the spit being partially connected to the main land. [ABSTRACT FROM AUTHOR]

River deposits are one of the main lines of evidence that tell us that Mars once had a climate different from today, and so changes in river deposits with time tell us something about how Mars climate changed with time. In this study, we focus in on one sedimentary basin – Aeolis Dorsa – which contains an exceptionally high number of exceptionally well-preserved river deposits that appear to have formed over an interval of > 0.5 Myr . We use changes in the river deposits' scale with stratigraphic elevation as a proxy for changes in river paleodischarge. Meander wavelengths tighten upwards and channel widths narrow upwards, and there is some evidence for a return to wide large-wavelength channels higher in the stratigraphy. Meander wavelength and channel width covary with stratigraphic elevation. The factor of 1.5–2 variations in paleochannel dimensions with stratigraphic elevation correspond to ∼2.6-fold variability in bank-forming discharge (using standard wavelength-discharge scalings and width-discharge scalings). Taken together with evidence from a marker bed for discharge variability at ∼ 10 m stratigraphic distances, the variation in the scale of river deposits indicates that bank-forming discharge varied at both 10 m stratigraphic ( 10 2 – 10 6 yr ) and ∼ 100 m stratigraphic ( 10 3 – 10 9 yr ) scales. Because these variations are correlated across the basin, they record a change in basin-scale forcing, rather than smaller-scale internal feedbacks. Changing sediment input leading to a change in characteristic slopes and/or drainage area could be responsible, and another possibility is changing climate ( ± 50 W / m 2 in peak energy available for snow/ice melt). [ABSTRACT FROM AUTHOR]

The hydromorphic regimes that underpinned Old World river-based civilizations are reviewed in light of recent research. Notable Holocene climatic changes varied from region to region, whilst the dynamics of floodplain environments were equally diverse, with river channel changes significantly affecting human settlement. There were longer-term trends in Holocene hydroclimate and multi-centennial length ‘flood-rich’ and ‘flood-poor’ episodes. These impacted on five identified flooding and settlement scenarios: (i) alluvial fans and aprons; (ii) laterally mobile rivers; (iii) rivers with well-developed levees and flood basins; (iv) river systems characterised by avulsions and floodouts; and (v) large river-fed wetlands. This gave a range of changes that were either more or less regular or incremental from year-to-year (and thus potentially manageable) or catastrophic . The latter might be sudden during a flood event or a few seasons ( acute ), or over longer periods extending over many decades or even centuries ( chronic ). The geomorphic and environmental impacts of these events on riparian societies were very often irreversible. Contrasts are made between allogenic and autogenic mechanism for imposing environmental stress on riverine communities and a distinction is made between channel avulsion and contraction responses. Floods, droughts and river channel changes can precondition as well as trigger environmental crises and societal collapse. The Nile system currently offers the best set of independently dated Holocene fluvial and archaeological records, and the contrasted effects of changing hydromorphological regimes on floodwater farming are examined. The persistence of civilizations depended essentially on the societies that maintained them, but they were also understandably resilient in some environments (Pharaonic Egypt in the Egyptian Nile), appear to have had more limited windows of opportunity in others (the Kerma Kingdom in the Nubian Nile), or required settlement mobility or exceptional engineering response (Huang He, Mesopotamia) to accommodate problems such as river avulsion, desiccation or local salinization. [ABSTRACT FROM AUTHOR]

Climate change scenarios for northern boreal regions indicate that there will be increasing temperature and precipitation, and the changes are expected to be larger in winter than in summer. These precipitation and discharge patterns, coupled with shorter ice cover/soil frost periods in the future would be expected to contribute significantly to changing flow paths of organic matter over a range of land use patterns. In order to study the impact of climate change on the seasonality of organic matter export we compared total organic carbon (TOC) and total organic nitrogen (TON) concentrations and export, during different seasons and climatically different years, over 12 years for 30 Finnish rivers separated into forest, agriculture and peat dominated catchments. The mean monthly TOC concentrations were highest during autumn and there was also a peak in May during the highest flow period. The mean monthly concentrations of TON were lowest during winter, increased in spring and remaining high throughout summer and autumn. The TOC/TON ratios were lowest during summer and highest during winter, and in all seasons the ratios were lowest in catchments with a high proportion of agricultural land and highest in peat-dominated catchments. The seasonality of TOC and TON exports reflected geographical location, hydrology and land use patterns. Most of the TOC and TON were transported during the high flow following the spring snowmelt and during rainfall in autumn. In all catchments the relative importance of the spring snowmelt decreased in wet and warm years. However, in peat-dominated catchments the proportion of spring period was over 30% of the annual export even in these wet and warm years, while in other catchments the proportion was about 20%. This might be linked to the northern location of the peat-dominated catchments and the permanent snow cover and spring snowmelt, even in warm years. [ABSTRACT FROM AUTHOR]

Riverbank collapse is a natural part of the evolution of rivers. An unprecedented period of dry conditions and low flows between 2005 and 2010 led to more than 162 reported riverbank collapse-related incidents along the Lower River Murray, in South Australia (downstream of Lock 1 at Blanchetown to Wellington). On 4 February, 2009 a 60 × 20 m (70,000 m 3 ) section of riverbank, near Long Island Marina, Murray Bridge, collapsed into the river, taking with it three unoccupied vehicles and several trees. This paper aims to: (i) model the Long Island Marina riverbank collapse incident in both 2D and 3D; (ii) examine the influence and sensitivity of river level fluctuations and climatic factors on riverbank stability; and (iii) determine the dominant triggers affecting collapse. The analysis has been undertaken using an integration of the limit equilibrium method, transient unsaturated flow modeling and digital elevation model and high resolution aerial images from a Geographic Information System. The paper demonstrates the efficacy of this framework and the accuracy of the predictions. It also reveals that river fluctuation, rather than climatic influences, dominates riverbank collapse in the Lower River Murray. [ABSTRACT FROM AUTHOR]