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• This study has compiled an unprecedented record of flooding for the Loire River. • 313 flood events were recorded on the Loire River between 1380 and 1845. • Numerous unknown flood events were recorded between the 14th and 16th centuries. • Ten periods of high hydrological activity were identified during the Little Ice Age. • Nearly all of these periods can also be found on other rivers in France and Europe. • Flood seasonality in the Loire varied greatly during the Little Ice Age. The Loire River watershed accounts for a fifth of metropolitan France. Nevertheless, knowledge of past floods of the Loire River and its tributaries is still very limited. This study aimed to carry out an unprecedented census of floods in the Loire River, during the Little Ice Age (LIA), from the 14th century to the mid-19th century, in order to detect periods of high and low hydrological activity. The abundant historical archives in the cities of Nevers and Decize, as well as other archives consulted, enabled us to record 303 flood events, including 220 in the study area between Digoin and Nevers in Burgundy. This census is heterogeneous over the centuries, with the majority of newly recorded flood events taking place during the 14th and 15th centuries, first half of the 16th century, and 18th and 19th centuries. The use of two types of flood indexes enabled this study to overcome the documentary bias, and detect several decadal periods of high or low hydrological activity during the LIA in the Loire River. Almost all these periods can be found on other rivers in both France and Europe, the Loire River being exposed to the confluence of several climatic influences, as confirmed by comparisons with the North Atlantic Oscillation (NAO), Grand Solar minima and temperature fluctuations. Nevertheless, the coldest periods of the LIA, coupled with negative NAO positions, correspond to periods of high hydrological activity in the Loire River. The study of flood seasonality also reveals a high degree of variability during the LIA, with a higher proportion of flood events occurring in summer and autumn compared with the current seasonal pattern. [ABSTRACT FROM AUTHOR]

• The isotopic fractionation caused by mining results in δ11B fluctuation in DQL. • The δ11B increase in XQL was caused by source change due to climate change. • Secondary minerals limit monthly variation of δ11B in Tataleng River. • Climate and tectonic may confuse paleoclimate information derived from δ11B. Da Qaidam Lake (DQL) and Xiao Qaidam Lake (XQL), located in close proximity with similar geological and hydrological settings, represent quintessential lakes harboring enriched boron (B) deposits on the northern Qinghai-Tibet Plateau (QTP). However, a significant disparity in both B concentrations and isotope values between these two lakes has emerged, showcasing distinct evolutionary trends in their B isotopes over the past three decades. The underlying mechanisms and evolutionary processes driving these variations remain ambiguous. This study elucidates the hydrochemical characteristics and δ11B values for brines, geothermal springs, and river waters around the DQL–XQL, concurrently monitoring hydrogeochemical parameters in XQL and Tataleng River at a monthly temporal scale. Our findings corroborate that: (1) The δ11B values of XQL waters have markedly increased from 0.52‰ to 2.81‰, while those of DQL waters have decreased from 6.17‰ to 4.16‰, exhibiting diametrically opposed isotopic trends in the face of warming–wetting climate change on the QTP. (2) Spatially, B concentration and δ11B values in the low salinity region of DQL are predominantly influenced by the redissolution of B-rich sediments, witnessing inconspicuous changes in the high salinity region. Temporally, the δ11B values of DQL waters experienced considerable fluctuations, ranging from 2.52‰ to 10.81‰ in the early 1990s, attributed to isotopic fractionation (solid–liquid separation) resulting from borate mining activities. After more than 30 years of recovery, its B isotope values have stabilized in recent years. (3) On a monthly time scale, δ11B values of XQL and Tataleng River waters exhibited pronounced seasonal variations regulated by water residence time and the formation of secondary minerals, manifesting as high values in the dry season and low values in the wet season. Rainy or humid climatic conditions encourage an increase in weathering flux in B-rich areas, leading to a higher transport of resources into the terminal salt lake. Over a multi-decadal time scale, alterations in the hydrological budget and mean weathering flux induced by a warming–wetting climate may modify the proportion of contributions from various sources, thereby regulating the δ11B values of XQL and Laguo Co. (4) When employing B isotopes to investigate the salt lakes evolution and paleo-environmental changes, it is imperative to consider the influence of alterations in water chemistry and isotope driven by changes in source-sink processes resulting from climate changes or tectonic movements. [ABSTRACT FROM AUTHOR]

• Identification of hydraulic variables through photos, videos and newspapers. • Topographic identification of hydraulic variables using Google Earth and Street View. • Detailed analysis of the hydraulic effects deduced from videos. • Use of a 2D fully-dynamic model applied on the reconstructed topography. • Checking the coherence of the hydrological inputs with the hydraulic effects. The description of the floods which have occurred in the past and an assessment of the adverse impacts they have entailed are among the duties required by the European Flood Directive. Indeed, to understand the consequences of a future flood on a city that in the past has already been affected by other flood events, it is very useful to reconstruct the hydraulic effects produced by those events. Such a task is particularly difficult for cases which occurred many years ago. For past events, it is often easier to have conventional hydrological data (for example, the hyetographs of the event) than conventional hydraulic data (recordings of flow rates, water depths, etc.). It is also difficult to obtain the topography valid for the period in which the event occurred. The greater the distance in time the greater the difficulty in gathering these data. In this paper we present a criterion for making a flow of information, using various non-conventional sources of information (such as amateur videos, photographs, traditional topographic surveys, news reports, etc.). In particular, it is shown how the data thus obtained can be used together in order to reconstruct numerically the hydraulic dynamics of a flood event in an urban area with a complete hydrodynamic model, which requires a particularly accurate computational domain. All these issues will be presented and discussed with reference to the numerical reconstruction of the flood event that occurred 23 years ago (1996) in the city of Crotone (Calabria, Italy). [ABSTRACT FROM AUTHOR]

• An alpine lacustrine core located in the central Tianshan Mountains is investigated. • Diatom-based temperature, pH and conductivity are reconstructed. • The influence factors modulating lake-water temperature and pH are analyzed. • Interplays among precipitation, temperature and glaciers on salinity are revealed. In order to deepen our understanding of water environment-related issues in the central Tianshan Mountains (TCTMs), it is necessary to study the change processes of hydrological variables and the underlying mechanisms within a longer time window that goes beyond the instrumental period. This study focuses on a high-resolution lacustrine sediment core drilled from an alpine lake in TCTMs with a hope that palaeohydrological changes inferred from diatom assemblages may provide an insight on details of water environment evolutions. The diatom inferred temperature was broadly consistent with the temperature records in its adjacent areas, representing a temperature trough during ∼1490 to ∼1835 CE and a general rising trend since ∼1835 CE. The diatom inferred pH (DI-pH) was generally low during ∼1490 to ∼1835 CE, and was high with a declined trend during ∼1835 to ∼2013 CE, being negatively correlated with TN or TOC and positively correlated with carbonate in sediments significantly. The diatom inferred conductivity (DI-Cond) was characterized with a significantly high salinity interval during ∼1490 to ∼1835 CE than that during ∼1835 to ∼2013 CE. The salinity during the past ∼520 years was modulated by interplays among precipitation driven by the Atlantic Multidecadal Oscillations, temperature-dictated evaporation, and temperature-led glacier melting. The water environment changes (lakewater temperature, DI-pH, DI-Cond and diatom assemblages) were identified with a remarkable shift at ∼1835 CE when the temperature began to climb up in TCTMs, implying that climate warming not only exerted influences on water resources but also on water properties in TCTMs. [ABSTRACT FROM AUTHOR]

• Predict lake level under climate scenarios by assimilating model and observation. • Incorporate the advantages of last ICESat-2 observations and hydrological model. • Integrated by Prophet forecasting procedure and Variational Bayesian Monte Carlo. • Enhance both short-term and long-term prediction accuracy. • Successfully predict lake level turning points driven by climate changes. Predicting future lake levels under climate change is critical for advancing our understanding of hydrological processes in a changing environment. However, continuous and long-term prediction of lake levels is challenging due to discrepancies in multi-source data and the lack of integration of hydrological models and climate scenarios. Physical and statistical models have been used for lake levels prediction, however, physical models are difficult to calibrate and statistical models often fail to account for the effects of climate changes. In this study, a lake level prediction model was proposed by assimilating the hydrophysical model based on water balance and the ICESat-2 observations using Variational Bayesian Monte Carlo. The model can predict monthly lake levels combining CMIP6-SWAT climate-driven projections and ICESat-2 observations. Short-term validation over 24 months showed the R2 was 0.91 and the RMSE was 5 cm between the proposed model and the ICESat-2 observation. The accuracy is superior to both the hydrophysical model based on water balance and the Prophet time series model. Long-term validation from 1978 to 2021 showed the proposed model has the potential to enhance prediction accuracy within 2 to 3 years compared with the hydrophysical model based on water balance and it is suitable for predicting long-term lake level trends. Notably, it successfully predicted the significant turning point around 2005 where lake levels shift from decline to increase based on past data. The water levels of Lake Qinghai were predicted to rise at a rate of 3.7 cm per year by 2050 under the SSP2-4.5 scenario. The proposed assimilation model combines the strengths of hydrological modeling based on water balance (incorporating the effects of climate change) and the latest ICESat-2 lake level observations (incorporating the effects of recent historical lake levels), improving the accuracy of short-term lake levels and long-term lake level trends prediction. Moreover, as the model is based on satellite remote sensing observations, it has the potential to be applied to any lake globally. [ABSTRACT FROM AUTHOR]

The groundwater of the Cabo de Gata detritic aquifer, in southeastern Spain, exhibit salinities of between 70–726 mmol/L of Cl − (brackish-salt to hypersaline waters). We have investigated the causes of the high salinity anomaly, which at certain points exceeds that of present-day seawater (600 mmol/L). Two hypotheses are considered as possible sources for the saline water: (1) The deeper, more saline groundwater date back to an old marine intrusion that occurred at the end of the last Ice Age (14–17 ka), when seawater salinity was higher than in the present day. This hypothesis is supported by the values of 14 C measured in this water (∼6–10 pmc), which indicate old water of up to 17 ka. However, the values of 18 O and 2 H are lower than would be expected. (2) The water is the result of mixing between fresh groundwater and seawater. The latter explanation agrees well with the low values of 18 O and 2 H. This mixture is later subject to evaporation, explaining its high salinity. Hydrogeochemical modelling was carried out for the most saline samples, assuming such mixing between freshwater and seawater followed by evaporation, and the results show a very good agreement between the measured and simulated values. According to the model calculation, the original mixture contained approximately 60% seawater and its volume subsequently was reduced through evaporation by around 30%. This mixing and evaporation could occur during the Flandrian Transgression (6000–8000 y), when this area accommodated a coastal lagoon. [ABSTRACT FROM AUTHOR]

Prewhitening, the process of eliminating or reducing short-term stochastic persistence to enable detection of deterministic change, has been extensively applied to time series analysis of a range of geophysical variables. Despite the controversy around its utility, methodologies for prewhitening time series continue to be a critical feature of a variety of analyses including: trend detection of hydroclimatic variables and reconstruction of climate and/or hydrology through proxy records such as tree rings. With a focus on the latter, this paper presents a generalized approach to exploring the impact of a wide range of stochastic structures of short- and long-term persistence on the variability of hydroclimatic time series. Through this approach, we examine the impact of prewhitening on the inferred variability of time series across time scales. We document how a focus on prewhitened, residual time series can be misleading, as it can drastically distort (or remove) the structure of variability across time scales. Through examples with actual data, we show how such loss of information in prewhitened time series of tree rings (so-called “residual chronologies”) can lead to the underestimation of extreme conditions in climate and hydrology, particularly droughts, reconstructed for centuries preceding the historical period. [ABSTRACT FROM AUTHOR]

Water depth above the flood deposits should be taken into account in calculations of the palaeoflood peak stages, which can provide more accurately estimate of palaeoflood stage. Here we present a new method, slackwater flow depth, to assess palaeoflood peak stage and to reduce the underestimation of palaeoflood stage. Palaeoflood slackwater deposits (SWDs) were identified by palaeohydrological criteria in cliff riverbank on the Yanhe River, middle Yellow River basin. Palaeoflood events recorded in four layers of SWD were dated by optical stimulated luminescence to 9.5–8.5 ka. The estimation of palaeoflood maximum stage was 778.3 m using the slackwater flow depth method and the palaeoflood peak discharge is 15,000 m 3 /s using the step-backwater method. Palaeoflood results greatly extend the current flood data series in the Yanhe River basin. The regional flood history including gauged flood, historical and palaeoflood data was compiled and evaluated for the major tributaries of the middle Yellow River. The relationship between palaeoflood peak discharges and drainage areas in this region fit well with the global maximum curves. The results of site-specific and regional palaeoflood evaluations demonstrate that the approach estimates the true palaeoflood peak stage and discharges and improves the flood frequency analysis of extreme and rare floods for a particular basin. Meanwhile, the advantages and uncertainties of this method need ongoing discussion in palaeoflood investigations. [ABSTRACT FROM AUTHOR]

• The systematic observations benefit the lake water isotopes (δ L) simulations. • This study well simulated the temporal variations of δ L of a small and open lake. • The MBM captured the influences of extreme weather events on the δ L. • The sensitivity test well evaluated the influences of weather seasonality on the δ L. Hydrologic and isotope mass-balance models (MBMs) are useful tools for the simulation and quantitative interpretation of lake water δ18O (δ L). Such studies of small, open lakes are important because δ L may show large responses to weather-driven hydrological variability. A δ L sequence was simulated for three-year and five-day interval data from Taozi Lake, a small, open lake in Changsha, in the East Asian monsoon region of China. The MBMs performed well, with the optimal model explaining 90% of the observed δ L variability. However, it was necessary to parameterize the precipitation input by increasing the lake water depth during heavy precipitation events to capture the observed sharp decreases in δ L. We found that the MBMs using air temperature and the equilibrated atmospheric vapor δ18O (δ A) produced a more negative δ L compared to the model using the surface water temperature and the observed δ A , and that the equilibrated δ A was somewhat arbitrary, which introduced a large error in the model output. A sensitivity test highlighted the importance of the seasonal variability of hydrometeorological and isotopic variables to reproduce the observed δ L variability. Additionally, the simulated average δ L showed a similar pattern of variation to the meteorological variables shifted by different ratios, but for the relative humidity, there was only a narrow window within which a realistic δ L series could be reproduced. Our results show that a realistic MBM can be established based on long-term observations, with implications for studies of hydrologic processes and paleoclimate reconstruction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Very high amounts of dissolved noble gases were identified in a deep desert aquifer. • Large water table fluctuations during past pluvial periods are reconstructed. • Hydrogeological settings highly affect the air entrapment and dissolution process. • Similar excess air dissolution patterns are identified in distinct desert aquifers. Illuminating past hydrological and climatological conditions in arid regions may provide insights into future trends in groundwater availability. The main objective of this study is to explore paleorecharge processes in the deep regional Nubian Sandstone Aquifer (NSA), which stretches below the hyperarid deserts of the Sinai Peninsula (Egypt) and the Negev (Israel), using dissolved noble gas data. Extremely high amounts of dissolved excess air (Ne concentrations up to 4 × solubility equilibrium) were observed in the ancient (81Kr-depleted) groundwater that was recharged during past pluvial epochs in the basin. The observed unique excess air signal and the clear spatiotemporal structure of the noble gas compositions in the aquifer are hypothesized to reflect two major characteristics of the groundwater system: (a) large-scale, long-term rises in the water table that facilitate the entrapment and dissolution of air bubbles under increased hydrostatic pressure, and (b) the geological settings in the southern recharge area in Sinai, including an almost horizontal position of the layers and intercalation of low-permeability rock formations within the aquifer, which inefficiently reject air bubbles from groundwater, thereby allowing for substantial entrapment of bubbles that dissolve as the water table rises. Enhanced dissolution of entrapped air was also observed in other paleo-groundwater-containing regional sandstone aquifers across North Africa, which, together with the recent findings from the NSA, suggest that large-scale water table fluctuations have likely extensively occurred during past pluvial periods over these (and possibly other) arid regions. A preliminary assessment of noble gas recharge temperatures (NGTs) indicates an apparent decoupling of surface and water table temperatures in the case of deep aquifers with a thick (hundreds of m) unsaturated zone. This observed decoupling calls for a re-evaluation of previously obtained NGT records and a need for future work to consider the modification of NGTs due to soil air fractionation and geothermal heating of the underlying deep unsaturated zones. [ABSTRACT FROM AUTHOR]

• Improvements to paleoflood hydrologic methods for alluvial rivers are explored. • Minimum paleodischarges were estimated using deposit d90 grain sizes. • Flood deposit depths were used to adjust channel geometries to reflect aggradation. • Paleodischarge estimation methods applicable to rivers lacking streamflow records. • Paleoflood record length and 'completeness' impacted flood frequency estimates. Extreme floods are underrepresented in stream gauge records. Sedimentological evidence of past floods (paleofloods) yields longer records, allowing extreme floods to be examined over several Holocene climate periods. This study examines the influence of hydrogeomorphic complexity (floodplain aggradation and spatially variable flood deposition) on paleoflood record "completeness" and their implications for flood magnitude estimates made with paleoflood hydrologic data. We collected two sediment cores 500 m apart from the same elevation on a natural levee along a bank of the Tennessee River near Guntersville, Alabama. We measured grain size from each core at a 1-cm resolution using a Malvern 3000 laser granulometer. Optically stimulated luminescence dating of flood deposits revealed approximate age ranges of 50 – 6500 years calibrated before present (yrs. B.P.) for the downstream 3.5 m core (i.e., BO1) and 190 – 8500 yrs. B.P. for the upstream 4.18 m core (i.e., EL2). First, a sensitivity analysis revealed adjusted floodplain elevations (AFE) for each paleoflood cross-sectional geometry to reflect floodplain aggradation over time enabled the detection of paleoflood magnitude differences, suggesting floodplain aggradation should be considered in paleoflood reconstruction within alluvial settings. Minimum paleodischarge intervals were estimated in a 1D HEC-RAS step backwater model by calculating the minimum paleoflood stage needed to transport the d90 of each paleoflood deposit. Big Oak and East Levee 2 sediment cores each contained 15 high magnitude, identifiable paleofloods. The majority of the BO1 paleofloods occurred in the last 2,000 years, while most EL2 paleofloods occurred between 2,000 and 5,000 yrs. B.P., suggesting localized geomorphic complexity produced distinct paleoflood records for the same hydrogeomorphic surface. Four paleoflood events correlate across the two cores based on their ages and grain size distributions, and we combined these four floods to create a 'harmonized' flood chronology for the site. The timing of these four floods corresponds with paleofloods that occurred in the last 2000 years in the middle section of the Tennessee River identified by prior paleoflood hydrologic studies. Flood frequency analysis (Bayesian Markov Chain Monte Carlo method) scenarios with ten configurations of paleoflood hydrologic data revealed differences in the number and timing of paleofloods in three paleoflood chronologies (BO1, EL2, and the harmonized) resulting from hydrogeomorphic complexities affected model distribution parameters, goodness-of-fit, and the estimated discharges of annual exceedance probabilities used to inform the design of critical flood infrastructure. As a consequence of longer records containing smaller floods, the estimated discharge of the 0.01 (100-yr), 0.001 (1000-yr), and 0.0001 (10,000-years) AEPs for EL2 were 16%, 11%, and 5% smaller, respectively, than BO1 estimates. Alluvial rivers present more challenges for reconstructing paleoflood records than bedrock, confined channel settings. The strategies presented in this paper can help integrate paleoflood hydrologic data into flood frequency analyses for alluvial rivers identifying and minimizing error stemming from hydrogeomorphic complexity. These strategies offer opportunities to expand the use of paleoflood hydrologic data in flood frequency analyses to include more rivers located in temperate environments where climate change is intensifying precipitation and a compelling need exists to anticipate and plan for changes in extreme flood occurrence. [ABSTRACT FROM AUTHOR]

Summary Palaeo-hydrological interpretations of lake sediment proxies can benefit from a robust understanding of the modern lake environment. In this study, we use Nar Gölü, a non-outlet, monomictic maar lake in central Turkey, as a field site for a natural experiment using observations and measurements over a 17-year monitoring period (1997–2014). We compare lake water and sediment trap data to isotopic, chemical and biotic proxies preserved in its varved sediments. Nar Gölü underwent a 3 m lake-level fall between 2000 and 2010. δ 18 O lakewater is correlated with this lake-level fall, responding to the change in water balance. Endogenic carbonate is shown to precipitate in isotopic equilibrium with lake water and there is a strong relationship between δ 18 O lakewater and δ 18 O carbonate , which suggests the water balance signal is accurately recorded in the sediment isotope record. Over the same period, sedimentary diatom assemblages also responded, and conductivity inferred from diatoms showed a rise. Shifts in carbonate mineralogy and elemental chemistry in the sediment record through this decade were also recorded. Intra-annual changes in δ 18 O lakewater and lake water chemistry are used to demonstrate the seasonal variability of the system and the influence this may have on the interpretation of δ 18 O carbonate . We use these relationships to help interpret the sedimentary record of changing lake hydrology over the last 1725 years. Nar Gölü has provided an opportunity to test critically the chain of connection from present to past, and its sedimentary record offers an archive of decadal- to centennial-scale hydro-climatic change. [ABSTRACT FROM AUTHOR]

Summary Flash floods represent one of the most common natural hazards in mountain catchments, and are frequent in Mediterranean environments. As a result of the widespread lack of reliable data on past events, the understanding of their spatio-temporal occurrence and their climatic triggers remains rather limited. Here, we present a dendrogeomorphic reconstruction of past flash flood activity in the Arroyo de los Puentes stream (Sierra de Guadarrama, Spanish Central System). We analyze a total of 287 increment cores from 178 disturbed Scots pine trees ( Pinus sylvestris L.) which yielded indications on 212 growth disturbances related to past flash flood impact. In combination with local archives, meteorological data, annual forest management records and highly-resolved terrestrial data (i.e., LiDAR data and aerial imagery), the dendrogeomorphic time series allowed dating 25 flash floods over the last three centuries, with a major event leaving an intense geomorphic footprint throughout the catchment in 1936. The analysis of meteorological records suggests that the rainfall thresholds of flash floods vary with the seasonality of events. Dated flash floods in the 20th century were primarily related with synoptic troughs owing to the arrival of air masses from north and west on the Iberian Peninsula during negative indices of the North Atlantic Oscillation. The results of this study contribute considerably to a better understanding of hazards related with hydrogeomorphic processes in central Spain in general and in the Sierra de Guadarrama National Park in particular. [ABSTRACT FROM AUTHOR]

Summary Slackwater palaeoflood deposits (SWDs) were identified in a bedrock gorge in the upper reaches of the Hanjiang River of central China. The Hanjiang River is the longest tributary of the Yangtze River, one of the most flood-prone rivers in China, and the main source of water for the South-to-North Water Transfer Project (SNWTP). Three main loess-soil profiles with late Pleistocene and Holocene palaeoflood SWD bedsets were found. Palaeoflood SWDs identified interbedded in the loess–soil sequence of late Pleistocene and Holocene age within the cliff riverbanks were studied by field observations and laboratory analysis, including particle−size distribution and Optically Stimulated Luminescence (OSL) dating. At least eight extreme flood events documented by palaeoflood SWDs occurred in the Wufeng reaches of the upper Hanjiang River. The discharge estimation associated with palaeoflood SWDs, indicates that the minimum flood peak discharges of these flood episodes range from 42,220 to 63,400 m 3 /s. The SWDs were OSL dated to between 12,600–12,400, 4200–4000, 3200–2800 and 1900–1700 a BP and these dates were corroborated with pottery remains retrieved from the profiles and dated by archaeological methods. These periods of increased flood magnitude coincide with contemporaneous global climatic events dated to 12,500, 4200, 3100 and 1900 a BP worldwide. These findings are of great significance in understanding the interactions between hydrological systems and climatic change in monsoonal zones. [ABSTRACT FROM AUTHOR]

Summary Tree-ring data have been used to augment limited instrumental records of climate and provide a longer view of past variability, thus improving assessments of future scenarios. For streamflow reconstructions, traditional regression-based approaches cannot examine factors that may alter streamflow independently of climate, such as changes in land use or land cover. In this study, seasonal water balance models were used as a mechanistic approach to reconstruct streamflow with proxy inputs of precipitation and air temperature. We examined a Thornthwaite water balance model modified to have seasonal components and a simple water balance model with a snow component. These two models were calibrated with a shuffled complex evolution approach using PRISM and proxy seasonal temperature and precipitation to reconstruct streamflow for the upper reaches of the West Walker River basin at Coleville, CA. Overall, the modified Thornthwaite model performed best during calibration, with R 2 values of 0.96 and 0.80 using PRISM and proxy inputs, respectively. The modified Thornthwaite model was then used to reconstruct streamflow during AD 1500–1980 for the West Walker River basin. The reconstruction included similar wet and dry episodes as other regression-based records for the Great Basin, and provided estimates of actual evapotranspiration and of April 1 snow water equivalence. Given its limited input requirements, this approach is suitable in areas where sparse instrumental data are available to improve proxy-based streamflow reconstructions and to explore non-climatic reasons for streamflow variability during the reconstruction period. [ABSTRACT FROM AUTHOR]

Summary Over the past decades, δ 18 O and δ 2 H analyses of lacustrine sediments became an invaluable tool in paleohydrology and paleolimnology for reconstructing the isotopic composition of past lake water and precipitation. However, based on δ 18 O or δ 2 H records alone, it can be challenging to distinguish between changes of the precipitation signal and changes caused by evaporation. Here we propose a coupled δ 18 O– δ 2 H biomarker approach that provides the possibility to disentangle between these two factors. The isotopic composition of long chain n -alkanes ( n -C 25 , n -C 27 , n -C 29 , n -C 31 ) were analyzed in order to establish a 16 ka Late Glacial and Holocene δ 2 H record for the sediment archive of Lake Panch Pokhari in High Himalaya, Nepal. The δ 2 H n -alkane record generally corroborates a previously established δ 18 O sugar record reporting on high values characterizing the deglaciation and the Older and the Younger Dryas, and low values characterizing the Bølling and the Allerød periods. Since the investigated n- alkane and sugar biomarkers are considered to be primarily of aquatic origin, they were used to reconstruct the isotopic composition of lake water. The reconstructed deuterium excess of lake water ranges from +57‰ to −85‰ and is shown to serve as proxy for the evaporation history of Lake Panch Pokhari. Lake desiccation during the deglaciation, the Older Dryas and the Younger Dryas is affirmed by a multi-proxy approach using the Hydrogen Index (HI) and the carbon to nitrogen ratio (C/N) as additional proxies for lake sediment organic matter mineralization. Furthermore, the coupled δ 18 O and δ 2 H approach allows disentangling the lake water isotopic enrichment from variations of the isotopic composition of precipitation. The reconstructed 16 ka δ 18 O precipitation record of Lake Panch Pokhari is well in agreement with the δ 18 O records of Chinese speleothems and presumably reflects the Indian Summer Monsoon variability. [ABSTRACT FROM AUTHOR]

Summary In many regions of the world flood events in mountain basins are one of the greatest risks to the local population, due to the pressure placed on land use by social and economic development. Conventional hydrologic–hydraulic methodological approaches are not usually feasible in mountainous basins because they are not gauged at all or, in the best-case scenario, are poorly gauged. In this context, palaeohydrological research offers a valuable alternative to the above approaches. However, many palaeohydrological data sources and associated methods have been proposed and initially used in large basins with extensive floodplains. As a result, when they are used in mountainous areas they must be adapted to include different techniques, since the problems to be addressed are different and less data is usually available. In this paper, we review classic data sources and different analytical methods and discuss their advantages and shortcomings with particular attention to mountain basins. For this purpose, examples are provided where improvements in the palaeohydrologic methods are proposed by incorporating uncertainties, describing sources of error or putting forward hypotheses for hydraulic calculation to make palaeoflood hydrology more objective and useful in risk assessment. [ABSTRACT FROM AUTHOR]

Summary Paleoflood hydrology typically deals with the reconstruction of floods in ungauged and poorly gauged basins by combining different sources of indirect evidence. Botanical indicators have been used repeatedly in the past, mostly through the study of scars in trees or germination dates of plants on newly created surfaces. In this paper we test the hypothesis that the inclination of trees – as induced by floods – can provide information on flood magnitude, and that this source of information can therefore be used for flood reconstructions. We used a mechanical root-plate rotational stiffness model in three gauged river reaches in Central Spain to test our hypothesis and combine approaches typically applied in dendrogeomorphic, dendrometric, mechanical structure, and hydraulic research. Results show a correlation between modeled and observed deformation at the stem base of trees induced by floods (coefficient of correlation 0.58 for all observations). However they also point to a clear underestimation of peak discharge reconstructions. We used different efficiency criteria to test the reliability of results and differences between river reaches. In addition, we carried out a sensitivity analysis and discussed sources of uncertainties which may reach up to 112%, mainly due to difficulties to determine the rotational stiffness of the root plate system a posteriori. The approach presented here is promising, but more research is clearly required to improve the quality of peak discharge estimations based on stem tilting. [ABSTRACT FROM AUTHOR]

Summary Incorporating the historical flood and paleoflood information to systematical observed data (i.e. simple sample) is extremely useful approach for enriching the datasets and improving the accuracy of parameter estimation, in turn to improve the reliability of hydrological frequency analysis. In this paper, the formulas for using Modified Weighted Function (MWF) method to estimate parameters of Pearson Type Three Distribution (PE3) in term of non-simple sample (with the incorporation of historical flood information to systematically recorded sample) are developed, called as MWFIHF, which makes MWF method available for non-simple sample. Monte Carlo experiment is carried out to simulate a large number of non-simple samples upon which statistical properties of MWFIHF are investigated. The results show that the proposed formulas for MWFIHF are satisfactory. Besides, the results of MWFIHF are compared to that of the original Weighted Function (WF) and Linear moments (L-M). It indicates that MWFIHF is obviously superior to WF and slightly better than L-M in terms of statistical unbiasness and effectiveness. These three approaches are also used to analyze flood extremes data collected at 26 gauges around China. It also demonstrates that, MWFIHF fits well to most of these real flood extremes events. [ABSTRACT FROM AUTHOR]

Summary A paleo-hydrological study was carried out along the upper-reach gorges of the Hanjiang River that drains from the Qinling and Dabashan Mountains. Two bedsets of paleoflood slackwater deposits were found embedded in Holocene loess soil sequences within riverbank cliffs. All of these were studied by field observations and laboratory analyses, including magnetic susceptibility, particle size distribution and optically stimulated luminescence (OSL) dating. These analyses provided a complete catalog of Holocene flood events on a watershed scale that is important for understanding the regional hydrological responses to monsoonal climatic change. The results show that these hydro-climatic events were dated to 9000–8500 and 3200–2800 a B.P. The paleoflood peak discharges were estimated to be 44,350–49,860 m 3 /s by using the HEC-RAS model and were verified by different approaches. These results have extended the flood data sequence of the Hanjiang River to a 10,000-year time-scale. The additional data allowed us to refine the flood frequency-peak discharge curve and potentially increase its accuracy. These results will play an important role in mitigating flood hazards and will be useful for hydraulic engineering and the development of water resources in the Hanjiang River basin. [ABSTRACT FROM AUTHOR]

Highlights: [•] Multiple approach hydrologic hazard framework for critical infrastructure (dams). [•] Intergration of extreme storms, paleofloods and flood hazard information. [•] Risk-based flood hazard estimates with very low annual exceedance probabilities. [ABSTRACT FROM AUTHOR]

Summary: Climate-change projections suggest altered precipitation, temperature, and hydrological patterns for the near future. To better understand these future changes, long-term evidence from paleoarchives is necessary to determine the natural variability and climate relations in surficial hydrology. In this study, we aim to demonstrate that distribution of sedimentary mouthparts (mandibles) of aquatic mayfly (Ephemeroptera) and caddisfly (Trichoptera) larvae are dependent on stream conditions and this relationship can be used in paleohydrological studies to reconstruct past changes in stream flow. The results from a river–lake continuum in eastern Finland showed that the surface sediment accumulation of mayfly and caddisfly mandibles was strongly related to stream flow with highest abundances found from the riverine sediments. A sediment core taken from the deep basin of the lake revealed mandible accumulation patterns that correlated with a previous independent paleohydrological reconstruction. We interpret that the primary forcer for mandible deposition to lake sediments is spring floods caused by snow melt, and hence the mandible accumulation, represents amount of winter precipitation. Subsequently, the results indicated strong stream flow and wet winters during the Medieval Climate Anomaly (MCA) and weaker stream flow and dry winters during and after the Little Ice Age (LIA). This wintertime reconstruction contrasts the general summertime trends of dry MCA and wet LIA. The present results confirm the usability of mayfly and caddisfly mandibles in paleohydrological studies and provide evidence for past hydrological dynamics that can be valuable when addressing the potential magnitude of future changes. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a method for using major flash flood events occurred at ungauged catchments to reduce the uncertainties in estimating regional flood quantiles. The approach is based on standard regionalization methods assuming that the flood peak distribution rescaled by a site-dependent index flood is uniform within a homogeneous region. A likelihood formulation and a Bayesian Markov Chain Monte Carlo (MCMC) algorithm are used to infer the parameter values of the regional distributions. This statistical inference technique has been selected for its rigorousness – various hypotheses are explicitly formulated in the likelihood function, its flexibility as for the type of data that can be treated, and its ability to compute accurate estimates of the confidence intervals for the adjusted parameters and for the corresponding flood quantiles. The proposed method is applied to two data sets from Slovakia and the South of France that consist of series of annual peak discharges at gauged sites and estimated peak discharges of extreme flash flood events that have occurred at ungauged sites. The results suggest that the confidence intervals of the quantiles can be significantly narrowed down provided that the set of ungauged extremes is the result of a comprehensive sampling over the selected region. This remains valid, even if the uncertainties in the estimated ungauged extreme discharges are considered. The flood quantiles estimated by the proposed method are also consistent with the results of site specific flood frequency studies based on historic and paleoflood information. [ABSTRACT FROM AUTHOR]

Summary: A major hydroclimatic change occured in southeastern South America at the beginning of the 1970s. This change was recorded in Laguna Mar Chiquita (central Argentina), the terminal saline lake of a 127,000km2 catchment as a dramatic rise in lake level larger than any observed over the past 230years. Based on available continuous lake level monitoring since 1967, our study aimed to develop a lake water balance model for investigating the link between climate and lake level variations. Since un-gauged downstream surfaces represented approximately 80% of the catchment, the main challenge of the model development and implementation came from estimating the magnitude of catchment inputs from sparsely available gauge data. We determined a strongly negative water balance in the un-gauged part of the catchment that can be attributed to evapotranspiration in two large surface water hydrosystems. The chloride balance indicated that the lake is hydrologically closed, without significant groundwater outflows. Using contrasted hydroclimatic conditions, the robustness of the model calibration was evaluated with the model residual, and a short validation proposed for the 1998–2006 time period. Sensitivity analyses were performed in order to identify the main forcing factors of lake variations. We determined that the abrupt lake level rise in the early 1970s could be attributed to increased runoff in the upper northern sub-basin, suggesting a tropical climatic influence. Based on available hydroclimatic data, we propose a continuous lake level simulation for the 1926–2006 time period which could be used as a reference curve for better constraining paleohydrological reconstructions from sedimentary proxies. [ABSTRACT FROM AUTHOR]

Summary: Caves in Grand Canyon, Arizona, USA fall into two main categories: those formed under unconfined conditions and those formed under confined conditions. This study focuses on the hydrology and paleohydrology of the confined caves in the Redwall–Muav aquifer, where the aquifer is overlain by rocks of the Supai Group and underlain by the Bright Angel Shale. Unconfined caves are discussed only in their relation to confined caves. Discharge for confined groundwater was, as it is today, primarily from the Redwall Limestone where it has been incised by the main canyon or its tributaries and where it has converged along a structural low or fault. Descent of the potentiometric surface (or water table) over time is recorded by one ore episode and six cave episodes: (1) emplacement of Cu–U ore, (2) precipitation of iron oxide in cavities, (3) dissolution of cave passages, (4) precipitation of calcite-spar linings over cave passage walls, (5) precipitation of cave mammillary coatings, (6) minor replacement of cave wall and ceiling limestone by gypsum, and (7) deposition of subaerial speleothems. The mammillary episode records the approximate position of the water table when the incision of the canyon was at that level. Discharge toward spring points has reorganized and adjusted with respect to ongoing canyon and side-canyon incision. The dissolution of Grand Canyon confined caves was the result of the mixing of epigene waters with hypogene waters so that undersaturation with respect to calcite was achieved. The karst hydrology of Grand Canyon may be unique compared to other hypogene cave areas of the world. [ABSTRACT FROM AUTHOR]

Summary: This study demonstrates the significant influences of the geological structure (especially folding and lithology) and the karst system on groundwater flow regime. Folds divert groundwater flow from the general hydraulic gradient; marly layers sustain several perched sub-aquifers above the regional aquifer; and karstification increases the hydraulic conductivity by several orders of magnitude. These phenomena are quantitatively demonstrated within the Yarqon-Taninim (YT) basin, Israel, which is a complex groundwater system, combining several (extremely) opposite characteristics: humid and arid recharge zones, phreatic and confined parts, shallow and deep sub-aquifers, stratified and relatively-homogeneous sub-basins, saline and fresh water bodies, as well as stagnant and fast-flowing groundwater regions. We have introduced a 3D geological-based grid for the basin (for the first time). It was implemented into a numerical code (FEFLOW), which was used thereafter to analyze quantitatively the flow regime, the groundwater mass balance, and the aquifer hydraulic properties. We present up to date conceptual understanding and numerical modeling of the YT flow field, especially at its mountainous parts. Based on the calibration procedure and the sensitivity analyses, we obtained the best-fitted hydraulic conductivity values for the aquifer mesh. The general phenomenon observed is that as groundwater flow quantity increases, the hydraulic conductivity also increases. We interpret this result by the karstification mechanism (including paleo-karst). Thus, where groundwater flow-lines converge and where groundwater discharge amount increases, the karstification process intensifies and permeability increases. Consequently, at the mountainous region, along the syncline axes, where groundwater flow-lines converge, higher conductivities are found. Modeling results also exhibit that at the lowland confined area, the geological structure does not play a major role in directing groundwater flow. Rather, the flow field is controlled by the well-developed karst system and the relatively homogenous carbonate section. It is hypothesizes that the extensive karstification took place at the Messinian Salinity Crises, ∼5.5Ma, during which groundwater heads as well as sea level were lowered by several 100m. [Copyright &y& Elsevier]

Summary: Availability of long-term information on the variability of water resources in a given area is particularly important for sustainable resource management. Developing watershed simulation models that can be run using annually-resolved proxy climate data provides a way to improve reconstructions of hydrological parameters over multi-century time scales. Through the addition of a snowmelt modeling component, we enhanced a simple water-balance model to simulate streamflow at seasonal resolution. The model was calibrated to the upper Meadow Valley Wash, Nevada, USA, using USGS gage number 09417500 streamflow records. PRISM data at 2.5arc-min resolution were used to reconstruct streamflow at the seasonal timescale (October through May) from 1896 to 2008, with and without a temperature-index snowmelt component. Best-fit model simulations had an R 2 of 0.81 against stream gage observations. Average predicted seasonal streamflow during calibration was 0.81cm with a standard deviation of 0.35cm, compared to the observed average seasonal streamflow of 0.76cm and standard deviation of 0.48cm. Despite some shortcomings for this watershed, the model approach has promise for providing scenario-based estimates of hydrologic variability in semi-arid mountain environments. [Copyright &y& Elsevier]

Summary: Knowledge of the anthropogenic impact on the hydrology of low-productive fens that are subject to environmental degradation is essential to improve currently utilized hydrological fen restoration strategies. We analyse the naturally and anthropogenically driven evolution of groundwater systems in an intensively managed fen area in The Netherlands using a series of three-dimensional palaeo-groundwater models at a high spatial and temporal resolution. These palaeo-models are representative for five time slices of the time frame 0–2000 AD (Anno Domini), which are defined according to the timing of the natural and anthropogenic developments that had major impacts on the groundwater system configuration. For each time slice, palaeo-geohydrological conditions are reconstructed, which allowed for the calculation of groundwater discharge patterns, water balances and groundwater flow patterns. Contrary to former studies on the evolution of groundwater systems, our palaeo-hydrological reconstruction indicates that current groundwater discharge flux into managed fens may exceed the late-natural groundwater discharge flux. The increased groundwater discharge flux relates to the development of groundwater systems in the river valley with the establishment of polders since 1350AD. Notably, more recent redirections of groundwater flow due to the reclamation of lakes and the establishment of abstractions wells, as well as the decreased groundwater recharge by anthropogenic land cover change, reduced the groundwater discharge flux only to a minor extent. This finding opposes the hypothesis that a decreased groundwater flux to fens underlies the environmental degradation of fens in intensively managed regions. The palaeo-hydrological reconstruction provides evidence that it is mainly the changes in the spatial configuration, and the shift in the predominant groundwater discharge mechanism, that underlies the environmental degradation of managed low-productive fens. We discuss the consequences of these hydrological changes for the suitability and availability of fen habitat sites. [Copyright &y& Elsevier]

Summary: The study was carried out in the northern part of the Aquitaine Basin extending in Southwest France. The basin has been intensively exploited for various purposes for many years. Although the geological context is well known, there are still some gaps in the knowledge about the hydrogeochemical regime, groundwater average residence time and the palaeohydrological conditions prevailing during the recharge period which would help to secure sustainable exploitation of the resources. Environmental isotopes (18O, 2H, 3H, 13C) together with radiocarbon were used to evaluate hydrochemical evolution, residence time and palaeorecharge conditions for Jurassic, Cretaceous and Eocene aquifers. Radiocarbon activity in the aquifers varies widely between 0 and 94pmc. After radiocarbon corrections the ages indicate both modern and old waters sometimes exceeding the limit for 14C dating. The Fontes and Garnier model is best adapted to the specificity of the carbonate system. The content in stable isotopes of water is varying between −7.7‰ and −4.9‰ for δ18O and −52.3‰ to −29.6‰ for δ2H. The wide ranges of stable isotopic values imply variable climatic conditions. A group of isotopically depleted samples was detected, indicating colder climatic conditions during the recharge. Radiocarbon ages calculation, together with isotopic signature, point out that the depletion in stable isotopic values fits the period between 20 and 15ka B.P. and therefore indicate the Last Glacial Maximum (LGM). According to the correction model, the transition from Pleistocene to Holocene would occur between 15 and 12ka B.P. Palaeohydrological data from the Northern Aquitaine Basin does not confirm a significant hiatus in the recharge history. The recharge conditions in South Europe seem to have occurred under discontinuous permafrost conditions as documented by many palaeoclimatological archives. This is in favour of an uninterrupted recharge of the confined aquifers of Northern Aquitaine Basin. Such information should be considered by modellers in their attempts to simulate the hydrogeological functioning of large confined aquifers on the very long time range. [Copyright &y& Elsevier]

• Effectiveness of dendrogeomorpic approach for past flood detection was evaluated. • The minimal detected discharge corresponded to ca Q 2 recurrence interval of floods. • The ca 50% of floods above Q 2 were successfully dated. • Different tree-ring-based results between two contrasting catchments were detected. Recently, dendrogeomorphic methods have been increasingly used for the dating past-flood events, and tree-ring-based approaches are generally considered valuable tools in palaeohydrology. Several limitations of the approach are known, but their effects on the resulting chronologies have not been assessed or quantified. Thus, this study attempts to critically evaluate and quantify the effectiveness of dendrogeomorphology in past-flood analysis. The tree-ring-based methods were tested on two long-term monitored, contrasting catchments in a region in the Outer Western Carpathians. In total, 101 sampled trees provided evidence of 126 growth disturbances, enabling the reconstruction of seven flood events approximately during the last 30 years in each catchment. After the comparison of monitored discharges with tree-ring records, standard dendrogeomorphic indices enabled the detection of approximately half of the flood events with discharges larger than the maximal sensitivity of the approach used (minimal detected discharge corresponding to ca. Q 2). Nevertheless, significant differences were identified between the two catchments. Values of dendrogeomorphic indices corresponded well to values of maximal discharges, and increasing the indices thresholds increased the proportion of detected floods in narrow mountainous catchment. In contrast, no effect on the proportion of detected flood events after indices threshold increase was detected in the case of a wide braided channel (in the second catchment). However, the indices values corresponded well to the flood volume. The differences were probably caused by the water-level behaviour in narrow and wide channels. Thus, it seems that the characteristics of channel reaches must be very carefully considered in regard to the interpretation of dendrogeomorphic results of past-flood events. [ABSTRACT FROM AUTHOR]

Summary: Modeling groundwater flow and geochemical evolution is a useful tool for studying the paleohydrogeology of coastal aquifer systems. Complex geochemical reaction patterns and long freshening time of coastal aquifers make these processes difficult to model. A stepwise inversion method is presented here for the identification of geochemical processes and the estimation of model parameters in two field cases. The first one deals with reactive solute transport through the Llobregat delta aquitard (Barcelona, Spain) in which saline water is being displaced by fresh water moving upwards from a lower aquifer. The inverse methodology provides optimum estimates of geochemical parameters and identifies methane oxidation as a key process controlling the geochemical evolution in the aquitard and leading to a fit to measured concentration profiles which improves previous modeling results. The methodology is applied also to a complex field case in the Aquia aquifer (MD, USA) which involves time scales on the order of 105 years. Available hydrogeochemical data are used to derive optimum estimates of transmissivities, leakage rates, dispersivities, selectivity coefficients, cation exchange capacity (CEC), and initial and boundary concentrations of chemical components. Inverse modeling in this case provides optimum parameter estimates and additional insight into the paleohydrology and paleogeochemistry of the Aquia aquifer. [Copyright &y& Elsevier]

Comparative water potential and chloride profiles (∼10 m deep) collected from four vegetation communities in the Trans-Pecos region of the Chihuahuan Desert were assessed to evaluate the potential for using vegetation patterns as a means of efficiently improving large-scale estimates of basin-floor recharge in semiarid and arid regions. Analytical solutions and multiphase flow and transport modeling constrained flux histories and current fluxes across the water table at each site. Chloride bulge profiles containing ∼12–15 kyr of atmospheric deposition and long-term drying water potential profiles typified most desertscrub and grassland sites. In contrast, evidence of episodic sub-root zone percolation and chloride profiles containing <250 yr of atmospheric deposition characterized the woodland site. The results suggested that the desertscrub and grassland areas support small upward fluxes across the water table (nonrecharge), whereas the woodland site supports significant downward fluxes across the water table (recharge). A nonrecharge–recharge transition was identified to be collocated with a grassland–woodland ecotone. The establishment of vegetation–recharge relationships such as this will improve estimates of basin-scale recharge by identifying regions where no recharge is expected and regions where recharge is expected and point measurements should be concentrated. An approach integrating remotely sensed spatial distributions of vegetation and indicator relationships to recharge is both timely and warranted, although several caveats, as revealed in this study, should be noted. For example, the relative importance and distribution of vertical conduits that permit percolation to the water table merits future investigation. [Copyright &y& Elsevier]

• A large ensemble climate simulation dataset was applied to flood risk assessment. • Pluvial and fluvial flood risk curves were derived without probabilistic modelling. • Pluvial flood risk was comparable with fluvial flood risk in the study area. • Fluvial flood causes deeper flood depths while pluvial flood more widely expands. • Pluvial flood needs more attention in low-lying urban areas. Flood disasters are caused by two types of flooding: pluvial and fluvial flooding. The different hydrodynamic characteristics of these two types have been intensively discussed in a literature. However, their impact and the resulting damage have not yet been examined in a comprehensive manner due to the lack of extreme rainfall data and/or computational costs of flood simulations. Recently, an increasing number of ensemble climate simulation data has become available, providing long-term rainfall data based on numerical climate simulations. This is a case study of a flooding in an urban area set in Nagoya City, Japan. We applied a large ensemble climate simulation database, d4PDF, to a pluvial and fluvial flood model and derived the flood risk curves for each type of flooding. The results indicated that pluvial flooding presents comparable economic risk to fluvial flooding (only 16% and 17% lesser damage at 50- and 100-year return periods, respectively) despite its significantly shallower flood depths (area with flood depth over 45 cm was only 10.5% and 5.4%, respectively). The significant impact of pluvial flooding is attributable to its wider flood area (despite shallower depths), impacting major economic assets sprawled over the city, including areas further away from the river. Furthermore, fluvial flood risk was managed by settling the Nagoya Castle (now the central economic district) on higher altitudes. The results suggest that pluvial flooding could have comparable economic risks to fluvial flooding in urban areas where major economic assets are not concentrated around streams as well as historical countermeasures are installed against fluvial flooding. [ABSTRACT FROM AUTHOR]

• A large landslide dam formed in October 2018 in the Yarlung Tsangpo Grand Canyon. • The landslide dam breached within 2 days with a peak flood over 30,000 m3/s. • A disaster chain of landslide-barrier lake-dam breaching-river flooding is presented. • An erosion-based numerical model was used to simulate the dam-breaching process. • Plausible dam breaching scenarios at larger flows are analysed for risk management. Ice-soil mixture landslide dams formed frequently in the Tibetan Plateau in response to global warming, which pose great threats to both upstream and downstream areas due to inundation and lake bursting. On 17 October 2018, a large landslide, induced by an ice-avalanche at the Sedongpu Basin of the Yarlung Tsangpo, blocked the main course of the river near Gyalha. The barrier lake level rose quickly and the dam was overtopped naturally at 13:30 on 19 October 2018, generating a dam-breaching flood with a peak flow rate of 32,000 m3/s. This paper presents a comprehensive study of the disaster chain of landslide-barrier lake-dam breaching-river flooding in the Yarlung Tsangpo Grand Canyon, detailed geological and hydrological characteristics of the study region, rapid prediction of the dam breaching hydrograph using an erosion-based numerical model, and analysis of the flood routing in a 460 km canyon reach along the Yarlung Tsangpo. The simulated peak discharge at the dam site is over 30,000 m3/s and the corresponding dam-breaching and flood routing hydrographs agree well with the observations. Two additional scenarios with larger inflow rates are also considered. Results show that with a larger inflow into the barrier lake, the erosion of the dam body becomes more rapid. When the inflow rate is increased by six times, the peak dam-breaching discharge can be doubled. The study serves as basis to manage the flood risks due to landslide dam bursting on the Yarlung Tsangpo or similar rivers. [ABSTRACT FROM AUTHOR]

• A comprehensive paleoflood investigation on the lower Green River, Utah. • At least 27 extreme floods in the past 700 years were retrieved. • Extreme floods are larger and more frequent than implied by gauged records. • A truly scientific understanding of extreme floods can only emerge from nature. Through a comprehensive paleoflood hydrological investigation we document natural evidence for at least 27 high-magnitude paleofloods at six sites on the Lower Green River, Utah. Hydraulic analysis, using the Sedimentation and River Hydraulic-2D model (SRH-2D), shows that the responsible peak paleoflood discharges ranged between 500 and 7500 m3/s. At least 14 of these paleoflood discharge peaks exceed a level twice that of the maximum systematic record of gauged flows: 1929 m3/s. Geochronological analyses, employing optically stimulated luminescence (OSL) and radiocarbon dating techniques, demonstrate that these 14 largest paleoflood peaks occurred during the past 700 years. Integration of the paleoflood data into flood frequency analyses (FFA) reveals considerably higher values for the upper tails of the flood distribution than does a FFA based solely on the systematic gauged record, indicating that extreme floods are larger and more frequent than implied by the relatively short gauged record. Through examination of three approaches to extreme flood estimation – conventional FFA, probable maximum flood estimation (PMF), and paleoflood hydrology (PFH) – we show the significance of the natural evidence for advancing scientific understanding of extreme floods that naturally occur in the Colorado River system. We argue that this kind of scientific understanding is absolutely essential for achieving a credible evaluation of extreme flood risk in a watershed of immense importance to economic prosperity of the southwestern U.S. [ABSTRACT FROM AUTHOR]

• Define the concept of "design flood and FLWL in operation period". • Propose a framework to determine design flood in operation period. • Apply t-copula and GA to solve curse of dimensionality in derivation of MLRC. • Increase hydropower generation using FLWL in operation period. The hydrological regimes of downstream reservoirs have been significantly altered due to the operation and regulation of upstream cascade reservoirs. The original design flood quantiles, namely "design flood in construction period", do not consider anthropogenic impacts in reservoir operation period, and have led to enormous conflicts between flood control and conservation. In this study, the "design flood and flood limited water level in operation period" are defined for practical application. We establish a general framework to measure the spatiotemporal pattern of streamflow and to estimate design floods of cascade reservoirs in operation period. The multivariate t-copula and a genetic algorithm strategy are proposed to solve the curse of dimensionality encountered in the derivation of most likely regional composition. The Jinsha River and Yalong River cascade reservoir system in China, which consists of 13 large reservoirs with the total storage capacity of 74.06 billion m3 and hydropower capacity of 71.47 GW, is selected as a case study. Results indicate that: (1) The curse of dimensionality can be well addressed by applying multivariate t-copula to build high dimensional joint distribution and using the genetic algorithm to achieve the most likely regional composition. (2) Compared with the design floods in construction period, the design floods of downstream reservoirs in operation period have been significantly reduced due to the upstream reservoir regulation. The 1000-year design peak flood discharge, 3-day, 7-day and 30-day flood volumes of Xiangjiaba reservoir decrease by 38.7%, 37.4%, 34.2% and 13.8%, respectively. (3) The flood limited water level of these reservoirs can be raised without increasing flood control risks in operation period. The cascade reservoirs in the Jinsha River and Yalong River can generate 3.28 billion kW h more hydropower (or increase 4.3%) annually during flood season. [ABSTRACT FROM AUTHOR]

• First hydroclimatic reconstructions by provenance-verified chronologies in Austria. • First dendrohydrological summer low-flow reconstruction in Central Europe. • EPS as scaling factor for illustrating the reconstructions' time-varying reliability. Atmospheric and streamflow drought back to 1600 were reconstructed with provenance-verified regional Pinus-sylvestris and Pinus-nigra chronologies of earlywood, latewood and ring width, detrended by signal-free regional curve standardization, from the Weinviertel, a dry region in Eastern Austria. Linear regression models with Weinviertel latewood indices as predictor variables were used to estimate regional April–August precipitation totals (R2 = 0.47) and seven-day minimum flow from May to October (best fit: R2 = 0.65). As a novelty, the well-known dendrochronology quality measure "Expressed Population Signal" in a modified version is used to define a scaling factor for empirically estimating the reconstructions' time-varying reliability. For the detection of drought years in the reconstructed time series, four stages of drought of increasing intensity were defined as conditions below median, and below the 33rd, 20th, and 5th percentile—representing 2-year, 3-year, 5-year and 20-year recurrence intervals. The method for the extension of time series of low flows into the past is applicable in the Weinviertel and can be a useful source of historical hydrological and meteorological information restricted by the uncertainties coming along with proxy records. Of the analyzed period back to 1600, the 19th century is the driest one closely followed by the 18th century, sharing the overall driest period from 1775 to 1813. The phase with the longest continuous atmospheric dry period is 1807–1811. The longest hydrological drought lasted from 1832 to 1839. [ABSTRACT FROM AUTHOR]