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Aim: Paleohydrological dynamics are well‐documented for European river systems, promoting shifting phases of isolation and connectivity of their aquatic fauna. These conditions coupled with high rates of hybridisation found in freshwater fishes may introduce considerable complexity and potential mito‐nuclear discordance of phylogenetic patterns. We evaluate this hypothesis using the first large‐scale analysis of nuclear SNPs in European species of grayling (Thymallus) compared to mtDNA data with the aim of reassessing the evolutionary history of this group of rheophilic fishes. Location: Freshwater systems in Europe. Methods: Based on mitochondrial (mitogenomes, control region) and nuclear (ddRADseq) data, we applied population‐genetic, phylogenetic, and biogeographic tools to evaluate lineage diversity in the context of paleohydrological alterations. Results: The results corroborated previously recognised high levels of lineage diversity, but revealed several cases of mito‐nuclear discordance and signals of both historical (natural) and human‐mediated introgression among major inter‐ and intraspecific lineages of Thymallus in Europe. A time‐calibrated phylogeny and ancestral area estimation, based on nuclear SNP data, supported a late Pliocene diversification of the genus in Europe and suggested an early colonisation of the Black Sea basin with subsequent dispersal into Central and Western Europe. Main Conclusions: The genetic structure of Thymallus in Europe recovered by nuclear SNPs contrasts considerably with that supported by mtDNA. Several instances of mito‐nuclear discordance underscore frequent contact of allopatric lineages in a dynamic paleohydrological landscape and reveal the weakness of basing both taxonomic and conservation decisions on inferences based on mtDNA alone. The Danube and Rhine drainages were inferred as important zones of contact between divergent phylogeographic lineages. Additionally, our data cast doubt on the genetic integrity of the endangered T. aeliani. Its divergence from T. thymallus, using nuclear SNPs, appears minimal as samples of T. aeliani group within Danubian lineages, despite carrying highly divergent reciprocally monophyletic mtDNA. [ABSTRACT FROM AUTHOR]

Water is a finite resource but an essential one. The continuously increasing demand leads to competition and conflict over limited resources. Syria, Jordan, and Israel compete over the water resources in the transboundary Yarmouk River basin where two water agreements dictate the allocation of water. The two arrangements are far from being efficient and fair while little cooperation is being made over sharing the resources that are being over-exploited. In this study, water sustainability was investigated under projected developments and trends based on the current use and allocation regime in the watershed using several scenarios. A one bucket soil moisture model was adopted and optimized in order to fully represent the ever-changing hydrology of the basin using the Water Evaluation and Planning (WEAP) tool. Demands along with the existing water infrastructure and their operation were modelled despite the lack of many data and the huge uncertainty in some. Simulation of business as usual scenario showed that continuing with the current use cannot be sustainable in the short and long term. The growth of both agriculture and population produced huge water shortages in all demand sectors. Under climate change scenarios RCP 4.5 and RCP 8.5, surface water availability and the retention of dams reduced significantly. The share of Jordan from the Yarmouk River was the most vulnerable to climate change impacts. Enhancing irrigation efficiency and a more stable population growth based on the UN medium variant population projection showed improvements in water coverage within all demand sectors. Analysis of future scenarios suggests that water shortage is expected in all riparian states of the basin but can be mitigated by reducing demands. [ABSTRACT FROM AUTHOR]

The Himalayan water tower provides crucial water resources for Asia. Permafrost degradation is deemed to exert important impacts on streamflow in the Himalayan rivers. Yet, the magnitudes of such impacts remain poorly quantified. Here, we established a robust hydrological model that incorporated active layer deepening and ground ice melt for the drainage basin of the largest river in the northern Himalayas-the Yarlung Zangbo River (YZR). We estimated that permafrost degradation led to ∼0.65 km3/yr decrease in surface runoff and ∼0.35 km3/yr increase in baseflow and ground ice melt contributed ∼0.25% to the annual streamflow in the YZR for the period 2001–2022. The "fill-and-spill" mechanism helps explain the seeming contradiction of observed increasing versus decreasing baseflow in different permafrost regions worldwide. We propose that the dilution of riverine dissolved organic carbon (DOC) concentrations by baseflow may lead to the riverine DOC hysteresis patterns. This study not only lays solid scientific basis for water resources management in the Himalayas, but also yields new insights into how to interpret measured river discharge and nutrient flux in permafrost regions over the globe. [ABSTRACT FROM AUTHOR]

Accurate and punctual precipitation data are fundamental to understanding regional hydrology and are a critical reference point for regional flood control. The aims of this study are to evaluate the performance of three widely used precipitation datasets—CRU TS, ERA5, and NCEP—as potential alternatives for hydrological applications in the Bahr el Ghazal River Basin in South Sudan, Africa. This includes examining the spatial and temporal evolution of regional precipitation using relatively accurate precipitation datasets. The findings indicate that CRU TS is the best precipitation dataset in the Bahr el Ghazal Basin. The spatial and temporal distributions of precipitation from CRU TS reveal that precipitation in the Bahr el Ghazal Basin has a clear wet season, with June–August accounting for half of the annual precipitation and peaking in July and August. The long-term annual total precipitation exhibits a gradual increasing trend from the north to the south, with the southwestern part of the Basin having the largest percentage of wet season precipitation. Notably, the Bahr el Ghazal Basin witnessed a significant precipitation shift in 1967, followed by an increasing trend. Moreover, the spatial and temporal precipitation evolutions reveal an ongoing risk of flooding in the lower part of the Basin; therefore, increased engineering counter-measures might be needed for effective flood prevention. [ABSTRACT FROM AUTHOR]

Gauge-measured precipitation (Pm) is prone to negative bias; therefore, using corrected gauge-measured precipitation (Pc) is critical in climate and hydrology studies, although it is utilized insufficiently in existing research. This study uses Pm and Pc to establish extreme precipitation indices (EPIs) and compares the differences in their evolution characteristics and their responses to large-scale circulation indices (LSCIs). Theil's slope and the modified Mann–Kendall test are used to identify the evolution characteristics of EPIs. Probabilistic condition selection and momentary conditional independence and the Liang-Kleeman information flow are adopted to evaluate the causal relationship between the EPIs and LSCIs. The main results are as follows: (1) The magnitude, intensity, and frequency of the Pc-based EPIs are higher than those of the Pm-based EPIs in China, except for the consecutive dry days (CDD). This result suggests that previous estimates of Pm-based EPIs underestimated the magnitude, intensity, and frequency at most stations, especially in the Southwestern River where droughts and flood areas may have been underestimated. Thus, the frequency of Southwestern River droughts and floods and their sudden transitions may be higher. (2) The slope increases in the Pc-based EPIs (except for the Southwestern River), and their significance levels are lower than those of the Pm-based EPIs. Conversely, the slope decreases in the Pc-based EPIs (except for the Southwestern River), and their significance levels (except for the Songliao River) are higher than those of the Pm-based EPIs. The internal variability of the climate system and the external forcing in some basins are the reasons for the significantly increasing slopes of very wet days (R95p), simple daily intensity index (SDII), and extremely wet days (R99p). However, the significant decreasing slopes are attributed to internal climate variability. (3) Unlike the Pm-based EPIs, the Pc-based EPIs did not alter the causal relationship with LSCIs, indicating that Pc did not change the causal relationship with LSCIs. The trend, magnitude, intensity, and frequency differ for Pc and Pm. Therefore, Pc and Pm data should be used cautiously in meteorological, hydrological, ecological, environmental, and agricultural simulations in future research. [ABSTRACT FROM AUTHOR]

The Amazon is the largest drainage basin on Earth and contains a wide variety of abiotic landscape features. In spite of this, the geodiversity in this basin has not yet been objectively evaluated. We address this knowledge gap by combining a meta-analysis of an existing global geodiversity map and its components with a systematic literature review, to identify the key characteristics of geodiversity in the Amazon drainage basin (ADB). We also evaluate how these global geodiversity component maps, that are based on the geology, geomorphology, soils and hydrology, could be refined to better reflect geodiversity in the basin. Our review shows that geology—through lithological diversity and geological structures—and hydrology—through hydrological processes that influence geomorphology and soil diversity—are the main determinants of geodiversity. Based on these features, the ADB can be subdivided into three principal regions: (i) the Andean orogenic belt and western Amazon, (ii) the cratons and eastern Amazon, and (iii) the Solimões-Amazon river system. Additional methods to map geomorphological and hydrological diversity have been identified. Future research should focus on investigating the relationship between the geodiversity components and assess their relationship with biodiversity. Such knowledge can enhance conservation plans for the ADB. This article is part of the Theo Murphy meeting issue 'Geodiversity for science and society'. [ABSTRACT FROM AUTHOR]

Hydrological models are widely used to assess the impact of climate variability and land use change on streamflow. However, it is uncertain whether these models are capable of simulating the impact given parameter interactions and inter-annual climate variability for large dry catchments. Two such catchments with extensive land clearing were selected to test three models – AWBM, Sacramento and SimHyd – in terms of their capacity to simulate streamflow during periods of vastly different levels of forest cover. AWBM outperformed others, and thus was further simplified as AWBM_Ca with minimum performance deterioration to have only one transferable parameter: the average storage capacity, Ca. A reduction of 21–28% in the Ca value for the post-clearing period indicates a decrease in the amount of water stored for transpiration and consequently an increase in runoff-generation capacity. AWBM_Ca can be used to predict the impact of forest cover change on streamflow with different Ca values. [ABSTRACT FROM AUTHOR]

The January 2011 flood event that impacted southeast Queensland is amongst the most extensive and severe floods in terms of loss of life and property damage that the region has experienced, despite it being only the eighth highest flood on record at the Brisbane City Gauge. The spring of 2010 was the wettest on record for Queensland, New South Wales, and the Murray-Darling Basin (Bureau of Meteorology 2011a) at that time. The flood mitigation dams in the region, Somerset Dam and Wivenhoe Dam, had to be operated for flood mitigation purposes during October 2010, which was the first occasion since February 2001 that Wivenhoe Dam had been called into action due to the Millennium Drought. The wet October was followed by a very dry November which, in turn, was followed by the wettest December on record for Brisbane. Somerset Dam and Wivenhoe Dam were again pressed into action on three separate occasions during December 2010. The resultant releases ensured that only minor flooding resulted in the Lower Brisbane River during these events. However, on the 5th of January 2011, another rainfall event started to unfold across the catchments of the dams. By the 10th of January 2011, an upper-level low combined with a humid easterly flow to bring very heavy rainfall and flash flooding to southeast Queensland and northeast New South Wales. The heaviest falls were in the areas north and west of Brisbane, with three-day totals exceeding 200 mm over most of the Brisbane River catchment. This rainfall event resulted in a flood of record in the Upper Brisbane River and Upper Lockyer Creek catchments that sadly resulted in a substantial loss of life in Toowoomba and the Lockyer Valley, and which required record releases from Wivenhoe Dam. The resultant downstream flooding saw some 14,000 properties impacted, principally in the Lockyer Valley Regional Council, Somerset Regional Council, Brisbane City Council, and Ipswich City Council local government regions. Flood damage was estimated to be around $2.53 billion. This paper discusses the event as it unfolded and the subsequent judicial inquiries, engineering reviews, and legal proceedings that resulted from the consequences of the operation of Somerset Dam and Wivenhoe Dam. [ABSTRACT FROM AUTHOR]

This study proposes an approach to evaluate the efficiency of low impact development (LID) in reducing urban runoff using a rainfall generator to disaggregate daily rainfall into sub‐hourly rainfall data, which are used as input of a hydrological model at the urban watershed scale. Twelve scenarios are analyzed combining four percentages of impervious area retrofitted with LIDs (25%, 50%, 75% and 100%), and three LID combinations of green roofs (GRs) and rain gardens (RGs). The rainfall generator Rainsim V.3 is used to generate 500 years of rainfall data with a 15‐min time step to analyze the performance of LIDs in the long‐term with the LID module of the Soil and Water Assessment Tool hydrological model. An urban watershed of 3 km2 located in Florence (Italy) is selected as a case study. Results show the performances of GRs and RG on peak flow reduction, highlighting a maximum flow reduction of single facilities ranging between 15% and 60% that can improve in case of their combination. The hydrological performances of LID combinations are very sensitive to the intensity of rainfall events, as well as percentages of area treated underlining the importance of simulating multiple scenarios of intervention to determine the most efficient combination of LIDs for a given case study and support their proper design from a urban water hydrology perspective. [ABSTRACT FROM AUTHOR]

Records of sedimentation collected from Cariboo Lake, situated in the northern Columbia Mountains, British Columbia, Canada, are analyzed to assess Holocene fluvial and glacial watershed dynamics. The aim of this study is to provide a proxy record of Holocene hydroclimate and glacier change from sediment archives at a higher temporal resolution compared to available records for the Interior Ranges of British Columbia. Deglacial and Holocene sediment accumulation is observed to reach a maximum thickness of 35 m in deep parts of the lake, using sub-bottom acoustic soundings. A transition from massive to well-stratified sediments is observed in the sub-bottom acoustic record during final phases of valley deglaciation in the region (~10.5–9 cal ka BP). Laminae couplets are interpreted to be deposited annually according to two 14C dates and a varve counting chronology. Two long cores, 2.9 and 3.8 m in length, were selected for analysis with estimated basal dates of 2 cal ka BP. Trends in downcore sediment characteristics were linked to environmental changes in the glaciated catchment headwaters at a temporal resolution of ~100 years. Upstream lake filtering of river floodplains and lakes prevented finding a higher temporal resolution linkage between the sediment characteristics and headwater fluvial and glacial activity. Despite some upstream filtering, the Cariboo River was found to be the primary source of sediment to the long core sites. Observed grain size and varve thickness from two long cores show above average trends, which are coincident with cooler temperatures and the primary glacier advances over the last 2 ka. [ABSTRACT FROM AUTHOR]

Due to the scarcity of meteorological observation stations in some areas, there is not enough data available for hydrological simulation as one of the main subjects of hydrology and environmental subjects. This can be partially solved by extracting the required data from global climate centers. The essential data for modeling rainfall-runoff of Dez watershed (16,000 km2), Khuzestan province, Iran, for a 20-year period (1990–2010) were obtained from NCEP CFSR climate center. The simulation (calibration and validation) was done by Soil and Water Assessment Tool (SWAT) and Identification of Unit Hydrographs and Component Flows from Rainfall, Evapotranspiration and Streamflow (IHACRES) models. The SWAT-CUP software has been used for optimization, calibrating and analyzing the uncertainty of the SWAT model by communicating with the model. The ability of the models to simulate the runoff of the basin was determined using the coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE). R2 and NSE for the SWAT model were 0.75, and 0.78 (calibration), and 0.59 and 0.72 (validation); for the IHACRES model, they were equal to 0.63 and 0.69 (calibration), and 0.54 and 0.66 (validation), respectively. The SWAT model performed better than the IHACRES model by efficiently using the climatic database of NCEP CFSR center. The IHACRES model was also able to simulate the runoff of the watershed with a relatively high correlation with the observational data. It is possible to simulate and predict rainfall-runoff of the Dez watershed using the tested models for taking the measures, which may avoid natural phenomenon including flooding. [ABSTRACT FROM AUTHOR]

Amidst intensifying global agricultural water demand, optimizing management practices and understanding the role of soil amendments, particularly biochar (BC), in modulating soil water dynamics are critical. Here, we review the potential impacts of BC on soil water dynamics, elucidate mechanistic underpinnings, and identify critical research gaps and prospective avenues. In general, BC modifies soil structure, hydraulic properties, surface albedo, and heat fluxes, which influence soil water storage, energy balance, and irrigation paradigms. Depending on soil texture and BC properties, BC demonstrates a greater reduction in bulk density and saturated hydraulic conductivity in coarse-textured soils compared to fine-textured soils. BC application generally increases water holding capacity (WHC) while exhibiting no consistent impact on soil water infiltration. Increased WHC of soils results from increased porosity, surface area, and soil aggregation. Increased porosity arises from a confluence of factors, encompassing new pores formation, reorganization of pores, increased soil aggregation, dilution effects of BC, reduced soil compaction, and biotic interactions, including increased population of burrowing invertebrates. BC tends to increase plant-available water in coarser soils, attributed to its hydrophilic nature, augmented specific surface area, and enhanced overall porosity. However, BC may induce soil water repellency, contingent upon variables such as feedstock composition, pyrolysis temperature, and specific soil attributes. While BC exhibits transformative potential in enhancing soil hydraulic properties, scalability concerns and economic viability pose challenges to its widespread agricultural application. Overall, BC offers promising avenues for sustainable water management. However, it is imperative to explore large-scale applications and conduct long-term field studies across different management, climate, and soil types to fully understand how different types of BC impact soil water dynamics. Highlights: Biochar generally improves soil water retention in coarse-textured soils. In coarse-textured soils, biochar increases porosity and PAW but decreases bulk density and Ksat. The effects of biochar on infiltration rates vary depending on soil types, as well as biochar particle size, production temperature, and depth of placement. Further studies on the mechanisms governing water retention in biochar-amended soils are warranted. Long-term studies encompassing various soil and biochar types are necessary. [ABSTRACT FROM AUTHOR]

Increased flood magnitude and frequency due to climate change can reduce the population productivity of organisms such as amphibian and fish species in river and stream systems; therefore, conserving habitats that maintain high productivity under such conditions is crucial. Here, we examined the relationship between the freshwater productivity of anadromous salmonids (measured as fry migrating to the ocean per spawner) and catchment hydrogeomorphology and identified the characteristics of rivers and streams that are prone to flood disturbance.We surveyed the spawner abundance and number of fry of pink salmon (Oncorhynchus gorbuscha) and measured environmental factors, including the average catchment slope and stream power, as characteristics of hydrogeomorphology, in 10 streams in the Shiretoko Peninsula, northern Japan. We then used generalised linear mixed models to predict the freshwater productivity of pink salmon populations in each catchment across the study region under current and future climatic conditions.The productivity of pink salmon in the study region differed among the sampled catchments and was negatively affected by the average catchment slope, stream power, and maximum daily precipitation averaged over the catchment. Namely, flood disturbance reduced the freshwater productivity of pink salmon, and salmon productivity in individual catchments was explained by catchment hydrogeomorphology. The predicted future productivity with increased precipitation was also lower than the current productivity.Our approach can be applied to other salmonids that have similar spawning behaviour to pink salmon. Highly productive catchments under the future climatic conditions predicted by the present study should be prioritised for conservation to ensure a sustainable salmonid population. [ABSTRACT FROM AUTHOR]

Soil moisture (SM) and soil freeze–thaw (FT) are two relatively active surface parameters that are significant to the sustainable development of the water–land–air–plant–human nexus. Over time, regional or global SM and FT datasets with different spatial resolutions have been developed. In response to the requirements of multiscale product validation and multisource uncertainty tracking, a soil moisture and soil temperature (ST) monitoring network in the Qinghai Lake Basin (QLB-NET) was established in September 2019. The QLB-NET is characterized by densely distributed in situ sites (82 sites) measuring SM and ST at 5-, 10-, and 30-cm depths, with 60 sites in a large-scale network covering an area of 36 km × 40 km and 22 sites evenly distributed across two small-scale 1 km × 1 km networks. Quantitative analyses of the in situ measurements show that the QLB-NET can provide stable and reliable ground truth for SM and FT over coarse grid scales, e.g., 36 km × 36 km, 25 km × 25 km, and 0.25° × 0.25°. When statistics are correspondingly performed over 50 out of 54, 25 out of 29, and 25 out of 28 sites, the results are described as follows: 1) the standard deviation of the mean SM varies between 0.0127 and 0.0196 m3 m−3, with the corresponding difference between the upper and lower quartiles being less than 0.02 m3 m−3; 2) the ground freeze–thaw state can be correctly identified with high probabilities ranging from 85.3% to 100% on two freeze–thaw transitional dates. The QLB-NET observed datasets are distributed online and will be continuously updated through cooperation with the National Tibetan Plateau Data Center (http://data.tpdc.ac.cn), facilitating product validation and uncertainty tracking, spatiotemporal analysis of SM change and FT transition, optimization of the SM and FT retrieving algorithms and scaling methods, and development of the mountainous microwave radiative transfer model. SIGNIFICANCE STATEMENT: This study aims to introduce the newly constructed QLB-NET in detail, including the site deployment strategy, the installation and maintenance, the sensor calibration, and the characteristics and quality of the in situ SM and ST measurements. Quantitative analyses of the in situ measurements show that the QLB-NET can provide stable and reliable ground truth for SM and FT over coarse grid scales, e.g., the SMAP 36 km × 36 km grid. The high-quality QLB-NET measurements will facilitate research of product validation and uncertainty tracking, spatiotemporal analysis of SM change and FT transition, optimization of the SM and FT retrieving algorithms and scaling methods, and development of the mountainous microwave radiative transfer model. [ABSTRACT FROM AUTHOR]

Innumerable small steppe rivers have been degraded and lost through the construction of dikes and dams, as well as changing regional hydrology. A failed restoration project involving mechanical clearance of the channel of the small river Chaplynka is investigated. Field and laboratory studies included sampling and analysis of water and silt deposits. Muller's Іgeo class, categorising the technogenic load on the water ecosystem, and a bottom accumulation coefficient illustrate the degradation of the catchment and the absence of hydraulic connection along the erstwhile river channel. The river flow has not returned. The most obvious shortcoming of the riverbed clearing operations was the dumping of the dredged material on the riverbank, from where it was washed back into the channel. Moreover, excavation of the channel drained shallow aquifers that are no longer replenished by depleted precipitation and infiltration. [ABSTRACT FROM AUTHOR]

The land surface model (LSM) is extensively utilized to simulate terrestrial processes between land surface and atmosphere in the Earth system. Hydrology simulation is the key component of the model, which can directly reflect the capability of LSM. In this study, three offline LSM simulations were conducted over China using the Community Land Model version 5.0 (CLM5) driven by different meteorological forcing datasets, namely China Meteorological Forcing Dataset (CMFD), Global Soil Wetness Project Phase 3 (GSWP3), and bias-adjusted ERA5 reanalysis (WFDE5), respectively. Both gridded and in situ reference data, including evapotranspiration (ET), soil moisture (SM), and runoff, were employed to evaluate the performance levels of three CLM5-based simulations across China and its ten basins. In general, all simulations realistically replicate the magnitudes, spatial patterns, and seasonal cycles of ET over China when compared with remote-sensing-based ET observations. Among ten basins, Yellow River Basin (YRB) is the basin where simulations are the best, supported by the higher KGE value of 0.79. However, substantial biases occur in Northwest Rivers Basin (NWRB) with significant overestimation for CMFD and WFDE5 and underestimation for GSWP3. In addition, both grid-based or site-based evaluations of SM indicate that systematic wet biases exist in all three CLM5 simulations for shallower soil layer over nine basins of China. Comparatively, the performance levels in simulating SM for deeper soil layer are slightly better. Moreover, all three types of CLM5 simulate reasonable runoff spatial patterns, among which CMFD can capture more detailed information, but GSWP3 presents more comparable change trends of runoff when compared to the reference data. In summary, this study explored the capacity of CLM5 driven by different meteorological forcing data, and the assessment results may provide important insights for the future developments and applications of LSM. [ABSTRACT FROM AUTHOR]

Flooding is a dominant physical process that drives the form and function of river‐floodplain ecosystems. Efficiently characterizing flooding dynamics can be challenging, especially over geographically broad areas or at spatial and temporal scales relevant for ecosystem management activities. Here, we empirically evaluated a low‐complexity geospatial model of floodplain inundation in six study segments of the Upper Mississippi River System (UMRS) by pairing spatially extensive, temporally limited and spatially limited, temporally extensive sampling designs. We found little evidence of systematic bias in model performance although discrepancies between model predictions and empirical data did occur locally. Assessments of model predictions revealed low segment‐wide discrepancies of wetted extent under contrasting flow conditions and agreement for inundation event detection and duration. Model performance for predicting event frequency and duration was similar among sites expected to exhibit contrasting patterns of hydrologic connectivity with the main channel. Our results suggest that low‐complexity models can efficiently characterize a critical physical process across geographically broad, complex river‐floodplain ecosystems. Such tools have the potential for advancing scientific understanding of landscape‐scale ecological patterns and for prioritizing management actions in large, complex river‐floodplain ecosystems like the UMRS. [ABSTRACT FROM AUTHOR]

Drainage basins delineate Earth's land surface into individual water collection units. Basin shape and river sinuosity determine water and sediment dynamics, affecting landscape evolution and connectivity between ecosystems and freshwater species. However, a high-resolution global dataset for the boundaries and geometry of basins is still missing. Using a 90 m resolution digital elevation model, we measured the areas, lengths, widths, aspect ratios, slopes, and elevations of basins over 50 km 2 globally. Additionally, we calculated the lengths and sinuosities of the longest river channels within these 0.67 million basins. We built a new global dataset, Basin90m, to present the basins and rivers, as well as their morphological metrics. To highlight the use cases of Basin90m, we explored the correlations among morphological metrics, such as Hack's law. By comparing with HydroSHEDS, HydroATLAS, and Google Earth images, we demonstrated the high accuracy of Basin90m. Basin90m, available in shapefile format, can be used on various GIS platforms, including QGIS, ArcGIS, and GeoPandas. Basin90m has substantial application prospects in geomorphology, hydrology, and ecology. Basin90m is available at 10.5880/GFZ.4.6.2023.004 (He et al., 2023). [ABSTRACT FROM AUTHOR]

The Lake Chad Basin is Africa's largest endorheic basin. Because water supply for the rural population and most of the urban population depends on groundwater, assessment of groundwater recharge is crucial. Recharge sources for the upper Quaternary aquifer are precipitation, rivers, and swamps. Using water chemistry, and environmental (18O, 2H, 3H) and carbon (14C) isotopes, recharge processes can be assessed and groundwater ages roughly estimated. For this purpose, more than 1,000 samples from groundwater, surface water and precipitation were analysed for hydrochemistry and environmental stable isotopes. Furthermore, 3H measurements and 14C values of dissolved inorganic carbon for groundwater from the northeastern part of the Basin are included in the evaluation. The environmental isotope distribution shows recent recharge from precipitation north of Lake Chad (Kanem Region), where very low 3H values indicate occurrence before the 1960s bomb peak. Focused recharge from fresh river water is typical for Salamat Region in south Chad and the Komadugu Yobe wetlands between Nigeria and Niger. Slightly high δ-values in water occur in the Waza Logone area between Chad and Cameroon. Groundwater along the Lake Chad shore and the Bahr el Ghazal corridor show high δ-values (δ18O –0.78 to 7.45‰, δ2H –13.6 to 30.8‰). Recharge is caused by surface water that undergoes evaporative processes before percolation. Groundwater ages of 600–4,150 years, estimated from 14C analyses combined with high SO4 concentrations, along the Bahr el Ghazal indicate that recharge was caused by residuals of the Mega Lake before it dried out completely. [ABSTRACT FROM AUTHOR]

This paper presents a validation of outputs from some GCMs of the CMIP6 project when used to assess climate projection and hydrological flows at a catchment scale for the case study area of the Lombardy region (Northern Italy). The modeling chain consists of (i) a choice of climatic scenarios from 10 GCMs of the CMIP6, (ii) the application of a stochastic downscaling procedure to make projections usable at the local scale, and (iii) the use of a semi-distributed physically based hydrological model Poli-Hydro for the generation of hydrological scenarios. Data on observed precipitation and temperature were collected from automatic weather stations, and the hydrological budget of four target catchments within the study area was assessed using Poli-Hydro. An ex-post (back-casting) analysis was performed upon the control data series from the GCMs by comparing statistics of relevant climate variables and model-simulated discharges against observed counterparts during the historical period 2002–2014. Then, during 2015–2021, the goodness of projections was assessed using confidence intervals. Our results show that the accuracy of GCMs in representing regional climate is not always reflected in a credible evaluation of local hydrology. The validation of climate patterns provides somewhat poor results; thus, the interaction among climate and hydrology needs to be explored carefully to warrant the credibility of hydrological scenarios. Overall, the spatial and temporal consistency of GCM projections, as explored here climatically and hydrologically, provides a clue about their dependability for basin scale management. [ABSTRACT FROM AUTHOR]

More than 20 yr of measurement data of the gravity missions GRACE (Gravity Recovery And Climate Experiment) and GRACE-FO (GRACE-Follow-On) allow detailed investigations of long-term trends in continental terrestrial water storage (TWS). However, the spatial resolution of conventional GRACE/GRACE-FO data products is limited to a few hundred kilometres which restrains from investigating hydrological trends at smaller spatial scales. In this study GRACE and GRACE-FO data have been used to calculate TWS trends with maximized spatial resolution. Conventionally, GRACE/GRACE-FO is presented as a series of either unconstrained gravity fields post-processed with spatial low pass filters or constrained inversions commonly known as Mascon products. This paper demonstrates that both approaches to suppress spatially correlated noise are mathematically equivalent. Moreover, we demonstrate that readily inverting all available sensor data from GRACE/GRACE-FO for a single TWS trend map, together with annual variations and a mean gravity field, provides additional spatial detail not accessible from the standard products. The variable trade-off between spatial and temporal resolution as a unique feature of satellite gravimetry allows for gravity products that are tailored towards specific geophysical applications. We show additional signal content in terms of long-term water storage trends for four dedicated examples (Lake Victoria, Northwest India, Bugachany Reservoir and High Plains Aquifer) for which external information from other remote sensing instruments corroborates the enhanced spatial resolution of the new mean-field trend product. [ABSTRACT FROM AUTHOR]

Strata produced by fluvial dunes can provide insight into the hydrological regime of ancient rivers. Recent experiments indicate that conditions of disequilibrium between bedforms and formative flows may be inferred from the coefficient of variation of preserved dune cross‐set thickness, suggesting that this quantity may act as a proxy for the flashiness of river floods relative to the time required for full bedform translation. To assess whether this idea is applicable to interpretations of the stratigraphic record, this study examines published data relating to more than 2600 cross‐sets from 53 sedimentary units of 19 river systems. The presented analyses must not be over‐interpreted, because the considered rivers span different environmental settings, the data sources are heterogeneous in terms of type and dimensionality, and some variables were established by applying empirical relationships. Yet, significant findings are revealed. Larger rivers exhibit discharge and bedform characteristics that are more conducive to disequilibrium; however, a modest increase in the coefficient of variation of cross‐set thickness, CV(Dst), as opposed to the expected decrease, is seen as a function of river size. Crucially, smaller CV(Dst) values are not systematically associated with conditions that should favour dune disequilibrium. Meanwhile, only ca 25% of the studied examples demonstrate cross‐set thickness statistics compatible with quantitative formulations of the autogenic control by variable dune topography – the notion of 'variability‐dominated' preservation. These findings indicate that the variability in cross‐set thickness may be a poor predictor of discharge variability, perhaps because of the multiplicity of factors controlling dune preservation, such as bedform hierarchy, transport stage and depth‐dependent variations in dune disequilibrium. To improve interpretations of cross‐stratified deposits, further research is needed: (i) to establish the value of process‐to‐product models for reverse product‐to‐process interpretations; and (ii) to define representative samples for preserved dune deposits accounting for temporal and spatial variability in preservation potential. [ABSTRACT FROM AUTHOR]

The British Columbia Ungauged Basin (BCUB) dataset is an open-source, extensible dataset of attributes describing terrain, soil, land cover, and climate indices of over one million ungauged basins in British Columbia, Canada including transboundary regions. The basin attributes included in the dataset follow those found in the large sample hydrology literature for their association with hydrological processes. The BCUB database is intended to support water resources research and practice, namely monitoring network analysis studies, or hydrological modelling where basin characterization is used for model calibration. The dataset, and the complete workflow to collect and process input data, to derive stream networks, delineate basins, and to extract basin attributes is available under a Creative Commons BY 4.0 license. The DOI link for the BCUB dataset is https://doi.org/10.5683/SP3/JNKZVT (Kovacek and Weijs, 2023). [ABSTRACT FROM AUTHOR]

Non-perennial rivers (NPRs) have three hydrological states; each state has its importance, function and implication for water resource management. The dynamics of these states have been inadequately assessed and understood. Hence, this study sought to determine the spatiotemporal variations in the hydrological conditions of NPRs, focusing on the Touws River--Karoo drylands and Molototsi River within the semi-arid region of the Limpopo Province of South Africa. Additionally, the study aimed to delineate and characterize the primary areas contributing to runoff in these two river systems. Sentinel-1 and Sentinel-2 satellite data sources were employed in this study. Specifically, the modified normalized difference water index (MNDWI) derived from Sentinel-2 was utilized to delineate water surface areas along the two rivers. Subsequently, these derived datasets were utilized to assess the hydrological states over a 32-month period (2019-2022). Based on the presence of water, the river's state was classified as flowing, pooled, or dry. The results showed that remote sensing can be used to determine the hydrological state of the two river systems with ~90% overall accuracy. However, there is about a 30% chance that a flow event can be missed using Sentinel-2 due to clouds and temporal resolution. Some of these gaps can be filled using synthetic aperture radar (SAR) data (Sentinel-1), as demonstrated with the Molototsi River. In the Molototsi catchment, the upper catchment contributes the majority of flows. For the Touws River, the southwestern part of the catchment was determined as the major contributing area for the observed flows. This suggests that the chosen observation site might not be representative of upper catchment dynamics; therefore, a monitoring site in the upper catchment is required. This study provided hydrological information and an approach that can be used to monitor the hydrological states for better understanding and management of NPRs and catchments. [ABSTRACT FROM AUTHOR]

The early to middle Holocene was marked by considerable variability in lake levels in the Lake Superior Basin due to a combination of meltwater runoff, isostatic adjustment, shifting glacial margins, and climate change. These processes likely had a large impact on the preservation and visibility of coastal archaeological sites dating from the Early Period (Paleoindian) to the Middle Period (Shield Archaic). Of particular interest is the brief interval after 9300 cal. B.P. when ancestral Lake Superior dropped to its lowest level (Houghton) and human populations may have made incursions deeper into the basin. Elsewhere in the Upper Great Lakes, this period is associated with offshore archaeological sites submerged by rising water levels later in the Holocene. New geological data from the Thunder Bay, ON, region yield exceptional insight into the paleohydrology of the Houghton phase and, hence, the underwater archaeological prospects of this low water phase in the northern Lake Superior Basin. These data indicate that the lake reached its lowest level by at least ~9100 cal. B.P. but was highly unstable, at least initially, due to a combination of climate and meltwater runoff. Early underwater sites may be confined to two short, hydrologically closed, lowstands between ~9100 and 8700 cal. B.P. and would have been impacted by at least one lake transgression. Such sites, however, may still hold better potential for organic preservation and the visibility of large cultural features compared to their terrestrial counterparts. Coastal sites occupied when the lake was hydrologically closed may be especially well‐preserved due to rapid inundation before the gradual, and generally erosional, Nipissing transgression occurred. [ABSTRACT FROM AUTHOR]

The Combination Service for Time-variable Gravity fields (COST-G) operationally provides combinations of monthly Earth gravity field models derived from observations of the microwave ranging instrument of the GRACE Follow-on (GRACE-FO) satellite mission, applying the quality control and combination methodology originally developed by the Horizon 2020 project European Gravity Service for Improved Emergency Management for the data of the GRACE satellites. In the frame of the follow-up Horizon 2020 project Global Gravity-based Groundwater Product (G3P), the GRACE-FO combination is used to derive global grids of groundwater storage anomalies. To meet the user requirements and achieve optimal signal-to-noise ratio, the combination has been further developed and extended to incorporate: • new time-series based on the alternative accelerometer transplant product generated in the frame of the project by the Institute of Geodesy at the Graz University of Technology, which specifically improves the estimation of the C 30 coefficient and also reduces the noise at medium to short wavelengths, and • the new time-series AIUB–GRACE-FO–RL02 of monthly GRACE-FO gravity fields, which is derived at the Astronomical Institute of the University of Bern by applying empirical noise modelling techniques. The COST-G quality control confirms the consistency of the contributing GRACE-FO time-series concerning the signal amplitude of seasonal hydrology in large river basins and the secular mass change in polar regions, but it also indicates rather diverse noise characteristics. The difference in the noise levels is taken into account in the combination process by relative weights derived by variance component estimation on the solution level. The weights are expected to be inverse proportional to the noise levels of the individual gravity field solutions. However, this expectation is violated when applying the weighting scheme as developed for the GRACE combination. The reason is found in the high-order coefficients of the gravity field, which are poorly determined from the low–low range-rate observations due to the observation geometry and suffer from aliasing due to the malfunctioning accelerometer onboard one of the GRACE-FO satellites. Hence, for the final G3P-combination a revised weighting scheme is applied where the gravity field coefficients beyond order 60 are excluded from the determination of the weights. The quality of the combined gravity fields is assessed by comparison of the noise content and the signal-to-noise ratio with the individual time-series. Independent validation is provided by the COST-G validation centre at the GFZ German Research Centre for Geosciences, where orbit fits of the low-flying Gravity and steady-state Ocean Circulation Explorer satellite are performed that confirm the high quality of the combined GRACE-FO gravity fields. By the end of the G3P project, the new combination scheme is implemented by COST-G as the new COST-G–GRACE-FO–RL02 and continued to be used for the operational GRACE-FO combination. [ABSTRACT FROM AUTHOR]

From 1999 a dispute between Bolivia and Chile concerning the status and use of the Silala River developed. In 2016 it was taken before the International Court of Justice. Over time, a key disagreement between the parties emerged, concerning artificial channels in the headwater wetlands of the Silala River in Bolivia and their impact on the river and groundwater discharge from Bolivia to Chile. To quantify this, a numerical groundwater model was developed by Chile, requiring a hydrogeological conceptual model of the Silala River Basin, reviewed here. This focussed on understanding the groundwater system and its interactions with the Silala River. The data and information used to gain this understanding included geological mapping, drilling, satellite imagery interpretation, geophysical surveys, hydrogeochemical analyses, groundwater level monitoring, surface flow monitoring, and groundwater pumping tests. These were focussed along the course of the river and wetlands. A three‐dimensional geological model of the Silala Basin was based on these investigations. The groundwater model area covers the topographic catchment, plus three adjacent closed (endorheic) topographical catchments to the northeast, which together form the groundwater catchment of the Silala River. The main deep regional aquifer is found in ignimbrite pyroclastic rocks and an interbedded alluvial deposit, but secondary perched aquifers on the flanks of the Silala River ravine contribute to the complexity. Although uncertainty remains, the hydrogeological conceptual model describes the main observed features of the system in a scientifically sound and coherent manner, with appropriate detail to support a credible numerical model. This article is categorized under:Science of Water > Hydrological ProcessesEngineering Water > Sustainable Engineering of Water [ABSTRACT FROM AUTHOR]

The Silala River basin is located in a remote area in the Andes Mountain range, where hydro‐meteorological and hydrogeological data are scarce. Consequently, the hydrological functioning of this river system was not well understood. Due to a dispute between Chile and Bolivia over the status and use of the waters of the Silala River, Chile requested the International Court of Justice to adjudge the Silala River system to be an international watercourse. To support the case, scientific studies were carried out in both countries to fill hydrological and hydrogeological knowledge gaps. This article reviews the Silala River basin topographic characterization, historical water use, and the dominant hydrological processes, and briefly summarizes an enhanced monitoring programme, reported in more detail elsewhere in this Special Issue. The longitudinal topographic profile and river slope show that Silala fluvial system is an exorheic watershed; waters from the Cajones and Orientals wetlands in Bolivia, the two headwater sources of the Silala fluvial system, naturally flow from Bolivia to Chile, demonstrating that the Silala River system is indeed an international watercourse. New hydro‐meteorological, hydrological and hydrogeological measurement stations were installed in both countries and provided improved process insights and spatiotemporal coverage within the basin. These new observations helped to populate hydraulic, hydrological, and hydrogeological models, aimed to improve understanding of the functioning of the system, including the effects of historical disturbance due to channelization of the Bolivian wetlands. This article is categorized under:Science of Water > Hydrological ProcessesHuman Water > Rights to Water [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) have the potential to generate large-impact hydrometeorological events over mountainous topography. In this study, we investigate ARs' impacts on the hydrology of Indus basin (IB) and Ganga basin (GB), two highly populated basins of the Himalayas. We used the recently developed 37-yr-long ERA5-based AR database over the Himalayas to explore the influence of ARs on total and extreme precipitation, snowfall, and floods over these basins. We find that ARs contribute ∼25% to the annual rainfall in the IB and ∼15% in the GB. Over the mountainous regions, ARs contribute more than 50% to winter precipitation in Karakoram (KA), Hindu–Kush (HK), central (CH), and western Himalayas (WH), and respectively explain over 75%, 57%, 42%, and 30% of their interannual variability. The seasonal rainfall extremes over the mountain foothills are most often (50%–100%) associated with ARs in winter and spring, whereas the summer and autumn extremes over the plains and mountains foothills appear moderately associated with ARs (10%–40%). The two most catastrophic flood events (2014 Kashmir flood and 2013 Uttarakhand flood) in these basins are found to be linked with category 5 ARs. Upon further examination of floods over a long period, we noted that 56% and 73% of the floods in IB and GB, respectively, are related to ARs. Thus, our results establish that the variance of ARs is a major source of hydroclimate variability in the two Himalayan basins. [ABSTRACT FROM AUTHOR]

Operational streamflow forecasting is critically important to managers of river basins that supply water, hydropower, and flood protection. While seasonal water supply forecasts (WSFs) are important for long‐term water resources planning operations, shorter term (e.g., 1–5 weeks) streamflow forecasts are critical for balancing water conservation with flood risk during wet periods. In this study, we designed a streamflow forecasting system with the water resources group at the Salt River Project (SRP), a provider of water and power to millions of customers in central Arizona (AZ), to provide streamflow forecasts for a diverse and operationally important set of watersheds in AZ. The forecast system uses machine learning to make seasonal WSFs, a rainfall–runoff model driven by ensemble meteorological forecasts to make 35‐day streamflow forecasts, and an innovative approach to improve the WSFs based on the 35‐day streamflow forecasts. This model integration allows for an assessment of the impact of different meteorological forecasts on WSFs, helping SRP to balance water conservation goals with shorter term flood risks. In addition, seasonal WSFs are improved in the early winter when they incorporate the 35‐day streamflow predictions. Furthermore, these improvements are larger than when they incorporate 7‐day streamflow predictions, demonstrating the value of using subseasonal to seasonal (S2S, >1–2 weeks) forecasts to improve seasonal WSFs in these watersheds. [ABSTRACT FROM AUTHOR]

The 2010 Chesapeake Bay Total Maximum Daily Load was established for the water quality and ecological restoration of the Chesapeake Bay. In 2017, the latest science, data, and modeling tools were used to develop revised Watershed Implementation Plans (WIPs). In this article, we examine the vulnerability of the Chesapeake Bay watershed to the combined pressures of climate change and growth in population, agricultural intensity, and economic activity for the 60‐year period 1995–2055. The results will be used to revise WIPs, as needed, to account for expected increases in loads. Assessing changes relative to 1995 for the years 2025, 2035, 2045, and 2055, mean annual precipitation increases of 3.11%, 4.21%, 5.34%, and 6.91%, respectively, air temperature increases of 1.12, 1.45, 1.84, and 2.12°C, respectively, and potential evapotranspiration increases of 3.36%, 4.43%, 5.54%, and 6.35%, respectively, are projected. Population in the watershed is expected to grow by 3.5 million between 2025 and 2055. Watershed model results show incremental increases in streamflow (2.3%–6.2%), nitrogen (2.6%–10.8%), phosphorus (4.5%–26.7%), and sediment (3.8%–18.8%) loads to the tidal Bay due to climate change. Growth in population, agricultural intensity, development, and economic activity resulted in relatively smaller increases in loads compared to climate change. [ABSTRACT FROM AUTHOR]

We present CAMELS-CH (Catchment Attributes and MEteorology for Large-sample Studies – Switzerland), a large-sample hydro-meteorological data set for hydrologic Switzerland in central Europe. This domain covers 331 basins within Switzerland and neighboring countries. About one-third of the catchments are located in Austria, France, Germany and Italy. As an Alpine country, Switzerland covers a vast diversity of landscapes, including mountainous environments, karstic regions, and several strongly cultivated regions, along with a wide range of hydrological regimes, i.e., catchments that are glacier-, snow- or rain dominated. Similar to existing data sets, CAMELS-CH comprises dynamic hydro-meteorological variables and static catchment attributes. CAMELS-CH (; available at 10.5281/zenodo.7784632) encompasses 40 years of data between 1 January 1981 and 31 December 2020, including daily time series of stream flow and water levels, and of meteorological data such as precipitation and air temperature. It also includes daily snow water equivalent data for each catchment starting from 2 September 1998. Additionally, we provide annual time series of land cover change and glacier evolution per catchment. The static catchment attributes cover location and topography, climate, hydrology, soil, hydrogeology, geology, land use, human impact and glaciers. This Swiss data set complements comparable publicly accessible data sets, providing data from the "water tower of Europe". [ABSTRACT FROM AUTHOR]

Accurate streamflow simulations rely on good estimates of the catchment-scale soil moisture distribution. Here, we evaluated the potential of Sentinel-1 backscatter data assimilation (DA) to improve soil moisture and streamflow estimates. Our DA system consisted of the Noah-MP land surface model coupled to the HyMAP river routing model and the water cloud model as a backscatter observation operator. The DA system was set up at 0.01° resolution for two contrasting catchments in Belgium: (i) the Demer catchment dominated by agriculture and (ii) the Ourthe catchment dominated by mixed forests. We present the results of two experiments with an ensemble Kalman filter updating either soil moisture only or soil moisture and leaf area index (LAI). The DA experiments covered the period from January 2015 through August 2021 and were evaluated with independent rainfall error estimates based on station data, LAI from optical remote sensing, soil moisture retrievals from passive microwave observations, and streamflow measurements. Our results indicate that the assimilation of Sentinel-1 backscatter observations can partly correct errors in surface soil moisture due to rainfall errors and overall improve surface soil moisture estimates. However, updating soil moisture and LAI simultaneously did not bring any benefit over updating soil moisture only. Our results further indicate that streamflow estimates can be improved through Sentinel-1 DA in a catchment with strong soil moisture–runoff coupling, as observed for the Ourthe catchment, suggesting that there is potential for Sentinel-1 DA even for forested catchments. Significance Statement: The purpose of this study is to improve streamflow estimation by integrating soil moisture information from satellite observations into a hydrological modeling framework. This is important preparatory work for operational centers that are responsible for producing the most accurate flood forecasts for the society. Our results provide new insights into how and where streamflow forecasting could benefit from high-spatial-resolution Sentinel-1 radar backscatter observations. [ABSTRACT FROM AUTHOR]

Rainfall-runoff modeling plays a crucial role in determining the regular water balance. Modifications in land use and land cover (LULC) significantly impact on the hydrological response of watersheds. The study aims to analyze the effect of land use change on river runoff with the use of hydrological modeling in the Wadi Ouahrane watershed in northwestern Algeria. The study was conducted for the period from 1987 to 2017. According to the LULC change study, cultivated land and built-up areas have increased, whereas forest and grassland areas have decreased. Sensitivity evaluation has shown that the CN (curve number) is the most important factor affecting the watershed hydrology. The Nash–Sutcliffe (NSE) and efficiency values for the Wadi Ouahrane watershed were 0.76–0.82 and 0.86–0.91 for the calibration period and 0.72–0.74 and 0.81–0.83 for the validation one, respectively. The assessment of the HEC-HMS response to the LULC change showed that the peak discharge for 2017 increased by 68% relative to the 1987 peak discharge. This research has improved the knowledge of the relationship between land use change and hydrological regimes in the Wadi Ouahrane watershed. [ABSTRACT FROM AUTHOR]

Climate change plays a vital role in the hydrology of any river basin, which may have multidimensional consequences. There is a need to conduct climate change impact assessment studies with updated models and scenarios. This study aimed to assess the impact of climate change on the streamflow and hydropower in Pakistan's Kunhar River basin. Three general circulation models (GCMs), under two Shared Socioeconomic Pathway scenarios (SSPs 2–45 and 5–85), the Soil and Water Assessment Tool, and the flow duration curve were used to project the change in climatic parameters, streamflow, and hydropower potential, respectively. The findings indicated that in the 2080s, the precipitation, maximum, and minimum temperatures are projected to increase by 10%, 2.0 °C, and 3.0 °C under the SSP 2–45 scenario and are projected to increase by 8%, 3.7 °C, and 4.4 °C under the SSP 5–85 scenario, respectively. The annual streamflow may increase by 15 to 11%, and the seasonal fluctuations are more likely to be dominant compared with the annual fluctuations. The hydropower potential will probably increase by 24 to 16% under the SSP 2–45 and 5–85 scenarios in the 2080s. However, seasonal changes in streamflow and hydropower may impact the hydropower plant operation in the basin. The Kunhar River's hydrology may change from snow-fed to a rainfall–runoff river. [ABSTRACT FROM AUTHOR]

Drainage for forestry has created ~ 1 million km of artificial waterways in Sweden, making it one of the largest human-induced environmental disturbances in the country. These extensive modifications of both peatland and mineral soil dominated landscapes still carry largely unknown, but potentially enormous environmental legacy effects. However, the consequences of contemporary ditch management strategies, such as hydrological restoration via ditch blocking or enhancing forest drainage to promote biomass production via ditch cleaning, on water resources and greenhouse gas (GHG) fluxes are unclear. To close the gap between science and management, we have developed a unique field research platform to experimentally evaluate key environmental strategies for drained northern landscapes with the aim to avoid further environmental degeneration. The Trollberget Experimental Area (TEA) includes replicated and controlled treatments applied at the catchment scale based on a BACI approach (before-after and control-impact). The treatments represent the dominant ecosystem types impacted by ditching in Sweden and the boreal zone: (1) rewetting of a drained peatland, (2) ditch cleaning in productive upland forests and (3) leaving these ditches unmanaged. Here we describe the TEA platform, report initial results, suggest ways forward for how to best manage this historical large-scale alteration of the boreal landscape, as well as warn against applying these treatments broadly before more long-term results are reported. [ABSTRACT FROM AUTHOR]

Flow direction modeling consists of (a) an accurate representation of the river network and (b) digital elevation model (DEM) processing to preserve characteristics with hydrological significance. In part 1 of our study, we presented a mesh‐independent approach to representing river networks on different types of meshes. This follow‐up part 2 study presents a novel DEM processing approach for flow direction modeling. This approach consists of (a) a topological relationship‐based hybrid breaching‐filling method to conduct stream burning for the river network and (b) a modified depression removal method for rivers and hillslopes. Our methods reduce modifications to surface elevations and provide a robust two‐step procedure to remove local depressions in DEM. They are mesh‐independent and can be applied to both structured and unstructured meshes. We applied our new methods with different model configurations to the Susquehanna River Basin. The results show that topological relationship‐based stream burning and depression‐filling methods can reproduce the correct river networks, providing high‐quality flow direction and other characteristics for hydrologic and Earth system models. Plain Language Summary: Flow direction and several other flow routing attributes are important inputs for hydrologic models. Existing methods have several limitations, including only supporting rectangle mesh systems. In this study, we extend our topology‐based river network representation method to define flow direction and other attributes. With its new features, our method can be used to generate high‐quality flow routing parameters for hydrologic models. Key Points: We use topological relationships in adaptive stream burningWe use a mesh‐independent approach to conduct depression fillingThe model produces several flow routing parameters, including flow direction [ABSTRACT FROM AUTHOR]

Extreme snow ablation can greatly impact regional hydrology, affecting streamflow, soil moisture, and groundwater supplies. Relatively little is known about the climatology of extreme ablation events in the eastern United States, and the causal atmospheric forcing mechanisms behind such events. Studying the Susquehanna River basin over a 50-yr period, here we evaluate the variability of extreme ablation and river discharge events in conjunction with a synoptic classification and global-scale teleconnection pattern analysis. Results indicate that an average of 4.2 extreme ablation events occurred within the basin per year, where some 88% of those events resulted in an increase in river discharge when evaluated at a 3-day lag. Both extreme ablation and extreme discharge events occurred most frequently during instances of southerly synoptic-scale flow, accounting for 35.7% and 35.8% of events, respectively. However, extreme ablation was also regularly observed during high pressure overhead and rain-on-snow synoptic weather types. The largest magnitude of snow ablation per extreme event occurred during occasions of rain-on-snow, where a basinwide, areal-weighted 5.7 cm of snow depth was lost, approximately 23% larger than the average extreme event. Interannually, southerly flow synoptic weather types were more frequent during winter seasons when the Arctic and North Atlantic Oscillations were positively phased. Approximately 30% of the variance in rain-on-snow weather type frequency was explained by the Pacific–North American pattern. Evaluating the pathway of physical forcing mechanisms from regional events up through global patterns allows for improved understanding of the processes resulting in extreme ablation and discharge across the Susquehanna basin. Significance Statement: The purpose of this study is to better understand how certain weather patterns are related to extreme snowmelt and streamflow events and what causes those weather patterns to vary with time. This is valuable information for informing hazard preparation and resource management within the basin. We found that weather patterns with southerly winds were the most frequent patterns responsible for extreme melt and streamflow, and those patterns occurred more often when the Arctic and North Atlantic Oscillations were in their "positive" configuration. Future work should consider the potential for these patterns, and related impacts, to change over time. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of ponds as a nature-based solution (NBS) to concurrently ameliorate flood and drought impacts, emphasizing the need for an integrated response to multi-extreme hydrological events. We incorporate ponds into agricultural landscapes in the Bagmati River Basin of Nepal and assess their performance using the Soil and Water Assessment Tool (SWAT+). Six different scenarios are thoroughly explored to see how these interventions affect the main components of the water balance, such as surface run-off, lateral flow, percolation, and evapotranspiration. The spatial efficiency of the ponds, particularly in their immediate surroundings and downstream areas, has been proven to be a crucial factor in their overall efficacy in attenuating extremes, which increases with the size of the intervention area. Although the effects of ponds on floods and droughts are minor, they could be significantly magnified by a synergistic use of other NBS tactics, such as conservation tillage or soil conservation techniques. Future studies should establish the most appropriate sites and volumes for these interventions, as well as further investigate the possible advantages of several NBS, to optimize flood and drought management in the Bagmati River Basin and other similarly susceptible places. [ABSTRACT FROM AUTHOR]

Aim: A key aspect of biodiversity research is to determine the environmental drivers affecting the degree to which ecological assemblages vary in space (beta diversity). The strength and significance of environmental drivers of beta diversity is, however, influenced by the spatial extent over which beta diversity is assessed. Beta diversity of riverine biota is affected by flow variability. We examined hydrology–beta diversity relationships at two spatial extents (reaches vs. entire systems) within rivers to determine if relationships with hydrological variables are scale dependent or generalisable across spatial scales. Location: Murray–Darling Basin, Australia. Taxon: Freshwater fish. Methods: Fish assemblage data were sourced from two monitoring programmes that sampled sites annually during 2014–2019 and spanned either reaches (<100 km) or the broader 'system' extent (>1000 km) of five tributaries. Beta diversity was examined by calculating pairwise (incidence and abundance) dissimilarities for each year to compare temporal trends in beta diversity. Multi‐site dissimilarities were modelled against hydrological variables using beta regression. Results: Inter‐annual change in assemblage composition was detected only at the extent of river reaches but not at the extent of river systems. Temporal variation in within‐river beta diversity showed inconsistent patterns when compared between the two spatial extents. Within‐river beta diversity relationships with hydrological gradients were inconsistent among rivers. Overall, statistical models explained much more variation in within‐river beta diversity when assessed at the reach extent when compared to broader river system extents. Main Conclusions: Our findings highlight that changes in within‐river beta diversity are likely to depend on the spatial extent of sampling. Furthermore, inconsistent beta diversity–hydrology relationships among rivers suggest that both empirical evidence and theoretical predictions adopted in ecohydrology may not be transferable among river systems. [ABSTRACT FROM AUTHOR]

Drainage basins delineate the Earth's land surface into individual water collection units. Basin shape and river sinuosity determine water and sediment dynamics, affecting landscape evolution and connectivity between ecosystems and freshwater species. However, a high-resolution global dataset for the boundaries and geometry of basins is still missing. Using a 90-meter resolution digital elevation model, we measured the areas, lengths, widths, aspect ratios, slopes, and elevations for basins greater than 50 km2 globally. Additionally, we calculated the lengths and sinuosities of the longest river channels within these 0.67 million basins. We built a new global dataset, Basin90m, to present the basins and rivers, as well as their morphological metrics. To highlight the use cases of Basin90m, we explored differences between the nine stream orders, spatial distribution of drainage systems, and correlations between morphological metrics, such as Hack's law. By comparing with HydroSHEDS, Goole Earth images, and a few other datasets, we have demonstrated the high accuracy of Basin90m. Basin90m, available in Shapefile format, can be used in various GIS platforms, including QGIS, ArcGIS, and GeoPandas. Basin90m has substantial application prospects in geomorphology, hydrology, and ecology. [ABSTRACT FROM AUTHOR]

Headwater streams are critical to the integrity of the stream network, yet they are being rapidly degraded, channelized, or lost through land-cover and land-use change, particularly in urbanizing areas. We refined the definition of a headwater stream, reviewed the headwater stream ecosystem literature using examples from southeastern Australia and globally, and identified 4 critical knowledge gaps that are hampering the management of these unique systems: 1) inadequate high-resolution mapping and, thus, low-accuracy estimates of headwater stream locations and extents within catchments; 2) insufficient characterization of headwater stream typologies across varying geological, topographical, climatic, and anthropogenic conditions; 3) incomplete quantification of headwater stream structure, function, and ecosystem services across varying scales; and 4) limited understanding of the effects of urbanization on headwater streams against a backdrop of climate change. We propose a series of research questions to address these gaps and, finally, hypothesize and discuss the most effective ways to protect headwater streams in urbanizing environments given our current state of understanding. Of particular importance are the need to 1) shift perceptions of these systems as dry, insignificant depressions in the landscape; 2) manage both the headwater stream catchment and the channel; and 3) prioritize protection of the natural flow regime. [ABSTRACT FROM AUTHOR]

Many hydro-meteorological disasters in small and steep watersheds develop quickly and significantly impact human lives and infrastructures. High-resolution rainfall data and machine learning methods have been used as modeling frameworks to predict those events, such as flash floods. However, a critical question remains: How long must the rainfall input data be for an empirical-based hydrological forecast? The present article employed an artificial neural network (ANN)hydrological model to address this issue to predict river levels and investigate its dependency on antecedent rainfall conditions. The tests were performed using observed water level data and high-resolution weather radar rainfall estimation over a small watershed in the mountainous region of Rio de Janeiro, Brazil. As a result, the forecast water level time series only archived a successful performance (i.e., Nash–Sutcliffe model efficiency coefficient (NSE) > 0.6) when data inputs considered at least 2 h of accumulated rainfall, suggesting a strong physical association to the watershed time of concentration. Under extended periods of accumulated rainfall (>12 h), the framework reached considerably higher performance levels (i.e., NSE > 0.85), which may be related to the ability of the ANN to capture the subsurface response as well as past soil moisture states in the watershed. Additionally, we investigated the model's robustness, considering different seeds for random number generating, and spacial applicability, looking at maps of weights. [ABSTRACT FROM AUTHOR]

We examine the extent to which the parameters of different types of catchments are sensitive to calibration criteria selection (i.e. parameter agreement), and explore possible connections with overall model performance and model complexity. To this end, we calibrate the lumped GR4J, GR5J and GR6J hydrological models – coupled with the CemaNeige snow module – in 95 catchments spanning a myriad of hydroclimatic and physiographic characteristics across Chile, using 12 streamflow-oriented objective functions. The results show that (i) the choice of objective function has smaller effects on parameter values in catchments with low aridity index and high mean annual runoff ratio, in contrast to drier climates; and (ii) catchments with better parameter agreement also provide better performance across model structures and simulation periods. More generally, this work provides insights on the type of catchments where it is more challenging to find sub-domains in the parameter space that satisfy multiple streamflow criteria. [ABSTRACT FROM AUTHOR]

The phenomenon of sudden drought after pluvial (or heavy pluvial after drought) is known as the Dry–Wet Abrupt Alternation (DWAA). This kind of disaster has been evaluated globally based on various DWAA indices. However, few validations have been performed to compare the various DWAA indices. Given that directly validating the identified DWAA events remains difficult because of the limited historical records of DWAA events, in this study, we developed a simple weighting analysis method to cross‐validate the detected DWAA events using three widely‐used indices. The weighting analysis method can be used to estimate the effectiveness of the DWAA indices by calculating the ratio of the synchronous DWAA events (the DWAA events could be synchronously detected by different indices) to the total number of the detected DWAA events. Results suggest that the standard weighted average of precipitation (SWAP) index has better performance for detecting DWAA events in the Pearl River Basin (PRB) compared to other indices. The soil moisture synchronization, meteorological concentration and real DWAA records further testify that the SWAP is more capable of detecting the DWAA events in the PRB. Based on the validation, the SWAP‐derived DWAA events show that both dry–wet (D–W) events and wet–dry events are severe in the upstream sub‐basins in the PRB, while D–W events are more frequent in the downstream PRB. Our study provides a simple but effective method to validate the detected DWAA. The finding underscores the need to validate DWAA detection generated from multiple indicators before further research, and it could help develop adaptation strategies to improve resilience to combined extremes under changing climate. [ABSTRACT FROM AUTHOR]

Understanding the impacts of climate change on basin hydrology is critical for developing effective water management practices. This study was conducted to investigate climate change and its impact on the hydrological processes of the Baro–Akobo River basin in Ethiopia. Five bias-corrected regional climate models and their ensemble were developed to examine future climate changes in the 2030s (2021–2050) and 2080s (2071–2100) periods under the two Representative Concentration Pathways (RCP) 4.5 and RCP8.5 scenarios compared to a baseline (1981–2010) period. The calibrated model performed well with Nash–Sutcliffe efficiency and coefficient of determination of each 0.73 for daily and 0.89 and 0.9 for monthly simulation, respectively. Though all RCMs agree concerning the increasing direction of the 2030 and 2080s maximum and minimum temperature changes, there is inconsistency in the magnitude and direction of monthly projected rainfall changes. With the ensemble, the maximum and minimum temperatures will increase by 2.6 and 3.6 °C, respectively, and rainfall will decrease by 5% in the 2080s under RCP8.5 scenarios. The dry and wet season rainfall are expected to decrease by 19 and 3.7% under the RCP8.5 scenarios in the 2080s. Consequently, future climate change could cause a decrease in the annual surface runoff and water yield, while evapotranspiration could increase under the RCP4.5 and RCP8.5 scenarios. This study provides useful insights about potential climate change impacts on the hydrology of the basin, which could be useful to inform decision-makers in developing strategies such as water harvesting to mitigate the impact of climate change. [ABSTRACT FROM AUTHOR]

Land use is a driver for hydrological and soil erosion responses at the watershed scale. This study aimed to assess the hydrological and soil erosion processes in small watersheds under three different land uses, at three time scales. We investigated four small watersheds in southern Brazil: Agricultural North watershed (ANW), Agricultural South watershed (ASW), Eucalyptus watershed (EW), and Grassland watershed (GW). The SWAT (Soil and Water Assessment Tool) model was used to simulate streamflow (SF) and sediment yield (SY) at monthly, daily and hourly time scales. EW had the lowest SF and SY, whereas ANW showed the highest SY with an increase of 90% and ASW had the highest SF with an increase of 70%. The SWAT model had a satisfactory performance in all time scales and watersheds for SF and SY (NSE and R2 ≥ 0.3 and Pbias ≤ ± 39%). Overall, land use has a major impact on hydrological and soil erosion responses, and the magnitude of these processes depends on the time scale. [ABSTRACT FROM AUTHOR]