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This study provides evidence for the multiscale nature of atmospheric rivers (ARs) by differentiating them based on high‐ (HF) and low‐frequency (LF) moisture transports. The HF‐dominant ARs exhibit migratory behavior as they are typically accompanied by extratropical cyclones. Their spatial distribution is seasonally synchronized with midlatitude storm activity. On the other hand, the LF‐dominant ARs stay in place as they are associated with quasi‐stationary circulation. They prevail in the subtropical monsoon regions in the summer hemisphere. The ARs are often jointly affected by HF and LF processes. Such intermediate ARs are frequently observed along the poleward boundary of subtropical highs. The latter two AR types are locally more persistent than the HF‐dominant ARs, implying the importance of LF dynamics in long‐lasting AR impacts. We suggest that multiscale analysis of ARs will offer valuable insights into their diversity and hydrological impacts. Plain Language Summary: Atmospheric rivers (ARs) are narrow corridors of intense water vapor transport often concurrent with extratropical cyclones. Through case studies and climatological analyses, however, this study shows that ARs are not only associated with high‐frequency (HF) moisture transport such as those driven by extratropical cyclones but also related to low‐frequency (LF) moisture transport driven by quasi‐stationary circulation. The HF‐dominant ARs are observed along the midlatitude storm tracks, while the LF‐dominant ARs appear in summer monsoon regions in low latitudes. There are also a non‐negligible number of ARs jointly influenced by HF and LF processes, particularly along the poleward flank of subtropical highs. Noticeably, ARs strongly influenced by LF processes have a longer local duration than others. It implies that LF dynamics, which have received relatively less attention, need to be incorporated for a better understanding and prediction of the long‐lasting AR impacts. This study highlights that ARs have diverse characteristics by HF and LF processes. Taking their multiscale nature into account thus will be helpful when delineating the dynamics and hydrological impacts of ARs. Key Points: High‐frequency moisture transport related to atmospheric rivers (ARs) is synchronized with transient storm activity in midlatitudesThe ARs are also fueled by low‐frequency (LF) moisture transport along the boundary of subtropical highs and in the summer monsoon regionsThe LF moisture transport plays a critical role in locally long‐duration AR events, increasing the risk of high‐rank AR events [ABSTRACT FROM AUTHOR]

Uncertainty sources in climate change impact studies can be addressed in two distinct phases, climate modelling and impact assessment. Generally, uncertainty from the climate modelling phase is the larger contributor and the impact phase uncertainty is sometimes marginalized. This paper aims to develop integrated uncertainty analysis approaches that deal with uncertainties at the impact level with all sources included. The existing uncertainty analysis method of Reliability Ensemble Averaging (REA) is modified for impact studies by bracketing the hydrological model parameter uncertainty. A novel probabilistic approach referred to as Bootstrapped Ensemble Uncertainty Modelling (BEUM) is also proposed for uncertainty analysis at the impact phase. Modified REA and BEUM are applied to streamflow projections of the Hulu Langat basin with uncertainties stemming from emission scenarios, general circulation models (GCM), downscaling method, and a hydrological model parametrization for a comprehensive integrated uncertainty assessment. The modified REA increased the reliability measure of each streamflow scenario and improved the uncertainty coverage percentage when compared with the original REA. The REA eliminated the projections of the less reliable GCMs, and therefore reduced uncertainty bands compared to the BEUM. The BEUM can create a large ensemble of streamflow projections through nonparametric bootstrapping of the limited impact scenarios and define the streamflow distribution for every quantile. Therefore, BEUM is able to encompass larger uncertainty intervals and explain the behavior of ensemble members through probabilistic distributions that can assist in decision making for climate change mitigation and adaptation planning. [ABSTRACT FROM AUTHOR]

Global climate model (GCM) outputs from Coupled Model Inter-comparison Project Phase 5 (CMIP5) were widely used to investigate climate change impacts last 10 years. It is important to know whether Coupled Model Inter-comparison Project Phase 6 (CMIP6) is more reliable than CMIP5. Number of studies compared GCMs from two CMIPs in simulating climate variables, but they are not in the field of hydrology for large quantities of watersheds. The objective of this study is to compare CMIP5 and CMIP6 climate model projections in projecting hydrological changes between future (2071-2100) and historical (1976-2005) periods and inter-model variability of hydrological impacts for the future period over 343 catchments in China's mainland. The results show that the GCMs in CMIP6 show more increase in daily mean temperature and mean annual precipitation. However, GCMs in CMIP6 and CMIP5 show similar increases in mean and peak streamflow. Moreover, GCMs in CMIP6 show less inter-model variability for streamflow in southern and northeastern China, but more in central China, which is consistent to that for precipitation after bias correction. Overall, this comparison provides the consistency of future change and uncertainty in predicted streamflow with climate simulations, which bring confidence for hydrological impact studies using CMIP6. [ABSTRACT FROM AUTHOR]

Appropriate adaptation planning is contingent upon information about the potential future impacts of climate change, and hydrological impact assessments are of particular importance. The UKSCAPE-G2G datasets were produced, as part of the NERC UK-SCAPE programme, to contribute to this information requirement. They use the Grid-to-Grid (G2G) national-scale hydrological model configured for both Great Britain and Northern Ireland (and the parts of the Republic of Ireland that drain to rivers in NI). Six separate datasets are provided, for two sets of driving data -- one observation-based (1980-2011) and one climate projection-based (1980-2080) -- for both river flows and soil moisture on 1 km x 1 km grids across GB and NI. The river flow datasets include grids of monthly mean flow, annual maxima of daily mean flow, and annual minima of 7-day mean flow (m³s-1). The soil moisture datasets are grids of monthly mean soil moisture content (m water/m soil), which should be interpreted as depth-integrated values for the whole soil column. The climate projection-based datasets are produced using data from the 12-member 12km regional climate model ensemble of the latest UK climate projections (UKCP18), which uses RCP8.5 emissions. The production of the datasets is described, along with details of the file format, and how the data should be used. Example maps are provided, as well as simple UK-wide analyses of the various outputs. These suggest potential future decreases in summer flows, annual minimum 7-day flows, and summer/autumn soil moisture, along with possible future increases in winter flows and annual maximum flows. References are given for published papers providing more detailed spatial analyses, and some further potential uses of the data are suggested. [ABSTRACT FROM AUTHOR]

There is a high demand for openly accessible hydroclimatic data for climate change adaptation. Different data sources are available, however, discrepancy between the data can confuse users and should be evaluated and explained. This study, investigates how climate impact indicators (CIIs) developed for global users in the Copernicus Climate Change Service (C3S) are comparable to other openly available global data for water and climate. We found that, for temperature, datasets are comparable and climate impacts are thus considered robust. Important discrepancies arise in the precipitation indicators. Of the CIIs analysed in this study, the hydrological CIIs differ most so they should be used with care. These differences are probably caused by model uncertainty (hydrological model, HM; global climate model, GCM), ensemble size and model selection. A HM ensemble, as well as a GCM ensemble combined with improved model performance and selection criteria, should be used to ensure high-quality global water and climate services. [ABSTRACT FROM AUTHOR]

A warmer climate impacts streamflows and these changes need to be quantified to assess future risk, vulnerability, and to implement efficient adaptation measures. The climate simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), which have been the basis of most such assessments over the past decade, are being gradually superseded by the more recent Coupled Model Intercomparison Project Phase 6 (CMIP6). Our study portrays the added value of the CMIP6 ensemble over CMIP5 in a first North America wide comparison using 3,107 catchments. Results show a reduced spread of the CMIP6 ensemble compared to the CMIP5 ensemble for temperature and precipitation projections. In terms of flow indicators, the CMIP6 driven hydrological projections result in a smaller spread of future mean and high flow values, except for mountainous areas. Overall, we assess that the CMIP6 ensemble provides a narrower band of uncertainty of future climate projections, bringing more confidence for hydrological impact studies. Plain Language Summary: Greenhouse gas emissions are causing the climate to warm significantly, which in turn impacts flows in rivers worldwide. To adapt to these changes, it is essential to quantify them and assess future risk and vulnerability. Climate models are the primary tools used to achieve this. The main data set that provides scientists with state‐of‐the‐art climate model simulations is known as the Coupled Model Intercomparison Project (CMIP). The fifth phase of that project (CMIP5) has been used over the past decade in multiple hydrological studies to assess the impacts of climate change on streamflow. The more recent sixth phase (CMIP6) has started to generate projections, which brings the following question: is it necessary to update the hydrological impact studies performed using CMIP5 with the new CMIP6 models? To answer this question, a comparison between CMIP5 and CMIP6 using 3,107 catchments over North America was conducted. Results show that there is less spread in temperature and precipitation projections for CMIP6. This translates into a smaller spread of future mean, high and low flow values, except for mountainous areas. Overall, we assess that using the CMIP6 data set would provide a more concerted range of future climate projections, leading to more confident hydrological impact studies. Key Points: A comparison of hydrological impacts using Coupled Model Intercomparison Project version 5 (CMIP5) and Coupled Model Intercomparison Project Phase 6 (CMIP6) ensembles is performed over 3,107 catchments in North AmericaThe CMIP6 ensembles provide a narrower band of uncertainty for hydrological indicators in the futureIt is recommended to update hydrological impact studies performed using CMIP5 with the CMIP6 ensemble [ABSTRACT FROM AUTHOR]

Aim: We studied the distribution of freshwater macroinvertebrate taxa and traits to distinguish ecological gradients among the mining‐controlled and natural headwaters, and rural and urban economic activity influences. Location: In 2016's dry season, macroinvertebrate samples were collected at 40 locations in the Mashcon watershed, northern Peruvian Andes. Six locations were in the headwaters directly influenced by mining, eight near‐pristine tributary headwaters, 14 agricultural locations at midstream and 12 urban locations downstream. Methods: Eight traits (five biological and three ecological) were selected according to data availability, and modalities scores were assigned using the weighted and the dominant‐trait approaches. The traits relative abundances and abiotic conditions were compared among watershed sections. The ecological interpretability of the ungrouped data was verified with a distance‐based redundancy analysis. Results: The high‐altitude mining section had fewer taxa types and abundance, and distinct body forms distributions and prevalent body sizes in macroinvertebrate communities, relatable to the control of the mining headwaters. Physiological and ecological traits (respiration, mobility and attachment, food sources, feeding habits, saprobity and pH preferenda) differed among traits quantification approaches and were less informative at high altitudes. The ecological conditions from the near‐pristine tributaries recovered in the vegetated midstream section, to again be affected in the downstream urban section. Main Conclusions: Our results suggest the presence of ecological impairment despite the excellent physicochemical quality of the water discharged by the mine. The obtainment of autecological information at a higher taxonomic resolution, e.g. for ubiquitous taxa like Acari and Chironomidae, would be needed to advance the freshwater quality assessment of ecologically and hydrogeochemically complex Andean mining ecosystems. [ABSTRACT FROM AUTHOR]

This study focuses on quantifying future anthropogenic changes in surface runoff associated with extreme precipitation in California's Sierra Nevada. The method involves driving a land surface model with output from a high resolution regional atmospheric simulation of the most extreme atmospheric rivers (ARs). AR events were selected from an ensemble of global climate model simulations of historical and late 21st century climate under the "high‐emission" RCP8.5 scenario. Average precipitation during the future ARs increases by ~25% but a much lower proportion falls as snow. The resulting future runoff increase is dramatic—nearly 50%, reflecting both the precipitation increase and simultaneous conversion of snow to rain. The "double whammy" impact on runoff is largest in the 2,000–2,500 m elevation band, where the snowfall loss and precipitation increase are both especially large. This huge increase in runoff during the most extreme AR events could present major flood control challenges for the region. Key Points: Atmospheric river storm events will become more extreme and result in intensified surface runoff along with reduced snowfallThe "double whammy" impact on runoff is dramatic in the future—nearly 50% on average, easily double and higher in certain locationsThe disproportionately enlarged runoff during extremes could raise significant challenges for water resource management and flood control [ABSTRACT FROM AUTHOR]

A key motivation for managing invasive alien plant (IAP) species is their impacts on streamflows, which, for the wetter half of South Africa, are about 970 m³∙ha−1∙a−1 or 1 444 mill. m³∙a−1 (2.9% of naturalised mean annual runoff), comparable to forest plantations. However, the implications of these reductions for the reliability of yields from large water supply systems are less well known. The impacts on yields from the WCWSS were modelled under three invasion scenarios: ‘Baseline’ invasions; increased invasions by 2045 under ‘No management’; and under ‘Effective control’ (i.e. minimal invasions). Monthly streamflow reductions (SFRs) by invasions were simulated using the Pitman rainfall−runoff catchment model, with taxon-specific mean annual and low-flow SFR factors for dryland (upland) invasions and crop factors for riparian invasions. These streamflow reduction sequences were input into the WCWSS yield model and the model was run in stochastic mode for the three scenarios. The 98% assured total system yields were predicted to be ±580 million m³∙a−1 under ‘Effective control’, compared with ±542 million m³∙a−1 under ‘Baseline’ invasions and ±450 mill. m³∙a−1 in 45 years’ time with ‘No management’. The ‘Baseline’ invasions already reduce the yield by 38 mill. m³∙a−1 (two thirds of the capacity of the Wemmershoek Dam) and, in 45 years’ time with no clearing, the reductions would increase to 130 mill. m³∙a−1 (capacity of the Berg River Dam). Therefore IAP-related SFRs can have significant impacts on the yields of large, complex water supply systems. A key reason for this substantial impact on yields is that all the catchments in the WCWSS are invaded, and the invasions are increasing. Invasions also will cost more to clear in the future. So, the best option for all the water-users in the WCWSS is a combined effort to clear the catchments and protect their least expensive source of water. [ABSTRACT FROM AUTHOR]

This study aimed to assess the hydrological and erosive effects of different levels of the fire severity in the drainage basin of the Trionto River (Calabria, southern Italy), which was partially burned by intense fires during the summer 2017. The analysis focused on the identification of wildfire areas using a supervised classification of remote sensing images with the minimum distance algorithm. The level of severity of each fire was then discriminated based on a procedure proposed by the U.S. Department of Agriculture and adapted to the study area. To evaluate how wildfire occurrence affects the hydrological behaviour at the basin scale, the SCS-Curve Number model was used to document pre- and post-fire conditions in relation with the level of fire severity. Finally, the influence on erosion was analysed for analogous conditions at the basin scale using the RUSLE equation. The effects on hydrological balance and soil loss were evaluated by comparing the pre-fire value with three different post-fire scenarios: (a) different levels of severity on the surface covered by the fire (real case); (b) maximum level of severity on the surface covered by the fire; (c) total loss of the canopy and formation of a hydrophobic layer on the surface soil. The results confirmed that the level of severity of the forest fires, combined with climatic factors, morphological conditions, and the pedological characteristics of the basin, significantly influence changes to the hydrology and rates of erosion. Moreover, these impacts proved to be mainly dependent on the consequent, often notable, heterogeneity in the spatial distribution of burned areas with different severity. [ABSTRACT FROM AUTHOR]

Abstract Ensuring water is available for human use usually requires dams and reservoirs that severely affect river ecosystems. Hydrological alteration by river damming represents one of the most prominent human impacts on freshwater ecosystems. This paper presents a methodological approach to assessing the natural patterns of flow variability and hydrological alterations in Mediterranean rivers. The methodology first defines the admissible range of flow variability under a natural flow regime. Then, the methodology measures the environmental impact of flow regulation according to the inferred hydrological alteration and classifies rivers into homogeneous groups according to the magnitude, frequency, duration and seasonality of the impacts. This paper applies the proposed methodology to thirty-three river segments below large reservoirs located in the three largest Spanish watersheds (Duero, Ebro and Tajo). For each segment, this study evaluates the general impoundment characteristics and geographical contexts and calculates the flow impacts and the divergence between the circulating flows and the reference area of admissible flow variability on a daily basis for the period 2000–2010. This assessment of dam regulation impacts provides a reference to plan measures for mitigating these impacts. The advantages of this flow regulation impact analysis over other analyses are discussed in terms of the implementation of environmental water costs as suggested by the European Water Framework Directive. This approach expands the current understanding of water environmental costs and represents a practical management tool for decreasing the environmental impacts of flow regulation and for increasing water-use efficiency. Highlights • Natural range of flow variability discriminates distinct hydrologic regime patterns. • Flow regulation impacts are not significantly influenced by climate or geomorphology. • Flow regulation impacts strongly depend on dam operation and water use. • Flow reductions in winter and increases in summer are common in Mediterranean rivers. • Deviations from natural flow variability should inform damming environmental costs. [ABSTRACT FROM AUTHOR]

Abstract The river flow regime and water resources are highly important for economic growths, flood security, and ecosystem dynamics in the Mekong basin – an important transboundary river basin in South East Asia. The river flow, although remains relatively unregulated, is expected to be increasingly perturbed by climate change and rapidly accelerating socioeconomic developments. Current understanding about hydrological changes under the combined impacts of these drivers, however, remains limited. This study presents projected hydrological changes caused by multiple drivers, namely climate change, large-scale hydropower developments, and irrigated land expansions by 2050s. We found that the future flow regime is highly susceptible to all considered drivers, shown by substantial changes in both annual and seasonal flow distribution. While hydropower developments exhibit limited impacts on annual total flows, climate change and irrigation expansions cause changes of +15% and −3% in annual flows, respectively. However, hydropower developments show the largest seasonal impacts characterized by higher dry season flows (up to +70%) and lower wet season flows (−15%). These strong seasonal impacts tend to outplay those of the other drivers, resulting in the overall hydrological change pattern of strong increases of the dry season flow (up to +160%); flow reduction in the first half of the wet season (up to −25%); and slight flow increase in the second half of the wet season (up to 40%). Furthermore, the cumulative impacts of all drivers cause substantial flow reductions during the early wet season (up to −25% in July), posing challenges for crop production and saltwater intrusion in the downstream Mekong Delta. Substantial flow changes and their consequences require careful considerations of future development activities, as well as timely adaptation to future changes. Graphical abstract Unlabelled Image Highlights • Climate change, hydropower and irrigation developments strongly alter the Mekong's future flows. • Total annual flows changes (-3% to 15%) are primarily driven by irrigation expansions and climate change. • Hydropower developments show strongest impacts on seasonal flows: up to +70% (dry season) and -15% (wet season). • Future flow changes pose serious consequences, requiring strategic development planning and effective adaptation. [ABSTRACT FROM AUTHOR]

Highlights • Impacts of future climate change scenarios on net aquifer recharge from rainfall. • Application in continental Spain, a varied territory sensitive to climate change. • Generation of potential climate scenarios by different ensembles of prediction. • Multi-criteria analysis of statistical downscaling techniques. • Simulation of climate scenarios within a distributed rainfall-recharge model. Abstract Climate change will modify the availability of groundwater resources in the future. Thus the evaluation of average aquifer recharge from precipitation, and its uncertainty, becomes a key subject in determining suitable countrywide water policies. The confident prediction of renewable groundwater resources requires an accurate evaluation of aquifer recharge over time and space, especially in large territories with varied conditions for aquifer recharge such as continental Spain. This study asses impacts of future potential climatic change scenarios on distributed net aquifer recharge (NAR) from precipitation over continental Spain. For this, the used method (1) generates future time series of climatic variables (precipitation, temperature) spatially distributed over the territory for potential aquifer recharge (PAR), and (2) simulates them within previously calibrated spatial PAR or NAR recharge models from the available historical information to provide distributed PAR or NAR time series. The information employed comes from the Spain02 project for the historical climatic data, from Alcalá and Custodio (2014, 2015) for the historical spatial NAR, and from the CORDEX EU project (2013) regional climate models (RCMs) simulations for the future climate scenarios. A distributed empirical precipitation-recharge model is defined by using a regular 10 km × 10 km grid, and assuming that precipitation (P) and temperature (T) are the most important climatic variables determining PAR, while their spatiotemporal variabilities determine the impacts of future potential climatic scenarios on renewable groundwater resources. Potential plausible pictures of future climate scenarios are defined by combining information coming from different RCMs and General Circulation models (GCMs), downscaling techniques, and ensemble hypothesis. These scenarios were simulated within the used precipitation-recharge model to estimate impacts on NAR. The results show that global mean NAR decreases by 12% on average over continental Spain. Over 99.8% of the territory, a variable degree of recharge reduction is obtained; the reduction is quite heterogeneously distributed in line with the variety of conditions for aquifer recharge over continental Spain. The standard deviation of annual mean NAR will increase by 8% on average in the future. The dependence of these changes regarding potential explanatory variables, such as elevation and latitude was also analysed. [ABSTRACT FROM AUTHOR]

In this investigation, hydrological time series of three ponds located in the province of Córdoba (southern Spain) at a daily scale has been analyzed. For the first time, a detailed evolution of the water level of Jarales, Conde, and Amarga ponds has been acquired by means of the installation of level loggers in the deepest point of each of the ponds. We have modeled the water level evolution using a simple one-dimensional model. Calibration of the model was very satisfactory in two of the ponds. The model was then setup and simulated for two future Scenarios: A (IPCC climate change scenario) and B (climate change + groundwater withdrawal within the basin). Two ponds were classified as discharge ponds, which are the hydrological regime of the majority of southern Spain's continental ponds. One was classified as a recharge pond. With regard to the results obtained in the simulations for Scenarios A and B, our results showed that IPCC scenario will reduce hydroperiod significantly in the three ponds, with a reduction of approximately 500 cm in the water level. With respect to groundwater withdrawal within the basins, results show a very high impact in the hydroperiod in Amarga and Conde ponds. [ABSTRACT FROM AUTHOR]

Precipitation extremes play a key role in flooding risks over the Huaihe River Basin, which is important to understand their hydrological impacts. Based on observed daily precipitation and streamflow data from 1958 to 2009, eight precipitation indices and three streamflow indices were calculated for the study of hydrological impacts of precipitation extremes. The results indicate that the wet condition intensified in the summer wet season and the drought condition was getting worse in the autumn dry season in the later years of the past 50 years. The river basin had experienced higher heavy rainfall-related flooding risks in summer and more severe drought in autumn in the later of the period. The extreme precipitation events or consecutive heavy rain day events led to the substantial increases in streamflow extremes, which are the main causes of frequent floods in the Huaihe River Basin. The large inter-annual variation of precipitation anomalies in the upper and central Huaihe River Basin are the major contributor for the regional frequent floods and droughts. [ABSTRACT FROM AUTHOR]

ABSTRACT Climate change is almost certain to affect snow and ice processes. Even at lower latitudes, changes in snow cover at high altitudes can significantly affect catchment hydrology. This article uses data from a transient Regional Climate Model projection ( HadRM3Q0) for 1950-2099 ( A1B emissions) to drive hydrological models for three nested catchments on the river Dee in north-east Scotland, to assess potential changes in flood frequency and timing using annual maxima and moving-window analyses. Some results are also shown for an upland catchment in northern England. Modelling is performed both with and without a snow module, to demonstrate the effects of snowfall/melt and how these change through time and vary between catchments. Modelled changes in flood magnitude and timing are nonlinear, with most changes for daily mean flows not significant. For longer duration (30-day) flows with snow there are significant decreases in peak magnitude, particularly for the smaller higher altitude Dee catchments, with peaks occurring months earlier in future (changes without snow are generally not significant). There is a general convergence in results with and without snow later in the period, as snow processes become less important, but convergence occurs at different times for different catchments and occurs differently for daily and 30-day peak flows due to the differential effects of snow at different durations. This not only highlights the importance of including snow processes for such catchments, particularly for longer duration flows, but also highlights the complexity of interactions: Physical catchment properties, the balance between precipitation occurrence and temperature, and how this balance alters as the climate changes will each be critical in determining the impact on the magnitude and timing of peak flows, making it hard to generalize results. [ABSTRACT FROM AUTHOR]

Abstract: Agriculture plays a key role in relation to global water stresses. Increasingly, water footprints (WF) are being used to indicate the impacts of the water use by production systems. International standards for WF are being developed and this paper contributes to these from a hydrological perspective. The impacts of water use through the life cycle of grape-wine production on water resources were assessed for two regions in New Zealand: Marlborough and Gisborne. The functional unit (FU) was a 750-mL bottle of wine at the winery gate. The WF was assessed using a full water-balance calculated by subtracting inflows from outflows. The net usage from groundwater and soil moisture storage was quantified as blue and green water footprints. We found a large variability of blue-WF even within a region. For the grape-growing stage, the average blue-WF was negative, at −81 L/FU and −415 L/FU for Marlborough and Gisborne indicating the water resources are being recharged on an annual timescale. The green-WF was negligible. The grey-WF, water required to dilute NO3-N leached in the vineyard phase, was 40 and 188 L/FU for Marlborough and Gisborne. However, the average concentration of NO3-N in the leachate was well within the drinking water standard of 11.3 mg/L (5.01 mg/L and 8.7 mg/L for Marlborough and Gisborne). The impacts of the winery phase were very small compared with that of the vineyard. The variability we have found indicates the importance of considering water issues at the local scale. Locale is the essence of terroir for wine. [Copyright &y& Elsevier]

Using updated hydrological datasets from three stations, including Cuntan, Yichang and Hankou, covering the period of January 1992-December 2008, the influence of Three Gorges Dam (TGD) on streamflow and sediment load of the Yangtze River was investigated. Results indicated that TGD did not seem to exert a significant influence on streamflow occurring at three stations and changes in streamflow can be mainly attributed to streamflows of tributaries. However, a sharp decrease in the sediment load after the impoundment of TGD was observed. Clear water after the impoundment caused erosion of riverbed and resulted in more sediment at the Hankou station than at the Yichang station. No distinct changes in the annual and monthly maximum sediment loads were observed before and after the impoundment. Therefore, annual and monthly maximum sediment load changes should be subjected mainly to river hydraulics. This study has practical relevance for understanding the influence of large hydraulic structures on the hydrological processes of large rivers. [ABSTRACT FROM AUTHOR]

Abstract: This study used climate change projections from different regional approaches to assess hydrological effects on the Thukela River Basin in KwaZulu-Natal, South Africa. Projecting impacts of future climate change onto hydrological systems can be undertaken in different ways and a variety of effects can be expected. Although simulation results from global climate models (GCMs) are typically used to project future climate, different outcomes from these projections may be obtained depending on the GCMs themselves and how they are applied, including different ways of downscaling from global to regional scales. Projections of climate change from different downscaling methods, different global climate models and different future emissions scenarios were used as input to simulations in a hydrological model to assess climate change impacts on hydrology. A total of 10 hydrological change simulations were made, resulting in a matrix of hydrological response results. This matrix included results from dynamically downscaled climate change projections from the same regional climate model (RCM) using an ensemble of three GCMs and three global emissions scenarios, and from statistically downscaled projections using results from five GCMs with the same emissions scenario. Although the matrix of results does not provide complete and consistent coverage of potential uncertainties from the different methods, some robust results were identified. In some regards, the results were in agreement and consistent for the different simulations. For others, particularly rainfall, the simulations showed divergence. For example, all of the statistically downscaled simulations showed an annual increase in precipitation and corresponding increase in river runoff, while the RCM downscaled simulations showed both increases and decreases in runoff. According to the two projections that best represent runoff for the observed climate, increased runoff would generally be expected for this basin in the future. Dealing with such variability in results is not atypical for assessing climate change impacts in Africa and practitioners are faced with how to interpret them. This work highlights the need for additional, well-coordinated regional climate downscaling for the region to further define the range of uncertainties involved. [Copyright &y& Elsevier]

Summary: Although no single weather-related event can be directly attributed to climate change, new techniques make it possible to estimate how much the chance of an event has been altered by anthropogenic emissions. This paper looks at the floods that occurred in England in Autumn/Winter 2000, by using large ensembles of 1-year climate model simulations representing April 2000–March 2001. These represent an industrial climate and four estimates of an hypothetical non-industrial climate (without historical greenhouse gas emissions), and are used to drive hydrological models for eight catchments in England. The simulated flows are used to assess the impact of historical emissions on the chance of occurrence of extreme floods in each catchment, through calculation of the fraction of attributable risk (FAR). Combining results for the four non-industrial climates, positive median values of FAR indicate that, for all but one catchment, emissions are likely to have led to an increased chance of flooding in the October–December period. Definitive conclusions are difficult however, as there are wide bands of uncertainty in FAR, with distributions generally spanning no attributable difference in risk (FAR =0). One catchment shows a decreased flood chance (negative median FAR), due to its high permeability, but an analysis of the effect of antecedent conditions shows that a longer period of climate data than 1year is probably required to obtain more representative values of FAR for such catchments. The inclusion of snowfall/snowmelt is also shown to be important for floods over the October–March period, as the reduced likelihood of snowmelt-induced floods in the warmer temperatures of the industrial climate moderates the increased flood chance due to other sources of flooding. [ABSTRACT FROM AUTHOR]

As climate change could have considerable influence on hydrology and corresponding water management, appropriate climate change inputs should be used for assessing future impacts. Although the performance of regional climate models (RCMs) has improved over time, systematic model biases still constrain the direct use of RCM output for hydrological impact studies. To address this, a distribution-based scaling (DBS) approach was developed that adjusts precipitation and temperature from RCMs to better reflect observations. Statistical properties, such as daily mean, standard deviation, distribution and frequency of precipitation days, were much improved for control periods compared to direct RCM output. DBS-adjusted precipitation and temperature from two IPCC Special Report on Emissions Scenarios (SRESA1B) transient climate projections were used as inputs to the HBV hydrological model for several river basins in Sweden for the period 1961 -2100. Hydrological results using DBS were compared to results with the widely-used delta change (DC) approach for impact studies. The general signal of a warmer and wetter climate was obtained using both approaches, but use of DBS identified differences between the two projections that were not seen with DC. The DBS approach is thought to better preserve the future variability produced by the RCM, improving usability for climate change impact studies. [ABSTRACT FROM AUTHOR]

Small dams represent an important local-scale resource designed to increase water supply reliability in many parts of the world where hydrological variability is high. There is evidence that the number of farm dams has increased substantially over the last few decades. These developments can have a substantial impact on downstream flow volumes and patterns, water use and ecological functioning. The study reports on the application of a hydrological modelling approach to investigate the uncertainty associated with simulating the impacts of farm dams in several South African catchments. The focus of the study is on sensitivity analysis and the limitations of the data that would be typically available for water resources assessments. The uncertainty mainly arises from the methods and information that are available to estimate the dam properties and the water use from the dams. The impacts are not only related to the number and size of dams, but also the extent to which they are used for water supply as well as the nature of the climate and the natural hydrological regimes. The biggest source of uncertainty in South Africa appears to be associated with a lack of reliable information on volumes and patterns of water abstraction from the dams. Citation Hughes, D. A. & Mantel, S. K. (2010) Estimating the uncertainty in simulating the impacts of small farm dams on streamflow regimes in South Africa. Hydrol. Sci. J. 55(4), 578-592. [ABSTRACT FROM AUTHOR]

• The macadamia industry is growing rapidly. • There is limited research on macadamia water use. • Macadamia is characterised by strict stomatal regulation. • Macadamia is drought-tolerant. • The hydrological implications of macadamia expansion remain unknown. Growing macadamia nut trees continues to gain popularity due to the delicacy and nutritional value associated with the nuts. These evergreen trees are grown in areas where rainfall quantity and distribution is often inadequate to sustain optimum yields. As a result, irrigation is often required to meet demands and achieve maximum profits. However, there is little detail on the minimum volume of water required during different growth stages to obtain optimal yields. This paper reviews existing studies on the plant-water relations of macadamia nut trees from the perspective of understanding their impacts on water resources. Macadamia trees have been found to use an average 75 L tree−1 day−1 in Australia, while values range between 4 and 71 L tree−1 day−1 for trees grown in South Africa. Macadamia trees are characterised by strict stomatal control, enabling them to maintain a favourable water status for prolonged periods under water stressed conditions. However, stress during the premature nut drop and oil accumulation stages decreases yield and quality. On the other hand, imposing stress at floral initiation increases yield. Therefore, stress manipulation may be a useful management tool for improved water use efficiency in commercial orchards. This requires accurate measurements of the thresholds for the maximum stress and minimum water required at these critical stages. Yield response to irrigation has been difficult to determine with confidence. Due to the cyclical nature of macadamia yields, it has been recommended that a minimum of five years is required to establish a relationship between water use and yield. There has been a limited amount of work done on the impacts of macadamia production on water resources and financial constraints are likely to limit this in the future. However, based on the rapid development of commercial macadamia orchards, future water-related research needs to consider macadamia production beyond tree and orchard scales, viewing macadamia as part of a socioecological system where orchard water use may impact on the availability and quality of water for other users, including the environment. [ABSTRACT FROM AUTHOR]

Nature-based solutions (NBS) as a sustainable strategy has recently received increasing attention for urban stormwater management. Thus, an evaluation of cost-effectiveness of NBS scenarios by integrating hydrological impacts and life cycle costs is significant for the decision-making process. This study first investigates the hydrological responses of a 5.2 km2 semi-urban watershed under various implementation NBS scenarios and highly spatially variable rainfall fields. The fractal dimension is considered as a scale invariance indicator to quantify the heterogeneous spatial distributions of NBS in each scenario across a range of scales. The hydrological responses of NBS scenarios are assessed by the fully distributed and physically based model (Multi-Hydro) under different rainfall conditions with a high spatial resolution of 10 m. In order to assess the cost-effective NBS scenarios, the hydrologic indicator (reduction of peak flow and total runoff volume) is integrated with the economic indicator (life cycle costs). The results show that the optimal NBS scenarios are characterised with fractal dimension ranges from 1.5 to 1.6 under all studied rainfall events. Considering the NBS scenarios under the strongest rainfall event, concentrating NBS downstream of the catchment can be more cost-effective. This study can provide some guidelines for the decision-making process on sustainable urban planning and improve the flood resilience of cities. • Evaluation of hydrological impacts of nature-based solutions scenarios. • Life cycle costs of nature-based solutions scenarios. • Assessing the cost-effectiveness of nature-based solutions scenarios. [ABSTRACT FROM AUTHOR]

The article offers information on two downscaling methods, the multivariate statistical downscaling (SD) and the dynamic downscaling, both designed for the study concerning the climate change's hydrological impact on the Seine basin in France. Initially, the SD based on conditional resampling and weather typing is described followed by the introduction of bias correction technique for dynamic downscaling based on quantile-quantile mapping. Moreover, the results of the study are taken into account using a practical impact study perspective.

The article offers information on the method and application example for comparing and evaluating the possible future regional climate scenarios in relation to hydrological impact studies. A two-step knowledge-based evaluation is used to evaluate the probable regional climate scenarios, which include an evaluation on the capability of climate scenarios to represent regional climate, another is an evaluation on the hydrological process that can be affected by climactic change. An experiment on three regional climate change scenarios shows different levels of adequacy, depending on the hydrological process being studied.

The article offers information on downscaling techniques used to assess the impacts of climate change on the hydrological systems. Advance downscaling techniques for hydrological modeling are used in the experiment to determine the hydrogical impacts of climactic change. Probabilistic modeling, pattern scaling and downscaling are being merged with downscaling techniques to assess the probabilistic projections. Different climactic variables such as precipitation, temperature, and rainfall are being studied to produce baseline and future scenario flow sequence, and seasonal statistics of climactic change.

Summary: Large differences in future climatic scenarios found when different global circulation models (GCMs) are employed have been extensively discussed in the scientific literature. However, differences in hydrological responses to the climatic scenarios resulting from the use of different hydrological models have received much less attention. Therefore, comparing and quantifying such differences are of particular importance for the water resources management of a catchment, a region, a continent, or even the globe. This study investigates potential impacts of human-induced climate change on the water availability in the Dongjiang basin, South China, using six monthly water balance models, namely the Thornthwaite–Mather (TM), Vrije Universitet Brussel (VUB), Xinanjiang (XAJ), Guo (GM), WatBal (WM), and Schaake (SM) models. The study utilizes 29-year long records of monthly streamflow and climate in the Dongjiang basin. The capability of the six models in simulating the present climate water balance components is first evaluated and the results of the models in simulating the impact of the postulated climate change are then analyzed and compared. The results of analysis reveal that (1) all six conceptual models have similar capabilities in reproducing historical water balance components; (2) greater differences in the model results occur when the models are used to simulate the hydrological impact of the postulated climate changes; and (3) a model without a threshold in soil moisture simulation results in greater changes in model-predicted soil moisture with respect to alternative climates than the models with a threshold soil moisture. The study provides insights into the plausible changes in basin hydrology due to climate change, that is, it shows that there can be significant implications for the investigation of response strategies for water supply and flood control due to climate change. [Copyright &y& Elsevier]

Climate change affects natural systems, leading to increased acceleration of global water cycle and substantial impacts on the productivity of tropical rivers and the several ecosystem functions they provide. However, the anticipated impacts of climate change in terms of frequency and intensity of extreme events (e.g., droughts and floods) on hydrological systems across regions could be substantially different. This study therefore aims to assess the impacts of climate change on the streamflow of a large river basin located in central Australia (Cooper Creek-Bulloo River Basin). Modified version of the hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV) was used in this study to generate daily streamflow. This model was first calibrated (2001–2010) and then validated for two independent periods (1993–1997 and 2011–2015). The model depicted a good performance in simulating observed streamflow. Climate projection data from multiple general circulation models (ACCESS1.0, CanESM2, CESM1-CAM5, CNRM-CM5, GFDL-ESM2M, HadGEM2-CC, MIROC5, NorESM1-M, ACCESS1-0, ACCESS1-3, CCSM4, CNRM-CM5, CSIRO-Mk3.6, GFDL-CM3, GFDL-ESM2M, HadGEM2, MIROC5, MPI-ESM-LR, and NorESM1-M) in various forms (raw, statistically downscaled, dynamically downscaled, and bias adjusted) were considered in this study. Results showed that three high resolution dynamically downscaled and bias adjusted models (ACCESS1-3, CNRM-CM5, and MPI-ESM-LR) from Terrestrial Ecosystem Research Network (TERN) dataset (v1.0.2) have better performance than other models considered, that is, in terms of capturing observed precipitation over the basin. Future climate projections of ensemble of these three models forced with RCP 4.5 and RCP 8.5 emission scenarios were then used to generate streamflow for 2050s (2040–2069) and 2080s (2070–2099). Results of the study indicated that mean annual precipitation was projected to decrease by up to −8% in 2050s and temperature was projected to increase by up to 4.66 °C in 2080s under the average and extreme emission scenarios, respectively. Mean annual, mean seasonal (December–February, March–May, June–August, September–November), and mean monthly streamflow were projected to decrease under different emission scenarios in 2050s and 2080s. These results indicate decreased water availability in the future as well as water cycle intensification. These changes in streamflow might have impacts on agriculture, natural ecosystem, and could lead to water restrictions. The outcome of this study can directly feed into frameworks for sustainable management of water resources and support adaptation strategies that rely on science and policy to improve water resources allocation in the region. [ABSTRACT FROM AUTHOR]

• Applied grid-based hydrological model and latest UK global and regional projections. • Clustering applied to highlight typical changes in high and low flows. • Generally decreases in low flows and increases in high flows to end of century. • Significant variation in results for different regions of Great Britain. Changes in river flows, especially extreme high and low flows, could be a particularly important impact of climate change in terms of the hazard to people and the environment. Here, a national-scale grid-based hydrological model is applied, with ensembles of global and regional climate projections from UK Climate Projections 2018, to investigate the potential future changes in both floods and droughts in a consistent way across the whole of Great Britain (gauged and ungauged locations). Using hydrological model outputs for the climate projection ensembles, a clustering technique is applied to highlight 'typical' sets of changes in individual indicators of floods or droughts, but also to look at concurrent changes in pairs of flood and drought indicators. The results for regions across the country generally indicate decreases in low flows combined with increases in high flows up to the end of the 21st century. There is significant variation in results for different regions, with those to the south/east tending to show greater decreases in low flows and a greater range of uncertainty in the projections for high flows. A grid-based cluster analysis also shows potentially important variation within regions, likely related to catchment properties. The potential future changes in derived climate hazards, such as the frequency or severity of floods and droughts, is a key piece of information required for adaptation planning, and the consideration of potential concurrent changes in a range of related hazards/risks, rather than viewing each in isolation, could be vital to avoid maladaptation. [ABSTRACT FROM AUTHOR]

• Coal mining and coal seam gas developments can have important hydrological impacts. • There is large uncertainty associated with the magnitude of these impacts. • There is potential for cumulative impacts from multiple developments in proximity. • A cumulative impact assessment approach is hereby presented and applied. This paper presents an assessment of the hydrological impacts of proposed coal mines and coal seam gas (CSG) developments in the Gloucester, Hunter, Namoi and Galilee subregions of eastern Australia. Surface water and groundwater modelling was carried out to assess the cumulative regional-scale hydrological impacts of multiple coal and coal seam gas developments. The hydrological metrics assessed were groundwater drawdown and changes in low-flow characteristics as measured by the number of low-flow or zero flow days per year. Uncertainty in the modelling was also considered, and the results are presented as the median and plausible range (5th to 95th percentile) from many simulations which attempt to capture a wide range of uncertainty. The results indicate that under the best-case (5th percentile) scenario, the impact of additional/proposed coal resource developments on groundwater drawdown and surface water characteristics can be quite small. However, under the worse-case (95th percentile), groundwater drawdown is very likely for up to 5 km from the coal resource developments, but unlikely beyond 20 km. Altered surface water characteristics can extend for many kilometres downstream, particularly in unregulated systems. The cumulative hydrological impact is enhanced where there are multiple developments in close proximity. The results are being used to inform policy and the approval process for coal resource developments. [ABSTRACT FROM AUTHOR]

Fires have significant impacts on soil erosion and water supply that may be exacerbated by future climate. The aims of this study were: To simulate the effects of a large fire event in the SWAT (Soil and Water Assessment Tool) hydrological model previously calibrated to a medium-sized watershed in Portugal; and to predict the hydrological impacts of large fires and future climate on water supply and soil erosion. For this, post-fire recovery was parametrized in SWAT based on satellite information, namely, the fraction of vegetation cover (FVC) calculated from the normalized difference vegetation index (NDVI). The impact of future climate was based on four regional climate models under the stabilization (RCP 4.5) and high emission (RCP 8.5) scenarios, focusing on mid-century projections (2020–2049) compared to a historical period (1970–1999). Future large fire events (>3000 ha) were predicted from a multiple linear regression model, which uses the daily severity rating (DSR) fire weather index, precipitation anomaly, and burnt area in the previous three years; and subsequently simulated in SWAT under each climate model/scenario. Results suggest that time series of satellite indices are useful to inform SWAT about vegetation growth and post-fire recovery processes. Different land cover types require different time periods for returning to the pre-fire fraction of vegetation cover, ranging from 3 years for pines, eucalypts, and shrubs, to 6 years for sparsely vegetated low scrub. Future climate conditions are expected to include an increase in temperatures and a decrease in precipitation with marked uneven seasonal distribution, and this will likely trigger the growth of burnt area and an increased frequency of large fires, even considering differences across climate models. The future seasonal pattern of precipitation will have a strong influence on river discharge, with less water in the river during spring, summer, and autumn, but more discharge in winter, the latter being exacerbated under the large fire scenario. Overall, the decrease in water supply is more influenced by climate change, whereas soil erosion increase is more dependent on fire, although with a slight increase under climate change. These results emphasize the need for adaptation measures that target the combined hydrological consequences of future climate, fires, and post-fire vegetation dynamics. [ABSTRACT FROM AUTHOR]