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Transformation plays a significant role in solving hydrological problems. In response to the comment on Singh and Das (2015) by Deng et al. (2015) regarding the transformation, boundary conditions and subsequent analytical solution of advection dispersion equation in semi-infinite heterogeneous porous media, it is argued that the transformation used by Singh and Das (2015) for finding the analytical solution is correct and mathematically valid. Also, the different expression of f (mt) used to obtain the solution are explained with their physical relevance in the field. [ABSTRACT FROM AUTHOR]

• A review has been conducted on the application of ML and RS in hydrology domain. • Analyses were conducted on surface hydrology, hydro-climatic extremes and GWM & WQ. • GIS and ML algorithms prove valuable in the realm of hydrological investigations. • State-of-the-art approach is attributed to hydrology and water resources. Water, one of the most valuable resources on Earth, is the subject of the study of hydrology, which is of utmost importance. Satellite remote sensing (RS) has emerged as a critical tool for comprehending Earth and atmospheric dynamics, including hydrology. With the assistance of satellite RS, the scientific community has achieved significant progress in recent years. Since machine learning (ML) and RS techniques were initially applied to the study of hydrology, there has been a tremendous increase in interest in studying potential areas for future advancements in hydrology. The growth can see in the publications of related papers. Considering these initiatives, the current review paper attempts to give a thorough analysis of the function of ML and RS techniques in four fields of hydrology. This review study considers hydrological topics of streamflow, rainfall-runoff, groundwater modelling and water quality, and hydroclimatic extremes. The use of learning strategies in the hydrological sciences is examined in all reviews and research papers. Several databases were utilised for this purpose, including Scopus-index, science direct, Web of Science, and Google Scholar. The overall results of this study show that employing RS techniques, ML and ensemble approaches is incomparably superior to using traditional methods in hydrological studies. [ABSTRACT FROM AUTHOR]

• We discuss the discomforts of hydrologists in their dialogue with society. • We propose 4 ways to better align scientific stance, research practices & discourse. • This helps to refocus research practices and engage in and with society. • Socio-hydrology allows a collective, interdisciplinary reflexive process. • This is potentially a way to integrate socio-hydrology in society. Although there is a deep historical relationship between hydrology and society, the relationship has considerably evolved in the last three decades. Hydrologists, in particular those involved in designing of decision-support tools, are experiencing a widening gap between an academic discipline which has progressively moved away from field-based applied natural science to computational hydrology, and the multiplication of stakeholders involved in the water-related issues addressed by research. The challenge for hydrology is now to negotiate this shift and to rethink its engagement in society. This paper provides a description of a planned process designed to improve hydrology-society interactions and to foster reflexivity in socio-hydrology. Based on an interdisciplinary reflexive process undertaken in Tunisia from 2016 to 2020, we identified three types of discomforts in the dialogue with society, inviting scientists to lucidly engage with these discomforts. We formulated four key reflexive propositions to achieve a better alignment of scientific stance, research practices and discourse. The first proposition concerns the need to explain more clearly the value systems scientists engage in and with society. The second concerns the need to position hydrology in society and not outside it, by reconsidering the functions that research fulfils in society. The third is an invitation to redefine the perimeter of the research interlocutors and the way to reach them. The fourth is to revisit scientific practices to build on the strengths of the dialogue between field-based natural science and computational hydrology. The paper concludes that adopting a reflexive posture towards these four dimensions of the dialogue between hydrology and society is an effective way to overcome discomforts and to refocus research stance, practices and discourse. It is a way to renew hydrology's place in society and to contribute to the current thinking in socio-hydrology initiated by hydrologists. [ABSTRACT FROM AUTHOR]

Highlights • More than 150 papers dealing with applications of GP in water resource engineering were reviewed. • Fundamentals of GP variants were provided and compared with each other. • Selection ways of GP parameters were discussed. • Future scope of studies were demonstrated. Abstract The state-of-the-art genetic programming (GP) method is an evolutionary algorithm for automatic generation of computer programs. In recent decades, GP has been frequently applied on various kind of engineering problems and undergone speedy advancements. A number of studies have demonstrated the advantage of GP to solve many practical problems associated with water resources engineering (WRE). GP has a unique feature of introducing explicit models for nonlinear processes in the WRE, which can provide new insight into the understanding of the process. Considering continuous growth of GP and its importance to both water industry and academia, this paper presents a comprehensive review on the recent progress and applications of GP in the WRE fields. Our review commences with brief explanations on the fundamentals of classic GP and its advanced variants (including multigene GP, linear GP, gene expression programming, and grammar-based GP), which have been proven to be useful and frequently used in the WRE. The representative papers having wide range of applications are clustered in three domains of hydrological, hydraulic, and hydroclimatological studies, and outlined or discussed at each domain. Finally, this paper was concluded with discussions of the optimum selection of GP parameters and likely future research directions in the WRE are suggested. [ABSTRACT FROM AUTHOR]

This paper developed an automatic mesh generator used for simulating real-world problems of hydrological cycles, fluid flow, salinity and thermal transport, sediment and water quality transport, etc. The 2-D overland area was discretized with quadrilaterals based on conformal mapping technique. A position-percent interpolation equation was established to determine nodal vertical-coordinates and match boundaries. For 3-D simulations of subsurface zones, an additional mesh generation method was proposed to create quadrilaterals for filling the empty regions along river reaches and around junctions with storage, ponds or lakes. In order to deal with special storage region with an odd number of boundary nodes, an additional triangle was inserted. Five topological optimization templates were proposed to improve the quality of degenerated elements. This paper proposed the basic algorithms to generate quadrilateral-prism meshes through stretching the quadrilateral mesh along vertical directions based on material domains. Aiming at four types of fractures, corresponding extraction methods were presented to preserve geometric features. In order to accommodate the need for overland and subsurface simulations, 1-D/2-D/3-D correspondence was established between rivers, junctions, ponds, lakes, control structures and finite element meshes. Finally, several realistic hydrologic and geologic examples for meshing multi-domain areas were provided to demonstrate the accuracy and effectiveness of the mesh generator developed in this paper. [ABSTRACT FROM AUTHOR]

• Groundwater level prediction for a long period of time is considered in this paper. • We proposed a graph-based machine learning using which the spatial relationships are taken into account. • Our results indicate that spatial correlations are helpful when one deals with geospatial data. • The proposed method is compared with standard techniques. Accurate prediction of groundwater level (GWL) over a period of time is of great importance for groundwater resources management. Machine learning techniques due to their great performance have recently been used for this problem. Previous methods, however, did not consider the spatial relationships between wells due to the difficulty to handle unstructured well location data. In this paper, a graph neural network (GNN) is used to forecast groundwater dynamics where it can represent each well as a node in the graph. The spatial information is, thus, extracted from an interconnected network using graph convolution layers with a self-adaptive adjacency matrix. The temporal features of the sequence are obtained by gated temporal convolutional networks. The model was applied and evaluated for wells in the southwest area of British Colombia in Canada using data about 11 years (2010–2020). The proposed model performs better in terms of all the defined evaluation metrics, when compared with two baseline models: long short-term memory (LSTM) and gated recurrent units (GRU). Moreover, when the spatial dependencies are completely unknown, the model can still learn them from the data and obtain comparable performance. Furthermore, the proposed model has a high efficiency since it can simultaneously model GWL change for all monitoring wells in the system. We also demonstrated that the spatial dependencies between each well could be intuitively interpreted from the learned adjacency matrix. [ABSTRACT FROM AUTHOR]

• Rainfall patterns and land uses in Chile create a unique natural laboratory. • First Forest hydrology review in Chile on water quantity and quality. • This paper review includes 75 studies since 1975. • Twenty research gaps are identified. The most significant is plant-soil-atmosphere relations. • A research agenda to support a future national planning legislation is proposed. This paper reviews the current knowledge of hydrological processes in Chilean temperate forests which extend along western South America from latitude 29° S to 56° S. This geographic region includes a diverse range of natural and planted forests and a broad sweep of vegetation, edaphic, topographic, geologic, and climatic settings which create a unique natural laboratory. Many local communities, endangered freshwater ecosystems, and downstream economic activities in Chile rely on water flows from forested catchments. This review aims to (i) provide a comprehensive overview of Chilean forest hydrology, to (ii) review prior research in forest hydrology in Chile, and to (iii) identify knowledge gaps and provide a vision for future research on forest hydrology in Chile. We reviewed the relation between native forests, commercial plantations, and other land uses on water yield and water quality from the plot to the catchment scale. Much of the global understanding of forests and their relationship with the water cycle is in line with the findings of the studies reviewed here. Streamflow from forested catchments increases after timber harvesting, native forests appear to use less water than plantations, and streams draining native forest yield less sediment than streams draining plantations or grassland/shrublands. We identified 20 key knowledge gaps such as forest groundwater systems, soil–plant-atmosphere interactions, native forest hydrology, and the effect of forest management and restoration on hydrology. Also, we found a paucity of research in the northern geographic areas and forest types (35-36°S); most forest hydrology studies in Chile (56%) have been conducted in the southern area (Los Rios Region around 39-40° S). There is limited knowledge of the geology and soils in many forested areas and how surface and groundwater are affected by changes in land cover. There is an opportunity to advance our understanding using process-based investigations linking field studies and modeling. Through the establishment of a forest hydrology science "society" to coordinate efforts, regional and national-scale land use planning might be supported. Our review ends with a vision to advance a cross-scale collaborative effort to use new nation-wide catchment-scale networks Long-term Ecosystem Research (LTER) sites, to promote common and complementary techniques in these studies, and to conduct transdisciplinary research to advance sound and integrated planning of forest lands in Chile. [ABSTRACT FROM AUTHOR]

Summary Surface runoff is the hydrological process at the origin of phenomena such as soil erosion, floods out of rivers, mudflows, debris flows and can generate major damage. This paper presents a method to create maps of surface runoff susceptibility. The method, called IRIP (Indicator of Intense Pluvial Runoff, French acronym), uses a combination of landscape factors to create three maps representing the susceptibility (1) to generate, (2) to transfer, and (3) to accumulate surface runoff. The method input data are the topography, the land use and the soil type. The method aims to be simple to implement and robust for any type of study area, with no requirement for calibration or specific input format. In a second part, the paper focuses on the evaluation of the surface runoff susceptibility maps. The method is applied in the Lézarde catchment (210 km 2 , northern France) and the susceptibility maps are evaluated by comparison with two risk regulatory zonings of surface runoff and soil erosion, and two databases of surface runoff impacts on roads and railways. Comparison tests are performed using a standard verification method for dichotomous forecasting along with five verification indicators: accuracy, bias, success ratio, probability of detection, and false alarm ratio. The evaluation shows that the susceptibility map of surface runoff accumulation is able to identify the concentrated surface runoff flows and that the susceptibility map of transfer is able to identify areas that are susceptible to soil erosion. Concerning the ability of the IRIP method to detect sections of the transportation network susceptible to be impacted by surface runoff, the evaluation tests show promising probabilities of detection (73–90%) but also high false alarm ratios (77–92%). However, a qualitative analysis of the local configuration of the infrastructure shows that taking into account the transportation network vulnerability can explain numerous false alarms. This paper shows that the IRIP method can be a valuable tool to facilitate field analysis and perform surface runoff zonings and opens interesting prospects for the use of the IRIP method in a context of risk management. [ABSTRACT FROM AUTHOR]

Summary The Canterbury/Christchurch earthquakes and aftershocks of 2010–2011 generated groundwater level responses throughout New Zealand. However, the greater part of damage was sustained by the city of Christchurch which is built on a layered sequence of artesian aquifers. In a previous paper we analysed the earthquake induced groundwater responses. We quantified groundwater responses by fitting a simple statistical model which differentiated between immediate earthquake induced response (spike) and post-seismic change (offset). The most notable feature of this analysis was the consistency of responses between the earthquakes: deeper wells correlate with negative offset and shallower wells correlate with positive offset. In that paper we argued that this is consistent with the upwards vertical movement of water. In this paper we focus on the physical mechanisms, and consider a model that further explains and supports this hypothesis. We postulate a groundwater flow model in which storativity and aquitard permeability are modelled as time-varying shocks. We analyse the solutions for a range of non-dimensional parameters and obtain type curves that exhibit the same behaviour as the observed responses. Finally we consider data from the 2010 M w 7.1 Darfield (Canterbury) earthquake. [ABSTRACT FROM AUTHOR]

Summary This paper investigates the challenge of representing structural differences in river channel cross-section geometry for regional to global scale river hydraulic models and the effect this can have on simulations of wave dynamics. Classically, channel geometry is defined using data, yet at larger scales the necessary information and model structures do not exist to take this approach. We therefore propose a fundamentally different approach where the structural uncertainty in channel geometry is represented using a simple parameterisation, which could then be estimated through calibration or data assimilation. This paper first outlines the development of a computationally efficient numerical scheme to represent generalised channel shapes using a single parameter, which is then validated using a simple straight channel test case and shown to predict wetted perimeter to within 2% for the channels tested. An application to the River Severn, UK is also presented, along with an analysis of model sensitivity to channel shape, depth and friction. The channel shape parameter was shown to improve model simulations of river level, particularly for more physically plausible channel roughness and depth parameter ranges. Calibrating channel Manning’s coefficient in a rectangular channel provided similar water level simulation accuracy in terms of Nash–Sutcliffe efficiency to a model where friction and shape or depth were calibrated. However, the calibrated Manning coefficient in the rectangular channel model was ∼2/3 greater than the likely physically realistic value for this reach and this erroneously slowed wave propagation times through the reach by several hours. Therefore, for large scale models applied in data sparse areas, calibrating channel depth and/or shape may be preferable to assuming a rectangular geometry and calibrating friction alone. [ABSTRACT FROM AUTHOR]

Summary The selection and identification of a suitable hydrological model structure is a more challenging task than fitting parameters of a fixed model structure to reproduce a measured hydrograph. The suitable model structure is highly dependent on various criteria, i.e. the modeling objective, the characteristics and the scale of the system under investigation and the available data. Flexible environments for model building are available, but need to be assisted by proper diagnostic tools for model structure selection. This paper introduces a qualitative method for model component sensitivity analysis. Traditionally, model sensitivity is evaluated for model parameters. In this paper, the concept is translated into an evaluation of model structure sensitivity. Similarly to the one-factor-at-a-time (OAT) methods for parameter sensitivity, this method varies the model structure components one at a time and evaluates the change in sensitivity towards the output variables. As such, the effect of model component variations can be evaluated towards different objective functions or output variables. The methodology is presented for a simple lumped hydrological model environment, introducing different possible model building variations. By comparing the effect of changes in model structure for different model objectives, model selection can be better evaluated. Based on the presented component sensitivity analysis of a case study, some suggestions with regard to model selection are formulated for the system under study: (1) a non-linear storage component is recommended, since it ensures more sensitive (identifiable) parameters for this component and less parameter interaction; (2) interflow is mainly important for the low flow criteria; (3) excess infiltration process is most influencing when focussing on the lower flows; (4) a more simple routing component is advisable; and (5) baseflow parameters have in general low sensitivity values, except for the low flow criteria. [ABSTRACT FROM AUTHOR]

Summary The implementation of Catchment Management Agencies (CMAs) was supposed to be the cornerstone of the rescaling process of the South African water reform policy. Yet, less than 10 years after the adoption of the National Water Act, the process was suspended for 4 years and by 2012 only two CMAs had been established. Combining approaches in geography and political science, this paper investigates the reasons for the delays in CMAs’ implementation in South Africa. It shows that the construction of interbasin transfers (IBTs) since the 1950s by the apartheid regime and nowadays the power struggles between CMAs and the Department of Water Affairs (DWA) are two of the main obstacles to the creation of CMAs planned by the 1998 National Water Act (NWA). Finally, the paper advocates taking the “hydrosocial cycle” as an analytical framework for designing new institutional arrangements that will include both rectifying the legacy of the past (the specific role of DWA) and acknowledging legitimate local interests. [ABSTRACT FROM AUTHOR]

Summary Most often drought analysis methodologies are based on point-wise time series record assessments with very specific local conclusions, but their areal, regional and in general spatial properties are examined to a lesser extent. This paper will provide general description of droughts in addition to the regional methodological approaches with rather simple but innovative manner. The study area is thought as composed of a set of sub-areas each with different dry (wet) period probabilities. In general, heterogeneous region has different probability of dry(wet) spell occurrence at each sub-area. In fact, whenever the probability at each sub-area is not equal to any other sub-area, it corresponds to heterogeneous region. The areal cover probability (ACP) of the region is derived by considering the point-wise probabilities on the assumptions that the occurrences of dry (wet) spells are mutually exclusive, independent with heterogeneous probability patterns. Additionally extreme value probabilities of areal drought coverage are derived for heterogeneous sub-area probabilities. All of the heterogeneous drought probability expressions reduce down to homogeneous case provided that sub-areal probabilities are equal to each other. The methodology presented in this paper paves ways for more realistic drought phenomenon spatial probability of occurrences when the sub-areal dry spell probabilities are dependent on each other but heterogeneous. [ABSTRACT FROM AUTHOR]

Summary Large scale urbanization has resulted in greater withdrawals of shared waters and this withdrawal has been largely dependent on the hegemony of the riparian’s. The last few decades has seen the upward surge of many countries in terms of development as well as hegemony. Existing structures of established water sharing framework typically evaluate only parameters related to historic water use such as historic water demand and supply, contribution to flow, and hydrology. Water conflicts and cooperation is affected by various issues related with development and hegemony. Characterization and quantification of development and hegemony parameters is a very complex process. This paper establishes a novel approach to predict river basins at risk; the approach addresses the issue of water conflict and cooperation within a methodologically more rigorous predictive framework. Fuzzy synthetic evaluation technique is used in this paper to undertake the risk assessment of international transboundary rivers. In this paper the fuzzy domain of risk consists of two fuzzy sets – hegemony and development, indices of which are developed with the help of fuzzy synthetic evaluation techniques. Then the compositional rule-base is framed to ascertain the fuzzy risk. This fuzzy risk can be further used to prioritize all the international river basins which can help in the identification of potentially high risk basins. Risk identification of international river basins is not only scientifically valuable, but also practically highly useful. Identifying those basins that are likely to be particularly prone to conflict or cooperation is of high interest to policy makers. [ABSTRACT FROM AUTHOR]

Highlights • Unsaturated soil hydraulic conductivity USHC control rainfall infiltration and slope stability. • We quantified the effect of USHC anisotropy on the hillslope hydrology/stability. • We applied a 3D hydrological model coupled with infinite slope stability model in two test cases. • Results confirm the control of USHC anisotropy on failure time and size of unstable area. Abstract Rainfall-induced shallow landslides cause significant damage involving loss of life and property. Many hydrological processes such as rainfall infiltration, soil water dynamics, and slope stability are controlled by unsaturated soil properties, such as unsaturated hydraulic conductivity. Natural soils often exhibit a certain degree of anisotropy in hydraulic conductivity due to stratification and compaction mechanisms in soil formation processes. In this paper we investigate the effect of soil hydraulic conductivity anisotropy (SHCA) on hillslope hydrology and stability using a three-dimensional hydrological model coupled with a probabilistic infinite slope stability model. The model is applied in two independent case studies. The first aims to quantify the combined effect of different anisotropy ratios (lateral/normal saturated hydraulic conductivity) and hillslope morphologies (convex, concave, and planar) on slope stability. Anisotropy ratios are assumed in this case higher than one (1, 2, 10). Results show that increasing the anisotropy ratio (from 1 to 10) anticipates the failure time (from 12 to 9 h after the start of rainfall) and that in concave morphologies the unstable area tends to be wider than planar and convex. The second application aims to simulate the soil moisture dynamic and the probability of failure at different depths (100, 500, and 900 mm) of a stratified volcanic soil, making leverage on the model flexibility to accommodate SHCA. No assumptions are made on the anisotropy ratio in this case study. Our results, based on model parameter calibration and verification against in-situ soil moisture measurements during the year 2009, showed good model performance in simulating the soil moisture dynamic (Kling-Gupta Efficiency higher than 0.78) and confirmed no failure for the simulated year. The promising results support the aspiration that the physically based hydrological model can complement and improve the current predictions of landslide early warning systems. [ABSTRACT FROM AUTHOR]

Highlights • Debris-covered glaciers have a distinct hydrological structure. • Debris cover reduces supraglacial catchment size and reduces melt rates. • Beneath continuous debris on the lower glacier the drainage network is inefficient. • An efficient conduit system drains the clean and dirty ice on the upper glacier. • A channelized and distributed system co-exist beneath the lower glacier. Abstract Supraglacial debris is known to strongly influence the distribution of glacier surface melt. Since melt inputs drive the formation and evolution of glacial drainage systems, it should follow that the drainage systems of debris-covered glaciers will differ from those of debris-free glaciers. This would have implications for the proglacial runoff regime, subglacial erosion and glacier dynamics. This paper presents analysis of return curves from 33 successful dye injections into the extensively debris-covered Miage Glacier, Italian Alps. It demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system. Where the debris cover is continuous, melt is lower and the surface topography is chaotic, with many small supraglacial catchments. These factors result in an inefficient englacial/subglacial drainage network beneath continuous debris, which drains to the conduit system emanating from the upper ablation zone. Melt rates are high in areas of clean and dirty ice above the continuous debris. Runoff from these areas is concentrated by inter-moraine troughs into large supraglacial streams, which encourages the early-season development of an efficient englacial/subglacial conduit system downstream of this area. Drainage efficiency from the debris-covered area increases over the melt season but dye-trace transit velocity remains lower than from moulins on the upper glacier. Future runoff models should account for the influence of supraglacial debris on the hydrological system. [ABSTRACT FROM AUTHOR]

Highlights • Discharge measurements are exposed to different levels of uncertainties. • Impacts of land use change could be masked by errors in discharge measurements. • 50−75% of errors in discharge measurement can mask impact of land use change. • Data quality controls will enhance precision of land use change impact. Abstract Analysis of hydrological impacts of land use change raises questions about whether, and how much, such impacts are misrepresented because of errors in river flow observations. In this paper, land use change impacts (represented by changes in watershed storage) and different ranges of discharge measurement error are compared to assess how errors in discharge measurement can potentially mask a land use change impact. Using a watershed from the Ethiopian highlands to exemplify this, we simulated five different levels of land use change impacts with five levels of watershed storage reductions (from 10% to 50% change) and the associated time series of runoff. Different levels of observation error were then introduced into these artificial time series. Comparison was made between every pair, i.e. a time series derived from a certain level of land use change (storage reduction) versus a time series corresponding to a given level of observation error, using a step-change t -test. Significant step-changes between pairs define the detectability of land use change impact. The analysis was made for the entire 30-year time series as well as for the most extreme annual weather conditions. The results showed that for the average year and wettest year, 75% or more error in observed discharge masks the maximum simulated land use change impact on hydrology. In dry years, a 50% error in discharge is enough to mask the same impact. Knowing (and improving) the level of data quality contributes to a better understanding of hydrological uncertainties and improves the precision in assessing land use change impacts. Both of these are essential elements in water resources development planning. [ABSTRACT FROM AUTHOR]

Highlights • Pore-scale model is presented to simulate fluid flow in columns filled with two stratified media. • Volumetric average of the simulated results yields a pressure discontinuity at the strata interface. • The emerged discontinuous pressure reduced the combined ability of the media to conduct fluid. • Under certain circumstance the flow rate in the stratified media is even direction-dependant. Abstract Water flow along or across the interfaces of contrasting materials is ubiquitous in hydrology and how to solve them in macroscopic models derived from volumetric average of the pore-scale processes remains elusive. While the change in the average velocity and pressure at water-sediment interface has been well established for channel flow over porous beds, whether a volumetric average alerts the pressure continuity when water flows across the interface of two porous materials is poorly understood despite its imperative implications in hydrological modelling. The primary purpose of this paper is to provide evidences via pore-scale simulations that volumetrically averaging the pore-scale processes indeed yields a discontinuous pressure when water flows across a material interface. We simulated two columns numerically reconstructed by filling them with stratified media: One is an idealised two-layer system and the other one is a 3D column filled by fine glass beads over coarse glass beads with their pore geometry acquired using x-ray computed tomography. The pore-scale simulation is to mimic the column experiment by driving fluid to flow through the void space under an externally imposed pressure gradient. Once fluid flow reaches steady state, its velocity and pressure in all voxels are sampled and they are then spatially averaged over each section perpendicular to the average flow direction. The results show that the average pressure drops abruptly at the material interface no matter which direction the fluid flows. Compared with the effective permeability estimated from the homogenization methods well established in the literature, the emerged discontinuous pressure at the interface reduces the combined ability of the two strata to conduct water. It is also found that under certain circumstances fluid flow is direction-dependant, moving faster when flowing in the fine-coarse direction than in the coarse-to-fine direction under the same pressure gradient. Although significant efforts are needed to incorporate these findings into practical models, we do elicit the emergence of discontinuous pressure at material interface due to volumetric average as well as its consequent implications in modelling of flow in heterogeneous and stratified media. [ABSTRACT FROM AUTHOR]

Highlights • Calibration on full time series is shown to be more robust than split-sample methods. • 30 Bootstrapping tests on 6 cases provide evidence towards this method being optimal. • Verification on 10 independent catchment-model pairs support the conclusions. • Caveats of split-sampling on model performance are demonstrated. • Length of the calibration period is proportional to the parameter set robustness. Abstract This paper investigates the issues related to the use of validation in hydrological model calibration. Traditionally, models are calibrated and then assessed on an independent period (split-sample) to determine their adequacy in simulating streamflow as compared to observations. In this study, two hydrological models and three North American catchments are used to evaluate the effects of using validation to assess the model parameters' robustness on the model's actual simulation capabilities and accuracy in simulating streamflow. The length of the calibration period is increased from 1 to 16 years, and for each case a large number of randomly selected combinations of years are used for calibration and for validation using the Nash-Sutcliffe Efficiency metric. The calibrated model is then run on an independent 8-year test-period to assess the model's actual performance in simulation mode in unknown conditions. The process is bootstrapped 30 times to ensure the robustness of the results. The tests pit the calibration/validation methods on increasing calibration period lengths against a full calibration on the entire available dataset. Results show that the calibration on the full dataset is the optimal strategy as it generates the most robust parameter sets, provides the best model accuracy on an independent testing period and does not require assumption-making on the modeler's part. The calibrated parameter sets for each test-case were evaluated using the relative bias and correlation metrics, which revealed that the method transfers well to these two other metrics. Results also demonstrate the pitfalls of the commonly used split-sampling strategy, where good parameter sets may be discarded due to model performance discrepancies between calibration and validation periods. The conclusions point to the need to use as many years as possible in the calibration step and to entirely disregard the validation aspect under certain conditions. [ABSTRACT FROM AUTHOR]

Highlights • Hysteresis is manifestation of an incomplete representation of a physical process. • A system might seem path-dependent due to lack of physical knowledge. • Hysteresis in hydrology is both rate- and scale- dependent. • Model structure to a large extent enables the reproduction of observed hysteresis. Abstract Hysteresis is a widely reported phenomenon in natural and engineered systems across different temporal and spatial scales. Its definition is non-unique and rather context-dependent, while systems with hysteretic behavior, including hydrological systems, are commonly referred to as path-dependent systems or systems with memory. Despite widespread existence of hysteretic processes, the current generation of hydrologic models do not directly account for hysteresis. In this paper, we review the fundamentals, theories, and general properties of hysteresis in the broad scientific literature and then focus on its representations in hydrological sciences. Through illustrative examples, we show how an incomplete understanding or representation of the underlying processes in a system can lead to considering the system as being path-dependent. We argue that, in most cases, hysteresis is a manifestation of our dimensionality-reducing approach to process understanding and representation. We further explain that modelling hysteresis in an ideal world requires a full-dimensional process representation, based on a perfect understanding of the processes, their heterogeneity, and their spatio-temporal scale dependency. We discuss, however, that the missing dimensions/physics in a hydrologic model may be compensated to some extent by enabling the model with formal hysteretic components. Moreover, we show that the conventional model structure and parameterization may be designed in a way to partially reproduce a desired hysteretic behavior. [ABSTRACT FROM AUTHOR]

Highlights • Spatiotemporal variability in stable H and O isotope composition in surface water was observed in the Sava River Basin (SRB). • δ 18O temporal variations of surface waters follow the pattern of precipitation with lower seasonal amplitude. • Mean residence time in river surface waters was estimated to be <2 years. • Complexity of spatial patterns of δ 18O in precipitation over SRB was described by latitude, longitude and altitude. • Precipitation controls spatial variation of δ 18O values in surface water across the SRB. Abstract The presented paper describes spatial and temporal variations in extended stable isotope datasets of hydrogen and oxygen (δ 2H and δ 18O) in the Sava River water that were used to estimate the mean residence time (MRT) of stream water using an exponential flow model. The re-examining MRT was <2 years in the Slovenian part of the Sava River and was in a good agreement with previous estimates and with the MRT estimated in the Sava River at Ostružnica near Belgrade, Serbia. A MRT >2.2 years was observed in the Danube River at Vinča also near Belgrade. The spatial distribution of δ 18O in precipitation over the Sava River Basin (SRB) was mapped based on the long-term weighted mean annual δ 18O values and established relationship with various geographical controls (latitude, longitude and altitude). The modelled δ 18O values in precipitation agree with the measured values in the surface river water at different locations indicating that the spatial variation in the isotopic composition of precipitation is the dominant factor controlling surface water isotope ratios over the SRB. [ABSTRACT FROM AUTHOR]

Highlights • We present a new method for water quality management with remotely sensed water temperature. • Testing of the method in both Chinese and Australian rivers suggested a well-performed method. • Comparison with previous models revealed its practicability and effectiveness. • It can be easily applied to rivers with insufficient ground observations worldwide. Abstract Globally, water quality degradation severely threatens the security of water resources. Understanding a river’s capacity to accommodate pollutants (or water environmental capacity: WEC) can help efficiently protect rivers. However, the requirement for comprehensive ground-observed hydrological and water quality data in previous methods makes it difficult to estimate WEC in areas with limited ground observations. This paper proposes a new framework for WEC estimation in data-scarce areas based on remotely sensed skin water temperature and limited ground observations. Two new models were developed to calculate the two critical parameters for WEC estimation: water temperature, and integrated pollutant degradation coefficients (k). Images of ASTER Surface Kinetic Temperature (AST_08) 90 m grid product were used to retrieve water temperatures. The above results were subsequently used to calculate a river’s capacity to accommodate pollutants, or WEC, in agriculturally dominated areas. The use of remote sensing techniques enables the methods to be applied over large spatial scales and to areas with limited ground observations. The application and testing of the framework in four rivers, including two Chinese rivers (the Huai and the Wei Rivers) and two Australian rivers (the Ovens and the Gwydir Rivers), suggest that the models performed well to calculate the real-time water temperature and the coefficient k based on limited ground-observations. Uncertainty analysis on water temperature calculated from remotely sensed land surface temperature and ground-observed meteorological air temperature suggests that remotely sensed water temperature had high concurrence with ground observations (RMSE = 3.08 °C with R2 = 0.88), while the sparse-spatially distributed meteorological stations reduced the accuracy in estimating water temperature (RMSE = 4.39 °C with R2 = 0.91). We found that the coefficient (k) increased with water temperature over different seasons in an exponential form but in a logarithmical form with streamflow velocity. Comparison with previous research and other models with abundant data revealed the practicability and effectiveness of our models, which can be easily applied to rivers with insufficient ground observations across the globe. [ABSTRACT FROM AUTHOR]

[Display omitted] • 31 USDA Experimental Forests & Ranges are hydrologic research (HydroEFRs). • Women of the HydroEFRs have published over 3,000 papers since 1977. • The number of women in the workforce at HydroEFRs declined from 1992 to 2021. • The ratio of women:men in the workforce at HydroEFRs increased from 1992 to 2021. • It is critical to maintain the HydroEFRs and invest in workforce diversity. The increase in the frequency and severity of water crises around the world necessitates maintaining or augmenting investments in the hydrologic sciences, including in a trained, diverse workforce. The USDA Forest Service operates a network of 85 Experimental Forests and Ranges, Experimental Watersheds, and cooperating sites (EFRs), 31 of which include long-term hydrologic studies (HydroEFRs). The HydroEFRs are centers for hydrologic science and education and play a key role informing watershed policy and management. The goals of this study were to understand (1) how, broadly, the women associated with the HydroEFRs (including women in the Forest Service workforce and women with cooperating agencies or universities who have worked at HydroEFRs) have contributed to hydrologic sciences and (2) how, more specifically, the number and roles of women in the Forest Service workforce associated with the HydroEFRs have changed over time. Data were collected from the EFR Data Explorer, the USDA Forest Service Human Resources Management (HRM) Data Metrics and Analysis Team (DMAT), literature reviews, and questionnaires to USDA EFR scientists-in-charge and to women who were or had been involved in hydrologic sciences at EFRs. Results showed that women associated with the HydroEFRs have made significant contributions to the hydrologic sciences, including authoring or co-authoring over 3,000 publications, with over 170,000 citations since 1977 and an H-index of 181. In their own words, the women indicated that they were also active in contributing to hydrologic fieldwork, providing stewardship for long-term data, and contributing to the social capital of the HydroEFRs through teamwork, collaboration, and mentoring. For the Forest Service, trends in employment records from 1992 through 2021 showed a 55% contraction of the entire FS R&D workforce, including a 59% loss in the number of women in the FS R&D workforce, a 50% loss in the number of women associated with HydroEFR duty stations, and a 26% loss in the number of women in hydrology positions. During this period, there was a greater loss of both women and men in lower-graded positions relative to higher-graded positions in the FS R&D workforce, with serial implications for the ability of the workforce to collect data, produce basic science publications, and conduct syntheses. Although the ratio of women:men declined across the Forest Service and FS R&D, the ratio of women:men increased at the HydroEFRs (driven by a higher ratio of women:men at higher grade levels) and for management positions within FS R&D and at the HydroEFRs.When asked, women valued their contributions to the hydrologic sciences and envisioned a more equitable future for women in hydrology. Overall, results show that HydroEFRs have played an important role in advancing the careers of women in the hydrologic sciences, who, in turn, have contributed to the groundbreaking hydrologic research that occurs at these long-term research sites. As water crises around the world continue to escalate, building a strong, diverse workforce in the hydrologic sciences and supporting the places where they can conduct their research is important. [ABSTRACT FROM AUTHOR]

• An inclusive review of ensemble machine learning methods in hydrology. • The paper covers the early pertinent published papers (since 2000) up to date. • In particular, surface hydrology, hydrogeology, and extreme hydrologic (flood & drought) events were studied. • Subjects include river flow, streamflow, surface water quality, sediment transport, debris flow, river icing, & rainfall-runoff. Recently, there has been a notable tendency towards employing ensemble learning methodologies in assorted areas of engineering, such as hydrology, for simulation and prediction purposes. The diversity of ensemble techniques available for implementation in hydrological sciences has led to the development and utilization of different strategies in the implementation. This review paper explores and refers to the advancement of ensemble methods, including the resampling ensemble methods (e.g., bagging, boosting, and dagging), model averaging, and stacking viz. generalized stacked, in different application fields of hydrology. The main hydrological topics in this review study cover subjects such as surface hydrology, river water quality, rainfall-runoff, debris flow, river icing, sediment transport, groundwater, flooding, and drought modeling and forecasting. The general findings of this survey demonstrate the absolute superiority of using ensemble strategies over the regular (individual) model learning in hydrology. In addition, the boosting techniques (e.g., boosting, AdaBoost, and extreme gradient boosting) have been more frequent and successfully implemented in hydrological problems than the bagging, stacking, and dagging approaches. [ABSTRACT FROM AUTHOR]

• The QPG-dominated flow behavior differs from the conventional linear flow behavior. • A comprehensive flow model that contains various modelling situations is established. • Production pressure drops for vertical/horizontal oil/water wells were predicted. • Future research should aim at more complicated conditions and more nonlinear factors. Transient flow of geofluids caused by a well production in a subsurface formation is a phenomenon of enormous importance in hydrology, geosciences and engineering. Geofluid transient flow has been proved to be a nonlinear physical process dominated by QPG (quadratic pressure gradient). Much research has indicated that neglecting a QPG term in flow models by assuming small pressure gradients can cause significant errors in predicted pressures. Despite the existence and importance of QPG, limited research on nonlinear QPG models has been performed when compared with the traditional linear flow models. On the basis of the previous linear and nonlinear QPG models, a comprehensive geofluid flow model for a well in a subsurface formation was established and solved. A general solution method for this model and its general solutions were obtained for vertical and horizontal wells in ordinary, fractured and fractured-vuggy formations. Next, flow regimes and typical transient flow characteristics were thoroughly analyzed by using a series of standard type curves. Then, the differences in type curves between linear and nonlinear QPG models were qualitatively and quantitatively studied. Afterwards, model validations and production predictions were performed. This comprehensive model contained various specific modeling situations. Some modeling situations that were reported in the previous studies were well-reviewed in this paper. The other previously unreported modelling situations were firstly studied and exhibited in this paper. At the end, the existing problems pending to be solved were put forward and future work on nonlinear QPG models was suggested. This paper is very helpful in understanding the QPG-dominated transient flow behavior more profoundly. [ABSTRACT FROM AUTHOR]

Hydrological and non-point source pollution (H/NPS) predictions in ungagged basins have become the key problem for watershed studies, especially for those large-scale catchments. However, few studies have explored the comprehensive impacts of rainfall data scarcity on H/NPS predictions. This study focused on: 1) the effects of rainfall spatial scarcity (by removing 11%–67% of stations based on their locations) on the H/NPS results; and 2) the impacts of rainfall temporal scarcity (10%–60% data scarcity in time series); and 3) the development of a new evaluation method that incorporates information entropy. A case study was undertaken using the Soil and Water Assessment Tool (SWAT) in a typical watershed in China. The results of this study highlighted the importance of critical-site rainfall stations that often showed greater influences and cross-tributary impacts on the H/NPS simulations. Higher missing rates above a certain threshold as well as missing locations during the wet periods resulted in poorer simulation results. Compared to traditional indicators, information entropy could serve as a good substitute because it reflects the distribution of spatial variability and the development of temporal heterogeneity. This paper reports important implications for the application of Distributed Hydrological Models and Semi-distributed Hydrological Models, as well as for the optimal design of rainfall gauges among large basins. [ABSTRACT FROM AUTHOR]

Extreme precipitation can cause flooding and may result in great economic losses and deaths. The return level is a commonly used measure of extreme precipitation events and is required for hydrological engineer designs, including those of sewerage systems, dams, reservoirs and bridges. In this paper, we propose a two-step method to estimate the return level and its uncertainty for a study region. In the first step, we use the generalized extreme value distribution, the L-moment method and the stationary bootstrap to estimate the return level and its uncertainty at the site with observations. In the second step, a spatial model incorporating the heterogeneous measurement errors and covariates is trained to estimate return levels at sites with no observations and to improve the estimates at sites with limited information. The proposed method is applied to the daily rainfall data from 273 weather stations in the Haihe river basin of North China. We compare the proposed method with two alternatives: the first one is based on the ordinary Kriging method without measurement error, and the second one smooths the estimated location and scale parameters of the generalized extreme value distribution by the universal Kriging method. Results show that the proposed method outperforms its counterparts. We also propose a novel approach to assess the two-step method by comparing it with the at-site estimation method with a series of reduced length of observations. Estimates of the 2-, 5-, 10-, 20-, 50- and 100-year return level maps and the corresponding uncertainties are provided for the Haihe river basin, and a comparison with those released by the Hydrology Bureau of Ministry of Water Resources of China is made. [ABSTRACT FROM AUTHOR]

The implementation of source water protection programs is relatively recent in Canada and the United States. Although protecting water at the watershed scale has been a focus of many of these programs, few Indigenous communities located within these watersheds are involved in the process. The purpose of this scoping review was to examine and map the extent, range, and nature of the published peer-reviewed literature on the adoption, implementation, and outcomes of source water protection programs involving Indigenous populations in Canada and the United States. This review followed a systematic process to identify and evaluate the literature. Searches were conducted in three aggregator databases (Web of Science™, ProQuest®, and GreenFILE™). Two independent reviewers conducted a systematic two-stage screening process using inclusion and exclusion criteria in the software DistillerSR©. Articles that met inclusion criteria were analyzed using thematic qualitative and descriptive quantitative methods. The findings indicate that: a) there is a lack of peer-reviewed studies focusing on the ecological outcomes of source water protection programs that are inclusive of Indigenous populations in Canada and the United States; b) the depth to which the literature describes Indigenous involvement in source water protection programs is minimal; and c) Indigenous involvement in source water protection programs is generally not reported as substantial. This review provides several recommendations to improve both the peer-reviewed literature on the topic and source water protection programs. There is a need to improve reporting in the literature on quantitative program results, the nature of Indigenous involvement in source water protection programs, and Indigenous-inclusive inter-jurisdictional success stories. It is also recommended that source water protection programs recognize Indigenous peoples as more than stakeholders groups, and that future studies pull from innovations in other fields to address complex problems and provide new insights to the field of source water protection. The methodology presented in this paper provides a template for researchers in engineering and environmental fields, such as hydrology, to identify and review published literature in a systematic, transparent, and rigorous manner. [ABSTRACT FROM AUTHOR]

Many water governance and management issues are complex. The complexity of these issues is related to crossing of multiple boundaries: political, social and jurisdictional, as well as physical, ecological and biogeochemical. Resolution of these issues usually requires interactions of many parties with conflicting values and interests operating across multiple boundaries and scales to make decisions. The interdependence and feedback among interacting variables, processes, actors and institutions are hard to model and difficult to forecast. Thus, decision-making related to complex water problems needs be contingent and adaptive. This paper draws on a number of ideas from complexity science and negotiation theory that may make it easier to cope with the complexities and difficulties of managing boundary crossing water disputes. It begins with the Water Diplomacy Framework that was developed and tested over the past several years. Then, it uses three key ideas from complexity science (interdependence and interconnectedness; uncertainty and feedback; emergence and adaptation) and three from negotiation theory (stakeholder identification and engagement; joint fact finding; and value creation through option generation) to show how application of these ideas can help enhance effectiveness of water management. [ABSTRACT FROM AUTHOR]

Data assimilation techniques such as the Ensemble Kalman Filter (EnKF) are often applied to hydrological models with minimal state volume/capacity constraints enforced during ensemble generation. Flux constraints are rarely, if ever, applied. Consequently, model states can be adjusted beyond physically reasonable limits, compromising the integrity of model output. In this paper, we investigate the effect of constraining the EnKF on forecast performance. A “free run” in which no assimilation is applied is compared to a completely unconstrained EnKF implementation, a ‘typical’ hydrological implementation (in which mass constraints are enforced to ensure non-negativity and capacity thresholds of model states are not exceeded), and then to a more tightly constrained implementation where flux as well as mass constraints are imposed to force the rate of water movement to/from ensemble states to be within physically consistent boundaries. A three year period (2008–2010) was selected from the available data record (1976–2010). This was specifically chosen as it had no significant data gaps and represented well the range of flows observed in the longer dataset. Over this period, the standard implementation of the EnKF (no constraints) contained eight hydrological events where (multiple) physically inconsistent state adjustments were made. All were selected for analysis. Mass constraints alone did little to improve forecast performance; in fact, several were significantly degraded compared to the free run. In contrast, the combined use of mass and flux constraints significantly improved forecast performance in six events relative to all other implementations, while the remaining two events showed no significant difference in performance. Placing flux as well as mass constraints on the data assimilation framework encourages physically consistent state estimation and results in more accurate and reliable forward predictions of streamflow for robust decision-making. We also experiment with the observation error, which has a profound effect on filter performance. We note an interesting tension exists between specifying an error which reflects known uncertainties and errors in the measurement versus an error that allows “optimal” filter updating. [ABSTRACT FROM AUTHOR]

Reaction-infiltration instability, in which chemical reactions can dissolve minerals and therefore create preferential pore-fluid flow channels in fluid-saturated rocks, may play an important role in controlling groundwater quality in groundwater hydrology. Although this topic has been studied for many years, there is a recent debate, which says that the use of large-density asymptotics in the previous studies is invalid. However, there is a crucial conceptual mistake in this debate, which leads to results and conclusions that are inconsistent with the fundamental laws of physics. It is well known that in terms of distance, time and velocity, there are only two independent variables. But they are treated as three independent variables, a procedure that is the main source of the physically unrealistic results and conclusions in the debate. In this paper, we will discuss the results and conclusions related to the debate, with emphasis on the issues leading to the corresponding errors. In particular, we demonstrate that there is an unappreciated constraint condition between the dimensional/dimensionless distance, time and velocity in the debate. By using this constraint condition, it can be confirmed that as the ratio of the reactant concentration in the incoming fluid stream to the mineral concentration approaches zero, the dimensionless transport parameter, H , automatically approaches infinity. Therefore, it is further confirmed that the previous work conducted by Chadam and others remains valid. [ABSTRACT FROM AUTHOR]

As a key policy tool, water diplomacy offers greater political engagement in the cooperative management of shared water. A range of initiatives has been dedicated to this end, almost invariably oriented around the interactions of nation states. Crucially, however, practitioners of water diplomacy also need to address water governance at sub-state levels. As a political, multi-level, and normative field, peace and conflict research offers a pluralism of approaches designed to bring actors together at all levels. Drawing upon this research, this paper offers new focal points for water diplomacy that can enhance its policy effectiveness and enrich its underlying academic current. More specifically, it presents three hitherto undervalued tools for water diplomacy: at the interstate level, to uncover the rich body of political norms that bind states to shared understandings of acceptable practice around water. At the intrastate level, to incorporate ethnography of water users and civil society groups’ responses to state-led waterworks projects, and at the communal level to employ disaggregated georeferenced data on water resources in conflict-prone areas. Taken together, these analytical tools provide a multi-faceted political gauge of the dynamics of water diplomacy, and add vital impetus to develop water diplomacy across multiple levels of policy engagement. [ABSTRACT FROM AUTHOR]

The assessment for impacts of climate variability and human activities on suspended sediment yield (SSY) change has long been a question of great interest. However, the sediment generation processes are sophisticated with high nonlinearity and great uncertainty, which give rise to extreme complexity for SSY change assessment in Newtonian approach. Consequently, few approaches can be simply but widely applied to decompose impacts of climatic variability and human activities on SSY change. Thus, it is an urgent need to develop advanced methods that are simple and robust. Since that the Newtonian approach is hardly achievable due to limitation of either observations or knowledge of mechanisms, there have been repeated calls to capture the hydrologic system in Darwinian approach for hydrological change prediction or explanation. As streamflow is the carrier of suspended sediment, SSY change are thus documented in changes of sediment concentrated flow and suspended sediment concentration – water discharge ( C - Q ) relationships. By deduced corollaries, a differential equation of sediment discharge change was derived to explicitly decompose impacts of climate variability and human activities in Darwinian hydrology. Besides, a new form of sediment rating curves was proposed and curved as C - Q relationships and probability distribution of sediment concentrated flow. River sediment flux can be revealed by this representation, which simply elucidates mechanism of SSY generation covering a range of time scales from finer than rainfall-event to long term. By the new sediment rating curves, the differential equation was partly solved using a segmentation algorithm proposed and validated in this paper, and then was submitted to water balance framework expressed by Budyko-type equation. Thus, for catchment management, hydrologists can obtain explicit explanation of how climate variation and human activities propagate through landscape and result in sediment discharge change. The differential equation is simple and robust for widely application in sediment discharge change assessment, as only discrete data of precipitation, potential evaporation and C - Q observed at gauging stations are required. [ABSTRACT FROM AUTHOR]

In this paper we suggest to innovatively use scaling laws and more specifically Universal Multifractals (UM) to analyse simulated surface runoff and compare the retrieved scaling features with the rainfall ones. The methodology is tested on a 3 km 2 semi-urbanised with a steep slope study area located in the Paris area along the Bièvre River. First Multi-Hydro, a fully distributed model is validated on this catchment for four rainfall events measured with the help of a C-band radar. The uncertainty associated with small scale unmeasured rainfall, i.e. occurring below the 1 km × 1 km × 5 min observation scale, is quantified with the help of stochastic downscaled rainfall fields. It is rather significant for simulated flow and more limited on overland water depth for these rainfall events. Overland depth is found to exhibit a scaling behaviour over small scales (10 m–80 m) which can be related to fractal features of the sewer network. No direct and obvious dependency between the overland depth multifractal features (quality of the scaling and UM parameters) and the rainfall ones was found. [ABSTRACT FROM AUTHOR]

In this paper we introduce the Kumaraswamy autoregressive moving average models (KARMA), which is a dynamic class of models for time series taking values in the double bounded interval ( a , b ) following the Kumaraswamy distribution. The Kumaraswamy family of distribution is widely applied in many areas, especially hydrology and related fields. Classical examples are time series representing rates and proportions observed over time. In the proposed KARMA model, the median is modeled by a dynamic structure containing autoregressive and moving average terms, time-varying regressors, unknown parameters and a link function. We introduce the new class of models and discuss conditional maximum likelihood estimation, hypothesis testing inference, diagnostic analysis and forecasting. In particular, we provide closed-form expressions for the conditional score vector and conditional Fisher information matrix. An application to environmental real data is presented and discussed. [ABSTRACT FROM AUTHOR]

Extreme flood estimation has been a key research topic in hydrological sciences. Reliable estimates of such events are necessary as structures for flood conveyance are continuously evolving in size and complexity and, as a result, their failure-associated hazards become more and more pronounced. Due to this fact, several estimation techniques intended to improve flood frequency analysis and reducing uncertainty in extreme quantile estimation have been addressed in the literature in the last decades. In this paper, we develop a Bayesian framework for the indirect estimation of extreme flood quantiles from rainfall-runoff models. In the proposed approach, an ensemble of long daily rainfall series is simulated with a stochastic generator, which models extreme rainfall amounts with an upper-bounded distribution function, namely, the 4-parameter lognormal model. The rationale behind the generation model is that physical limits for rainfall amounts, and consequently for floods, exist and, by imposing an appropriate upper bound for the probabilistic model, more plausible estimates can be obtained for those rainfall quantiles with very low exceedance probabilities. Daily rainfall time series are converted into streamflows by routing each realization of the synthetic ensemble through a conceptual hydrologic model, the Rio Grande rainfall-runoff model. Calibration of parameters is performed through a nonlinear regression model, by means of the specification of a statistical model for the residuals that is able to accommodate autocorrelation, heteroscedasticity and nonnormality. By combining the outlined steps in a Bayesian structure of analysis, one is able to properly summarize the resulting uncertainty and estimating more accurate credible intervals for a set of flood quantiles of interest. The method for extreme flood indirect estimation was applied to the American river catchment, at the Folsom dam, in the state of California, USA. Results show that most floods, including exceptionally large non-systematic events, were reasonably estimated with the proposed approach. In addition, by accounting for uncertainties in each modeling step, one is able to obtain a better understanding of the influential factors in large flood formation dynamics. [ABSTRACT FROM AUTHOR]

The real fluid flow in porous media is consistent with the mass conservation which can be described by the nonlinear governing equation including the quadratic gradient term (QGT). However, most of the flow models have been established by ignoring the QGT and little work has been conducted to incorporate the QGT into the flow model of the multiple fractured horizontal (MFH) well with stimulated reservoir volume (SRV). This paper first establishes a semi-analytical model of an MFH well with SRV including the QGT. Introducing the transformed pressure and flow-rate function, the nonlinear model of a point source in a composite system including the QGT is linearized. Then the Laplace transform, principle of superposition, numerical discrete method, Gaussian elimination method and Stehfest numerical inversion are employed to establish and solve the seepage model of the MFH well with SRV. Type curves are plotted and the effects of relevant parameters are analyzed. It is found that the nonlinear effect caused by the QGT can increase the flow capacity of fluid flow and influence the transient pressure positively. The relevant parameters not only have an effect on the type curve but also affect the error in the pressure calculated by the conventional linear model. The proposed model, which is consistent with the mass conservation, reflects the nonlinear process of the real fluid flow, and thus it can be used to obtain more accurate transient pressure of an MFH well with SRV. [ABSTRACT FROM AUTHOR]

Land use/land cover (LULC) change is a consequence of human-induced global environmental change. It is also considered one of the major factors affecting groundwater recharge. Uncertainties and inconsistencies in LULC maps are one of the difficulties that LULC timeseries analysis face and which have a significant effect on hydrological impact analysis. Therefore, an accuracy assessment approach of LULC timeseries is needed for a more reliable hydrological analysis and prediction. The objective of this paper is to assess the impact of land use uncertainty and to improve the accuracy of a timeseries of CORINE (coordination of information on the environment) land cover maps by using a new approach of identifying spatial–temporal LULC change trajectories as a pre-processing tool. This ensures consistency of model input when dealing with land-use dynamics and as such improves the accuracy of land use maps and consequently groundwater recharge estimation. As a case study the impact of consistent land use changes from 1990 until 2013 on groundwater recharge for the Flanders-Brussels region is assessed. The change trajectory analysis successfully assigned a rational trajectory to 99% of all pixels. The methodology is shown to be powerful in correcting interpretation inconsistencies and overestimation errors in CORINE land cover maps. The overall kappa (cell-by-cell map comparison) improved from 0.6 to 0.8 and from 0.2 to 0.7 for forest and pasture land use classes respectively. The study shows that the inconsistencies in the land use maps introduce uncertainty in groundwater recharge estimation in a range of 10–30%. The analysis showed that during the period of 1990–2013 the LULC changes were mainly driven by urban expansion. The results show that the resolution at which the spatial analysis is performed is important; the recharge differences using original and corrected CORINE land cover maps increase considerably with increasing spatial resolution. This study indicates that improving consistency of land use map timeseries is of critical importance for assessing land use change and its environmental impact. [ABSTRACT FROM AUTHOR]

Flood frequency analyses (FFAs) are needed for flood risk management. Many methods exist ranging from classical purely statistical approaches to more complex approaches based on process simulation. The results of these methods are associated with uncertainties that are sometimes difficult to estimate due to the complexity of the approaches or the number of parameters, especially for process simulation. This is the case of the simulation-based FFA approach called SHYREG presented in this paper, in which a rainfall generator is coupled with a simple rainfall-runoff model in an attempt to estimate the uncertainties due to the estimation of the seven parameters needed to estimate flood frequencies. The six parameters of the rainfall generator are mean values, so their theoretical distribution is known and can be used to estimate the generator uncertainties. In contrast, the theoretical distribution of the single hydrological model parameter is unknown; consequently, a bootstrap method is applied to estimate the calibration uncertainties. The propagation of uncertainty from the rainfall generator to the hydrological model is also taken into account. This method is applied to 1112 basins throughout France. Uncertainties coming from the SHYREG method and from purely statistical approaches are compared, and the results are discussed according to the length of the recorded observations, basin size and basin location. Uncertainties of the SHYREG method decrease as the basin size increases or as the length of the recorded flow increases. Moreover, the results show that the confidence intervals of the SHYREG method are relatively small despite the complexity of the method and the number of parameters (seven). This is due to the stability of the parameters and takes into account the dependence of uncertainties due to the rainfall model and the hydrological calibration. Indeed, the uncertainties on the flow quantiles are on the same order of magnitude as those associated with the use of a statistical law with two parameters (here generalised extreme value Type I distribution) and clearly lower than those associated with the use of a three-parameter law (here generalised extreme value Type II distribution). For extreme flood quantiles, the uncertainties are mostly due to the rainfall generator because of the progressive saturation of the hydrological model. [ABSTRACT FROM AUTHOR]

In the natural environment, soil water repellency decreases infiltration, increases runoff, and increases erosion in slopes. In the built environment, soil water repellency offers the opportunity to develop granular materials with controllable wettability for slope stabilization. In this paper, the influence of soil water repellency on the hydrological response of slopes is investigated. Twenty-four flume tests were carried out in model slopes under artificial rainfall; soils with various wettability levels were tested, including wettable (Contact Angle, CA < 90°), subcritical water repellent (CA ∼ 90°) and water repellent (CA > 90°). Various rainfall intensities (30 mm/h and 70 mm/h), slope angles (20° and 40°) and relative compactions (70% and 90%) were applied to model the response of natural and man-made slopes to rainfall. To quantitatively assess the hydrological response, a number of measurements were made: runoff rate, effective rainfall rate, time to ponding, time to steady state, runoff acceleration, total water storage and wetting front rate. Overall, an increase in soil water repellency reduces infiltration and shortens the time for runoff generation, with the effects amplified for high rainfall intensity. Comparatively, the slope angle and relative compaction had only a minor contribution to the slope hydrology. The subcritical water repellent soils sustained infiltration for longer than both the wettable and water repellent soils, which presents an added advantage if they are to be used in the built environment as barriers. This study revealed substantial impacts of man-made or synthetically induced soil water repellency on the hydrological behavior of model slopes in controlled conditions. The results shed light on our understanding of hydrological processes in environments where the occurrence of natural soil water repellency is likely, such as slopes subjected to wildfires and in agricultural and forested slopes. [ABSTRACT FROM AUTHOR]

Most industrial and field studies of transport processes in Discrete Fracture Networks (DFNs) involve strong simplifying assumptions, especially at the meshing stage. High-accuracy simulations are therefore required for validating these simplified models and their domain of validity. The present paper proposes an efficient workflow based on open-source software to obtain transport simulations. High-quality computational meshes for DFNs are first generated using the conforming meshing approach FraC. Then, a tracer transport model implemented in the open-source code DuMux is used for simulating tracer transport driven by the advection-dispersion equation. We adopt the box method, a vertex-centered finite volume scheme for spatial discretization, which ensures concentration continuity and mass conservation at intersections between fractures. Numerical results on simple networks for validation purposes and on complex realistic DFNs are presented. An a-posteriori convergence study of the discretization method shows an order of convergence O ( h ) for tracer concentration with h the mesh size. [ABSTRACT FROM AUTHOR]

This paper outlines the design and experimentation of an Empirical Multistructure Framework (EMF) for lumped conceptual hydrological modeling. This concept is inspired from modular frameworks, empirical model development, and multimodel applications, and encompasses the overproduce and select paradigm. The EMF concept aims to reduce subjectivity in conceptual hydrological modeling practice and includes model selection in the optimisation steps, reducing initial assumptions on the prior perception of the dominant rainfall-runoff transformation processes. EMF generates thousands of new modeling options from, for now, twelve parent models that share their functional components and parameters. Optimisation resorts to ensemble calibration, ranking and selection of individual child time series based on optimal bias and reliability trade-offs, as well as accuracy and sharpness improvement of the ensemble. Results on 37 snow-dominated Canadian catchments and 20 climatically-diversified American catchments reveal the excellent potential of the EMF in generating new individual model alternatives, with high respective performance values, that may be pooled efficiently into ensembles of seven to sixty constitutive members, with low bias and high accuracy, sharpness, and reliability. A group of 1446 new models is highlighted to offer good potential on other catchments or applications, based on their individual and collective interests. An analysis of the preferred functional components reveals the importance of the production and total flow elements. Overall, results from this research confirm the added value of ensemble and flexible approaches for hydrological applications, especially in uncertain contexts, and open up new modeling possibilities. [ABSTRACT FROM AUTHOR]

Snow processes in mid- and north-latitude basins and their interaction with runoff generation at hyperresolution (<1 km and 5 km), representing land surface processes based on simplified couplings of snow thermal physics and the water cycle in the soil-vegetation-atmosphere (SVA) layers. This paper evaluates a new hydrological model capable of simulating river flows for a range of basin scales (100 km 2 to >10,000 km 2 ), and a particular focus on mid- and north-latitude regions. The new model combines the runoff generation and fully distributed routing framework of the Coupled Routing and Excess STorage (CREST) model with a new land surface process model that strictly couples water and energy balances at the SVA layer, imposing closed energy balance solutions. The model is vectorized and parallelized to achieve long-term (>30 years) high-resolution (30 m to 500 m and subhourly) simulations of large river basins utilizing high-performance computing. The model is tested in the Connecticut River basin (20,000 km 2 ), where flooding is frequently associated with interactions of snowmelt triggered by rainfall events. Model simulations of distributed evapotranspiration (ET) and snow water equivalence (SWE) at daily time step are shown to match accurately ET estimates from MODIS (average NSCE and bias are 0.77 and 6.79%) and SWE estimates from SNODAS (average correlation and normalized root mean square error are 0.94 and of 19%); the modeled daily river flow simulations exhibit an NSCE of 0.58 against USGS streamflow observations. [ABSTRACT FROM AUTHOR]

The hydrologic design of nonstationary flood extremes is an emerging field that is essential for water resources management and hydrologic engineering design to cope with changing environment. This paper aims to investigate and compare the capability of four nonstationary hydrologic design strategies, including the expected number of exceedances (ENE), design life level (DLL), equivalent reliability (ER), and average design life level (ADLL), with the last three methods taking into consideration the design life of the project. The confidence intervals of the calculated design floods were also estimated using the nonstationary bootstrap approach. A comparison of these four methods was performed using the annual maximum flood series (AMFS) of the Weihe River basin, Jinghe River basin, and Assunpink Creek basin. The results indicated that ENE, ER and ADLL yielded the same or very similar design values and confidence intervals for both increasing and decreasing trends of AMFS considered. DLL also yields similar design values if the relationship between DLL and ER/ADLL return periods is considered. Both ER and ADLL are recommended for practical use as they have associated design floods with the design life period of projects and yield reasonable design quantiles and confidence intervals. Furthermore, by assuming that the design results using either a stationary or nonstationary hydrologic design strategy should have the same reliability, the ER method enables us to solve the nonstationary hydrologic design problems by adopting the stationary design reliability, thus bridging the gap between stationary and nonstationary design criteria. [ABSTRACT FROM AUTHOR]

Watershed management (WSM) is the most widely adopted technology in developed as well as developing countries due to its suitability across climatic conditions. Watershed technology is suitable to protect and enhance soil fertility, which is deteriorating at an alarming rate with agricultural intensification in high as well as low rainfall regions. Of late, WSM is considered as an effective poverty alleviation intervention in the rain fed regions in countries like India. This paper aims at providing a basic watershed policy and implementation framework based on a critical review of experiences of WSM initiatives across South Asia. The purpose is to provide cross learnings within South Asia and other developing countries (especially Africa) that are embarking on WSM in recent years. Countries in the region accord differential policy priority and are at different levels of institutional arrangements for implementing WSM programmes. The implementation of watershed interventions is neither scientific nor comprehensive in all the countries limiting the effectiveness (impacts). Implementation of the programmes for enhancing the livelihoods of the communities need to strengthen both technical and institutional aspects. While countries like India and Nepal are yet to strengthen the technical aspects in terms of integrating hydrogeology and biophysical aspects into watershed design, others need to look at these aspects as they move towards strengthening the watershed institutions. Another important challenge in all the countries is regarding the distribution of benefits. Due to the existing property rights in land and water resources coupled with the agrarian structure and uneven distribution and geometry of aquifers access to sub-surface water resources is unevenly distributed across households. Though most of the countries are moving towards incorporating livelihoods components in order to ensure benefits to all sections of the community, not much is done in terms of addressing the equity aspects of WSM. [ABSTRACT FROM AUTHOR]

Submarine groundwater discharge is an important part of the hydrological cycle, but remains under-investigated for confined aquifers with no surface outcrop at the beach. This paper considers the offshore directed flow of fresh groundwater in the unconfined and confined aquifers along the coast of the Western Netherlands. Salinity patterns based on hydrological, geological, and geophysical field data are presented in five shore-normal hydrogeological cross-sections, extending from the beach to 4 km inland. The offshore continuation of the fresh groundwater is discussed using analytical models and cone penetration tests (CPTs) performed at the beach. All CPTs taken around the low water line of the intertidal zone reveal that changes from saline to fresh groundwater are always associated with a low-permeable layer. Such a low-permeable layer, which can be as thin as a few decimetres, may form the confining layer between the unconfined and confined aquifers, or can occur within of the unconfined aquifer. Due to its high vertical resolution, a CPT is an effective method to detect these variations in salinity and lithology. At each of the investigated locations, freshwater was present in the confined aquifer. Assuming that this fresh groundwater is part of an active flow system, the submarine freshwater tongue is estimated to extend at least a few hundred meters offshore, based on analytical model calculations. Hydrochemical data from an old offshore borehole, however, suggest this may be an underestimate and that the submarine freshwater tongue originates from former times when the coastline was located further westward than nowadays. [ABSTRACT FROM AUTHOR]

Over the past few decades, floods have been seen as one of the most common and largely distributed natural disasters in the world. If floods could be accurately forecasted in advance, then their negative impacts could be greatly minimized. It is widely recognized that quantification and reduction of uncertainty associated with the hydrologic forecast is of great importance for flood estimation and rational decision making. Bayesian forecasting system (BFS) offers an ideal theoretic framework for uncertainty quantification that can be developed for probabilistic flood forecasting via any deterministic hydrologic model. It provides suitable theoretical structure, empirically validated models and reasonable analytic-numerical computation method, and can be developed into various Bayesian forecasting approaches. This paper presents a comprehensive review on Bayesian forecasting approaches applied in flood forecasting from 1999 till now. The review starts with an overview of fundamentals of BFS and recent advances in BFS, followed with BFS application in river stage forecasting and real-time flood forecasting, then move to a critical analysis by evaluating advantages and limitations of Bayesian forecasting methods and other predictive uncertainty assessment approaches in flood forecasting, and finally discusses the future research direction in Bayesian flood forecasting. Results show that the Bayesian flood forecasting approach is an effective and advanced way for flood estimation, it considers all sources of uncertainties and produces a predictive distribution of the river stage, river discharge or runoff, thus gives more accurate and reliable flood forecasts. Some emerging Bayesian forecasting methods (e.g. ensemble Bayesian forecasting system, Bayesian multi-model combination) were shown to overcome limitations of single model or fixed model weight and effectively reduce predictive uncertainty. In recent years, various Bayesian flood forecasting approaches have been developed and widely applied, but there is still room for improvements. Future research in the context of Bayesian flood forecasting should be on assimilation of various sources of newly available information and improvement of predictive performance assessment methods. [ABSTRACT FROM AUTHOR]

The integration of interdisciplinary scientific and societal knowledge plays an increasing role in sustainability science and more generally, in global change research. In the field of water resources, interdisciplinarity has long been recognized as crucial. Recently, new concepts and ideas about how to approach water resources management more holistically have been discussed. The emergence of concepts such as socio-hydrology indicates the growing relevance of connections between social and hydrological disciplines. In this paper, we determine how well social sciences are integrated with hydrological research by using two approaches. First, we conducted a questionnaire survey with a sample of hydrology researchers and professionals (N = 353) to explore current opinions and developments related to interdisciplinary collaboration between hydrologists and social scientists. Second, we analyzed the disciplinary composition of author teams and the reference lists of articles pertaining to the socio-hydrology concept. We conclude that interdisciplinarity in water resources research is on a promising track but may need to mature further in terms of its aims and methods of integration. We find that current literature pays little attention to the following questions: What kind of interdisciplinarity do different scholars want? What are social scientists’ preferred roles and knowledge from a hydrology perspective? [ABSTRACT FROM AUTHOR]