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Following the rise of R as a scientific programming language, the increasing requirement for more transferable research and the growth of data availability in hydrology, R packages containing hydrological models are becoming more and more available as an open-source resource to hydrologists. Corresponding to the core of the hydrological studies workflow, their value is increasingly meaningful regarding the reliability of methods and results. Despite package and model distinctiveness, no study has ever provided a comparison of R packages for conceptual rainfall-runoff modelling from a user perspective by contrasting their philosophy, model characteristics and ease of use. We have selected eight packages based on our ability to consistently run their models on simple hydrology modelling examples. We have uniformly analysed the exact structure of seven of the hydrological models integrated into these R packages in terms of conceptual storages and fluxes, spatial discretisation, data requirements and output provided. The analysis showed that very different modelling choices are associated with these packages, which emphasises various hydrological concepts. These specificities are not always sufficiently well explained by the package documentation. Therefore a synthesis of the package functionalities was performed from a user perspective. This synthesis helps to inform the selection of which packages could/should be used depending on the problem at hand. In this regard, the technical features, documentation, R implementations and computational times were investigated. Moreover, by providing a framework for package comparison, this study is a step forward towards supporting more transferable and reusable methods and results for hydrological modelling in R.

This article reconsiders the concept of a perceptual model of hydrological processes as the first stage to be considered in developing a procedural model for a particular catchment area. While various perceptual models for experimental catchments have been developed, the concept is not widely used in defining or evaluating catchment models. This is, at least in part, because of the evident complexity possible in a perceptual model and the approximate nature of procedural model structures and parameterizations, particularly where there is a requirement for parameter parsimony. A perceptual model for catchments in Cumbria, North-West England, is developed as an exemplar and illustrated in terms of time varying distribution functions. Two critical questions are addressed: how can perceptual model hypotheses be tested at scales of interest, and how can constraints then be imposed on the basis of qualitative perceptual knowledge in conditioning predictive models? It is suggested that there is value in perceptual information, particularly in thinking about predicting the impacts of future change and that we still have much to learn about moving from observational and perceptual complexity to parsimonious predictability. This article is categorized under: Science of Water. © 2021 The Authors. WIREs Water published by Wiley Periodicals LLC.

The concept of time of concentration in the analysis of catchment responses dates back over 150 years to the introduction of the rational method. Since then it has been used in a variety of ways in the formulation of both unit hydrograph and distributed catchment models. It is normally discussed in terms of the velocity of flow of a water particle from the furthest part of a catchment to the outlet. This is also the basis for the definition in the International Glossary of Hydrology. While conceptually simple, this definition is, however, wrong when applied to catchment responses where, in terms of how surface and subsurface flows produce hydrographs, it is more correct to discuss and teach the concept based on celerities and time to equilibrium. While this has been recognized since the 1960s, some recent papers and texts remain confused over the definition and use of the time of concentration concept. The paper sets out the history of its use and clarifies its relationship with time to equilibrium but suggests that both terms are not really useful in explaining hydrological responses. An Appendix is included that quantifies the differences between the definitions of response times for subsurface and surface flows under simple assumptions that might be useful in teaching. © Author(s) 2020.

Phosphorus losses from land to water will be impacted by climate change and land management for food production, with detrimental impacts on aquatic ecosystems. Here we use a unique combination of methods to evaluate the impact of projected climate change on future phosphorus transfers, and to assess what scale of agricultural change would be needed to mitigate these transfers. We combine novel high-frequency phosphorus flux data from three representative catchments across the UK, a new high-spatial resolution climate model, uncertainty estimates from an ensemble of future climate simulations, two phosphorus transfer models of contrasting complexity and a simplified representation of the potential intensification of agriculture based on expert elicitation from land managers. We show that the effect of climate change on average winter phosphorus loads (predicted increase up to 30% by 2050s) will be limited only by large-scale agricultural changes (e.g., 20–80% reduction in phosphorus inputs).

This article discusses a coupled water level forecasting system constructed for the River Dee (UK) using parsimonious, physically interpretable, time series models. Tidal forecasts, provided by a simple harmonic model, and observed water levels at the upstream boundary are used to drive a nonlinear hydrological model which forecasts water levels at three gauged sites on the flood plain. The assimilation of observed data and use of the model for real-time forecasting is presented. The results generated indicate that the forecasts of river water can be both timely and accurate except close to the tidal boundary where the the tide is affected by the weir at Chester.

The Delft Flood Early Warning System provides a versatile framework for real-time flood forecasting. The UK Environment Agency has adopted the Delft framework to deliver its National Flood Forecasting System. The Delft system incorporates new flood forecasting models very easily using an "open shell" framework. This paper describes how we added the data-based mechanistic modelling approach to the model inventory and presents a case study for the Eden catchment (Cumbria, UK).

1. Rivers and their catchments are complex, dynamic and non-equilibrium systems. Although the general functioning of these ecosystems is familiar, the characteristics of particular sites are often poorly known and accurate prediction of future behaviour to inform management decisions is extremely difficult. 2. Simple relationships between river nutrient concentrations and the health of river ecosystems do not exist. Natural variability and practical and technical constraints reduce our ability to set nutrient targets to protect river ecosystems. Particularly challenging is the use of simple dose–response relationships as regulatory threshold targets, whereby sections of river are classified as either passing or failing to meet good ecological status. 3. Ecologically meaningful frameworks are needed that take account of the epistemic uncertainty associated with our predictions. Such frameworks should have clearly defined goals; be holistic; allow for natural variability; help to define ecologically acceptable environmental regimes; recognise that significant uncertainties mean that we will often be using indices rather than absolute measures; and use measures that explicitly include uncertainty estimates. Such approaches allow those outside the decision-making process to understand the level of environmental precaution included in the management of complex systems.

Discrete observations on recession flows, local depth to the water table and the extent of saturated areas were used in the Vallcebre small research basin for obtaining the distribution functions of the TOPMODEL catchment parameters that drive the behaviour of the saturated store. Using this parameter information within GLUE framework, the robustness of discharge simulations was improved and the uncertainty of flow separation between two components was significantly reduced when compared with the results obtained with customary calibration with flow data at the outlet. Nevertheless, the analysis of the uncertainty in the determination of the local value of the topographic index at the piezometer location demonstrated that this may be a relevant limitation of the approach, particularly for high values of the topographic index, and a careful selection of the piezometer is recommended. The use of the extent of saturated areas provided the best and more representative results, although the simulated patterns of saturated areas did not match well the observed ones, because the role of local controls beyond the topographic index. © 2008 Elsevier Ltd. All rights reserved.

The application of a modified version of dynamic TOPMODEL for two subcatchments at Plynlimon, Wales is described. Conservative chemical mixing within mobile and immobile stores has been added to the hydrological model in an attempt to simulate observed stream chloride concentrations. The model was not fully able to simulate the observed behaviour, in particular the short- to medium-term dynamics. One of the primary problems highlighted by the study was the representation of dry deposition and cloud-droplet-deposited chloride, which formed a significant part of the long-term chloride mass budget. Equifinality of parameter sets inhibited the ability to determine the effective catchment mixing volumes and coefficients or the most likely partition between occult mass inputs and chloride mass inputs determined by catchment immobile-store antecedent conditions. Some success was achieved, in as much as some aspects of the dynamic behaviour of the signal were satisfactorily simulated, although spectral analysis showed that the model could not fully reproduce the 1/f power spectra of observed stream chloride concentrations with its implications of a wide distribution of residence times for water in the catchment.

The objective of this research is to improve the comprehension of the hydrological behaviour of natural catchments. The main originality of this work is to associate different types of measurement in order to obtain a better vision of hydrological processes responsible for streamflow generation. First, the hydrological behaviour is studied at the catchment scale by the application of environmental tracing. A three-component mixing model based on the silica and calcium concentrations of water allows one to distinguish the contributions of direct precipitation, soil water and groundwater during flood generation. Despite the different hydrological responses observed between the four subcatchments studied, a common behaviour is apparent. Soil contribution increases with a rise in the basin humidity. The subsurface water dominates the generation of major floods, which occur in wet conditions. In order to discover the processes responsible for the important soil water contributions, a large-scale time-domain reflectometry experiment (64 probes) was conducted. On the whole, this experiment indicates that the water flow in soil is spatially quite heterogeneous and depends on local properties. Macropore flows were clearly identified during a rainfall simulator experiment. Preferential flows may be responsible for the important contribution of soil water and the heterogeneity of the soil moisture. In order to test this hypothesis, a dye-tracing experiment was done. This new investigation confirms that an important part of soil water reaches the stream by preferential flows. So as to synthesize all these observations, a conceptual model is proposed. This model respects both the hydrochemical responses highlighted by the environmental tracing experiment and the observations done at the local scale. This conceptual model suggests that the important contribution of soil water is due to the extent of the hydrographic network and the role of preferential flows.

Residence times and flow paths of pipe and stream flow were studied during low flow in the Nant Gerig and Gwy experimental catchments at Plynlimon in mid-Wales, UK, using a two-month time series of natural deuterium and electrical conductivity data from perennial and ephemeral pipe flow, stream flow, groundwater and rainfall. Low flow in both the perennial pipe and the stream was maintained by ‘old’ groundwater discharge. This groundwater was at least 40 days old. Flow in the ephemeral pipe was dominated by old groundwater and was only slightly affected by direct inputs of new water. Although direct rainfall inputs contributed minimally to runoff in the perennial pipe and the stream, rainfall influenced the isotopic and chemical character of the groundwater. Rainfall also affected the water-table elevation, which determined the flashiness of the perennial pipe flow and whether the ephemeral pipe flowed. The isotope and electrical conductivity data suggest that storm runoff in both the main pipe and the stream is overwhelmingly old water. A sensitivity analysis suggests that the old water is supplied both from near-stream groundwater and upslope groundwater delivered by the ephemeral pipes.