. (2013) 'Concepts of hydrological connectivity : research approaches, pathways and future agendas.', Earth-science reviews., 119 . pp. 17-34. Further information on publisher's website:http://dx.doi.org/10.1016/j.earscirev.2013.02.001Publisher's copyright statement: NOTICÅ: this is the author's version of a work that was accepted for publication in Earth-Science Reviews. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reected in this document. Changes may have been made to this work since it was submitted for publication. A denitive version was subsequently published in Earth-Science Reviews, 119, 2013Reviews, 119, , 10.1016Reviews, 119, /j.earscirev.2013.001. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. to direct future research into process-based hydrological connectivity this paper: i) evaluates the 20 extent to which different concepts of hydrological connectivity have emerged from different 21 approaches to measure and predict flow in different environments; ii) discusses the extent to which 22 these different concepts are mutually compatible; and iii) assesses further research to contribute to 23 a unified understanding of hydrological processes. Existing research is categorised into five different 24 approaches to investigating hydrological connectivity: i) evaluating soil -moisture patterns (soil-25 moisture connectivity); ii) understanding runoff patterns and processes on hillslopes (flow -process 26 connectivity); iii) investigating topographic controls (terrain-connectivity) including the impact of 27 road networks on hydrological connectivity and catchment runoff; iv) developing models to explore 28 and predict hydrological connectivity; and v) developing indices of hydrological connectivity . Analysis 29 of published research suggests a relationship between research group, approach, geographic setting 30 and the interpretation of hydrological connectivity. To further understanding of hydrological 31 connectivity our knowledge needs to be developed using a range of techniques and approaches, 32 there should be common understandings between researchers approaching the concept from 33 different perspectives, and these meanings need to be communicated effectively with those 34 responsible for land management. 35 36

Abstract:Integrated environmental modeling (IEM) is inspired by modern environmental problems, decisions, and policies and enabled by transdisciplinary science and computer capabilities that allow the environment to be considered in a holistic way. The problems are characterized by the extent of the environmental system involved, dynamic and interdependent nature of stressors and their impacts, diversity of stakeholders, and integration of social, economic, and environmental considerations. IEM provides a science-based structure to develop and organize relevant knowledge and information and apply it to explain, explore, and forecast the behavior of environmental systems in response to human and natural sources of stress. During the past several years a number of workshops were held that brought IEM practitioners together to share experiences and discuss future needs and directions. In this paper we organize and present the results of these discussions. IEM is presented as a landscape containing four interdependent elements: applications, science, technology, and community. The elements are described from the perspective of their role in the landscape, current practices, and challenges that must be addressed. Workshop participants envision a global scale IEM community that leverages modern technologies to streamline the movement of science-based knowledge from its sources in research, through its organization into databases and models, to its integration and application for problem solving purposes. Achieving this vision will require that the global community of IEM stakeholders transcend social, political, and organizational boundaries and pursue greater levels of collaboration. Among the highest priorities for community action are the development of standards for publishing IEM data and models in forms suitable for automated discovery, access, and integration; education of the next generation of environmental stakeholders, with a focus on transdisciplinary research, development, and decision making; and providing a web-based platform for community interactions (e.g., continuous virtual workshops).

This paper assesses the extent to which a topographically defined description of the spatial arrangement of catchment wetness can be used to represent landscape hydrological connectivity in temperate river catchments. A physically based distributed hydrological model is used to characterize the space‐time patterns of surface overland flow connection to the drainage network. These characterizations are compared with a static descriptor of the spatial structure of topographically controlled local wetness, called here the Network Index. Theoretically, if topography is the primary control upon hydrological response, the level of catchment wetness required to maintain connectivity along a flow path should be greater for flow paths that have a lower value of the topographically controlled local wetness. We find that our static descriptor can be used to generalize a significant proportion of the time‐averaged spatial variability in connectivity, in terms of both the propensity to and duration of connection. Although the extent to which this finding holds will vary with the extent of topographic control of hydrological response, in catchments with relatively shallow soils and impervious geology our index could improve significantly the estimation of the transfer of sediment and dissolved materials to the drainage network and so assist with both diffuse pollution and climate change impact studies. The work also provides a second reason for the concept that there are Critical Source Areas in river catchments: these arise from the extent to which that material can be delivered to the drainage network, as well as the generation of risky material itself.

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It is generally accepted that within particular physiographic and climatic regions catchments exhibit differences in their hydrological response. These differences result from the interaction of spatial variability in catchment characteristics, variability of rainfall inputs and surface and subsurface hydrological processes. These interactions are complex and difficult to unravel. Hydrologically similar surfaces (HYSS) have been used to identify catchment areas that have a similar response to rainfall and have been identified at a number of scales. HYSS have been identified at the subcatchment scale for the Rambla de Nogalte in SE Spain. Areas with similar at-a-point hydrological storages were distinguished by using a combination of geology, land use and topography. This mapping was compared with discharge estimates made throughout the catchment following a seven-year return interval flood in September 1997. From this significant flood source areas were identified from reaches showing rapidly increasing channel discharge, and associated with HYSS that combined suitable internal characteristics with good connectivity to the main channel. This paper presents a simulation model that has been developed to investigate the way in which the hydrological response of areas within a HYSS respond to changes in source area, gradient, connectivity to the channel, storm size and intensity profile. This is one of the first studies using a hillslope model to investigate spatial patterns of runoff-response in semi-arid areas and results have implications for scaling up hydrological response, and on how the dynamics of runoff producing areas vary both under changing storm conditions and over time. It is implicit in our results that the nature of stream-slope coupling differs substantively between semi-arid and humid areas.

Abstract. Benchmarking model performance across large samples of catchments is useful to guide model selection and future model development. Given uncertainties in the observational data we use to drive and evaluate hydrological models, and uncertainties in the structure and parameterisation of models we use to produce hydrological simulations and predictions, it is essential that model evaluation is undertaken within an uncertainty analysis framework. Here, we benchmark the capability of several lumped hydrological models across Great Britain by focusing on daily flow and peak flow simulation. Four hydrological model structures from the Framework for Understanding Structural Errors (FUSE) were applied to over 1000 catchments in England, Wales and Scotland. Model performance was then evaluated using standard performance metrics for daily flows and novel performance metrics for peak flows considering parameter uncertainty. Our results show that lumped hydrological models were able to produce adequate simulations across most of Great Britain, with each model producing simulations exceeding a 0.5 Nash–Sutcliffe efficiency for at least 80 % of catchments. All four models showed a similar spatial pattern of performance, producing better simulations in the wetter catchments to the west and poor model performance in central Scotland and south-eastern England. Poor model performance was often linked to the catchment water balance, with models unable to capture the catchment hydrology where the water balance did not close. Overall, performance was similar between model structures, but different models performed better for different catchment characteristics and metrics, as well as for assessing daily or peak flows, leading to the ensemble of model structures outperforming any single structure, thus demonstrating the value of using multi-model structures across a large sample of different catchment behaviours. This research evaluates what conceptual lumped models can achieve as a performance benchmark and provides interesting insights into where and why these simple models may fail. The large number of river catchments included in this study makes it an appropriate benchmark for any future developments of a national model of Great Britain.

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Abstract:Much attention has been given to the surface controls on the generation and transmission of runoff in semi-arid areas. However, the surface controls form only one part of the system; hence, it is important to consider the effect that the characteristics of the storm event have on the generation of runoff and the transmission of flow across the slope. The impact of storm characteristics has been investigated using the Connectivity of Runoff Model (CRUM). This is a distributed, dynamic hydrology model that considers the hydrological processes relevant to semi-arid environments at the temporal scale of a single storm event. The key storm characteristics that have been investigated are the storm duration, rainfall intensity, rainfall variability and temporal structure. This has been achieved through the use of a series of defined storm hydrographs and stochastic rainfall. Results show that the temporal fragmentation of high-intensity rainfall is important for determining the travel distances of overland flow and, hence, the amount of runoff that leaves the slope as discharge. If the high-intensity rainfall is fragmented, then the runoff infiltrates a short distance downslope. Longer periods of high-intensity rainfall allow the runoff to travel further and, hence, become discharge. Therefore, storms with similar amounts of high-intensity rainfall can produce very different amounts of discharge depending on the storm characteristics. The response of the hydrological system to changes in the rainfall characteristics can be explained using a four-stage model of the runoff generation process. These stages are: (1) all water infiltrating, (2) the surface depression store filling or emptying without runoff occurring, (3) the generation and transmission of runoff and (4) the transmission of runoff without new runoff being generated. The storm event will move the system between the four stages and the nature of the rainfall required to move between the stages is determined by the surface characteristics. This research shows the importance of the variable-intensity rainfall when modelling semi-arid runoff generation. The amount of discharge may be greater or less than the amount that would have been produced if constant rainfall intensity is used in the model.