Global river hydrography and network routing: baseline data and new approaches to study the world's large river systems
TL;DR: A new modeling framework that integrates hydrographic baseline data at a global scale with new modeling tools, specifically a river network routing model (HydroROUT) that is currently under development that is designed to provide an avenue for advanced hydro-ecological applications at large scales in a consistent and highly versatile way is presented.
Abstract: Despite significant recent advancements, global hydrological models and their input databases still show limited capabilities in supporting many spatially detailed research questions and integrated assessments, such as required in freshwater ecology or applied water resources management. In order to address these challenges, the scientific community needs to create improved large-scale datasets and more flexible data structures that enable the integration of information across and within spatial scales; develop new and advanced models that support the assessment of longitudinal and lateral hydrological connectivity; and provide an accessible modeling environment for researchers, decision makers, and practitioners. As a contribution, we here present a new modeling framework that integrates hydrographic baseline data at a global scale (enhanced HydroSHEDS layers and coupled datasets) with new modeling tools, specifically a river network routing model (HydroROUT) that is currently under development. The resulting ‘hydro-spatial fabric’ is designed to provide an avenue for advanced hydro-ecological applications at large scales in a consistent and highly versatile way. Preliminary results from case studies to assess human impacts on water quality and the effects of dams on river fragmentation and downstream flow regulation illustrate the potential of this combined data-and-modeling framework to conduct novel research in the fields of aquatic ecology, biogeochemistry, geo-statistical modeling, or pollution and health risk assessments. The global scale outcomes are at a previously unachieved spatial resolution of 500 m and can thus support local planning and decision making in many of the world's large river basins. Copyright © 2013 John Wiley & Sons, Ltd.
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McGill University1, WWF-India2, University of Basel3, WWF-Canada4, The Nature Conservancy5, University of Nevada, Reno6, Delft University of Technology7, Konstanz University of Applied Sciences8, King's College London9, Umeå University10, Swedish University of Agricultural Sciences11, University of Washington12, Harvard University13, University of Wisconsin-Madison14, Conservation International15, Michigan Technological University16, Stanford University17, Leibniz Association18, Free University of Berlin19, University of Tübingen20
TL;DR: A comprehensive assessment of the world’s rivers and their connectivity shows that only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length.
Abstract: Free-flowing rivers (FFRs) support diverse, complex and dynamic ecosystems globally, providing important societal and economic services. Infrastructure development threatens the ecosystem processes, biodiversity and services that these rivers support. Here we assess the connectivity status of 12 million kilometres of rivers globally and identify those that remain free-flowing in their entire length. Only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length and 23 per cent flow uninterrupted to the ocean. Very long FFRs are largely restricted to remote regions of the Arctic and of the Amazon and Congo basins. In densely populated areas only few very long rivers remain free-flowing, such as the Irrawaddy and Salween. Dams and reservoirs and their up- and downstream propagation of fragmentation and flow regulation are the leading contributors to the loss of river connectivity. By applying a new method to quantify riverine connectivity and map FFRs, we provide a foundation for concerted global and national strategies to maintain or restore them. A comprehensive assessment of the world’s rivers and their connectivity shows that only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length.
1,071 citations
TL;DR: A geo-statistical model is developed to estimate the volume of global lakes with a surface area of at least 10 ha based on the surrounding terrain information and calculates mean and median hydraulic residence times for all lakes to be 1,834 days and 456 days, respectively.
Abstract: Lakes are key components of biogeochemical and ecological processes, thus knowledge about their distribution, volume and residence time is crucial in understanding their properties and interactions within the Earth system. However, global information is scarce and inconsistent across spatial scales and regions. Here we develop a geo-statistical model to estimate the volume of global lakes with a surface area of at least 10 ha based on the surrounding terrain information. Our spatially resolved database shows 1.42 million individual polygons of natural lakes with a total surface area of 2.67 × 106 km2 (1.8% of global land area), a total shoreline length of 7.2 × 106 km (about four times longer than the world’s ocean coastline) and a total volume of 181.9 × 103 km3 (0.8% of total global non-frozen terrestrial water stocks). We also compute mean and median hydraulic residence times for all lakes to be 1,834 days and 456 days, respectively. Lakes play a key role in our ecosystems and thus it is vital to understand their distribution and volume. Here, the authors present a new global lake database (HydroLAKES) and develop a new geo-statistical model to show global lake area, shoreline length, water volume and hydraulic residence times.
729 citations
TL;DR: In this article, a graph-based river routing model is proposed to simultaneously assess flow regulation and fragmentation by dams at multiple scales using data at high spatial resolution, which can serve as a component of river fragmentation and connectivity assessments; as a standardized, easily replicable monitoring framework at global and basin scales; and as part of regional dam planning and management strategies.
Abstract: The global number of dam constructions has increased dramatically over the past six decades and is forecast to continue to rise, particularly in less industrialized regions. Identifying development pathways that can deliver the benefits of new infrastructure while also maintaining healthy and productive river systems is a great challenge that requires understanding the multifaceted impacts of dams at a range of scales. New approaches and advanced methodologies are needed to improve predictions of how future dam construction will affect biodiversity, ecosystem functioning, and fluvial geomorphology worldwide, helping to frame a global strategy to achieve sustainable dam development. Here, we respond to this need by applying a graph-based river routing model to simultaneously assess flow regulation and fragmentation by dams at multiple scales using data at high spatial resolution. We calculated the cumulative impact of a set of 6374 large existing dams and 3377 planned or proposed dams on river connectivity and river flow at basin and subbasin scales by fusing two novel indicators to create a holistic dam impact matrix for the period 1930?2030. Static network descriptors such as basin area or channel length are of limited use in hierarchically nested and dynamic river systems, so we developed the river fragmentation index and the river regulation index, which are based on river volume. These indicators are less sensitive to the effects of network configuration, offering increased comparability among studies with disparate hydrographies as well as across scales. Our results indicate that, on a global basis, 48% of river volume is moderately to severely impacted by either flow regulation, fragmentation, or both. Assuming completion of all dams planned and under construction in our future scenario, this number would nearly double to 93%, largely due to major dam construction in the Amazon Basin. We provide evidence for the importance of considering small to medium sized dams and for the need to include waterfalls to establish a baseline of natural fragmentation. Our versatile framework can serve as a component of river fragmentation and connectivity assessments; as a standardized, easily replicable monitoring framework at global and basin scales; and as part of regional dam planning and management strategies.
418 citations
Cites background or methods from "Global river hydrography and networ..."
...Our framework combines global high resolution hydrographic data (Lehner et al 2008) with a graph- based river routing model (HydroROUT, Lehner and Grill 2013, Grill et al 2014)....
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...Selecting a useful and homogeneous subbasin breakdown, such as provided by HydroBASINS, is thus a critical task....
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...These new approaches take into account network structure (Bunn et al 2000, Erős et al 2011) and utilize newly developed hydrographical data (Lehner and Grill 2013)....
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...In addition to river basins, we used a set of subbasin units termed HydroBASINS (Lehner and Grill 2013) to assess the sensitivity of our index calculations to spatial scale....
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...HydroBASINS is a delineation of global watersheds and was developed to provide nested subdivisions of large river basins to conduct disaggregated spatial analyses in river systems....
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TL;DR: A global database of planform river hydromorphology and a statistical approach are used to show that global river and stream surface area is 773,000 ± 79,000 square kilometers (0.58 ± 0.06%) of Earth’s nonglaciated land surface, an area 44 ± 15% larger than previous spatial estimates.
Abstract: The turbulent surfaces of rivers and streams are natural hotspots of biogeochemical exchange with the atmosphere. At the global scale, the total river-atmosphere flux of trace gasses such as carbon dioxide depends on the proportion of Earth's surface that is covered by the fluvial network, yet the total surface area of rivers and streams is poorly constrained. We used a global database of planform river hydromorphology and a statistical approach to show that global river and stream surface area at mean annual discharge is 773,000 ± 79,000 square kilometers (0.58 ± 0.06%) of Earth's nonglaciated land surface, an area 44 ± 15% larger than previous spatial estimates. We found that rivers and streams likely play a greater role in controlling land-atmosphere fluxes than is currently represented in global carbon budgets.
406 citations
Rutgers University1, National Center for Atmospheric Research2, University of Virginia3, Pennsylvania State University4, University of Utah5, University of California, Berkeley6, Boise State University7, Oregon State University8, ETH Zurich9, University at Buffalo10, University of Saskatchewan11, United States Geological Survey12, University of Kansas13, University of California, Santa Barbara14, University of California, Riverside15, Duke University16, University of Freiburg17, University of Arizona18, Ghent University19, University of Bristol20, Northeastern University21, Purdue University22, Pacific Northwest National Laboratory23, University of Colorado Boulder24, Texas A&M University25, University of Washington26, United States Department of Agriculture27, University of California, Merced28, University of Nevada, Reno29, University of Tokyo30
TL;DR: In this paper, the authors bring together hydrologists, critical zone scientists, and ESM developers to explore how hillslope structures may modulate ESM grid-level water, energy, and biogeochemical fluxes.
Abstract: Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope‐scale terrain structures that fundamentally organize water, energy, and biogeochemical stores and fluxes at subgrid scales. Here we bring together hydrologists, Critical Zone scientists, and ESM developers, to explore how hillslope structures may modulate ESM grid‐level water, energy, and biogeochemical fluxes. In contrast to the one‐dimensional (1‐D), 2‐ to 3‐m deep, and free‐draining soil hydrology in most ESM land models, we hypothesize that 3‐D, lateral ridge‐to‐valley flow through shallow and deep paths and insolation contrasts between sunny and shady slopes are the top two globally quantifiable organizers of water and energy (and vegetation) within an ESM grid cell. We hypothesize that these two processes are likely to impact ESM predictions where (and when) water and/or energy are limiting. We further hypothesize that, if implemented in ESM land models, these processes will increase simulated continental water storage and residence time, buffering terrestrial ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited knowledge of the subsurface, where water is stored (supporting vegetation) and released to stream baseflow (supporting aquatic ecosystems). We conclude with a set of organizing hypotheses and a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.
274 citations
Cites methods from "Global river hydrography and networ..."
...Catchment delineation is available globally (e.g., Lehner & Grill, 2013; Verdin, 2017), and this idea has been applied in several large‐scale models (e.g., Beighley et al., 2009, 2011; Goteti et al., 2008; Koster et al., 2000; Yamazaki et al., 2011, 2009), in which the land‐atmosphere flux exchange…...
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References
More filters
TL;DR: It is hypothesized that producer and consumer communities characteristic of a given river reach become established in harmony with the dynamic physical conditions of the channel.
Abstract: From headwaters to mouth, the physical variables within a river system present a continuous gradient of physical conditions. This gradient should elicit a series of responses within the constituent...
9,145 citations
"Global river hydrography and networ..." refers background in this paper
...Flows in traditional GHMs that include lateral transport occur on the premise of a river continuum whereby conditions at every location in the river network are influenced by upstream processes (Vannote et al., 1980)....
[...]
Book•
01 Jan 1993TL;DR: In-depth, self-contained treatments of shortest path, maximum flow, and minimum cost flow problems, including descriptions of polynomial-time algorithms for these core models are presented.
Abstract: A comprehensive introduction to network flows that brings together the classic and the contemporary aspects of the field, and provides an integrative view of theory, algorithms, and applications. presents in-depth, self-contained treatments of shortest path, maximum flow, and minimum cost flow problems, including descriptions of polynomial-time algorithms for these core models. emphasizes powerful algorithmic strategies and analysis tools such as data scaling, geometric improvement arguments, and potential function arguments. provides an easy-to-understand descriptions of several important data structures, including d-heaps, Fibonacci heaps, and dynamic trees. devotes a special chapter to conducting empirical testing of algorithms. features over 150 applications of network flows to a variety of engineering, management, and scientific domains. contains extensive reference notes and illustrations.
8,496 citations
"Global river hydrography and networ..." refers methods in this paper
...Connectivity relationships are based on the ‘ForwardStar’ concept, which is considered the most efficient network representation (Ahuja et al., 1993; Cherkassky et al., 1996)....
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City College of New York1, University of Michigan2, University of Wisconsin-Madison3, Swiss Federal Institute of Aquatic Science and Technology4, University of Hong Kong5, University of New Hampshire6, Griffith University7, Southern Cross University8, University of Washington9, University of Western Australia10
TL;DR: The first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts is presented.
Abstract: Protecting the world’s freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the world’s population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.
5,401 citations
"Global river hydrography and networ..." refers background in this paper
...Vörösmarty et al. (2010) offer a suite of 23 maps of driver sources at 0.5 pixel resolution globally which were part of their study on threats to global river systems (http://www.riverthreat.net/)....
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...In a recent integrated approach, Vörösmarty et al. (2010) conducted a study that combines various disciplines, models, and data sources in an attempt to holistically assess anthropogenic threats to global scale freshwater biodiversity and river systems....
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TL;DR: Numerical experiments combining climate model outputs, water budgets, and socioeconomic information along digitized river networks demonstrate that (i) a large proportion of the world's population is currently experiencing water stress and (ii) rising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025.
Abstract: The future adequacy of freshwater resources is difficult to assess, owing to a complex and rapidly changing geography of water supply and use. Numerical experiments combining climate model outputs, water budgets, and socioeconomic information along digitized river networks demonstrate that (i) a large proportion of the world's population is currently experiencing water stress and (ii) rising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025. Consideration of direct human impacts on global water supply remains a poorly articulated but potentially important facet of the larger global change question.
4,355 citations
"Global river hydrography and networ..." refers background in this paper
...…spatial resolutions, ranging from basin scale lumped models to the most commonly applied 0.5 pixel resolution, and various lateral routing schemes have been developed accordingly (Oki and Sud, 1998; Graham et al., 1999; Renssen and Knoop, 2000; Vörösmarty et al., 2000a; Döll and Lehner, 2002)....
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...Major goals of these models include the estimation of water availability, water use, and/or water scarcity at global or regional scales (e.g. Vörösmarty et al., 2000b; Alcamo et al., 2003; Arnell et al., 2004; Oki and Kanae, 2006; Rost et al., 2008; Döll et al., 2009; Hanasaki et al., 2010; Siebert…...
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TL;DR: This literature review has focused this literature review around four key principles to highlight the important mechanisms that link hydrology and aquatic biodiversity and to illustrate the consequent impacts of altered flow regimes.
Abstract: The flow regime is regarded by many aquatic ecologists to be the key driver of river and floodplain wet- land ecosystems. We have focused this literature review around four key principles to highlight the important mech- anisms that link hydrology and aquatic biodiversity and to illustrate the consequent impacts of altered flow regimes: Firstly, flow is a major determinant of physical habitat in streams, which in turn is a major determinant of biotic com- position; Secondly, aquatic species have evolved life history strategies primarily in direct response to the natural flow regimes; Thirdly, maintenance of natural patterns of longitu- dinal and lateral connectivity is essential to the viability of populations of many riverine species; Finally, the invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. The impacts of flow change are manifest across broad taxonomic groups including riverine plants, invertebrates, and fish. Despite growing recognition of these relationships, ecologists still struggle to predict and quantify biotic responses to altered flow regimes. One obvious difficulty is the ability to distin- guish the direct effects of modified flow regimes from im- pacts associated with land-use change that often accom- panies water resource development. Currently, evidence about how rivers function in relation to flow regime and the flows that aquatic organisms need exists largely as a series of untested hypotheses. To overcome these problems, aquatic science needs to move quickly into a manipulative or experimental phase, preferably with the aims of restora- tion and measuring ecosystem response.
3,018 citations
"Global river hydrography and networ..." refers background in this paper
...Degree of regulation from dams at a global scale The alteration of the downstream river flow regime is widely recognized as one of the main adverse environmental impacts of dam and reservoir construction (Bunn and Arthington, 2002)....
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