There are millions of river barriers worldwide, ranging from wooden locks to concrete dams, many of which form associated impoundments to store water in small ponds or large reservoirs. Besides their benefits, there is growing recognition of important environmental and social trade-offs related to these artificial structures. However, global datasets describing their characteristics and geographical distribution are often biased towards particular regions or specific applications, such as hydropower dams affecting fish migration, and are thus not globally consistent. Here, we present a new river barrier and reservoir database developed by the Global Dam Watch (GDW) consortium that integrates, harmonizes, and augments existing global datasets to support large-scale analyses. Data curation involved extensive quality control processes to create a single, globally consistent data repository of instream barriers and reservoirs that are co-registered to a digital river network. Version 1.0 of the GDW database contains 41,145 barrier locations and 35,295 associated reservoir polygons representing a cumulative storage capacity of 7,420 km3 and an artificial terrestrial surface water area of 304,600 km2.

The scale at which low-carbon electricity will need to be deployed to meet economic growth, electrification, and climate goals in Africa is unprecedented, yet the potential land use and freshwater impacts from this massive build-out of energy infrastructure is poorly understood. In this study, we characterize low-impact onshore wind, solar photovoltaics, and hydropower potential in Southern Africa and identify the cost-optimal mix of electricity generation technologies under different sets of socio-environmental land use and freshwater constraints and carbon targets. We find substantial wind and solar potential after applying land use protections, but about 40% of planned or proposed hydropower projects face socio-environmental conflicts. Applying land and freshwater protections results in more wind, solar, and battery capacity and less hydropower capacity compared to scenarios without protections. While a carbon target favors hydropower, the amount of cost-competitively selected hydropower is at most 45% of planned or proposed hydropower capacity in any scenario—and is only 25% under socio-environmental protections. Achieving both carbon targets and socio-environmental protections results in system cost increases of 3-6%. In the absence of land and freshwater protections, environmental and social impacts from new hydropower development could be significant.

As governments and non-state actors strive to minimize global warming, a primary strategy is the decarbonization of power systems which will require a massive increase in renewable electricity generation. Leading energy agencies forecast a doubling of global hydropower capacity as part of that necessary expansion of renewables. While hydropower provides generally low-carbon generation and can integrate variable renewables, such as wind and solar, into electrical grids, hydropower dams are one of the primary reasons that only one-third of the world’s major rivers remain free-flowing. This loss of free-flowing rivers has contributed to dramatic declines of migratory fish and sediment delivery to agriculturally productive deltas. Further, the reservoirs behind dams have displaced tens of millions of people. Thus, hydropower challenges the world’s efforts to meet climate targets while simultaneously achieving other Sustainable Development Goals. In this paper, we explore strategies to achieve the needed renewable energy expansion while sustaining the diverse social and environmental benefits of rivers. These strategies can be implemented at scales ranging from the individual project (environmental flows, fish passage and other site-level mitigation) to hydropower cascades to river basins and regional electrical power systems. While we review evidence that project-level management and mitigation can reduce environmental and social costs, we posit that the most effective scale for finding balanced solutions occurs at the scale of power systems. We further hypothesize that the pursuit of solutions at the system scale can also provide benefits for investors, developers and governments; evidence of benefits to these actors will be necessary for achieving broad uptake of the approaches described in this paper. We test this hypothesis through cases from Chile and Uganda that demonstrate the potential for system-scale power planning to allow countries to meet low-carbon energy targets with power systems that avoid damming high priority rivers (e.g., those that would cause conflicts with other social and environmental benefits) for a similar system cost as status quo approaches. We also show that, through reduction of risk and potential conflict, strategic planning of hydropower site selection can improve financial performance for investors and developers, with a case study from Colombia.

Seasonal changes of temperature and precipitation cause inland open surface water and ice cover extents to vary dramatically through the year from local to global scales. These dynamics of land, water, and ice have a significant impact on climate and often are critical to natural ecosystem functioning. However, global seasonal dynamics of both water and ice extent have not been well quantified. Here, we present the quantification of monthly surface water and ice areas for 2019 with associated uncertainties. Time-series reference data were created for a probability sample of 10 m grid cells by interpreting the entire 2019 time-series of 10 m Sentinel-2 data and a subset of 3 m PlanetScope data in selected places with a mix of land and water. From the probability sample reference data, we estimate that 4.86 +/- 0.16 million km(2) had inland water presence at some point during the year. Globally, only 23% of the total area with water was permanent water that remained open year-round (1.13 +/- 0.19 million km(2)). Permanent water with seasonal ice cover extended 1.97 +/- 0.21 million km(2), comprising 41% of the total area with water. Seasonal water-land transitions (both with and without ice/snow cover) covered the remaining 36% of the total area with water (1.76 +/- 0.19 million km(2)). February had the maximum extent of ice over areas of inland permanent and seasonal water, totaling 2.49 +/- 0.25 million km(2), and January - March had a larger global extent of ice cover than of open water. To investigate the spatiotemporal distribution of ice cover and the suitability of Landsat, prototype maps of surface water ice cover phenology were created by integrating the ice/snow and no data labels from the quality assurance layer of the GLAD ARD of Potapov et al. (2020) with the monthly surface water layers of Pickens et al. (2020), both of which are Landsat- based. While limited by data availability, these maps reveal the high spatiotemporal variability of ice phenology. The near-daily observations near the poles and the 10 m resolution bands of Sentinel-2 provide unprecedented potential to examine surface water and ice dynamics for 2016 forward and to investigate the drivers and impacts of this variability.

Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth's largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multiobjective optimization to identify portfolios of sites that simultaneously minimize impacts on river flow, river connectivity, sediment transport, fish diversity, and greenhouse gas emissions while achieving energy production goals. We find that uncoordinated, dam-by-dam hydropower expansion has resulted in forgone ecosystem service benefits. Minimizing further damage from hydropower development requires considering diverse environmental impacts across the entire basin, as well as cooperation among Amazonian nations. Our findings offer a transferable model for the evaluation of hydropower expansion in transboundary basins.

Dams, reservoirs, and other water management infrastructure provide benefits, but can also have negative impacts. Dam construction and removal affects progress toward the UN sustainable development goals at local to global scales. Yet, globally-consistent information on the location and characteristics of these structures are lacking, with information often highly localised, fragmented, or inaccessible. A freely available, curated, consistent, and regularly updated global database of existing dams and other instream infrastructure is needed along with open access tools to support research, decision-making and management needs. Here we introduce the Global Dam Watch (GDW) initiative ( www.globaldamwatch.org ) whose objectives are: (a) advancing recent efforts to develop a single, globally consistent dam and instream barrier data product for global-scale analyses (the GDW database); (b) bringing together the increasingly numerous global, regional and local dam and instream barrier datasets in a directory of databases (the GDW directory); (c) building tools for the visualisation of dam and instream barrier data and for analyses in support of policy and decision making (the GDW knowledge-base) and (d) advancing earth observation and geographical information system techniques to map a wider range of instream structures and their properties. Our focus is on all types of anthropogenic instream barriers, though we have started by prioritizing major reservoir dams and run-of-river barriers, for which more information is available. Our goal is to facilitate national-scale, basin-scale and global-scale mapping, analyses and understanding of all instream barriers, their impacts and their role in sustainable development through the provision of publicly accessible information and tools. We invite input and partnerships across sectors to strengthen GDW’s utility and relevance for all, help define database content and knowledge-base tools, and generally expand the reach of GDW as a global hub of impartial academic expertise and policy information regarding dams and other instream barriers.

Long-term protection is needed to secure threatened freshwater ecosystems and the social and biodiversity values they provide. In the face of existing and future pressures, current approaches to freshwater protection are often inadequate for maintaining ecosystem values into the future. While terrestrial and marine ecosystem protection are well recognized and have area-based protection goals in global conventions, freshwater ecosystem characteristics have remained poorly represented in these goals. Freshwater ecosystems are commonly secondary or unaddressed components of area-based terrestrial protection. The design and management for terrestrial-based protection are generally inadequate for addressing freshwater ecosystem processes and attributes critical for maintaining their natural patterns and the values they provide to people and nature. Given that freshwater-dependent species are declining at a faster rate than marine and terrestrial species, and the reliance and use of freshwater ecosystems by people living around such areas, approaches to protect them must balance the needs of people and nature and accommodate these complexities.

Spatial prioritization is a critical step in conservation planning, a process designed to ensure that limited resources are applied in ways that deliver the highest possible returns for biodiversity and human wellbeing. In practice, many spatial prioritizations fall short of their potential by focusing on places rather than actions, and by using data of snapshots of assets or threats rather than estimated impacts. We introduce spatial action mapping as an approach that overcomes these shortfalls. This approach produces a spatially explicit view of where and how much a given conservation action is likely to contribute to achieving stated conservation goals. Through seven case examples, we demonstrate simple to complex versions of how this method can be applied across local to global scales to inform decisions about a wide range of conservation actions and benefits. Spatial action mapping can support major improvements in efficient use of conservation resources and will reach its full potential as the quality of environmental, social, and economic datasets converge and conservation impact evaluations improve.

Spatial prioritization is a critical step in conservation planning, a process designed to ensure that limited resources are applied in ways that deliver the highest possible returns for biodiversity and human wellbeing. In practice, many spatial prioritizations fall short of their potential by focusing on places rather than actions, and by using data of snapshots of assets or threats rather than estimated impacts. We introduce spatial action mapping as an approach that overcomes these shortfalls. This approach produces a spatially explicit view of where and how much a given conservation action is likely to contribute to achieving stated conservation goals. Through seven case examples, we demonstrate simple to complex versions of how this method can be applied across local to global scales to inform decisions about a wide range of conservation actions and benefits. Spatial action mapping can support major improvements in efficient use of conservation resources and will reach its full potential as the quality of environmental, social, and economic datasets converge and conservation impact evaluations improve.

Approximately one-third of long rivers remain free-flowing, and rivers face a range of ongoing and future threats. In response, there is a heightened call for actions to reverse the freshwater biodiversity crisis, including through formal global targets for protection. The Aichi Biodiversity Targets called for the protection of 17% of inland water areas by 2020. Here, we examine the levels and spatial patterns of protection for a specific type of inland water area-rivers designated as free-flowing. Out of a global total of 11.7 million kilometers of rivers, 1.9 million kilometers (16%) are within protected areas and 10.1 million kilometers are classified as free-flowing, with 1.7 million kilometers of the free-flowing kilometers (17%) within protected areas. Thus, at the global level, the proportion of rivers in protected areas is just below the Aichi Target, and the proportion of free-flowing rivers within protected areas equals that target. However, the extent of protection varies widely across river basins, countries, and continents, and many of these geographic units have a level of protection far lower than the target. Further, high discharge mainstem rivers tend to have lower extent of protection. We conclude by reviewing the limitations of measuring river protection by the proportion of river kilometers within protected areas and describe a range of mechanisms that can provide more effective protection. We also propose a set of recommendations for a more comprehensive quantification of global river protection.

Fine particles in rivers comprise a substantial fraction (>50%) of the mass leaving a landscape, while at shorter timescales they represent significant carriers of nutrients and contaminants with the potential to both degrade and enhance aquatic habitats. Predicting fine particle dynamics within rivers remains challenging due to a complex relationship between sediment and water availability from the landscape. This inherent complexity results in watershed-specific understandings of suspended sediment dynamics, typically parameterized as empirical functions of catchment land use, geology, and climate. However, observations of significant fine particle storage within river corridors may indicate that the flux of suspended sediment depends on reach-scale hydraulics. To better understand these dynamics, we synthesized over 40 years of suspended sediment concentration (SSC), hydraulic geometry, river flow, and grainsize data collected by the US Geological Survey from hundreds of rivers spanning a large variety of environments across the continental United States. This data synthesis reveals a strong nonlinear trend between reach-scale hydraulics and the suspended sediment flux, with a secondary dependence on particle properties. The multi-site synthesis reveals that by normalizing the suspended sediment flux by the bankfull shear stress and flux results in a collapse of the observed data onto a single function that describes a self-organizing structure for suspended sediment transport in watersheds. This general relationship indicates strong support for the role of autogenic processes in setting the flux of fine particles and erosion rates of watersheds.

Water insecurity is a defining feature of the Anthropocene, with degraded water quality and unreliable flows putting the well-being of upstream and downstream communities, both human and aquatic, at risk. Within this context, the protection of drinking water at its source - 'source water protection' - is growing as a complementary water security solution to conventional built infrastructure, particularly but not only to address non-point source pollution. An assessment of the likely source catchments of 4000 cities, supplying water to as many as 1.7 billion city dwellers, found that 85% of the total area of the catchments overlaps with freshwater ecoregions of high biodiversity value. Source water protection could contribute to conserving important freshwater biodiversity elements in these catchments, through activities such as land protection, restoration, and agricultural and ranching best-management practices. Empirical evidence supporting the benefits of these types of activities to freshwater species and ecosystems is sparse, especially when considered at the scales required to achieve meaningful conservation objectives. This article explores the potential of source water protection to deliver freshwater conservation benefits, and solutions are proposed to address the challenges related to evidence gaps, trade-offs, and financing. The broader opportunity for leveraging water security investments for biodiversity conservation, and the overall efficiencies that may accrue from optimizing for multiple benefits simultaneously, are discussed in the context of global frameworks such as the Sustainable Development Goals.

河流生态修复对于改善退化的河流生态系统具有重要作用.以美国缅因州佩诺布斯科特河的生态修复项目为例,介绍了一种流域生态修复系统规划方法,具体说明了方法的应用过程.该方法以流域为评估单位,以数据和多种分析方法为支撑;强调在规划之初开展以数据为基础的现状分析,并与利益相关方共同规划修复目标以保证项目长期可持续开展;根据威胁识别保护策略,定量地分析保护情景;最终选择可行的高生态效益保护方案.同时倡导在推动流域修复的同时实施监测与适应性管理,为保护项目的长效机制提供有效反馈.通过对比分析国内外河流生态修复在目标、理念、具体方法及项目监测调整上的差异,为今后国内的河流生态修复研究与实践提供参考.

1. The Strategic Plan for Biodiversity (2011-2020), adopted at the 10th meeting of the Conference of the Parties to the Convention on Biological Diversity, sets 20 Aichi Biodiversity Targets to be met by 2020 to address biodiversity loss and ensure its sustainable and equitable use. Aichi Biodiversity Target 11 describes what an improved conservation network would look like for marine, terrestrial and inland water areas, including freshwater ecosystems.2. To date, there is no comprehensive assessment of what needs to be achieved to meet Target 11 for freshwater biodiversity. Reports on implementation often fail to consider explicitly freshwater ecosystem processes and habitats, the pressures upon them, and therefore the full range of requirements and actions needed to sustain them.3. Here the current progress and key gaps for meeting Aichi Target 11 are assessed by exploring the implications of each of its clauses for freshwater biodiversity.4. Concerted action on Aichi Biodiversity Target 11 for freshwater biodiversity by 2020 is required in a number of areas: a robust baseline is needed for each of the clauses described here at national and global scales; designation of new protected areas or expansion of existing protected areas to cover known areas of importance for biodiversity and ecosystem services, and a representative sample of biodiversity; use of Other Effective Area-Based Conservation Measures (OECMs) in places where designating a protected area is not appropriate; and promoting and implementing better management strategies for fresh water in protected areas that consider its inherent connectivity, contextual vulnerability, and required human and technical capacity.5. Considering the specific requirements of freshwater systems through Aichi Biodiversity Target 11 has long-term value to the Sustainable Development Goals discussions and global conservation policy agenda into the coming decades. Copyright (C) 2016 John Wiley & Sons, Ltd.

Water funds seek to promote long-term watershed conservation with multiple benefits for biodiversity and human well-being. This approach has grown rapidly, particularly in Latin America where more than 30 water funds were in operation or development by 2014. To meet the need for evidence to guide ongoing decisions, we assessed the goals and strategies of 16 programs that were operating in 2013–2014 in association with the Latin American Water Funds Partnership. Our findings underscore the diversity within this approach to investment in watershed services. The various financial, governance, and management mechanisms adopted by these programs reflected their distinct biophysical, socio-economic, and political contexts. All 16 water funds aimed to secure water quality (15/16) and/or quantity (including the timing of flows) (14/16). The majority of programs also explicitly strived for co-benefits to local livelihoods (9/16) and biodiversity (11/16). Public funding secured through legislation provided the most funding to date, but private, NGO, and development bank source were also important for some programs. While programs have actively engaged rural land stewards, this stakeholder group was represented on governance boards in just 4 of 16 funds. Additionally, while the majority of water funds with activities on the ground (13/16) reported biophysical and social impact monitoring (8/16), many faced significant logistical, technical, and funding challenges to its implementation. We recommend greater inclusion of rural land stewards on governance boards, increased engagement of the private sector, and a sustained commitment to an evidence-based approach to increase the likelihood that programs will attain their goals.

The principles of systematic conservation planning are now widely used by governments and non-government organizations alike to develop biodiversity conservation plans for countries, states, regions, and ecoregions. Many of the species and ecosystems these plans were designed to conserve are now being affected by climate change, and there is a critical need to incorporate new and complementary approaches into these plans that will aid species and ecosystems in adjusting to potential climate change impacts. We propose five approaches to climate change adaptation that can be integrated into existing or new biodiversity conservation plans: (1) conserving the geophysical stage, (2) protecting climatic refugia, (3) enhancing regional connectivity, (4) sustaining ecosystem process and function, and (5) capitalizing on opportunities emerging in response to climate change. We discuss both key assumptions behind each approach and the trade-offs involved in using the approach for conservation planning. We also summarize additional data beyond those typically used in systematic conservation plans required to implement these approaches. A major strength of these approaches is that they are largely robust to the uncertainty in how climate impacts may manifest in any given region.

Rising energy consumption in coming decades, combined with a changing energy mix, have the potential to increase the impact of energy sector water use on freshwater biodiversity. We forecast changes in future water use based on various energy scenarios and examine implications for freshwater ecosystems. Annual water withdrawn/manipulated would increase by 18-24%, going from 1,993,000-2,628,000 Mm(3) in 2010 to 2,359,000-3,271,000 Mm(3) in 2035 under the Reference Case of the Energy Information Administration (EIA). Water consumption would more rapidly increase by 26% due to increased biofuel production, going from 16,700-46,400 Mm(3) consumption in 2010 to 21,000-58,400 Mm(3) consumption in 2035. Regionally, water use in the Southwest and Southeast may increase, with anticipated decreases in water use in some areas of the Midwest and Northeast. Policies that promote energy efficiency or conservation in the electric sector would reduce water withdrawn/manipulated by 27-36 m(3)GJ(-1) (0.1-0.5 m(3)GJ(-1) consumption), while such policies in the liquid fuel sector would reduce withdrawal/manipulation by 0.4-0.7 m(3)GJ(-1) (0.2-0.3 m(3)GJ(-1) consumption). The greatest energy sector withdrawal/manipulation are for hydropower and thermoelectric cooling, although potential new EPA rules that would require recirculating cooling for thermoelectric plants would reduce withdrawal/manipulation by 441,000 Mm(3) (20,300 Mm(3) consumption). The greatest consumptive energy sector use is evaporation from hydroelectric reservoirs, followed by irrigation water for biofuel feedstocks and water used for electricity generation from coal. Historical water use by the energy sector is related to patterns of fish species endangerment, where water resource regions with a greater fraction of available surface water withdrawn by hydropower or consumed by the energy sector correlated with higher probabilities of imperilment. Since future increases in energy-sector surface water use will occur in areas of high fish endemism (e.g., Southeast), additional management and policy actions will be needed to minimize further species imperilment.

ABSTRACTSustainable management of global water resources requires changing of dam operations to maintain river, floodplain and estuary ecosystems. Re‐operating dams for ecological objectives must be evaluated rigorously because of the complexity of ecological responses to streamflow, uncertainty in the long‐term and large‐scale conservation impacts on freshwater ecosystems and the foregone environmental or social benefits from other uses of water. Prescribed releases at five demonstration sites in the Sustainable Rivers Project, a partnership between the US Army Corps of Engineers (Corps) and The Nature Conservancy to plan and implement environmental flow prescriptions at Corps dams nationwide, have been evaluated in terms of their immediate and direct ecological outcomes. Advancing dam re‐operation as a freshwater conservation strategy at these and other sites will require additional evidence about longer‐term and broader impacts on biodiversity and ecosystems. A pragmatic framework for monitoring and evaluating dam re‐operation as a conservation strategy includes a balanced assessment of direct responses and long‐term effects, institutional partnerships that can implement monitoring and evaluation at an ecosystem scale and improved reporting of scientific investigations to facilitate long‐term monitoring and cross‐site learning. Copyright © 2011 John Wiley & Sons, Ltd.

Summary1. The Upper Yangtze River drains a catchment of c. 1 million km2 from its headwaters on the Tibetan Plateau to the city of Yichang below the Three Gorges Dam. The Upper Yangtze River Basin supports a diverse aquatic fauna, including 118 endemic fish species. The river basin has a long history of human use and environmental alteration and is further threatened by the demands of a large population and rapid economic development.2. We identified a set of areas that, with adequate protection and/or management, might maintain the aquatic biodiversity and ecological processes representative of the basin. Methods were developed to address the scope and scale of conservation planning across the entire Upper Yangtze Basin in a short time‐frame using available data. The analytical framework is a watershed hierarchy of five catchment size classes derived from a globally available hydrography dataset called HydroSHEDs. Catchments were assigned to ecosystem types according to catchment area and patterns of climate, catchment morphology, geology and sources of water. Catchments were also ranked by ecological condition using an index of cumulative anthropogenic impacts.3. We defined conservation priorities as a combination of expert‐designated focal areas that support endemic fish assemblages and habitat in good condition; sites selected with the conservation planning software MARXAN to meet representation targets for ecosystems and optimise ecological condition and longitudinal connectivity; and a set of rivers selected to provide refugia for fishes affected by a hydropower and flood control infrastructure development project.4. Areas selected as conservation priorities include 3200 km (27% of total length) of large rivers, 9900 km (39% of total length) of small rivers and 30% of small stream catchments in the basin. To evaluate the degree to which the set of conservation priority areas supports threatened and endemic fishes, we conducted a gap analysis using survey records and historic range maps of 131 threatened and/or endemic fish species. The conservation priority areas contain survey records or portions of the known historic range of 116 (88%) of the 131 species we evaluated, with an average of 49% of the survey records and/or 26% of the known historic ranges of each species.

Alaska’s North Slope is especially vulnerable to climatic change because higher latitudes are subject to positive snow- and sea ice-atmosphere feedbacks under warming conditions and because the dynamics of frozen seascapes and landscapes are tightly determined by thermal regime. Shifts in timing and magnitude of freeze–thaw processes are observed to have or expected to have non-linear, threshold-crossing impacts on sea ice, landforms, and biota. Observed changes in North Slope surface air temperatures and precipitation were non-monotonic over the last century, but have trended upward for the last several decades. These changes are linked to hemispheric climate dynamics, reflected in North Pacific and Arctic Oscillation circulation indices. Projected anthropogenic climate changes—with the possibility of continued warming, increased storm frequency and intensity, and decreased insulating snow cover—portend an uncertain future for this domain. Current or foreseen physical system shifts include: (1) declining seasonal and permanent sea ice extent and character, (2) rapid coastal erosion due to storm exposure over a longer near-shore ice-free season, (3) deeper soil active layer over warmer permafrost, along with altered thermokarst processes—contributing to thaw lake expansion, surface drainage re-organization, and hillslope instability. Biogeophysical responses encompass (1) modified surface-atmosphere energy balance from snow cover, vegetation, and hydrologic change and (2) shifted soil and wetland biogeochemical dynamics, including accelerated carbon efflux. Climate-driven plant community shifts on the North Slope result from the interplay of climate, vegetation response, and landscape processes. Some transitions involve stabilizing, others destabilizing plant-permafrost feedbacks. Impacts on caribou, migratory avifauna, and freshwater biota are through direct effects of climate on organism physiology and reproductive biology and indirectly through disruption of habitat mosaics (including along migratory routes) and shifts in competition and trophic linkages. The North Slope’s physical and biological vulnerabilities to shifting climate and observed leading indicators of change are compelling reasons for land managers to consider climatic instability as a threat in conjunction with other known stressors while seeking strategies for protection of this domain’s natural heritage and ecosystem services.