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Sustainable hydropower in the 21st century

Sustainable hydropower in the 21st century a,1 b a c d Emilio F. Moran , Maria Claudia Lopez , Nathan Moore , Norbert Müller , and David W. Hyndman a b Department of Geography, Environment and Spatial Sciences, Michigan State University, East Lansing, MI 48824; Department of Community Sustainability, Michigan State University, East Lansing, MI 48824; Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824; and Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824 This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected in 2010. Contributed by Emilio F. Moran, September 25, 2018 (sent for review July 27, 2018; reviewed by Carlos A. Nobre and Nigel John Smith) Hydropower has been the leading source of renewable energy environmental and social concerns made the costs unacceptable. across the world, accounting for up to 71% of this supply as of 2016. Since then, the contribution of hydropower to the United States’ This capacity was built up in North America and Europe between electrical supply has steadily declined to 6.1% of energy consump- 1920 and 1970 when thousands of dams were built. Big dams tion, and other energy sources, such as nuclear, gas, coal, solar, and stopped being built in developed nations, because the best sites for wind, began to replace it. Dam removal rather than construction has dams were already developed and environmental and social become the norm in North America and Europe, because many that concerns made the costs unacceptable. Nowadays, more dams are were built before 1950 are at the end of their useful lives, they would being removed in North America and Europe than are being built. be too costly to repair, many no longer serve their initial purpose, The hydropower industry moved to building dams in the developing and their social and environmental negative externalities became world and since the 1970s, began to build even larger hydropower unacceptable (7). European countries with favorable topography dams along the Mekong River Basin, the Amazon River Basin, and and rain patterns, such as France and Switzerland, continue to have the Congo River Basin. The same problems are being repeated: hydropower as an important part of their energy mix through disrupting river ecology, deforestation, losing aquatic and terrestrial technological innovations at existing dams. In contrast, 3,450 dams biodiversity, releasing substantial greenhouse gases, displacing thou- have been removed to date in Sweden, Spain, Portugal, the United sands of people, and altering people’s livelihoods plus affecting the Kingdom, Switzerland, and France (https://www.damremoval.eu). food systems, water quality, and agriculture near them. This paper Hundreds of dams were removed in the United States (546 from studies the proliferation of large dams in developing countries and 2006 to 2014) (7) and Europe at enormous financial cost. This sit- the importance of incorporating climate change into considerations of uation contrasts with what is happening in developing countries. whether to build a dam along with some of the governance and Developing countries, where millions of people are still not compensation challenges. We also examine the overestimation of connected to the electric grid (8), have been ramping up hydro- benefits and underestimation of costs along with changes that are electric dam construction for decades. These often involve needed to address the legitimate social and environmental concerns megaprojects, which repeat the problems identified with big dams of people living in areas where dams are planned. Finally, we propose built in the past by the United States and European nations: dis- innovative solutions that can move hydropower toward sustainable rupting river ecology, causing substantial deforestation, generating practices together with solar, wind, and other renewable sources. loss of aquatic and terrestrial biodiversity, releasing large amounts of greenhouse gases, displacing thousands of people, and affecting hydropower dams energy Amazon social and environmental impacts | | | | sustainability Significance e need innovative sustainable solutions to meet energy North American and European countries built many large dams Wdemands, guarantee food security, and ensure water until 1975, after which both started to abandon a significant availability around the globe. Over the years, dams have been part of their installed hydropower because of the negative used for land management and flood control; to store water for social and environmental impacts. However, there has been a irrigation and agriculture; to provide recreation and navigation, recent trend of new large hydropower dams being built in and to address management of aquatic resources (1, 2). There developing countries, particularly in megabiodiversity river basins, are over 82,000 large dams in the United States alone (3, 4). In such as the Amazon, the Congo, and the Mekong. The socioeco- addition, over 2 million small low-head dams fragment US rivers nomic and environmental damages in these river systems are (5), and their cumulative impacts are largely unknown, since they even greater than the early costs in North America and Europe. have escaped careful environmental assessment. This paper discusses how the hydropower sector needs to not Beginning in the late 19th century, the first hydroturbines were only focus on energy production but also, include the negative invented to power a theater in Grand Rapids, Michigan and then, social and environmental externalities caused by dams and rec- to power streetlights in Niagara Falls, New York. Alternating ognize the unsustainability of current common practices. current then made possible the first hydropower plant at Redlands Power Plant, California in 1893. Beginning in the 1920s, the US Author contributions: E.F.M., M.C.L., N. Moore, N. Müller, and D.W.H. designed research; Army Core of Engineers began to build hydropower plants. The N. Moore prepared the SI Appendix; and E.F.M., M.C.L., N. Moore, N. Müller, and D.W.H. Tennessee Valley Authority in 1933 developed hydropower in the wrote the paper. Tennessee River with the clearly stated goal of promoting rural Reviewers: C.A.N., Institute for Advanced Studies–University of São Paulo; and N.J.S., University of Florida. electrification, later widely imitated throughout the country—the most notable being the Hoover Dam in 1937. The New Deal gave The authors declare no conflict of interest. an enormous boost to hydropower construction, tripling output in This open access article is distributed under Creative Commons Attribution-NonCommercial- NoDerivatives License 4.0 (CC BY-NC-ND). 20 years until it accounted for 40% of electrical use in the United States (6). Hydropower dams were an important part of North See QnAs on page 11863. American and European energy development. To whom correspondence should be addressed. Email: moranef@msu.edu. Starting in the late 1960s, big dams stopped being built in de- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. 1073/pnas.1809426115/-/DCSupplemental. veloped nations, because the best sites for dams were already de- veloped, the costs became too high, and most importantly, growing Published online November 5, 2018. www.pnas.org/cgi/doi/10.1073/pnas.1809426115 PNAS | November 20, 2018 | vol. 115 | no. 47 | 11891–11898 SUSTAINABILITY INAUGURAL ARTICLE SCIENCE the food systems, water quality, and agriculture near them (9–12). changes in the ecological system brought by big dams alter their The sustainability of these undertakings is commonly insufficiently livelihoods in negative ways (35, 36). A report of the World scrutinized by those promoting them. The priority in large dam Commission on Dams (WCD) (37) documented the socioeco- construction is to generate energy to serve growing industries and nomic problems due to dam development projects; 40–80 million urban populations—these two things often overwhelm socioeco- people were displaced, and it has proven challenging to resettle nomic and environmental considerations (13). Left behind are lo- them properly. Scudder (38) estimates that 80 million people cal communities saddled with socioenvironmental damages and were displaced in the last century because of dams. In addition, loss of livelihoods (14). Often, they do not even gain access to the living conditions and food security of communities living electricity, because they are not provided the power from the large downstream are often placed in peril. In the Tucuruí Dam region dams, and they are not sufficiently compensated for their disrupted of the Brazilian Amazon, the fish catch declined by 60% almost lives. All countries need renewable energy, and hydropower should immediately, and more than 100,000 people living downstream be part of this portfolio. However, there is a need to find sus- were affected by the loss of fisheries, flood recession agriculture, tainable and innovative solutions that combine hydropower de- and other natural resources (37). A conservative estimate is that velopment with other energy sources, thus providing benefits that 472 million people worldwide have been negatively affected by will outweigh, reduce, or even eliminate the negative environmental, dam construction downstream from dams (39). However, the behavioral, cultural, and socioeconomic externalities resulting from impact on downstream communities is still understudied (40). large dams. Large dams seem to be everything that one should not try to Here, we review the socioeconomic and environmental situation build if one cares about sustainability. To move toward sustain- in several major river basins where dams are being built. We ex- ability, future hydropower development needs to give more at- amine the proliferation of large dams in developing countries, the tention to how climate change may affect hydropower production lack of attention to climate change in the decision of whether to and make greater efforts to reduce the environmental and social build a dam, some of the governance and compensation chal- costs borne by people near the dams. In addition, those harmed by lenges, and the overestimation of benefits and underestimation of the dams need to be adequately compensated, the number of costs. We also identify changes that are needed to address the people that must be resettled should be reduced, and most im- legitimate social and environmental concerns of people living in portantly, innovative technologies that reduce all of these negative areas where dams are planned and propose innovative solutions to outcomes should be developed, especially instream turbines and meet the food, water, and energy needs of citizens in those regions. other forms of renewable energy. These solutions have relevance worldwide, as hydropower can also Dams, Climate Change, and Land Use Change contribute to meeting goals of reducing fossil fuel emissions and building sustainable communities with diversified energy sources. Hydropower development in developing countries seems to overlook climate change scenarios. In developed countries, some Hydropower in Developing Countries dams (e.g., Hoover Dam) are already putting new turbines at a An estimated 3,700 dams that produce more than 1 MW are lower elevation to prepare for projected future water shortages either planned or under construction primarily in developing in the Colorado River due to climate change. Lake Mead, which countries (15). It is easy to understand why: hydropower repre- stores the water for the Hoover Dam, has seen a 40% decline in sents the largest renewable source of electricity (71% of global its water level (41); despite technology improvements, its peak production of renewable energy) (16), and it is estimated that power output is down from 2 to 1.5 GW. Improvements have only 22% of the global potential is exploited to date (15). Sub- also been successfully undertaken in the Southeast United States stantially increasing the share of renewable energy in the global in several dams through the relicensing process that mandates energy mix by 2030 is among the Sustainable Development improvements in river flows, facilitating fish migrations and en- Goals. Hydropower development is a global phenomenon and hancing dissolved oxygen levels in water discharges to maintain multinational in its significance. It is affecting the most impor- river ecology (42). According to a recent US Energy Information tant river basins in the world, including the Amazon, the Congo, Administration Outlook, the vast majority of the world’s newly and the Mekong (12, 17), creating enormous disruption in these installed renewable energy over the next 25 years will come from ecologically important regions. The financial costs of the dams hydroelectric dams, mostly in the developing world. Here, cli- are immense, and many believe that the benefits do not outweigh mate change impacts are already felt but again, are not being the costs (18, 19). The hydrologic consequences of large-scale addressed by dam builders. Projections for the Amazon Basin dams and reservoirs are extensive (20); however, microhydro- point toward a broad drying trend in the southern and eastern power is largely a net positive for communities and has minimal regions (ref. 43, figure 27–2), especially under higher-greenhouse environmental impact (21, 22). Sharp declines in available gas emissions scenarios. Variability (particularly in droughts) has freshwater due to dam construction drive seasonal changes in also been increasing for these regions (43, 44); this is projected river discharge as well as loss of downstream freshwater habitat, to continue and will diminish reliable water supplies to dams. floodplains, and even coastal erosion and salinity changes (23–26). The Jirau Dam and Santo Antonio Dam on the Madeira River in The negative consequences for ecosystem structure and compo- the Brazilian Amazon, completed only 5 years ago, are predicted sition (e.g., habitat fragmentation, loss of aquatic and terrestrial to produce only a fraction of the 3 GW each that they were biodiversity) and function (e.g., nutrient flows, primary pro- projected to produce because of climate change and the small duction) can be severe (7, 18, 19). Reservoirs can also be signifi- storage capacity of run-of-the-river reservoirs. The Belo Monte cant sources of greenhouse gases, especially methane (10, 23, 27– Dam on the Xingu River, completed in 2016, will also produce 30), and reductions in river flow can increase pollutant concen- less due to climate variability and a relatively small reservoir: trations (31, 32). only 4.46 of the 11.23 GW that it was built to generate even in The human costs of large dams are no less important. The optimistic scenarios in 10 of 12 mo of the year due to insufficient social, behavioral, cultural, economic, and political disruption water levels (43, 45). Since 2005, the Amazon has experienced that populations near dams face are routinely underestimated three droughts that broke all historical records (and 3 extreme (19, 33, 34). Ansar et al. (18) in a global analysis of 245 large flooding years) (46, 47). Most climate models predict higher dams built between 1934 and 2007 found that costs of large dams temperatures and lower rainfall in the Xingu Basin, the Tapajos were 96% higher than predicted costs and that 1 out of 10 large Basin, and the Madeira Basin (43, 44). The intensity and fre- dams cost up to three times more than originally estimated. For quency of extreme events continue to challenge the energy fishermen relying on fishing resources for their subsistence, the promises from investments in large hydropower projects. 11892 | www.pnas.org/cgi/doi/10.1073/pnas.1809426115 Moran et al. Hydropower is the world’s primary renewable energy resource, of sediment load on the river, sedimentation problems occur but questions have been raised about its reliability under pro- faster than loss of structural integrity (60). Before 1960, sedi- jected climate change. In Brazil, which depends on hydropower mentation rates were not consistently factored into dam design for up to 67% of its electrical energy (48), this is a crisis waiting criteria; thus, many dams are expected to fill at rates exceeding to happen. However, the response to likely reduced capacity from design expectations (61, 62). Today, engineers typically design climate change has been to accelerate dam construction in these reservoirs to incorporate a 100-year sediment storage pool. subbasins, even when this has meant not following international However, these calculations often fail to include changes in laws of free and open consultation with local and indigenous watershed land use (such as road construction, which can in- people (49), rather than investing in technologies with lesser en- crease sediment yield by two orders of magnitude) and projected vironmental impact, such as instream turbines (50, 51), and extreme events due to climate change that will likely increase investing in other sources of renewable energy, like solar, biomass, sediment transport toward reservoirs. This tendency to overlook and wind, to diversify the energy mix (45, 52). More concerning is factors that could increase sediment loads continues today in the plan that most future hydropower in South America will come tropical countries. For example, the Madeira River carries 430 from the river-rich Amazon Basin, where there will likely be se- Mt of sediment per year (63), which is orders of magnitude greater rious environmental and social consequences (36). The same can sediment than most rivers. Two dams were completed during this be said for Asia, where the Mekong is currently being dammed at decade on the Madeira—Jirau and Santo Antonio—and addi- an accelerating pace (53, 54). These basins contain 18% of global tional ones are planned, despite numerous warnings that their freshwater fish diversity (17); therefore, the construction of dams designs have underestimated the high sedimentation rates (64–66). in these basins poses a threat to fish biodiversity and imperils the In less than 5 years since their completion, experienced dredgers food security of the region’s inhabitants. who earlier mined for gold in the Madeira (and who had been In a similar manner to climate change, dam builders frequently removed from the area to build the dam) have had to be called fail to consider the effects of land use change on the hydropower back to remove sediment accumulating in these two reservoirs at potential of a dam. Stickler et al. (14) examined the loss of energy “unexpected” rates according to the dam builders. This is an un- generation potential under deforestation scenarios in the Amazon justified surprise given the number of scientific papers that had River Basin. In the Xingu Basin, site of the Belo Monte Dam, they warned about the likelihood of such rapid sedimentation (64–67). estimate that ∼38% of the industry’s power estimates could be Areas at Risk reduced due to predicted deforestation and that power generated could fall below one-half of installed capacity in all but 2 months of Some river basins are being targeted for hydropower develop- the year (14). Regional deforestation can inhibit rainfall and soil ment given their potential to produce energy but with little moisture sufficiently in tropical moist forest regions to constrain consideration to reducing the environmental and social conse- energy generation (55). One-half of precipitation in the Amazon quences of such energy development. A summary table of rele- Basin is estimated to be due to internal moisture recycling; thus, vant comparative data for three megadiversity rivers is included deforestation can reduce precipitation independent of the expected in SI Appendix. decline from global climate change(56).Relianceonlarge dams The Amazon Basin—an area of 6 million km —is the location for generating hydropower can be questioned as a reliable strategy of 147 planned dams, 65 of which are in Brazil (68). Brazil is also under climate change scenarios. Alternatives that can address the investing in developing hydropower resources in Bolivia and Peru energy production shortfall in drought years need to be considered. with a view to buy their energy—estimated at 180 GW in Peru and A recent assessment found that the best scenarios include rapid 20 GW in Bolivia (69). The scale is multinational and will affect development of wind, biomass, and solar to complement the very high-biodiversity ecosystems along with a rich diversity of existing installed hydropower. The latter is not expected to meet ethnic and cultural groups and the wellbeing of millions. Brazil has the demands of the future, which will be more reliably provided by among the largest hydroelectric potential in the world, estimated a complement from solar, biomass, and wind power generation, at 260 GW (41% of this is in the Amazon Basin), making it certain with existing hydropower providing stability to the grid (52). that hydropower projects will continue to be constructed (45). The Xingu Basin, the Tapajos Basin, and the Madeira Basin account Dam Failures and Dam Removal for ∼80% of the Amazon Basin potential (Table 1). It is easy to forget, as one seeks “green energy” technologies, that The Amazon River system holds the most diverse fish assem- dams have a finite lifespan (i.e., that they are not really a sustain- blages on Earth (70) and one of the most productive inland fish- able long-term strategy). Dams being built in Brazil are planned for eries (71, 72). There are some 2,320 fish species in the Amazon a 30-year lifespan, which could be extended with technical retrofits Basin, whichisthe most by farofany riversysteminthe world(17). and newer turbines (45). Two sources of dam failure are the aging The Congo is next with 1,269 species, and then, the Mekong is third of the construction materials and accumulation of sediment behind with 599 species. Local livelihoods and diets of riverine populations the dam impoundment. As dams age, they are prone to failure, depend heavily on these fisheries that provide the main source of sometimes resulting in numerous fatalities and great loss of prop- animal protein (73–76). Impacts of dams on fisheries in the Ama- erty. Heavy rains from a single tropical storm in 1994 caused more zon Basin have been studied, showing that the dams have affected than 230 dams to fail in Georgia (57). The Oroville Dam Spillway fish populations and fish dynamics. After dams were installed on began to fail in California in 2016 after heavy rains, resulting in the the Tocantins River, the number of fish was reduced by 25% (77). evacuation of 190,000 people from their homes. More famously, The blockage of fish migration has been described as one of the the Teton Dam in Idaho failed in 1976, with resulting losses ex- main impacts (65, 75, 78, 79). There is also strong evidence that the ceeding $2 billion in 2017 dollars. Many US dams have significant changes in sediment movement associated with dams modify car- potential for failure. Many built during the peak construction pe- bon and phosphorus availability, thus altering fisheries (80). riod in the United States (1930–1950) are past their 50-year life- The Mekong Basin has become the world’s top investment span, with 85% of them reaching that milestone by 2020 (58). region for large hydropower dams, mostly from China; 72 new The cost of repairing a small dam can be up to three times the projects are planned in Laos, 10 are planned in Sarawak cost of removing it (59), which is an important reason for the Malaysia, and more than 50 are planned in Cambodia (81, 82). growing trend to remove dams today. If the costs of dam removal In the Mekong River, there are currently 11 hydropower dams were considered in a dam’s costs, would their construction be under construction; 60 million people who live off the rich justified? More than 60 dams per year are being removed in the fisheries on that river will be affected by dams, with the potential United States, a trend that began in 2006. Varying by the amount loss in livelihoods expected to be greater than US $2 billion, Moran et al. PNAS | November 20, 2018 | vol. 115 | no. 47 | 11893 SUSTAINABILITY INAUGURAL ARTICLE SCIENCE Table 1. The three largest Brazilian watersheds and their hydroelectric potentials (Agência Nacional de Aguas 2013 and Empresa de Pesquisa Energética 2015) Percentage of total hydroelectric Basin Total area (km ) Hydroelectric potential (MW) potential in the Amazon Madeira 548,960 14,700 19 Xingu 509,685 22,795 30 Tapajos 492,263 24,626 32 which is equivalent to the value of their fish catch. The potential of activists, and assassinations was common (92). This is a result of hydropower in the Mekong is about 53,000 MW, with 23,000 of a failure of the hydropower sector to address governance and MW in the Upper Mekong Basin (China) and 30,000 MW in the sustainability issues. Communities affected by dams have fre- Lower Mekong Basin [Lao People’s Democratic Republic (PDR), quently complained about the lack of consultation and attention Thailand, Cambodia, and Vietnam]. The basin is one of the most to known negative impacts on society and environment as well as productive and diverse inland fisheries in the world (83), and 16% the questionable promises made by the energy sector (cheaper of species are threatened by the dam construction (84). energy bills, more jobs, better infrastructure, such as schools and The Congo River is the world’s second largest in terms of flow hospitals). Benefit-sharing mechanisms, such as compensations, (42,000 m /s) after the Amazon and the second longest river in were proposed by the WCD report as a way to share the benefits Africa (4,700 km) after the Nile River. The Inga megadam is of the dams with local communities (93, 94). In Brazil, munici- planned on the largest waterfall in the world by volume (Inga palities are supposed to get some revenues from dams; however, Falls). The proposed massive dam is part of a dream to develop a these resources sometimes never arrive (95). In Belo Monte, power grid across Africa that will spur the continent’s industrial Santo Antonio, and Jirau, which were installed on the Brazilian economic development. Grand Inga could produce up to 40,000 Amazon, the electric bills of people went up rather than down, MW of electricity, over twice the power generation of Three and the jobs promised to locals went mostly to outsiders and Gorges Dam in China and more than one-third of the total disappeared within 5 years. Community organizers and indigenous electricity currently produced in Africa. However, rather than leaders are the most frequent targets of violence and repression this development improving the lives of locals, plans are to export (36, 92, 96–98). the energy produced to South Africa to cater to mining companies Millions of people worldwide are affected by dam construction (85). Ninety-one percent of the people in the Democratic Re- either because they are permanently resettled due to the filling public of Congo have no electricity, and yet, the continent’s biggest of the reservoirs or because their livelihoods get disrupted with infrastructure investment, at US $80 billion, would benefit the construction and operation of the dam (86). However, there mining with little benefit to the Congolese people (https:// do not seem to be mechanisms to fully compensate them for www.internationalrivers.org/campaigns/grand-inga-dam-dr-congo). their losses (99). People who are displaced often get an under- valued price for their land or buildings that does not consider the Role of Governance in Hydropower’s Sustainability social, cultural, and religious value of their land or the way that Whether in the Amazon, the Congo, or the Mekong, the most people make their livelihoods on the land or the stretch of river overlooked dimension of hydropower projects is the effects on (96, 100, 102). In addition, it does not consider that, after local social systems and institutions (84, 86, 87). Local commu- resettlement, people often lose their social networks and other nities typically do not have a significant say in hydropower de- types of social wealth, which has economic, cultural, social, and velopment (88, 89). This results in a decoupling of decision health consequences (86, 99). Communities that are not dis- making that can result in local priorities being overlooked and placed, like those that are downstream, generally do not get any the interests of urban industrial sectors driving decisions. In compensation, although the effects of the dam on their liveli- addition, policies and regulations are often regional or national hoods are just as great as the effects on those who require and commonly do not recognize the transboundary system dy- resettlement (39, 102). This problem seems to be even more namics, thus neglecting important considerations, such as rights, significant considering that most people affected by the dam are social and cultural values, and access to resources (90, 91). In- the poorest and more vulnerable in their societies, and they are stitutions can be specific to each sector (e.g., water allocation often indigenous and traditional communities (19). Monetary or regulations, property rights, renewable energy policy tools) as nonmonetary compensation mechanisms should consider that well as apply across sectors (e.g., political and civil rights, de- men and women are impacted differently by a dam and ensure centralization policies). Similarly, institutions can operate at that the most vulnerable are compensated (102). different scales of governance (i.e., local rules and norms, state As one seeks to build a just and sustainable hydropower sector regulations, national laws) and shape how groups make food, it is important to build mechanisms that guarantee that exter- water, and energy choices. However, one needs to start thinking nalities will be internalized; in other words, those who benefit about the governance not as three different sectors but as a from hydropower and are far away (and thus do not face exter- nexus, in which multiple layers account for the different scales, nalities from its exploitation) need to compensate local pop- levels, and sectors (90). Institutional analyses of case studies ulations where hydropower is produced to offset the negative become necessary to create an integrated policy assessment of costs from energy production (13). They should also offset the the cases under consideration. For example, energy production heavy losses from transmitting power across great distances. A through water appropriation highlights local–regional–national– key function for institutions is reducing transaction costs that transnational tradeoffs, in which water, energy, food, and liveli- hinder the identification of such inequities and externalities as hood costs and benefits are inequitably treated. well as the functioning of offset programs. Often, large dams are promoted with the idea that locals will Creating compensation mechanisms that are not always mone- gain some benefits out of them. However, the evidence suggests tary is an important innovation needed for future energy devel- otherwise. A recent study using a database of 220 dam-related opment plans. To date, little attention has been given to conflicts found that, in dams surrounded by controversies and compensation forms that strengthen communities and individuals conflict, the use of repression, criminalization, violent targeting affected by dams. This can be done by investing in understanding 11894 | www.pnas.org/cgi/doi/10.1073/pnas.1809426115 Moran et al. the social capital and history of these communities and working allow running fish to spawn rather than die trying. At Belo with them to sustain the integrity of their social, economic, and Monte, 16.2 tons of fish died, as they were unable to get past the political relationships. The contrary has been more common: dam during the 2016 migration (107). Prioritizing energy pro- resettling people without concern for any of these issues and duction at the expense of the fish biodiversity and abundance in sometimes, even seeming to purposely break up any preexisting the rivers must stop. Releases of water from a dam should mimic social organization as a way of preventing their ability to act a river’s natural seasonal fluctuations to maintain stream health. after the dam is built to lobby for adequate compensation (103). Experiments in Sweden that mimic the natural stream flow were able to improve the quality of the downstream ecology with only Innovative Solutions for Hydropower small reductions in hydropower production (108). Several things are needed to transform the hydropower sector to (iv) Energy generation through dams requires thinking about enable the benefits to exceed the costs and to ensure that dams the governance implications of the dam construction and associ- contribute to sustainable energy systems. (i) Environmental impact ated energy distribution and use. Policy makers often see energy as assessments (EIAs) and social impact assessments (SIAs) need to the entry point to the system and use water as a way to generate it be capable of stopping a dam from being built. (ii)EIAsand SIAs without recognizing the effects on food and livelihoods. The three must be carried out by firms serving citizens rather than the dam sectors are dependent on each other, but policies are rarely con- builders, and they are essentials tools worldwide, whether in Brazil ceived with a nexus approach, which has to change. The challenge or Europe (104). (iii) Hydropower designs need to truly allow fish is even larger when the food–water–energy nexus has implications passage and mimic the seasonal river flows. (iv) Better governance that go beyond one country, either because the impacts are suf- needs to be created around dams. (v) Greater transparency with fered by different countries or when multinationals or different society about the true costs and benefits (including social, cultural, states are involved in the construction or distribution of energy. economic, political, and environmental costs and the costs of dam The current construction of binational hydroelectric dams on the removal at the end of the dam lifespan) is needed. (vi) Sustain- Bolivia/Brazil border is a clear example of this challenge. Flooding ability evaluation measures from the design through operation from Jirau has led to flooding in Bolivia (36). stage should be used. (vii) Innovative technologies that do not (v) To overcome the limitations of current dam-building prac- require damming the river or resettling population are needed. tices, one needs to incorporate how regional to national policies Addressing these issues can transform the hydropower sector. affect the local issues in the design of dams, and such information (i) EIAs and SIAs need to have real teeth. They should be needs to be made available to the likely affected societies in a carried out with sufficient lead time to provide a credible assess- transparent manner. There is a lack of regional to multinational ment and have built-in capacity to stop the building of a dam if planning that considers the impacts of dams in a manner that needed protections to biodiversity and human populations are not ensures connectivity of the ecosystems (109, 110). The goal is to in place (33). Public hearings and sufficient social engagement improve assessments to incorporate community concerns and to addressing the consequences from the dam have to be allowed design new dams in ways that they can improve livelihoods by before final approval is given. SIAs are fundamentally important increasing crop productivity, maintain fisheries yields, increase to determine how many people will need to be resettled and lay food security, and improve access to water and energy from the out the mechanisms for appropriate indemnity and compensation. project. Following WCD recommendations or a rigorous cost/ There also need to be mechanisms to ensure that these recom- benefit analysis would have resulted in Belo Monte not being built. mendations are carried out rather than leaving this up to the The analysis showed that there was a 72% chance that the costs of construction companies (33). Compliance with Article 169 of the Belo Monte would be greater than the benefits (111), something International Labor Organization (105), requiring previous and that has proven correct. By the guidelines set out by Scudder (86), free consultation with indigenous and traditional populations, an experienced scholar of dams and resettlement across the world, should be expected as part of the predam planning in a manner many or even most large dams should not have been built. Those that allows full discussion of the pros and cons without under- guidelines and those of other bodies, such as the WCD, agree on estimating costs and inflating benefits to those affected. much of what is wrong with the current rush to build large dams (ii) EIAs and SIAs should not be carried out by the firms and the apparent difficulty in meeting those minimal guidelines. engaged in building the dam or their subsidiaries (as is currently New tools are being proposed by scholars that permit basin- common in some countries); these need to include biodiversity wide policy instruments using existing laws. For example, the and social impact studies by independent organizations respond- multinational Amazon Cooperation Treaty and Brazil’s National ing to civil society with no conflict of interest with the government, Water Law (112) promote integrated water management and energy sectors, or construction companies. Actual practice sug- could be tools to change how decisions are made. An in- gests that EIAs and SIAs are commonly carried out by consulting ternational panel of experts could use existing knowledge to firms hired by and responding to prospective dam builders, and determine vulnerabilities using tools, such as the Dam Envi- their data and results are often not made publicly available to ronmental Vulnerability Index (113), at the subbasin scale. stakeholders until long after the dam is built. Benefits are rou- These tools and engaged civil society and other stakeholders in a tinely inflated, and costs are minimized in current EIAs and SIAs joint panel could more accurately consider the environmental (33). When benefits are not forthcoming and costs are large, the and social costs. The energy sector in countries like Brazil and population ends up in court seeking compensation for damages, India has recently promoted and begun constructing small dams and these costs are paid by society and not by the dam builders. or PCHs as a more benign technology than large dams, yet there (iii) At present, most devices (“ladders”) to help migrating is very little evidence for this claim (45). The United States has a species get across dammed areas do not work or are not even put long history of building low-head or small dams (2 million of in place. Targets for fish passage are being missed by several them); however, Fencl et al. (5) note that the claim of their orders of magnitude—even in the best of cases, only 3% make it minimal impact is largely untested. By virtue of their abundance, (106); the authors make a case to admit the failure of these small dams can substantially impact flowing aquatic ecosystems ladders and propose dam removal in cases where fish passages (114). Small hydrodams possess the same characteristics as large are not working. They propose a cautionary tale for developing dams, with the only difference being their size. China and India countries’ current efforts, arguing that fish passages do not are the current leaders in small hydrodams. Their power gen- compensate for the damage to the fisheries, since they generally eration benefits, particularly in isolated mountainous terrain, do not work. This needs to change, and attention must be given cannot be dismissed. However, their ecological, hydrological, to greatly improved designs that avoid species extinctions and and social impacts should be scrutinized just like large dams, and Moran et al. PNAS | November 20, 2018 | vol. 115 | no. 47 | 11895 SUSTAINABILITY INAUGURAL ARTICLE SCIENCE more importantly, they are losing ground to wind power in en- that the optimal scenario is one in which wind energy leads the ergy auctions (i.e., their cost per kilowatt is no longer competi- way, with biomass and solar further strengthening a diversification tive compared with wind power generation). Small hydropower is of the electric sector. Hydropower will continue to provide a subject to both environmental impact assessments and environ- substantial foundation of base energy, but the growth in the next mental impact reports when power produced is above 10 MW, two decades is expected to favor wind, biomass, and solar and they are considered as having a high impact on the envi- production (52). ronment in existing legislation (115). The hydropower industry needs sustainability evaluation mea- (vi) One alternative to traditional damming of rivers that sures that can stand public and independent scientific scrutiny. should be considered is instream turbine technology (50, 51), Many of these have been proposed but are rarely implemented. The also known as “zero-head.” This offers a less ecologically in- recommendations of the WCD provide guidelines for social and trusive means to tap into hydropower without many of the neg- environmental sustainability for hydropower projects. Since 2001, ative externalities identified earlier in this paper. Instream the WCD guidelines have influenced international accords, finan- turbines are suitable for rivers with flow velocity exceeding cial safeguards, and national laws. For example, the WCD recog- −1 1ms and can produce steady power (also known as “base nized the importance of a full evaluation of energy options to meet power”), since the flow velocity in rivers typically varies much energy mix needs before putting a hydropower project on paper. less than wind. Hydrokinetic energy has been used for a long The WCD also promotes alternative siting scenarios for dams that time since the time when river currents were harnessed to crush are already assumed will be approved. Too frequently, energy and grains in mills. New small turbine technologies have been quietly water planning is secretively guarded by governments (sometimes in developing to harness base power, and large turbine companies collusion with dam builders), is closed to the participation of civil (e.g., Voith) are developing smaller turbines and have tested and society, and does not follow the WCD guidelines. For hydropower shown their potential value (116, 117) in six continents and at planning to become sustainable, government and industry must hundreds of sites (116). Such turbines can be low maintenance, prioritize transparency by inviting civil society to the table to discuss be ecologically friendly to fish, and serve local communities’ and agree on what a country’s energy matrix should look like. A energy needs in a green manner. A number of smaller companies growing chorus of scholars across fields of science is calling for (116–118) are testing prototypes and moving toward com- modular solutions that combine wind, solar, and hydropower to mercialization. Smart HydroPower has already commercialized provide alternative energy sources that are environmentally, so- 40 instream turbines worldwide (https://www.smart-hydro.de). cially, and financially desirable (45, 52, 122). Instream technology These companies seem to be conscious of the importance of can provide off-grid energy for isolated communities, such as those delivering energy to local communities and of the need to reduce in the Amazon and other regions where distance and isolation keep negative impacts of large hydropower dams. Recent corruption them without access to energy, thereby enhancing their access to scandals in Brazil surrounding Belo Monte, where huge payoffs inexpensive energy and providing sustainable energy for economic were made to politicians to approve the dam despite strong development; that, when combined with solar panels on individual evidence against building it, suggest that the motivation for fa- homes to complement the instream hydropower, gives them energy voring big dams may be tied to complex webs of corruption or security. One could also install instream turbine parks as a much particular financial interests. This may be widely true, particu- less disruptive alternative to small dams and produce energy at larly in places with either authoritarian regimes and/or where much lower cost to local communities and the grid. financial interests favor large projects, such as big dams, because The most important advantage of hydropower in contrast to they offer considerable opportunities to divert funds (119). Of other renewable energy sources, like wind and solar, is that it can the $11.1 trillion expected to be spent on global infrastructure be dispatched quickly at any time, enabling utilities to balance load between 2005 and 2030, $1.9 trillion will be spent on hydropower variations on the electric distribution system (123). As we move projects (120), and 60% of those funds involve civil construction forward in the 21st century, electric companies need to diversify and resettlement costs, both areas known to be susceptible to their energy projects even more than they have. The cost of solar diversion of funds (119). Corruption risks start with undue in- and wind is dropping, efficiencies are up, and increasingly, they are fluence on the selection of sites, undue influence from project price competitive for the energy produced. Hydropower can be developers, bribes, and misappropriation of funds (121). Such part of a sustainable future if it moves away from big dams and corruption undermines public trust in hydropower and under- toward a combination of instream turbines and diversified energy mines its sustainability. The current trend to build large dams in sources in ways that do not disrupt stream ecology and fisheries developing countries may be characterized in this manner, and and the lives of people on the great rivers of the world. Existing global financial institutions should refuse to be a part of such dams in places like Brazil already produce substantial energy schemes. Scudder (86) argues that the World Bank Group, as for the integrated grid, and what is needed is investment in the largest sponsor funding large dams, should take the lead to diversification with solar and wind power. Hydropower has an ensure that their funds meet international standards for envi- important role to play as a provider of inexpensive energy ronmental restoration and compensation to communities. Voi- complemented by instream hydro and partnering with solar, vodic and Nobre (46) suggested that increasing hydropower biomass, and wind to provide power toward a sustainable future. capacity from the Amazon is not necessary; instead, they pro- pose innovations in biologically inspired technologies (biomass ACKNOWLEDGMENTS. We thank National Science Foundation Grant 1639115 energy production for example) as a way to outgrow the current and Fundacao de Amparo a Pesquisa do Estado de Sao Paulo Grant 2012/ model of development, which fails to consider the value of 51465-0 for providing support for this research. None of these agencies should biodiversity and cultural diversity in its calculations. Recent as- be held responsible for the findings and results presented herein as they are sessment of alternatives for the future of energy in Brazil suggests the sole responsibility of the authors. 1. Tullos D, Tilt B, Liermann CR (2009) Introduction to the special issue: Understanding 4. US Army Corps of Engineers (2016) National Inventory of Dams. Available at nid. and linking the biophysical, socioeconomic and geopolitical effects of dams. usace.army.mil/. Accessed October 12, 2018. 5. Fencl JS, Mather ME, Costigan KH, Daniels MD (2015) How big of an effect do small J Environ Manage 90(Suppl 3):S203–S207. 2. 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Energy Policy 36:4048–4056. 11898 | www.pnas.org/cgi/doi/10.1073/pnas.1809426115 Moran et al. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Proceedings of the National Academy of Sciences of the United States of America Pubmed Central

Sustainable hydropower in the 21st century

Proceedings of the National Academy of Sciences of the United States of America , Volume 115 (47) – Nov 5, 2018

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a,1 b a c d Emilio F. Moran , Maria Claudia Lopez , Nathan Moore , Norbert Müller , and David W. Hyndman a b Department of Geography, Environment and Spatial Sciences, Michigan State University, East Lansing, MI 48824; Department of Community Sustainability, Michigan State University, East Lansing, MI 48824; Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824; and Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824 This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected in 2010. Contributed by Emilio F. Moran, September 25, 2018 (sent for review July 27, 2018; reviewed by Carlos A. Nobre and Nigel John Smith) Hydropower has been the leading source of renewable energy environmental and social concerns made the costs unacceptable. across the world, accounting for up to 71% of this supply as of 2016. Since then, the contribution of hydropower to the United States’ This capacity was built up in North America and Europe between electrical supply has steadily declined to 6.1% of energy consump- 1920 and 1970 when thousands of dams were built. Big dams tion, and other energy sources, such as nuclear, gas, coal, solar, and stopped being built in developed nations, because the best sites for wind, began to replace it. Dam removal rather than construction has dams were already developed and environmental and social become the norm in North America and Europe, because many that concerns made the costs unacceptable. Nowadays, more dams are were built before 1950 are at the end of their useful lives, they would being removed in North America and Europe than are being built. be too costly to repair, many no longer serve their initial purpose, The hydropower industry moved to building dams in the developing and their social and environmental negative externalities became world and since the 1970s, began to build even larger hydropower unacceptable (7). European countries with favorable topography dams along the Mekong River Basin, the Amazon River Basin, and and rain patterns, such as France and Switzerland, continue to have the Congo River Basin. The same problems are being repeated: hydropower as an important part of their energy mix through disrupting river ecology, deforestation, losing aquatic and terrestrial technological innovations at existing dams. In contrast, 3,450 dams biodiversity, releasing substantial greenhouse gases, displacing thou- have been removed to date in Sweden, Spain, Portugal, the United sands of people, and altering people’s livelihoods plus affecting the Kingdom, Switzerland, and France (https://www.damremoval.eu). food systems, water quality, and agriculture near them. This paper Hundreds of dams were removed in the United States (546 from studies the proliferation of large dams in developing countries and 2006 to 2014) (7) and Europe at enormous financial cost. This sit- the importance of incorporating climate change into considerations of uation contrasts with what is happening in developing countries. whether to build a dam along with some of the governance and Developing countries, where millions of people are still not compensation challenges. We also examine the overestimation of connected to the electric grid (8), have been ramping up hydro- benefits and underestimation of costs along with changes that are electric dam construction for decades. These often involve needed to address the legitimate social and environmental concerns megaprojects, which repeat the problems identified with big dams of people living in areas where dams are planned. Finally, we propose built in the past by the United States and European nations: dis- innovative solutions that can move hydropower toward sustainable rupting river ecology, causing substantial deforestation, generating practices together with solar, wind, and other renewable sources. loss of aquatic and terrestrial biodiversity, releasing large amounts of greenhouse gases, displacing thousands of people, and affecting hydropower dams energy Amazon social and environmental impacts | | | | sustainability Significance e need innovative sustainable solutions to meet energy North American and European countries built many large dams Wdemands, guarantee food security, and ensure water until 1975, after which both started to abandon a significant availability around the globe. Over the years, dams have been part of their installed hydropower because of the negative used for land management and flood control; to store water for social and environmental impacts. However, there has been a irrigation and agriculture; to provide recreation and navigation, recent trend of new large hydropower dams being built in and to address management of aquatic resources (1, 2). There developing countries, particularly in megabiodiversity river basins, are over 82,000 large dams in the United States alone (3, 4). In such as the Amazon, the Congo, and the Mekong. The socioeco- addition, over 2 million small low-head dams fragment US rivers nomic and environmental damages in these river systems are (5), and their cumulative impacts are largely unknown, since they even greater than the early costs in North America and Europe. have escaped careful environmental assessment. This paper discusses how the hydropower sector needs to not Beginning in the late 19th century, the first hydroturbines were only focus on energy production but also, include the negative invented to power a theater in Grand Rapids, Michigan and then, social and environmental externalities caused by dams and rec- to power streetlights in Niagara Falls, New York. Alternating ognize the unsustainability of current common practices. current then made possible the first hydropower plant at Redlands Power Plant, California in 1893. Beginning in the 1920s, the US Author contributions: E.F.M., M.C.L., N. Moore, N. Müller, and D.W.H. designed research; Army Core of Engineers began to build hydropower plants. The N. Moore prepared the SI Appendix; and E.F.M., M.C.L., N. Moore, N. Müller, and D.W.H. Tennessee Valley Authority in 1933 developed hydropower in the wrote the paper. Tennessee River with the clearly stated goal of promoting rural Reviewers: C.A.N., Institute for Advanced Studies–University of São Paulo; and N.J.S., University of Florida. electrification, later widely imitated throughout the country—the most notable being the Hoover Dam in 1937. The New Deal gave The authors declare no conflict of interest. an enormous boost to hydropower construction, tripling output in This open access article is distributed under Creative Commons Attribution-NonCommercial- NoDerivatives License 4.0 (CC BY-NC-ND). 20 years until it accounted for 40% of electrical use in the United States (6). Hydropower dams were an important part of North See QnAs on page 11863. American and European energy development. To whom correspondence should be addressed. Email: moranef@msu.edu. Starting in the late 1960s, big dams stopped being built in de- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. 1073/pnas.1809426115/-/DCSupplemental. veloped nations, because the best sites for dams were already de- veloped, the costs became too high, and most importantly, growing Published online November 5, 2018. www.pnas.org/cgi/doi/10.1073/pnas.1809426115 PNAS | November 20, 2018 | vol. 115 | no. 47 | 11891–11898 SUSTAINABILITY INAUGURAL ARTICLE SCIENCE the food systems, water quality, and agriculture near them (9–12). changes in the ecological system brought by big dams alter their The sustainability of these undertakings is commonly insufficiently livelihoods in negative ways (35, 36). A report of the World scrutinized by those promoting them. The priority in large dam Commission on Dams (WCD) (37) documented the socioeco- construction is to generate energy to serve growing industries and nomic problems due to dam development projects; 40–80 million urban populations—these two things often overwhelm socioeco- people were displaced, and it has proven challenging to resettle nomic and environmental considerations (13). Left behind are lo- them properly. Scudder (38) estimates that 80 million people cal communities saddled with socioenvironmental damages and were displaced in the last century because of dams. In addition, loss of livelihoods (14). Often, they do not even gain access to the living conditions and food security of communities living electricity, because they are not provided the power from the large downstream are often placed in peril. In the Tucuruí Dam region dams, and they are not sufficiently compensated for their disrupted of the Brazilian Amazon, the fish catch declined by 60% almost lives. All countries need renewable energy, and hydropower should immediately, and more than 100,000 people living downstream be part of this portfolio. However, there is a need to find sus- were affected by the loss of fisheries, flood recession agriculture, tainable and innovative solutions that combine hydropower de- and other natural resources (37). A conservative estimate is that velopment with other energy sources, thus providing benefits that 472 million people worldwide have been negatively affected by will outweigh, reduce, or even eliminate the negative environmental, dam construction downstream from dams (39). However, the behavioral, cultural, and socioeconomic externalities resulting from impact on downstream communities is still understudied (40). large dams. Large dams seem to be everything that one should not try to Here, we review the socioeconomic and environmental situation build if one cares about sustainability. To move toward sustain- in several major river basins where dams are being built. We ex- ability, future hydropower development needs to give more at- amine the proliferation of large dams in developing countries, the tention to how climate change may affect hydropower production lack of attention to climate change in the decision of whether to and make greater efforts to reduce the environmental and social build a dam, some of the governance and compensation chal- costs borne by people near the dams. In addition, those harmed by lenges, and the overestimation of benefits and underestimation of the dams need to be adequately compensated, the number of costs. We also identify changes that are needed to address the people that must be resettled should be reduced, and most im- legitimate social and environmental concerns of people living in portantly, innovative technologies that reduce all of these negative areas where dams are planned and propose innovative solutions to outcomes should be developed, especially instream turbines and meet the food, water, and energy needs of citizens in those regions. other forms of renewable energy. These solutions have relevance worldwide, as hydropower can also Dams, Climate Change, and Land Use Change contribute to meeting goals of reducing fossil fuel emissions and building sustainable communities with diversified energy sources. Hydropower development in developing countries seems to overlook climate change scenarios. In developed countries, some Hydropower in Developing Countries dams (e.g., Hoover Dam) are already putting new turbines at a An estimated 3,700 dams that produce more than 1 MW are lower elevation to prepare for projected future water shortages either planned or under construction primarily in developing in the Colorado River due to climate change. Lake Mead, which countries (15). It is easy to understand why: hydropower repre- stores the water for the Hoover Dam, has seen a 40% decline in sents the largest renewable source of electricity (71% of global its water level (41); despite technology improvements, its peak production of renewable energy) (16), and it is estimated that power output is down from 2 to 1.5 GW. Improvements have only 22% of the global potential is exploited to date (15). Sub- also been successfully undertaken in the Southeast United States stantially increasing the share of renewable energy in the global in several dams through the relicensing process that mandates energy mix by 2030 is among the Sustainable Development improvements in river flows, facilitating fish migrations and en- Goals. Hydropower development is a global phenomenon and hancing dissolved oxygen levels in water discharges to maintain multinational in its significance. It is affecting the most impor- river ecology (42). According to a recent US Energy Information tant river basins in the world, including the Amazon, the Congo, Administration Outlook, the vast majority of the world’s newly and the Mekong (12, 17), creating enormous disruption in these installed renewable energy over the next 25 years will come from ecologically important regions. The financial costs of the dams hydroelectric dams, mostly in the developing world. Here, cli- are immense, and many believe that the benefits do not outweigh mate change impacts are already felt but again, are not being the costs (18, 19). The hydrologic consequences of large-scale addressed by dam builders. Projections for the Amazon Basin dams and reservoirs are extensive (20); however, microhydro- point toward a broad drying trend in the southern and eastern power is largely a net positive for communities and has minimal regions (ref. 43, figure 27–2), especially under higher-greenhouse environmental impact (21, 22). Sharp declines in available gas emissions scenarios. Variability (particularly in droughts) has freshwater due to dam construction drive seasonal changes in also been increasing for these regions (43, 44); this is projected river discharge as well as loss of downstream freshwater habitat, to continue and will diminish reliable water supplies to dams. floodplains, and even coastal erosion and salinity changes (23–26). The Jirau Dam and Santo Antonio Dam on the Madeira River in The negative consequences for ecosystem structure and compo- the Brazilian Amazon, completed only 5 years ago, are predicted sition (e.g., habitat fragmentation, loss of aquatic and terrestrial to produce only a fraction of the 3 GW each that they were biodiversity) and function (e.g., nutrient flows, primary pro- projected to produce because of climate change and the small duction) can be severe (7, 18, 19). Reservoirs can also be signifi- storage capacity of run-of-the-river reservoirs. The Belo Monte cant sources of greenhouse gases, especially methane (10, 23, 27– Dam on the Xingu River, completed in 2016, will also produce 30), and reductions in river flow can increase pollutant concen- less due to climate variability and a relatively small reservoir: trations (31, 32). only 4.46 of the 11.23 GW that it was built to generate even in The human costs of large dams are no less important. The optimistic scenarios in 10 of 12 mo of the year due to insufficient social, behavioral, cultural, economic, and political disruption water levels (43, 45). Since 2005, the Amazon has experienced that populations near dams face are routinely underestimated three droughts that broke all historical records (and 3 extreme (19, 33, 34). Ansar et al. (18) in a global analysis of 245 large flooding years) (46, 47). Most climate models predict higher dams built between 1934 and 2007 found that costs of large dams temperatures and lower rainfall in the Xingu Basin, the Tapajos were 96% higher than predicted costs and that 1 out of 10 large Basin, and the Madeira Basin (43, 44). The intensity and fre- dams cost up to three times more than originally estimated. For quency of extreme events continue to challenge the energy fishermen relying on fishing resources for their subsistence, the promises from investments in large hydropower projects. 11892 | www.pnas.org/cgi/doi/10.1073/pnas.1809426115 Moran et al. Hydropower is the world’s primary renewable energy resource, of sediment load on the river, sedimentation problems occur but questions have been raised about its reliability under pro- faster than loss of structural integrity (60). Before 1960, sedi- jected climate change. In Brazil, which depends on hydropower mentation rates were not consistently factored into dam design for up to 67% of its electrical energy (48), this is a crisis waiting criteria; thus, many dams are expected to fill at rates exceeding to happen. However, the response to likely reduced capacity from design expectations (61, 62). Today, engineers typically design climate change has been to accelerate dam construction in these reservoirs to incorporate a 100-year sediment storage pool. subbasins, even when this has meant not following international However, these calculations often fail to include changes in laws of free and open consultation with local and indigenous watershed land use (such as road construction, which can in- people (49), rather than investing in technologies with lesser en- crease sediment yield by two orders of magnitude) and projected vironmental impact, such as instream turbines (50, 51), and extreme events due to climate change that will likely increase investing in other sources of renewable energy, like solar, biomass, sediment transport toward reservoirs. This tendency to overlook and wind, to diversify the energy mix (45, 52). More concerning is factors that could increase sediment loads continues today in the plan that most future hydropower in South America will come tropical countries. For example, the Madeira River carries 430 from the river-rich Amazon Basin, where there will likely be se- Mt of sediment per year (63), which is orders of magnitude greater rious environmental and social consequences (36). The same can sediment than most rivers. Two dams were completed during this be said for Asia, where the Mekong is currently being dammed at decade on the Madeira—Jirau and Santo Antonio—and addi- an accelerating pace (53, 54). These basins contain 18% of global tional ones are planned, despite numerous warnings that their freshwater fish diversity (17); therefore, the construction of dams designs have underestimated the high sedimentation rates (64–66). in these basins poses a threat to fish biodiversity and imperils the In less than 5 years since their completion, experienced dredgers food security of the region’s inhabitants. who earlier mined for gold in the Madeira (and who had been In a similar manner to climate change, dam builders frequently removed from the area to build the dam) have had to be called fail to consider the effects of land use change on the hydropower back to remove sediment accumulating in these two reservoirs at potential of a dam. Stickler et al. (14) examined the loss of energy “unexpected” rates according to the dam builders. This is an un- generation potential under deforestation scenarios in the Amazon justified surprise given the number of scientific papers that had River Basin. In the Xingu Basin, site of the Belo Monte Dam, they warned about the likelihood of such rapid sedimentation (64–67). estimate that ∼38% of the industry’s power estimates could be Areas at Risk reduced due to predicted deforestation and that power generated could fall below one-half of installed capacity in all but 2 months of Some river basins are being targeted for hydropower develop- the year (14). Regional deforestation can inhibit rainfall and soil ment given their potential to produce energy but with little moisture sufficiently in tropical moist forest regions to constrain consideration to reducing the environmental and social conse- energy generation (55). One-half of precipitation in the Amazon quences of such energy development. A summary table of rele- Basin is estimated to be due to internal moisture recycling; thus, vant comparative data for three megadiversity rivers is included deforestation can reduce precipitation independent of the expected in SI Appendix. decline from global climate change(56).Relianceonlarge dams The Amazon Basin—an area of 6 million km —is the location for generating hydropower can be questioned as a reliable strategy of 147 planned dams, 65 of which are in Brazil (68). Brazil is also under climate change scenarios. Alternatives that can address the investing in developing hydropower resources in Bolivia and Peru energy production shortfall in drought years need to be considered. with a view to buy their energy—estimated at 180 GW in Peru and A recent assessment found that the best scenarios include rapid 20 GW in Bolivia (69). The scale is multinational and will affect development of wind, biomass, and solar to complement the very high-biodiversity ecosystems along with a rich diversity of existing installed hydropower. The latter is not expected to meet ethnic and cultural groups and the wellbeing of millions. Brazil has the demands of the future, which will be more reliably provided by among the largest hydroelectric potential in the world, estimated a complement from solar, biomass, and wind power generation, at 260 GW (41% of this is in the Amazon Basin), making it certain with existing hydropower providing stability to the grid (52). that hydropower projects will continue to be constructed (45). The Xingu Basin, the Tapajos Basin, and the Madeira Basin account Dam Failures and Dam Removal for ∼80% of the Amazon Basin potential (Table 1). It is easy to forget, as one seeks “green energy” technologies, that The Amazon River system holds the most diverse fish assem- dams have a finite lifespan (i.e., that they are not really a sustain- blages on Earth (70) and one of the most productive inland fish- able long-term strategy). Dams being built in Brazil are planned for eries (71, 72). There are some 2,320 fish species in the Amazon a 30-year lifespan, which could be extended with technical retrofits Basin, whichisthe most by farofany riversysteminthe world(17). and newer turbines (45). Two sources of dam failure are the aging The Congo is next with 1,269 species, and then, the Mekong is third of the construction materials and accumulation of sediment behind with 599 species. Local livelihoods and diets of riverine populations the dam impoundment. As dams age, they are prone to failure, depend heavily on these fisheries that provide the main source of sometimes resulting in numerous fatalities and great loss of prop- animal protein (73–76). Impacts of dams on fisheries in the Ama- erty. Heavy rains from a single tropical storm in 1994 caused more zon Basin have been studied, showing that the dams have affected than 230 dams to fail in Georgia (57). The Oroville Dam Spillway fish populations and fish dynamics. After dams were installed on began to fail in California in 2016 after heavy rains, resulting in the the Tocantins River, the number of fish was reduced by 25% (77). evacuation of 190,000 people from their homes. More famously, The blockage of fish migration has been described as one of the the Teton Dam in Idaho failed in 1976, with resulting losses ex- main impacts (65, 75, 78, 79). There is also strong evidence that the ceeding $2 billion in 2017 dollars. Many US dams have significant changes in sediment movement associated with dams modify car- potential for failure. Many built during the peak construction pe- bon and phosphorus availability, thus altering fisheries (80). riod in the United States (1930–1950) are past their 50-year life- The Mekong Basin has become the world’s top investment span, with 85% of them reaching that milestone by 2020 (58). region for large hydropower dams, mostly from China; 72 new The cost of repairing a small dam can be up to three times the projects are planned in Laos, 10 are planned in Sarawak cost of removing it (59), which is an important reason for the Malaysia, and more than 50 are planned in Cambodia (81, 82). growing trend to remove dams today. If the costs of dam removal In the Mekong River, there are currently 11 hydropower dams were considered in a dam’s costs, would their construction be under construction; 60 million people who live off the rich justified? More than 60 dams per year are being removed in the fisheries on that river will be affected by dams, with the potential United States, a trend that began in 2006. Varying by the amount loss in livelihoods expected to be greater than US $2 billion, Moran et al. PNAS | November 20, 2018 | vol. 115 | no. 47 | 11893 SUSTAINABILITY INAUGURAL ARTICLE SCIENCE Table 1. The three largest Brazilian watersheds and their hydroelectric potentials (Agência Nacional de Aguas 2013 and Empresa de Pesquisa Energética 2015) Percentage of total hydroelectric Basin Total area (km ) Hydroelectric potential (MW) potential in the Amazon Madeira 548,960 14,700 19 Xingu 509,685 22,795 30 Tapajos 492,263 24,626 32 which is equivalent to the value of their fish catch. The potential of activists, and assassinations was common (92). This is a result of hydropower in the Mekong is about 53,000 MW, with 23,000 of a failure of the hydropower sector to address governance and MW in the Upper Mekong Basin (China) and 30,000 MW in the sustainability issues. Communities affected by dams have fre- Lower Mekong Basin [Lao People’s Democratic Republic (PDR), quently complained about the lack of consultation and attention Thailand, Cambodia, and Vietnam]. The basin is one of the most to known negative impacts on society and environment as well as productive and diverse inland fisheries in the world (83), and 16% the questionable promises made by the energy sector (cheaper of species are threatened by the dam construction (84). energy bills, more jobs, better infrastructure, such as schools and The Congo River is the world’s second largest in terms of flow hospitals). Benefit-sharing mechanisms, such as compensations, (42,000 m /s) after the Amazon and the second longest river in were proposed by the WCD report as a way to share the benefits Africa (4,700 km) after the Nile River. The Inga megadam is of the dams with local communities (93, 94). In Brazil, munici- planned on the largest waterfall in the world by volume (Inga palities are supposed to get some revenues from dams; however, Falls). The proposed massive dam is part of a dream to develop a these resources sometimes never arrive (95). In Belo Monte, power grid across Africa that will spur the continent’s industrial Santo Antonio, and Jirau, which were installed on the Brazilian economic development. Grand Inga could produce up to 40,000 Amazon, the electric bills of people went up rather than down, MW of electricity, over twice the power generation of Three and the jobs promised to locals went mostly to outsiders and Gorges Dam in China and more than one-third of the total disappeared within 5 years. Community organizers and indigenous electricity currently produced in Africa. However, rather than leaders are the most frequent targets of violence and repression this development improving the lives of locals, plans are to export (36, 92, 96–98). the energy produced to South Africa to cater to mining companies Millions of people worldwide are affected by dam construction (85). Ninety-one percent of the people in the Democratic Re- either because they are permanently resettled due to the filling public of Congo have no electricity, and yet, the continent’s biggest of the reservoirs or because their livelihoods get disrupted with infrastructure investment, at US $80 billion, would benefit the construction and operation of the dam (86). However, there mining with little benefit to the Congolese people (https:// do not seem to be mechanisms to fully compensate them for www.internationalrivers.org/campaigns/grand-inga-dam-dr-congo). their losses (99). People who are displaced often get an under- valued price for their land or buildings that does not consider the Role of Governance in Hydropower’s Sustainability social, cultural, and religious value of their land or the way that Whether in the Amazon, the Congo, or the Mekong, the most people make their livelihoods on the land or the stretch of river overlooked dimension of hydropower projects is the effects on (96, 100, 102). In addition, it does not consider that, after local social systems and institutions (84, 86, 87). Local commu- resettlement, people often lose their social networks and other nities typically do not have a significant say in hydropower de- types of social wealth, which has economic, cultural, social, and velopment (88, 89). This results in a decoupling of decision health consequences (86, 99). Communities that are not dis- making that can result in local priorities being overlooked and placed, like those that are downstream, generally do not get any the interests of urban industrial sectors driving decisions. In compensation, although the effects of the dam on their liveli- addition, policies and regulations are often regional or national hoods are just as great as the effects on those who require and commonly do not recognize the transboundary system dy- resettlement (39, 102). This problem seems to be even more namics, thus neglecting important considerations, such as rights, significant considering that most people affected by the dam are social and cultural values, and access to resources (90, 91). In- the poorest and more vulnerable in their societies, and they are stitutions can be specific to each sector (e.g., water allocation often indigenous and traditional communities (19). Monetary or regulations, property rights, renewable energy policy tools) as nonmonetary compensation mechanisms should consider that well as apply across sectors (e.g., political and civil rights, de- men and women are impacted differently by a dam and ensure centralization policies). Similarly, institutions can operate at that the most vulnerable are compensated (102). different scales of governance (i.e., local rules and norms, state As one seeks to build a just and sustainable hydropower sector regulations, national laws) and shape how groups make food, it is important to build mechanisms that guarantee that exter- water, and energy choices. However, one needs to start thinking nalities will be internalized; in other words, those who benefit about the governance not as three different sectors but as a from hydropower and are far away (and thus do not face exter- nexus, in which multiple layers account for the different scales, nalities from its exploitation) need to compensate local pop- levels, and sectors (90). Institutional analyses of case studies ulations where hydropower is produced to offset the negative become necessary to create an integrated policy assessment of costs from energy production (13). They should also offset the the cases under consideration. For example, energy production heavy losses from transmitting power across great distances. A through water appropriation highlights local–regional–national– key function for institutions is reducing transaction costs that transnational tradeoffs, in which water, energy, food, and liveli- hinder the identification of such inequities and externalities as hood costs and benefits are inequitably treated. well as the functioning of offset programs. Often, large dams are promoted with the idea that locals will Creating compensation mechanisms that are not always mone- gain some benefits out of them. However, the evidence suggests tary is an important innovation needed for future energy devel- otherwise. A recent study using a database of 220 dam-related opment plans. To date, little attention has been given to conflicts found that, in dams surrounded by controversies and compensation forms that strengthen communities and individuals conflict, the use of repression, criminalization, violent targeting affected by dams. This can be done by investing in understanding 11894 | www.pnas.org/cgi/doi/10.1073/pnas.1809426115 Moran et al. the social capital and history of these communities and working allow running fish to spawn rather than die trying. At Belo with them to sustain the integrity of their social, economic, and Monte, 16.2 tons of fish died, as they were unable to get past the political relationships. The contrary has been more common: dam during the 2016 migration (107). Prioritizing energy pro- resettling people without concern for any of these issues and duction at the expense of the fish biodiversity and abundance in sometimes, even seeming to purposely break up any preexisting the rivers must stop. Releases of water from a dam should mimic social organization as a way of preventing their ability to act a river’s natural seasonal fluctuations to maintain stream health. after the dam is built to lobby for adequate compensation (103). Experiments in Sweden that mimic the natural stream flow were able to improve the quality of the downstream ecology with only Innovative Solutions for Hydropower small reductions in hydropower production (108). Several things are needed to transform the hydropower sector to (iv) Energy generation through dams requires thinking about enable the benefits to exceed the costs and to ensure that dams the governance implications of the dam construction and associ- contribute to sustainable energy systems. (i) Environmental impact ated energy distribution and use. Policy makers often see energy as assessments (EIAs) and social impact assessments (SIAs) need to the entry point to the system and use water as a way to generate it be capable of stopping a dam from being built. (ii)EIAsand SIAs without recognizing the effects on food and livelihoods. The three must be carried out by firms serving citizens rather than the dam sectors are dependent on each other, but policies are rarely con- builders, and they are essentials tools worldwide, whether in Brazil ceived with a nexus approach, which has to change. The challenge or Europe (104). (iii) Hydropower designs need to truly allow fish is even larger when the food–water–energy nexus has implications passage and mimic the seasonal river flows. (iv) Better governance that go beyond one country, either because the impacts are suf- needs to be created around dams. (v) Greater transparency with fered by different countries or when multinationals or different society about the true costs and benefits (including social, cultural, states are involved in the construction or distribution of energy. economic, political, and environmental costs and the costs of dam The current construction of binational hydroelectric dams on the removal at the end of the dam lifespan) is needed. (vi) Sustain- Bolivia/Brazil border is a clear example of this challenge. Flooding ability evaluation measures from the design through operation from Jirau has led to flooding in Bolivia (36). stage should be used. (vii) Innovative technologies that do not (v) To overcome the limitations of current dam-building prac- require damming the river or resettling population are needed. tices, one needs to incorporate how regional to national policies Addressing these issues can transform the hydropower sector. affect the local issues in the design of dams, and such information (i) EIAs and SIAs need to have real teeth. They should be needs to be made available to the likely affected societies in a carried out with sufficient lead time to provide a credible assess- transparent manner. There is a lack of regional to multinational ment and have built-in capacity to stop the building of a dam if planning that considers the impacts of dams in a manner that needed protections to biodiversity and human populations are not ensures connectivity of the ecosystems (109, 110). The goal is to in place (33). Public hearings and sufficient social engagement improve assessments to incorporate community concerns and to addressing the consequences from the dam have to be allowed design new dams in ways that they can improve livelihoods by before final approval is given. SIAs are fundamentally important increasing crop productivity, maintain fisheries yields, increase to determine how many people will need to be resettled and lay food security, and improve access to water and energy from the out the mechanisms for appropriate indemnity and compensation. project. Following WCD recommendations or a rigorous cost/ There also need to be mechanisms to ensure that these recom- benefit analysis would have resulted in Belo Monte not being built. mendations are carried out rather than leaving this up to the The analysis showed that there was a 72% chance that the costs of construction companies (33). Compliance with Article 169 of the Belo Monte would be greater than the benefits (111), something International Labor Organization (105), requiring previous and that has proven correct. By the guidelines set out by Scudder (86), free consultation with indigenous and traditional populations, an experienced scholar of dams and resettlement across the world, should be expected as part of the predam planning in a manner many or even most large dams should not have been built. Those that allows full discussion of the pros and cons without under- guidelines and those of other bodies, such as the WCD, agree on estimating costs and inflating benefits to those affected. much of what is wrong with the current rush to build large dams (ii) EIAs and SIAs should not be carried out by the firms and the apparent difficulty in meeting those minimal guidelines. engaged in building the dam or their subsidiaries (as is currently New tools are being proposed by scholars that permit basin- common in some countries); these need to include biodiversity wide policy instruments using existing laws. For example, the and social impact studies by independent organizations respond- multinational Amazon Cooperation Treaty and Brazil’s National ing to civil society with no conflict of interest with the government, Water Law (112) promote integrated water management and energy sectors, or construction companies. Actual practice sug- could be tools to change how decisions are made. An in- gests that EIAs and SIAs are commonly carried out by consulting ternational panel of experts could use existing knowledge to firms hired by and responding to prospective dam builders, and determine vulnerabilities using tools, such as the Dam Envi- their data and results are often not made publicly available to ronmental Vulnerability Index (113), at the subbasin scale. stakeholders until long after the dam is built. Benefits are rou- These tools and engaged civil society and other stakeholders in a tinely inflated, and costs are minimized in current EIAs and SIAs joint panel could more accurately consider the environmental (33). When benefits are not forthcoming and costs are large, the and social costs. The energy sector in countries like Brazil and population ends up in court seeking compensation for damages, India has recently promoted and begun constructing small dams and these costs are paid by society and not by the dam builders. or PCHs as a more benign technology than large dams, yet there (iii) At present, most devices (“ladders”) to help migrating is very little evidence for this claim (45). The United States has a species get across dammed areas do not work or are not even put long history of building low-head or small dams (2 million of in place. Targets for fish passage are being missed by several them); however, Fencl et al. (5) note that the claim of their orders of magnitude—even in the best of cases, only 3% make it minimal impact is largely untested. By virtue of their abundance, (106); the authors make a case to admit the failure of these small dams can substantially impact flowing aquatic ecosystems ladders and propose dam removal in cases where fish passages (114). Small hydrodams possess the same characteristics as large are not working. They propose a cautionary tale for developing dams, with the only difference being their size. China and India countries’ current efforts, arguing that fish passages do not are the current leaders in small hydrodams. Their power gen- compensate for the damage to the fisheries, since they generally eration benefits, particularly in isolated mountainous terrain, do not work. This needs to change, and attention must be given cannot be dismissed. However, their ecological, hydrological, to greatly improved designs that avoid species extinctions and and social impacts should be scrutinized just like large dams, and Moran et al. PNAS | November 20, 2018 | vol. 115 | no. 47 | 11895 SUSTAINABILITY INAUGURAL ARTICLE SCIENCE more importantly, they are losing ground to wind power in en- that the optimal scenario is one in which wind energy leads the ergy auctions (i.e., their cost per kilowatt is no longer competi- way, with biomass and solar further strengthening a diversification tive compared with wind power generation). Small hydropower is of the electric sector. Hydropower will continue to provide a subject to both environmental impact assessments and environ- substantial foundation of base energy, but the growth in the next mental impact reports when power produced is above 10 MW, two decades is expected to favor wind, biomass, and solar and they are considered as having a high impact on the envi- production (52). ronment in existing legislation (115). The hydropower industry needs sustainability evaluation mea- (vi) One alternative to traditional damming of rivers that sures that can stand public and independent scientific scrutiny. should be considered is instream turbine technology (50, 51), Many of these have been proposed but are rarely implemented. The also known as “zero-head.” This offers a less ecologically in- recommendations of the WCD provide guidelines for social and trusive means to tap into hydropower without many of the neg- environmental sustainability for hydropower projects. Since 2001, ative externalities identified earlier in this paper. Instream the WCD guidelines have influenced international accords, finan- turbines are suitable for rivers with flow velocity exceeding cial safeguards, and national laws. For example, the WCD recog- −1 1ms and can produce steady power (also known as “base nized the importance of a full evaluation of energy options to meet power”), since the flow velocity in rivers typically varies much energy mix needs before putting a hydropower project on paper. less than wind. Hydrokinetic energy has been used for a long The WCD also promotes alternative siting scenarios for dams that time since the time when river currents were harnessed to crush are already assumed will be approved. Too frequently, energy and grains in mills. New small turbine technologies have been quietly water planning is secretively guarded by governments (sometimes in developing to harness base power, and large turbine companies collusion with dam builders), is closed to the participation of civil (e.g., Voith) are developing smaller turbines and have tested and society, and does not follow the WCD guidelines. For hydropower shown their potential value (116, 117) in six continents and at planning to become sustainable, government and industry must hundreds of sites (116). Such turbines can be low maintenance, prioritize transparency by inviting civil society to the table to discuss be ecologically friendly to fish, and serve local communities’ and agree on what a country’s energy matrix should look like. A energy needs in a green manner. A number of smaller companies growing chorus of scholars across fields of science is calling for (116–118) are testing prototypes and moving toward com- modular solutions that combine wind, solar, and hydropower to mercialization. Smart HydroPower has already commercialized provide alternative energy sources that are environmentally, so- 40 instream turbines worldwide (https://www.smart-hydro.de). cially, and financially desirable (45, 52, 122). Instream technology These companies seem to be conscious of the importance of can provide off-grid energy for isolated communities, such as those delivering energy to local communities and of the need to reduce in the Amazon and other regions where distance and isolation keep negative impacts of large hydropower dams. Recent corruption them without access to energy, thereby enhancing their access to scandals in Brazil surrounding Belo Monte, where huge payoffs inexpensive energy and providing sustainable energy for economic were made to politicians to approve the dam despite strong development; that, when combined with solar panels on individual evidence against building it, suggest that the motivation for fa- homes to complement the instream hydropower, gives them energy voring big dams may be tied to complex webs of corruption or security. One could also install instream turbine parks as a much particular financial interests. This may be widely true, particu- less disruptive alternative to small dams and produce energy at larly in places with either authoritarian regimes and/or where much lower cost to local communities and the grid. financial interests favor large projects, such as big dams, because The most important advantage of hydropower in contrast to they offer considerable opportunities to divert funds (119). Of other renewable energy sources, like wind and solar, is that it can the $11.1 trillion expected to be spent on global infrastructure be dispatched quickly at any time, enabling utilities to balance load between 2005 and 2030, $1.9 trillion will be spent on hydropower variations on the electric distribution system (123). As we move projects (120), and 60% of those funds involve civil construction forward in the 21st century, electric companies need to diversify and resettlement costs, both areas known to be susceptible to their energy projects even more than they have. The cost of solar diversion of funds (119). Corruption risks start with undue in- and wind is dropping, efficiencies are up, and increasingly, they are fluence on the selection of sites, undue influence from project price competitive for the energy produced. Hydropower can be developers, bribes, and misappropriation of funds (121). Such part of a sustainable future if it moves away from big dams and corruption undermines public trust in hydropower and under- toward a combination of instream turbines and diversified energy mines its sustainability. The current trend to build large dams in sources in ways that do not disrupt stream ecology and fisheries developing countries may be characterized in this manner, and and the lives of people on the great rivers of the world. Existing global financial institutions should refuse to be a part of such dams in places like Brazil already produce substantial energy schemes. Scudder (86) argues that the World Bank Group, as for the integrated grid, and what is needed is investment in the largest sponsor funding large dams, should take the lead to diversification with solar and wind power. Hydropower has an ensure that their funds meet international standards for envi- important role to play as a provider of inexpensive energy ronmental restoration and compensation to communities. Voi- complemented by instream hydro and partnering with solar, vodic and Nobre (46) suggested that increasing hydropower biomass, and wind to provide power toward a sustainable future. capacity from the Amazon is not necessary; instead, they pro- pose innovations in biologically inspired technologies (biomass ACKNOWLEDGMENTS. We thank National Science Foundation Grant 1639115 energy production for example) as a way to outgrow the current and Fundacao de Amparo a Pesquisa do Estado de Sao Paulo Grant 2012/ model of development, which fails to consider the value of 51465-0 for providing support for this research. None of these agencies should biodiversity and cultural diversity in its calculations. Recent as- be held responsible for the findings and results presented herein as they are sessment of alternatives for the future of energy in Brazil suggests the sole responsibility of the authors. 1. Tullos D, Tilt B, Liermann CR (2009) Introduction to the special issue: Understanding 4. US Army Corps of Engineers (2016) National Inventory of Dams. Available at nid. and linking the biophysical, socioeconomic and geopolitical effects of dams. usace.army.mil/. Accessed October 12, 2018. 5. Fencl JS, Mather ME, Costigan KH, Daniels MD (2015) How big of an effect do small J Environ Manage 90(Suppl 3):S203–S207. 2. 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Energy Policy 36:4048–4056. 11898 | www.pnas.org/cgi/doi/10.1073/pnas.1809426115 Moran et al.

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References