Our directory of things of interest

University Directory

Hydropower: could the costs outweigh the benefits?

  • Written by  Mark Rowe
  • Published in Energy
The Three Gorges Dam in China, which spans the Yangtze River by the town of Sandouping, in Hubei province, is the world's biggeest in terms of installed capacity The Three Gorges Dam in China, which spans the Yangtze River by the town of Sandouping, in Hubei province, is the world's biggeest in terms of installed capacity Image: Isabel Kendzior
14 Jan
Hydropower is considered essential if the world is to reach net zero, but do the broader cost to ecosystems and local communities outweigh the benefits? 

Most ‘solutions’ to climate change tend to polarise opinion, but few are as profoundly divisive as hydropower. To its advocates, it’s a reliable, versatile and low-cost source of clean electricity and an exemplar of responsible water management. After all, what fuel could possibly be more renewable than water, which is constantly replenished by nature? But critics point to a wide range of deleterious environmental and societal impacts.

Like a river winding towards the sea, the direction of travel for hydropower appears to be headed only one way. Hydropower output has increased 70 per cent over the past two decades. In 2020, it supplied one sixth of global electricity generation and was the single largest source of low-carbon power, accounting for more than all other renewables combined. In Norway, 99 per cent of electricity comes from hydropower; in Brazil, that figure is 85 per cent. The total global installed capacity of hydropower was 1,307 gigawatts (GW) in 2019, with at least 18GW believed to have been added each year since then and the same forecast for 2022.

Hydropower can also claim a stamp of approval from the UN, which considers it to be integral to the achievement of four of the Sustainable Development Goals (availability and sustainable management of water; providing access to affordable, reliable, sustainable and modern energy; upgrading infrastructure with clean, environmentally sound technologies; reducing carbon emissions in the energy sector). The International Energy Agency (IEA) is also on board, describing hydropower as the ‘forgotten giant’ of low-carbon electricity. In a June 2021 report, it warned that the growth of hydropower plants worldwide is set to slow (but not reverse) significantly this decade. For the IEA, hydropower is integral to capping dangerous temperature rise and it believes that any slowdown would jeopardise the ambitions of countries across the globe to reach net-zero emissions. IRENA, the International Renewable Energy Agency, has calculated that the world’s existing hydropower capacity will need to grow by around 60 per cent by 2050 if we’re to keep the rise in global temperature to well below 2°C.

The International Hydropower Association (IHA), an industry group, maintains that no country has come close to achieving 100 per cent renewables without hydropower in its energy mix; it says using hydropower instead of fossil fuels for electricity generation has avoided the release of more than 100 billion tonnes of carbon dioxide in the past 50 years, exceeding the greenhouse gas (GHG) emissions averted by nuclear power. 

Given all of these advantages, all of which are embraced not only by lobbyists but by serious-minded, informed inter-governmental agencies, what’s not to like about hydropower?

shutterstock 2031700001Lac de l'Hongrin is a reservoir in Vaud, Switzerland, held at bay by Hongrin dam, used both for hydroelectricty and to control flooding


Hydropower critics point to a number of issues with the renewable energy source, many of which stem from the fact that the technology relies on vast dams that impede the flow of rivers. A recent report by the US-based International Rivers (IR) found that a quarter of the world’s rivers now run dry before reaching the ocean and only 59 of the world’s 177 largest rivers are wholly free flowing. It can be difficult, the report noted wryly, to place a giant chunk of concrete in the middle of a river and find a way to make that ‘environmentally benign’.

The same report called on the world’s largest dam-building companies to take urgent steps to address the continuing scale and severity of the resulting biodiversity impacts. The study highlighted the biodiversity footprint of the world’s two largest dam-builders, PowerChina and China Three Gorges, and their subsidiaries, which between them account for more than half of the global hydropower construction market. It also concluded that dam constructors lack clearly defined ‘no-go’ policies to exclude problematic projects, resulting in irreversible damage to some of the most ecologically sensitive sites and rarest species.

According to Wetlands International, ill-advised dams, irrigation schemes and other development projects abstract or remove water, changing the volume, speed and quality of water that flows through ecosystems and driving the fragmentation and loss of rivers, lakes and floodplains. Such changes have disastrous consequences up and downstream. Pesticides, PCBs and even mercury can be trapped in reservoirs and accumulate in high concentrations before passing into fish, which then may be consumed by predators and humans, as well as affecting water sources for riverside villages.

International Rivers also points to the social impacts: dams have displaced 80 million people and adversely impacted another 479 million who live downstream, the vast majority of them indigenous people.

1. Geographical 2022 01 HydropowerGenerationChangeMapWhile hydropower has seen a considerable rise in Asia, it also plays an important part of the energy mix in most other regions, even if the absolute quantity of hydropower output isn't as high. As shown in this map, however, growth isn't even across the world, with some countries showing a hydropower decline over the past 20 years. Hydropower is the main renewable resource in Africa. It's less visible when considering absolute utilisation due to the continent’s low share of global power generation (only four per cent, despite being home to 17 per cent of the world’s population); however, strong growth in energy demand on the continent is contributing to an equally strong growth in the use of hydropower. Map: Benjamin Hennig

‘We should simply stop building large-scale hydro developments,’ says Professor Emilio Moran of the Center for Global Change and Earth Observations at Michigan State University. ‘People have tried for decades to get dam builders to properly consult with local communities but they still get resettled and not compensated adequately.’ Th e World Bank is particularly culpable, he adds, as it has continued to fund major dam projects despite a ruling by the World Dams Commission (WDC) in 2000 that local impacts of mega dams must be taken into consideration. The commission issued comprehensive guidelines for dam building with the aim of avoiding the staggering displacement of peoples witnessed during the building of the Three Gorges Dam in China, which saw 1.3 million people resettled. The commission concluded that ‘in too many cases, an unacceptable and often unnecessary price has been paid to secure those benefits, especially in social and environmental terms, by people displaced, by communities downstream, by taxpayers and by the natural environment’.

Three major nations – Brazil, China and India – didn’t sign up to the WDC. One consequence of this was the construction of the Belo Monte Dam in Brazil, the fourth-largest dam on the planet, which proceeded despite protests from 140 organisations across the world. Campaigners say that insufficient credible research and baseline information make it impossible to quantify the impact of such dams. They also say the enfeeblement of the WDC means that construction companies lack clear requirements regarding biodiversity and defined ‘no go’ policies that might exclude problematic projects.

‘You build a dam and you lose 60 per cent of the productivity of the river very quickly,’ says Moran. ‘The top feeders disappear inside two decades; the populations of the top catfish in the Amazon are collapsing. We have enough evidence to say that if you are going to build a huge dam, then certain things will happen.’ IR cites dams as a key culprit in the 84 per cent loss of freshwater species experienced since 1970.

Another recent study by IR found that more than 500 dams under construction or planned worldwide are located in national parks, Ramsar wetland sites and other protected areas of high biodiversity. At least 3,700 major dams, each with a capacity of more than one megawatt, are either planned or under construction, primarily in countries with emerging economies. In Brazil, the Amazon is undammed, but its major tributaries have 412 dams; a moratorium on building on the main river and elsewhere in Brazil has been lifted by President Jair Bolsonaro.

And, just as has happened with officially approved logging of rainforests, dams can also facilitate unwanted secondary effects and illegal activity. The Julius Nyerere Dam in Tanzania, which is under construction in the Selous Game Reserve (a UNESCO World Heritage site), has drawn attention because it will directly submerge habitats of some of Africa’s most iconic and endangered species, such as the black rhinoceros. The construction of 120 kilometres of roads into the heart of the reserve will also exacerbate the persistent problem of poaching, which had nearly wiped out the reserve’s elephant and rhino populations. In Indonesia, the construction of the Batang Toru Dam in North Sumatra has prompted conservationists to warn that it could precipitate the extinction of the Tapanuli orangutan, only recently described as a distinct species.

Another problem is that many large dams remain an absolute barrier to fish migration. Climate change makes this more pressing because, as temperatures warm, migratory species such as salmon and steelhead require access to cold-water spawning areas that are increasingly found only above dams.

Many of these problems have been crystallised in Nepal, where the nation’s waterways and river basins are pockmarked with uncoordinated dams. According to a 2018 report by the Asian Development Bank (ADB), construction of hydropower plants for generating energy to meet domestic and export demands in Nepal has been a government priority and has resulted in 223 dams at different phases of development at discrete locations on the country’s rivers.

The three major river basins of Nepal – the Koshi, Gandaki and Karnali – host about 230 species of freshwater fish and scores of zooplankton and phytoplankton species, forming a rich and unique aquatic ecosystem. Some fish species live within short stretches of Nepal’s rivers, while others are believed to travel along the Ganges to the Bay of Bengal for spawning and swim back to the river basins in Nepal with their juvenile offspring to complete their reproductive cycle. The ADB study found that fish populations were in alarming decline because of the cumulative impacts of restricted passage and cited dam construction, the creation of dry stretches below dams, illegal and destructive fishing, habitat destruction and water pollution from agriculture and industry. With no designated agency to manage them, there’s insufficient legal provision for the protection and governance of aquatic biodiversity.


Lake Turkana, which forms part of the border between Ethiopia and Kenya, is cited as an example of a dam where local indigenous people found themselves downstream and down the list of priorities. The Omo River empties into the lake, which is the largest desert lake in the world and a key breeding site for hippos and the Nile crocodile. But a 240-metre-high dam upstream in Ethiopia, along with a cascade of successive dams, has altered subsistence livelihoods of some 500,000 people and led to Lake Turkana National Park being listed as ‘in danger’ by the IUCN.

‘For generations, indigenous people in the Turkana basin have protected the Omo-Turkana basin's biodiversity, which has supported their lives and livelihoods,’ says Ikal Ang’elei, a Kenyan leader from the Omo-Turkana communities and a Goldman Environmental Prize winner.

Pumped storage boxStwlan Dam and the Moelwyn mountains near Blaenau Ffestiniog in Snowdonia. Image: Rob Thorley


The knock-on effects for humans are also profound. As elsewhere, fisheries in Nepal are significant sources of nutrition, income and recreation; they are also, as can be overlooked, a traditional way of sustaining life and livelihood. The ADB cautioned that while the rate of river damming is expected to increase rapidly, the aquatic fauna’s migratory behaviour and routes, and range of movement for feeding and reproduction were neither properly studied nor understood. ‘In the absence of this information, it is difficult to identify locations for dams on the rivers without significantly obstructing the animals’ migratory route,’ the authors wrote.

A similar warning has come from South-East Asia, where the environmental impacts of a succession of dams on ecosystems are vividly unfolding on the Mekong, which has the world’s largest inland freshwater fishery, feeding more than 60 million people who live within its basin. Its extraordinary aquatic biodiversity is second only to that of the Amazon, yet much of it faces elimination over the next 20 years, according to the Mekong River Commission.

Research carried out between 2012 and 2017 concluded that the 11 large dams on the Mekong’s lower main stream and the 120 tributary dams planned by 2040 seriously threatened the region’s ecology, economy and food security. The cumulative impact of these hydropower plans would be to reduce the amount of sediment reaching the Mekong Delta by 97 per cent, causing fish stocks to decline by up to 80 per cent by 2040, hitting food resources for Thailand, Laos, Cambodia and Vietnam. The report cautioned that ‘no Mekong migratory fish species will be able to survive in the reservoirs of dams planned by 2040’ and that climate change, combined with the loss of fish, may cause ‘acute levels of food insecurity in communities in Laos and Cambodia’.

In response, the ADB and the UN Food and Agriculture Organisation point to mitigation measures that can be deployed to facilitate fish movement across dams, such as fish ladders and locks or bypass channels. In some instances, suggestions include breeding fish in hatcheries and annually releasing them up and downstream of the dam to maintain their populations.

2. Geographical 2022 01 HydropowerGenerationChartThe 70th Statistical Review of World Energy, published by BP, notes that hydropower, along with wind and solar, observed a continued rise in output during 2020, despite an overall decline in demand during the pandemic. As long-term observations show, this global growth over the past two decades has been largely fuelled by the rise of hydropower generation in Asia. Growth in other regions was much more moderate or stagnated. In a time series of the past 20 years, this chart shows how the annual hydropower generation changed by world region between 2000 and 2020

Stay connected with the Geographical newsletter!
signup buttonIn these turbulent times, we’re committed to telling expansive stories from across the globe, highlighting the everyday lives of normal but extraordinary people. Stay informed and engaged with Geographical.

Get Geographical’s latest news delivered straight to your inbox every Friday!


While the environmental impacts of dams appear clear, conservationists also challenge the notion that dams are a clean source of power. A 2017 study by Washington State University found that methane makes up 80 per cent of the emissions from water storage reservoirs created by dams. Biological activities in a reservoir – such as decaying vegetation and nutrient runoff from watersheds upstream – are more important indicators of GHG emissions. The nutrient runoff can be from natural processes or from farming, logging and land development. The authors estimated that total emissions from all reservoirs worldwide account for 1.3 per cent of all man-made GHG emissions.

International Rivers puts that figure as high as four per cent. Josh Klemm, a policy director at IR, reckons that the UN has made a fundamental error by deciding not to include emissions from reservoirs and dams in its GHG frameworks. ‘Hydropower and climate change mitigation don’t really mix – the impacts of the former on the latter are significant. Many countries see hydropower as being viable in the long term – that it will help them to meet their GHG commitments under the Paris Agreement. We believe that that is absolutely not the case.’

'Once you fill the reservoir,’ he continues, ‘the vegetation is submerged and within a couple of decades, it has decomposed to produce methane. It’s a double punch – not only have you taken out a heap of vegetation that can absorb CO2, you’re introducing methane. Renewable energy doesn’t automatically mean sustainable, green or climate friendly, it just happens to not rely on fossil fuels.’

Another headache is that those living near a dam rarely benefit from the electricity that it generates. ‘Hydropower is historically awful at giving energy access to all,’ says Klemm. ‘It’s generated in one place and exported to urban centres or to the mining industry, not the local communities. You’re effectively delivering high levels of energy poverty in areas such as sub- Saharan Africa.’


Pumped storage hydropower (PSH) is a type of hydroelectric energy storage. It's a configuration of two water reservoirs at different elevations that can generate power as water moves down from one to the other (discharge), passing through a turbine as it does so. The system also requires power as it pumps water back into the upper reservoir (recharge). PSH acts similarly to a giant battery, because it can store power and then release it when needed.

The principle isn’t new – the first known uses were in Italy and Switzerland during the 1890s – and the technology is found across the world and tentatively supported by groups such as International Rivers. PSH currently accounts for 95 per cent of all utility-scale energy storage in the USA, which currently has 43 PSH plants. The advantages cited include long-term storage of water, the ability to rapidly jump start grids after blackouts and to distribute surplus water to irrigate crops. Drawbacks include negative impacts on wildlife and ecosystems, as well as the challenge of finding compatible and adjacent dams.

In the UK, the first major PSH system was commissioned in 1963 near Ffestiniog, in north Wales. The power station at the lower reservoir has four water turbines, which can generate 360MW of electricity within 60 seconds of the need arising. The upper reservoir is Llyn Stwlan, which can discharge 27 cubic metres per second of water to the turbine generators.

In a 2018 article, researchers at Michigan State University highlighted the Grand Inga Dam project on the Congo River, which is expected to increase the total electricity currently being generated on the African continent by an incredible 33 per cent. However, the study points out that the main goal for the US$80 billion installation is to provide electricity to industry. ‘Over 90 per cent of the energy from this project is going to go to South Africa for mining – the people in the Congo will not get that power,’ say the authors. On the Mekong River, much of the power from dams on the river’s main stream in Laos is planned for export to Thailand.

IR has little time for many of the mitigation issues, questioning how they can, in practice, be implemented. ‘The mitigation efforts are overstated,’ says Klemm, who says that these are often attempts to roll back on the ‘egregious’ dams built during the 1970s and ’80s, where a million people at a time would be displaced.

‘In principle, it’s good that multi-stakeholder projects are taking place, but typically, they don’t give equal space to all, especially the downstream peoples,’ Klemm says. Equally, where dams are promoted as multi-purpose, producing energy alongside water for drinking and crop irrigation, Klemm sees financial interests dominate. ‘The energy case is always the more compelling and politically more beneficial as a government can appease a certain part of their country.’

shutterstock 510889183The Selous Game Reserve in Tanzania is home to a wide diversity of wildlife, but parts are threatened by the Julius Nyerere dam being built nearby. Image: Attil A Jandi

Stay connected with the Geographical newsletter!
signup buttonIn these turbulent times, we’re committed to telling expansive stories from across the globe, highlighting the everyday lives of normal but extraordinary people. Stay informed and engaged with Geographical.

Get Geographical’s latest news delivered straight to your inbox every Friday!


Yet despite the shortcomings highlighted by environmentalists, no-one is calling for hydropower to be withdrawn overnight and replaced by tidal, wind or other renewables, not least because, as Moran points out: ‘Some of these dams are so big, we’re stuck with them. Hydropower should be greener than fossil fuels. My take is that it can be produced more sustainably.’

Instead it makes sense, Klemm suggests, to harness existing hydropower in a more beneficial manner. ‘It’s not an either–or issue now – everybody is trying to grapple with that question.’

On this at least, there is some rare common ground between all parties. Advocates of hydropower, such as the IHA, point to its flexibility and that this quality means that it can be integrated with and enhance the roll-out of solar and wind power. The logic is that many hydropower plants can ramp their electricity generation up and down rapidly. Notionally, this would remove the need for baseload power supplies from traditional oil- or gas-fired power stations when wind or solar power is reduced by weather conditions.

The IR report of October 2021 concluded, positively, that ‘there is still time to avert the worst outcomes if we act swiftly. Action plans and technologies are already available to help conserve and restore freshwater ecosystems.’

One option favoured by Moran is to deploy small turbines to produce hydro-electric energy without the need for huge dams. These would use photovoltaics – in effect, floating solar farms powered by water that can be deployed in existing reservoirs. ‘If you do this on ten per cent of the reservoirs in the Amazon basin, you generate twice as much electricity as you would otherwise; if you deploy them where dams are proposed, you will get 67 per cent of the planned energy. But you take out the big bads – the environmental and societal impacts. These can use fish-friendly turbines – they could revolutionise dams.’

Such plants are already in situ, with projects of more than 100MW operating in both China and Japan, with panels fixed together on a float to form a pontoon. Such projects involve central inverters, which connect the PV panels, placed on stilts on land to avoid interfering with neighbouring farmland. The principle has also been adopted in the UK, with a floating solar farm of 23,000 panels providing energy to water treatment plants near Heathrow airport. The cooler temperatures of the water also make the plants more efficient than land-based equivalents.

Moran is acutely aware of the financial muscle of dam constructors, who may not automatically welcome smaller projects. ‘They don’t like plans for floating solar panels because there isn’t so much money in that. The Belo Monte Dam in Brazil cost US$31 billion. If you do things greener, you won’t get US$31 billion.’ He also points to the practical point that decision makers also prefer simple projects. ‘A department of energy would rather deal with one big dam than 1,000 smaller projects.’


The expansion of dams isn’t inevitable. The building of dams in Europe and the USA reached a peak during the 1960s and has been in decline since then, with more now being dismantled than installed. Today, hydropower only supplies six per cent of US electricity. Dams are now being removed at a rate of more than one a week on both sides of the Atlantic.

‘If you go down the road of thinking dams will help reduce emissions, you are missing just so many opportunities,’ says Klemm. ‘It’s a mistake to have your energy transition resting on hydropower. The default starting point – that we have to dam all of our rivers to create the electricity we need – is over. The best sites for dams have all long been taken anyway; they’re just not competitive any more. The largest dam constructors are more focused on offshore wind – they recognise where their business is moving to.’

Moran remains wary of which way trends might turn next. ‘I’m concerned because of the drift towards authoritarianism, even in the West,’ he says. ‘Big dams tend to be decided by fiat – they aren’t democratic decisions, they only happen in authoritarian or autocratic countries, or where the influence is from autocratic countries. These leaders like to say, “We are producing energy for you, so here it is.”’

Yet Klemm believes that meaningful changes in the way in which we source renewable energy are now inevitable. ‘We are getting better at using and deploying solar and wind, at connecting their grids over longer distances to even out the bumpy bits,’ he says. ‘But we need to make the case more loudly for free-running rivers – that they are important for people, the climate, wildlife and for economics.’

Moran, too, is determined to remain upbeat, although you can almost hear him grit his teeth. ‘I got into the issues around dams after working to stop rainforest logging, so I recognise the challenges. I remain optimistic, despite evidence to the contrary. We just have to keep working on generating the evidence [of their damage]. A transition to a greener hydropower can be done, but it has to be done carefully.’

Subscribe to Geographical today for just £38 a year. Our monthly print magazine is packed full of cutting-edge stories and stunning photography, perfect for anyone fascinated by the world, its landscapes, people and cultures. From climate change and the environment, to scientific developments and global health, we cover a huge range of topics that span the globe. Plus, every issue includes book recommendations, infographics, maps and more!

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...


Kacper Kowalski's aerial photos capture the graphic shapes of our…


Invasive species are considered one of the greatest threats to…


Professor Steve Fletcher, director of the Global Plastics Policy Centre…


The international conservation agreement CITES is nearly half a century old.…


With Scotland’s salmon under threat, environmental groups are planting trees…


As coastal development continues to grow, research begins to reveal the…


Research into rhesus macaques on a remote island finds that survivors of…


 The release of the latest IPCC report suggests it's 'now…


A new technique to collect animal DNA from thin air could…


As animal species decline, plants that rely on them to…


Calls to make ecocide a crime are gaining ground


In South Africa, a new wave of poaching has taken…


A volcanologist unpicks the devastating eruption of Hunga Tonga-Hunga Ha’apai


Some areas of the ocean are richer in microplastics than…


The ocean floor is home to rich deposits of metals…


The industry will only keep growing. Could algae help to…


A monumental effort is underway to map the world’s fungal…


In his project Black Dots, Nicholas JR White set out upon the…


China’s Amur tiger population is recovering, reflecting the country’s changing…


Scientists are pushing back against the notion that the food…