Is Hydropower Really Sustainable?
Hydropower is the generation of electricity using the energy from flowing water. It is considered a renewable energy source as it relies on the water cycle, in which water evaporates, forms clouds, precipitates, and flows back down to the ocean (Kalemci, 2023). Sustainability is commonly defined as meeting the needs of the present without compromising the ability of future generations to meet their own needs (Brundtland Commission, 1987). When evaluating the sustainability of hydropower, we must consider its environmental, social, and economic impacts both today and in the long-term future.
Hydropower’s Benefits
One of the main benefits of hydropower is that it provides renewable energy. Hydropower relies on the natural water cycle, where water is continuously renewed through precipitation and river flows. As a renewable resource, hydropower can theoretically produce electricity indefinitely, without depleting any finite resources (Source 1).
Additionally, hydropower can provide reliable baseload power. The constant flow of water in rivers allows hydropower plants to generate electricity around the clock. Unlike some renewable sources like wind and solar that fluctuate based on weather conditions, hydropower can produce steady output to meet continuous electricity demand (Source 3).
Hydropower’s Drawbacks
While hydropower is a renewable energy source, it does have some notable drawbacks and negative environmental impacts. One major issue is that dams and reservoirs heavily disrupt natural ecosystems and habitats (MIT Climate 2021). Building a dam floods large areas of land, destroying forests, wetlands, and wildlife habitats in the process. The flooded land was likely home to many plant and animal species that now must find new areas to live or risk extinction (EPA 2021).
Another significant drawback is that reservoirs and dammed rivers emit methane, a potent greenhouse gas. Organic matter like vegetation and soil decomposes in oxygen-poor reservoirs, releasing methane into the atmosphere. Some studies estimate hydropower methane emissions can be substantial, up to 35% higher than other energy sources like solar or wind power on a per kWh basis (UCSUSA 2013).
Furthermore, dams obstruct natural fish migration patterns, disrupting ecosystems that depend on fish populations. The changes in water flow and temperature caused by dams can also degrade water quality. In the U.S., most large river systems have been heavily modified and fragmented by dams, negatively impacting freshwater fish stocks (EIA 2021).
Small vs Large Hydropower
Many arguments around the sustainability of hydropower focus on the scale of hydroelectric dams. Smaller, “run-of-river” hydropower projects are often touted as more sustainable alternatives to larger dams. Run-of-river projects divert a portion of a river through a canal or channel to generate electricity but do not require large reservoirs for water storage. This avoids some of the major environmental impacts of large dams like habitat destruction from flooding, altered water flows, and reduced sediment transport downstream (Energy.gov).
Smaller hydropower projects generate less than 30 megawatts of electricity, compared to large dams which can generate thousands of megawatts. While individually small projects have a lower impact, the combined effects of many small dams on a river system can still be significant. One study found that 78% of European rivers have been fragmented by dams and other barriers, with over half a million small barriers in addition to several thousand large dams (Forbes). Regulatory oversight is often weaker for small projects as well, allowing more to be built without proper environmental assessments.
So while the footprint of individual small hydropower projects is lower, the cumulative impacts of many small dams must be considered when evaluating sustainability. Proper siting, design, and regulatory oversight remain important regardless of project size.
Impact on Wildlife
Hydropower dams can have a devastating effect on wildlife and ecosystems. According to a 2019 article in The Hill, “The rapid loss of free-flowing rivers has serious implications for both nature and people. First, dams fragment aquatic habitats and block fish migration” (source). Dams prevent fish like salmon from being able to migrate from their spawning grounds to the ocean and back. Fish ladders and other bypass methods are often ineffective. This can lead to the decline or even extinction of fish species that rely on river connectivity.
In addition, the flooding caused by dams drowns existing wildlife habitats along rivers. The Union of Concerned Scientists explains, “Flooding land for a hydroelectric reservoir has an extreme environmental impact: it destroys forest, wildlife habitat, agricultural land, and scenic lands” (source). The new artificial lake habitats created by reservoirs are also poor substitutes for the rich ecosystems that existed before flooding.
GHG Emissions
Hydropower facilities can produce greenhouse gas emissions, primarily in the form of methane. Methane is a potent greenhouse gas, with a global warming potential much higher than carbon dioxide.[1] Reservoirs created by hydropower dams can emit methane due to the decomposition of organic matter flooded by the reservoir. However, the amount of emissions varies significantly based on the climate, area flooded, and organic matter in the flooded region.
The IPCC estimates the median GHG emission intensity from hydropower at 24 gCO2e/kWh. However, some tropical reservoirs can have intensities exceeding 100 gCO2e/kWh.[2] Proper site selection and reservoir management can help mitigate methane emissions from hydropower.
It’s also important to account for the GHG emissions avoided due to renewable hydropower displacing fossil fuel electricity generation. Hydropower prevents approximately 3 gigatons of CO2 emissions per year globally, about 9% of total emissions.[3] While reservoirs cause methane emissions, hydropower avoids significant CO2 emissions from coal, gas, and oil.
Overall, the GHG impact of hydropower depends on site-specific factors. With proper planning and management, hydropower can play an important role in reducing global GHG emissions and mitigating climate change.
[1] https://www.energy.gov/eere/water/tracking-carbon-footprint-hydropower
[2] https://www.hydropower.org/factsheets/greenhouse-gas-emissions
[3] https://www.iea.org/events/iea-at-cop27-the-role-of-hydropower-in-achieving-climate-resilience
Social Impact
The construction of large hydroelectric dams often necessitates the displacement of local communities and indigenous peoples. One significant impact is the loss of cultural heritage sites and sacred areas. For example, the Three Gorges Dam in China submerged numerous archaeological and cultural sites, displacing over 1.2 million people in the process.
According to a 2004 UN report, Social Impacts and Social Risks in Hydropower Programs, hydro dams lead to “the economic, social and environmental decline of the directly affected communities”. Communities may lose their homes, livelihoods, and traditional ways of life.
Resettlement programs for displaced peoples are often inadequate. A 2022 study from Michigan State University found hydro dam construction associated with decreased population and economic stagnation in nearby communities (Source). The cultural and social disruption hydro dams cause can persist for generations.
Economic Considerations
While hydropower has relatively low operating costs since it does not require fuel, it does have very high upfront infrastructure costs. Building a hydroelectric dam and power plant requires major capital investment, with costs that can easily run into the billions of dollars. According to the Institute for Water Resources, the average cost of dam construction is around $2,000 per kW of installed capacity, much higher than fossil fuel plants.
However, over the long-term, hydropower can produce revenue for many decades. Since the fuel (water) is free, and there are low maintenance costs, hydroelectric plants can continue generating electricity for 80 years or more. The Department of Energy states that because of the long lifespan, hydropower is often one of the lowest-cost sources of renewable energy, costing about $0.85 per megawatt-hour to produce. This steady long-term revenue and affordable pricing can offset the high initial investment over time.
Overall, the economic viability of hydropower depends on the ability to finance the major upfront infrastructure costs and have proper oversight to ensure the long-term revenues surpass the initial investment. With the right circumstances, hydropower can be an affordable and profitable renewable energy source.
Regulations and Oversight
Hydropower projects in the United States are highly regulated, especially when it comes to environmental protections. The main federal regulator is the Federal Energy Regulatory Commission (FERC), which issues licenses for hydropower projects https://www.ferc.gov/industries-data/hydropower. FERC licenses include requirements for fish passage, minimum water flows, recreation access, and protection of cultural resources.
For new dams, the environmental review process is extensive. Developers must conduct studies on the potential impacts to wildlife, water quality, recreation, and more. Environmental groups provide input during the licensing process to advocate for river protections. Approval can take 5-10 years with all the requirements https://www.hydro.org/policy/priorities/.
Other agencies are also involved in hydropower oversight, like the U.S. Fish and Wildlife Service, National Marine Fisheries Service, and U.S. Forest Service. The regulations aim to balance power generation with minimizing harm to the natural environment and communities affected by dams https://en.wikipedia.org/wiki/Hydropower_policy_of_the_United_States.
The Future of Hydropower
As the world transitions to renewable energy, hydropower will continue to play a crucial role in the energy mix. Hydropower currently provides around 16% of the world’s electricity from renewable sources, and has the potential to grow substantially, especially in developing countries (https://www.iea.org/energy-system/renewables/hydroelectricity). However, future hydropower development must focus on sustainability.
There are concerns that large hydropower dams can negatively impact local ecosystems and communities. More sustainable approaches can include investing in modernization and upgrades to existing plants, developing small run-of-river projects with lower environmental impacts, and integrating pumped storage hydropower to balance intermittent renewables like wind and solar. Strict environmental regulations and working with local communities will also be key.
If done right, hydropower can continue serving as a reliable source of renewable electricity for years to come. With the proper safeguards and sustainability measures in place, hydropower can help lead the transition to a decarbonized energy future while minimizing impacts on local environments and people (https://www.energy.gov/eere/water/articles/hydropower-key-clean-energy-future-heres-why).
