Big dams are bad for both the global climate and the local environment. Small hydropower projects can reduce carbon without harming local ecosystems.
This graph from the Energy Information Administration communicates the reality of renewable energy in America better than any other single source. Renewable energy covers only a small slice, 8 percent, of the country’s needs. And despite the focus on biofuels and solar power, the chart shows that more than a third of that slice comes from hydropower. In the wider world, an even greater proportion of renewable energy comes from hydropower—83.8 percent of renewable generation, according to the International Energy Agency.
The environmental line on hydropower has been that it's good for the global climate, but bad for the local environment. But as the push for hydropower gains strength in places like Africa and the Amazon, environmental groups are arguing that hydropower contributes to climate change, too. Friends of the Earth International and Rivers International released this Google Earth video that explains how the risks of new, big dams counter their low-carbon footprint, particularly as the world warms up.
The groups argue that climate change exacerbates the hazards of dams, while modifying their benefits. As rivers dry up, hydro projects will produce less energy, less reliably. Dams built now depend on historical data, which won’t predict flows in the future. Melting glaciers and weird weather heighten the risks of floods. A dam is a huge, inflexible investment, and climate change requires adaptation. Large hydropower projects also contribute to water scarcity: Huge amounts of water evaporate from dammed reservoirs.
And although large hydropower projects don’t slough carbon into the atmosphere, they do contribute to climate change by producing methane from rotting algae in reservoirs. There’s some debate about how bad this problem is, but the environmental groups put the impact at the same level as effects from the global air travel industry.
Hydropower doesn’t have to come with these risks, though. Small hydroelectric projects can tap into a river’s energy without damming it. In the United States, a government laboratory put the potential of small hydro at a substantial 30 gigawatts. That energy could come from “run of the river” projects that don’t require dams, or from projects built on existing dams. The Department of Energy is also investing in small hydro pilot projects that could tap lower energy spots on a river. Business Week reported two years ago on a project in Brazil that suspended turbines in the middle of the river. (Like the government-funded Alden Turbine, the project would allow fish to pass freely up and down the river.) Developers can also place small hydro projects in places where they’ll have little environmental impact, like irrigation canals and the streams exiting water treatment plants.
These types of project can’t produce the same scale of energy as large dams can. But they contribute to community resilience by distributing the responsibility for energy generation. In places like Africa, where many communities are not connected to the grid, investing in small, distributed energy projects make more sense than placing a huge bet on a dam. But even in places with robust grids, distributed renewable energy can help mitigate the harms that huge, unsustainable projects require—whatever the energy source.