Hydropower's Impact: Reducing Air Pollution, Improving Our Health

Hydropower is a widely used renewable source of energy. However, it is not without its environmental impacts. While hydropower has helped cut down air pollution by reducing carbon emissions, it has also been associated with water pollution and other ecological consequences. The construction of reservoirs for hydropower generation can lead to the release of methane and carbon dioxide, contributing to atmospheric warming and climate change. Additionally, hydropower dams can alter the temperature and chemical composition of water, affecting the biological integrity of river ecosystems and causing water loss downstream. The benefits of hydropower in reducing air pollution must be weighed against these environmental concerns to ensure sustainable practices.

How much air pollution has hydropower cut down?

Hydropower's carbon footprint

Hydropower is a widely used renewable source of energy. However, it is not without environmental impacts, and its carbon footprint can vary greatly depending on the specific context.

The IPCC states that hydropower has a median greenhouse gas (GHG) emission intensity of 24 gCO₂-eq/kWh, which is significantly lower than the median figure for gas (490 gCO₂-eq/kWh). Independent research suggests that the use of hydropower instead of fossil fuels has helped avoid more than 100 billion tonnes of carbon dioxide in the past 50 years, equivalent to the total annual carbon footprint of the United States for 20 years. The United States National Hydropower Association estimates that hydropower cuts down 200 million metric tons of carbon yearly, equal to the carbon emissions of 38 million passenger cars.

However, it is important to note that hydropower reservoirs can also produce carbon dioxide and methane, a potent greenhouse gas with 80 times the warming power of CO2 in the first 20 years after its release. When a reservoir is created and filled with water, submerged vegetation decomposes and breaks down, releasing these gases. The construction of reservoirs also changes the way carbon is emitted and stored in river systems, and some reservoirs have carbon footprints equal to or greater than fossil fuels. A study by EDF found that of the nearly 1,500 hydropower plants worldwide that were examined, more than 100 facilities had greenhouse gas emissions that caused more warming than fossil fuels.

The environmental impacts of hydropower extend beyond carbon emissions. Hydropower dams can alter the temperature and chemical makeup of water, harming the biological integrity of river ecosystems. They can also block fish passage, change the concentration of nutrients, and reduce water quality and downstream river flow. Additionally, the construction and operation of hydroelectric power plants can produce global warming emissions.

To accurately assess the carbon footprint of hydropower, it is important to consider the full electrical portfolio and account for both gross and net emissions. While hydropower has the potential to reduce air pollution, it is crucial to prioritize minimizing climate impacts in the design, construction, and geographic placement of new hydropower facilities to ensure that they deliver climate benefits.

Water pollution

While hydropower generators do not directly emit air pollutants, the construction and operation of dams, reservoirs, and hydroelectric generators can negatively impact the environment and contribute to water pollution.

One of the main concerns is the degradation of water quality as it flows through hydroelectric dams and reservoirs. This degradation affects a wide range of plant and animal life and hinders aquatic activities such as fishing. The formation of a reservoir results in the creation of layers with varying oxygen levels, with higher concentrations at the top and lower concentrations at the bottom. These areas with low oxygen levels, known as hypoxic areas, can negatively impact aquatic life. Additionally, the presence of algae can negatively impact the taste, colour, and odour of water, making it unsuitable for human consumption. Certain types of algae are poisonous and can pose risks to human health if ingested.

The operation of hydropower dams can also lead to changes in natural water temperatures, water chemistry, river flow characteristics, and silt loads. These changes can have detrimental effects on native plants and animals in and around the river. The construction of dams and reservoirs may also require the relocation of people and can obstruct fish migration, further impacting the biodiversity of the region.

Furthermore, the manufacturing of concrete and steel for hydropower dams can produce emissions, especially if fossil fuels are used as energy sources. While the long operating lifetime of hydropower plants (50-100 years) can offset these emissions, it is important to consider the immediate and local environmental impacts. Additionally, greenhouse gases, such as carbon dioxide and methane, can form in human-made water storage reservoirs due to the decomposition of biomass in the water.

To mitigate these issues, it is crucial to encourage the responsible development and operation of hydropower projects while protecting the local ecosystem and communities that depend on healthy rivers for economic benefits, such as river recreation, fishing, and wildlife preservation.

Impact on wildlife

Hydropower is a clean and renewable energy source that does not emit air pollutants. However, the infrastructure required to harness hydropower can have a significant impact on wildlife. Hydropower plants often involve the construction of dams and reservoirs, which can disrupt the natural flow of river systems. This can lead to:

• Blocked fish migration routes, which can deplete fish populations over time. This has consequences for both human food supply and marine ecosystem stability.
• The death and injury of fish that come into contact with turbine blades. While the exact percentage is not known, estimates range from 2% to 10%.
• Changes in water temperature and chemistry, which can affect the ecology and physical characteristics of the river, impacting native plants and animals.
• Upstream flooding, which can harm native plants, wildlife habitats, critical natural areas, and agricultural land.
• The displacement of both human and wildlife populations.

The construction of hydropower infrastructure can also lead to the destruction of forests, wildlife habitats, and agricultural land. In some cases, entire communities have had to be relocated to make way for reservoirs.

While hydropower has been associated with negative impacts on wildlife, it is important to note that the sector is working to improve its sustainability. The most common approach to managing biodiversity impacts is by applying the mitigation hierarchy, which includes avoiding, minimising, mitigating, and compensating for any adverse effects. Additionally, the development of new turbine technologies is being sponsored by the U.S. Department of Energy to reduce fish deaths.

Global warming emissions

Hydropower is a clean, renewable, and environmentally friendly source of energy. It is a low-carbon alternative to electricity generation by fossil fuels. If hydropower was replaced with coal, the International Hydropower Association (IHA) estimates that over 4 billion metric tonnes of additional greenhouse gases would be emitted annually—a figure that would increase global emissions from fossil fuels and industry by at least 10%.

The greenhouse gas footprint of hydropower has been questioned, particularly concerning emissions from reservoir creation. In certain conditions, a reservoir will release greenhouse gases due to the decomposition of flooded organic material. These emissions are typically highest in the first 10 to 20 years, then decrease over time. However, a reservoir can also act as a carbon sink, absorbing more emissions than it emits. The net emissions of a reservoir depend on its type, size, location, depth, shape, and other factors.

The Intergovernmental Panel on Climate Change (IPCC) notes that hydropower has a median greenhouse gas (GHG) emission intensity of 24 gCO₂-eq/kWh, which is significantly lower than the median figure for gas at 490 gCO₂-eq/kWh. The IHA's analysis of almost 500 reservoirs worldwide using the G-res Tool confirms this low carbon footprint, with a median value of 23 gCO₂-eq/kWh for lifecycle GHG emissions.

The G-res Tool evaluates the land's pre-impoundment state, including natural and human-related emissions, to estimate the net change in GHG emissions attributable to a reservoir's creation. It also considers the reservoir's freshwater services, such as water supply, flood and drought management, and recreation. Overall, hydropower has a low carbon footprint and helps reduce global warming emissions compared to other energy sources.

Climate change

Hydropower is the oldest form of clean electricity, producing around 3930 TWh every year. As a renewable energy resource, it contributes to the avoidance of greenhouse gas (GHG) emissions and the mitigation of global warming. Compared to burning coal, hydropower prevents the emission of about 3 GT CO2 per year, or up to four billion tonnes of additional greenhouse gas emissions annually. This represents around 9% of global annual CO2 emissions.

Hydropower also supports the rapid growth of solar and wind power, thanks to the flexibility and storage it offers to power grids that are increasingly reliant on variable power supplies. Beyond energy, hydropower provides water services, with reservoir storage capacity that can be used for drinking water supply, irrigation, and flood control. As global temperatures rise, increasing water storage capacity through dams will be essential for adapting to a warmer world and combating the increasing frequency of droughts and flooding.

However, like other types of infrastructure, hydropower is vulnerable to the negative impacts of climate change. Climate change is likely to alter river discharge patterns, impacting water availability and hydropower generation. To address this challenge, the International Energy Agency (IEA) has emphasised the role of hydropower in achieving climate resilience. The IEA's presence at COP27 highlighted the potential for joint development of hydropower resources to improve climate action planning and implementation at national, regional, and global levels.

In conclusion, hydropower is a cheap and mature technology that contributes significantly to climate change mitigation. With further development, it could play a key role in adapting to the impacts of climate change, particularly regarding water resource availability.

Frequently asked questions