Hydropower development:
environmental and social impacts

Hydropower development has significant environmental and social impacts that require careful consideration and management. Although hydroelectric power plants produce electricity without directly emitting air pollutants, their construction and operation can have profound impacts on the environment and society.

Environmental impacts of hydropower

The construction of hydroelectric power plants, especially large dam projects, causes multifaceted changes in natural ecosystems. These changes affect both terrestrial and aquatic components of the environment.

Land Flooding and Habitat Loss One of the most obvious consequences is the flooding of vast areas when reservoirs are created. This results in the destruction of forests, natural wildlife habitats, agricultural lands and valuable landscapes. The loss of terrestrial habitats lasts for the entire life of the reservoir. For example, the construction of all 1,956 identified reservoirs would, according to some studies, result in a new global reservoir area of 240,000 km², which would almost double the existing artificial reservoir area of 300,000 km².

Flooding of lands results in habitat loss for terrestrial species. This poses a serious threat to biodiversity, as many animal and plant species are deprived of their usual habitat. Agricultural lands located in the flooded area are also lost, which can have economic consequences for local populations.

Changes in hydrological regime and water quality Dams and reservoirs significantly alter the natural hydrological regime of rivers. They can reduce river flows, increase water temperature and worsen its quality. Water retention in reservoirs leads to changes in natural water level fluctuations, which affects coastal ecosystems.

Changes in streamflow characteristics, water temperature, water chemistry, and sediment transport can all negatively impact native plants and animals in and around a river. Dams often leave downstream riverbeds nearly dry, which is particularly detrimental to communities that depend on river ecosystem services. Increased evaporation from a reservoir’s large open water surface reduces average annual flow downstream, which in turn disrupts freshwater habitats.

Greenhouse Gas Emissions Reservoirs can be sources of greenhouse gases such as methane and carbon dioxide. These gases are formed by the anaerobic decomposition of organic matter submerged when the reservoir is created. Although hydropower is often considered a low-carbon energy source, studies show significant variability in emissions from one reservoir to another. Some reservoirs may have higher greenhouse gas emissions per unit of electricity produced than fossil fuel power plants. The exact greenhouse gas emissions from hydroelectric reservoirs remain uncertain and depend on a variety of location- and region-specific factors.

The decomposition of organic material, such as plants, when reservoirs are flooded releases these gases. Methane emissions are particularly important because methane is a potent greenhouse gas. These emissions contribute to climate change, and the associated rise in temperature could accelerate species extinctions.

Impact on Fish Migration and Aquatic Biodiversity Dams are physical barriers that can prevent fish such as salmon and shad from migrating to spawning grounds upstream. This can devastate populations, as happened to Chinook salmon on the Klamath River on the Oregon-California border. Hydroelectric turbines can also kill and injure some fish that pass through them.

Disruption of fish migration routes is a serious problem for the conservation of aquatic ecosystems. Decreases in fish populations can have a cascading effect throughout the food chain. Although technical solutions such as fish ladders and fish elevators exist, their effectiveness may be limited. For example, the Safety Harbor Dam on the Susquehanna River in Pennsylvania uses elevators to lift migrating shad from the base of the dam to the top of the reservoir. Research and development is underway on turbines that could reduce fish mortality to less than 2%, compared to 5 to 10% for the best existing turbines.

Erosion and sediment accumulation Dams can alter the patterns of sediment transport and deposition in a river. Sediment retention in a reservoir can lead to erosion of the riverbed and banks downstream, and reduce the supply of nutrients to deltas and coastal areas. Sediment accumulation in the reservoir itself reduces its useful storage capacity over time and can affect the operation of a hydroelectric power station.

Impacts from Construction Materials The production of concrete and steel used in the construction of hydroelectric dams requires equipment that can produce emissions. If the energy sources for producing these materials are fossil fuels, the emissions from this equipment may be associated with the electricity generated by the hydroelectric power station. However, given the long lifespan of a hydroelectric power station (50 to 100 years), these initial emissions are often offset by subsequent emission-free electricity production. However, sand and gravel mining also causes habitat destruction.

Regional climate change The construction of large hydraulic structures such as dams can have an impact on regional climate. This may include changes in the local water balance and possibly in rainfall patterns. Research suggests the need for more comprehensive environmental assessments and policy measures to address impacts on biodiversity, climate, land use and human activities before dam construction is planned.

Social impacts of hydropower

Hydropower development has significant impacts on the lives of people, especially those living near rivers and dependent on their resources. These impacts can be varied and affect economic, cultural and social aspects of life.

Resettlement of Populations The creation of reservoirs often requires the relocation of people living in flooded areas. This can result in the loss of homes, land, and traditional ways of life. The process of relocation itself is complex and can cause social tensions and economic hardship for affected communities.

Impact on Traditional Livelihoods Hydropower projects may alter the traditional livelihoods of rural populations. Changes in ecosystem conditions caused by hydropower plants disrupt natural hydrological regimes. Hydropower plants divert water, often leaving riverbeds almost dry, which subsequently impacts communities that depend on the ecosystem services of the rivers. Potential environmental impacts may generate social impacts that are highly variable and specific to certain communities. As a result, traditional livelihoods of rural populations are likely to change in terms of environmental, agricultural, economic and socio-cultural activities.

In the Balkan Peninsula, for example, the Social Impact Model estimates that 470,000 people are potentially affected by existing hydropower plants. This number could rise to around 1.3 million if we assume that all hydropower plants currently under construction or planned are commissioned in the future. This means that around 3% of the Balkan region’s 42 million people could potentially see changes to their livelihoods. These figures are considered conservative estimates, as they represent the number of people living in close proximity to the affected river sections.

Loss of cultural heritage Reservoirs can cover not only natural areas and agricultural lands, but also archaeological sites of cultural and historical value. The loss of such sites is an irreparable loss for the cultural heritage of the region and all of humanity.

Impact on public health Changes in water quality and the environment associated with hydroelectric projects can indirectly affect public health. Stagnant water in reservoirs can facilitate the breeding of disease vectors. Deterioration of drinking water quality is also a threat.

Conflicts and Inequality The planning and implementation of hydropower projects can lead to conflicts between different interest groups: local populations, investors, and government agencies. Often, the benefits of projects are unevenly distributed, and the most vulnerable groups of the population may bear a disproportionately heavy burden of negative consequences.

Mitigation of negative impacts and sustainable development

Despite significant environmental and social problems, there are approaches aimed at reducing the negative impact of hydropower and increasing its sustainability.

Careful siting and design Careful siting of hydroelectric power plants is key to minimising environmental impacts. Comprehensive environmental assessments should be carried out before construction decisions are made. Innovative technologies and optimised operating modes can also help reduce negative impacts.

Biodiversity protection measures Various methods are used to mitigate the impact on fish populations, such as the construction of fish passes and fish ladders that help fish to cross dams and reach spawning grounds. Turbines with a fish-friendly design are being developed to reduce mortality and injury. Biodiversity conservation is recognized as a key parameter for sustainable development. However, many new hydropower projects underestimate their impact on biodiversity.

Taking into account the interests of local people It is important to ensure that local people participate in the decision-making process and that the benefits of projects are fairly distributed. Compensation and support programs should be developed for those who are forced to relocate or lose traditional sources of income.

Climate change and risks to hydropower Climate change itself poses a threat to hydropower. Changing rainfall patterns and increased droughts can reduce water flows to hydroelectric plants. For example, the southwestern United States is experiencing a 22-year megadrought that has dramatically reduced water levels in Lake Powell and Lake Mead, which feed hydroelectric plants such as the Hoover Dam. This highlights the need for the sector to adapt to changing climate conditions.

Hydropower supports the global energy balance, but its development requires a balanced approach. Economic benefits must be carefully weighed against environmental and social costs. Comprehensive impact assessments, the introduction of advanced technologies and consideration of the interests of all stakeholders are important elements to ensure that hydropower projects contribute to sustainable development rather than exacerbate existing problems.