The hydroelectric dams have historically been seen as a clean and renewable source of energy. However, several recent studies have questioned their positive impact in all geographical contexts, especially in tropical zones, where it has been shown that they can contribute significantly to climate change due to the release of greenhouse gases.
Greenhouse Gases in Reservoirs
According to an investigation by Catalan Institute of Climate Sciences, dams located in tropical areas generate greenhouse gases (GHG) due to the accumulation of dead vegetation at the bottom of the reservoirs. The anaerobic decomposition of this organic matter mainly produces methane (CH4), a gas that has a greenhouse effect 34 times greater than carbon dioxide (CO2). This process occurs more pronouncedly in warm climates, such as the tropics, where high temperatures accelerate the decomposition of biomass.
Contribution to Climate Change
GHG emissions generated by the 186.500 km² of dammed water in the tropical zone They account for approximately 1,6% of global greenhouse gas emissions. This equates to around 18 million tonnes of methane per year. Even though hydroelectric dams produce 'clean' energy, these emissions show that they are not a completely ecologically sound solution.
In addition to methane, reservoirs also release carbon dioxide (CO2), nitrous oxide (N2O) and other substances harmful to the atmosphere. This calls into question the viability of large hydroelectric projects, especially when compared to other renewable energy generation methods that do not generate such high emissions, such as solar or wind power.
Energy Production and Dam Size
La hydroelectric power production The impact of hydropower on the dam can vary considerably depending on the size of the dam. While small, well-planned and strategically located reservoirs can generate energy with a low environmental impact, large, pharaonic hydraulic works in unsuitable areas, such as tropical areas, can generate more negative effects than positive ones, both from an environmental and economic point of view.
It is common to find that the reservoirs in tropical areas They do not have a large terrain gradient, which requires the construction of larger dams and, therefore, are more likely to generate severe environmental impacts. high temperatures and the lack of sufficient movement in the waters of tropical reservoirs promotes the accumulation of large quantities of organic matter that, when decomposed, emit greenhouse gases.
Case Studies: Emissions in Tropical Reservoirs
In countries like Brazil, hydroelectric dams have been the subject of study because of their effects on climate change. Large hydroelectric projects there have shown that, rather than being a clean solution, the negative effects often outweigh the positive ones.
An example is the reservoir of balbina, in the Amazon rainforest. This reservoir has been one of the most criticized dams due to its poor energy performance compared to its very high environmental impact. Despite its capacity to generate energy, the Balbina reservoir releases a massive volume of methane due to its geographical structure and its location in a tropical area rich in biomass.
Impact on Biodiversity and Ecosystems
The construction of large dams not only alters the natural flows of rivers, but also causes a considerable loss in biodiversityNative species of fish, plants and animals that depend on the natural cycles of the river see their habitat destroyed or altered, which can lead to local extinction of some species.
Furthermore, ecosystem fragmentation and altered nutrient and sediment transport can have long-term effects on both water quality and the health of aquatic ecosystems. These effects are often exacerbated by eutrophication, a process by which excess nutrients cause uncontrolled growth of algae and other aquatic plants, reducing oxygen levels in the water and affecting aquatic species.
Displacement of Human Communities
One of the great social and human costs of building reservoirs is the displacement of communitiesIn many hydroelectric projects, the need to flood large areas of land means that entire villages are forced to abandon their homes. This forced displacement, sometimes without proper compensation, generates strong social conflicts and affects the quality of life of thousands of people.
In Brazil, for example, projects such as the Belo Monte They have not only generated controversy for their environmental impact, but also for the displacement of indigenous and peasant communities, whose lives depended directly on the river that is now dammed.
Is it possible to reduce emissions from reservoirs?
Despite the numerous negative effects, there are ways to mitigate greenhouse gas emissions from reservoirs. One of the main strategies is to reduce the amount of organic matter that reaches the reservoir by improving the management of watersheds and applying tertiary purification techniques in water treatment plants.
In addition, the construction of dams in siliceous lithology zones Instead of calcareous ones, or in areas with greater forest cover, it can help reduce CO2 emissions. It is also essential to consider the emissions cost of each hydroelectric project when assessing its viability, since in some cases hydroelectric power can generate more emissions than fossil fuels in certain contexts.
Future Considerations
The growing debate on the impact of hydroelectric dams on climate change forces us to reconsider our energy strategies, especially in tropical zonesWhile small, well-located reservoirs may be a viable solution, large hydropower projects in unsuitable areas come with high environmental and social costs. It is crucial to carefully assess the impacts of each project and apply appropriate mitigation measures if a project is implemented.
In order to reduce global greenhouse gas emissions, planning of hydroelectric projects must take a broader approach, considering not only the energy potential, but also the long-term effects on the environment and affected communities.