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Belo Monte Dam has tripled greenhouse gases in the eastern Amazon

Belo Monte hydroelectric dam on the Xingu River 2017, photo by Fernanda Brandt (CC)


Research published in the Science Advances journal shows that greenhouse gases in the eastern Amazon have tripled after the construction of the Belo Monte dam. The study showed that “post damming greenhouse gas (GHG) emissions in this dam area are up to three times higher than pre-impoundment fluxes and equivalent to about 15 to 55 kg CO2eq MWh−1”. To arrive at these results, the researchers measured the methane (CH4) and carbon dioxide (CO2) fluxes in the Belo Monte area during the high and low water seasons of the first two years after reservoir filling and compared them to pre-existing natural GHG emissions in the affected region. In response to this, the researchers call on governments to “consider alternatives for energy generation that avoid the damming of large rivers and the creation of new flooded areas in this region”.

The Amazon is of vital importance to the earth. It is home to the greatest diversity of flora and fauna in the world. It helps regulate the climate and about 15% of the planet’s freshwater flows through its waterways. Far from being maintained as a sanctuary and with as little human intervention as possible, this ecosystem has been exponentially modified by mining, cattle ranching, oil, extensive logging, and hydroelectric projects.

The increase in the number of hydroelectric projects in the large rivers of the Amazon River Basin will continue to substantially impact the communities and ecosystems that depend on these rivers. There are currently not one, not two, but hundreds of hydroelectric dams in the Amazon, and many more are planned.

The Belo Monte complex is located on the Xingu River in the state of Pará, Brazil. It is so far considered the largest hydroelectric dam in the Amazon and ranks fifth among the 10 largest dams worldwide (Energy Newspaper, 2021). Its electricity generation capacity is 11,233 MW.

Amazon River basin and the location of the Belo Monte hydroelectric complex study area used to evaluate emissions before and after the reservoir. Source:

Belo Monte is a run-of-river (ROR) dam, which means it diverts a portion of the water through a barrier to harness its power to operate the turbines that generate electricity. Unlike other dams, RORs do not store water but return it to the river continuously.

This feature has served the dams in passing to promote themselves as “more sustainable” and “clean energy” projects. However, this discourse has omitted that the impact of a structure the magnitude of Belo Monte was unknown to date. That is why a team of researchers decided to study the emissions produced by this dam to update the knowledge about new hydroelectric power plants in the Amazonian scenario (BERTASSOLI et. al., 2021).

The researchers affirm that, in the case of the Belo Monte Dam, “the global warming potential (GWP) of this reservoir, during the first years of operation, represents up to ~10% of natural gas power plants (422 to 548 kg CO2eq MWh-1) and is comparable to those associated with nuclear power plants (8 to 45 kg CO2eq MWh-1) or other renewable sources such as photovoltaic (29 to 80 kg CO2eq MWh-1) and wind (8 to 20 kg CO2eq MWh-1)”.

In addition, the study emphasizes the importance of spatial variations in CH4 estimates in newly flooded tropical reservoirs. They argue that estimates of the GHG footprint of hydropower reservoirs are likely based on a low number of sampling sites and this could result in a decrease in the “disproportionate contribution of hot spots (i.e., drawdown zones) and periods of intense ebullition (i.e., caused by water level fluctuation)”.

Finally, the researchers insist that the significant social and environmental costs of dams, of whatever type, be taken seriously when determining the feasibility of hydropower projects. They propose that environmental studies should be based on predictive models to estimate GHG emissions from future dams. But, above all, they insist on the need to seek alternative energy generation that avoids the damming of large rivers and the creation of new flooded areas in this region.

The full study is available free of charge and for non-commercial use at the following link:


Blog written by Laisa Massarenti Hosoya and Clara Páez 

Other references:

Agencia FAPESP (2021) Reservatório de Belo Monte triplicou emissão local de gases de efeito estufa

Deutsche Welle (2019) ¿Por qué la Amazonía es tan importante para el mundo?

El periódico de la Energía (2021) Las 10 centrales hidroeléctricas más grandes