Why are three of Brazil’s mega dams in the Amazon on the brink of failure?

Brazil’s mega dams rank among the most powerful in the world, but droughts driven by climate change have decreased the dams’ output to as low as 3% of their potential. Hydropower accounts for around half the energy Brazilians use. 

First Look

Santo Antônio is one of three mega dams located in the depths of Brazil’s lush Amazon rainforest that were once hailed the future of the country’s green energy production.

The “run-of-river” mega dams – whose turbines are moved by natural river flows rather than water cascading from towering reservoirs – were Brazil President Luiz Inácio Lula da Silva’s bet on a green future when he was first in power in the 2000s.

Santo Antônio, Jirau, and Belo Monte were built in the Amazon rainforest despite strong opposition from environmental groups and have become among the top five most powerful dams in the country. Belo Monte, which started operating in 2016, has the fourth-largest capacity in the world.

But the mega dams are running well below capacity as river levels shrink due to a record drought in the Amazon, highlighting how climate change is becoming a growing challenge to Brazil’s green ambition.

“Unlike with old power plants, the river is the boss, if it gets too dry it stops working,” said a guide who took tourists around the Santo Antônio dam earlier this year.

Santo Antônio had to deactivate 43 out of its 50 turbines early in September as river levels neared a record low due to the drought, having had to shut completely for the same reason for two weeks in October 2023.

The three mega dams worked at only a fraction of their full capacity in September, exacerbating a trend whereby hydropower companies have consistently failed to meet the “minimum assured energy” output set out in their contracts with the government.

Santo Antônio only worked at less than 10% of its capacity in the first 20 days of September, Jirau at 5%, and Belo Monte at less than 3% of its full potential, according to government data. By comparison, Santo Antônio and Jirau worked at around double the capacity in the equivalent period of 2021, a year in which Brazil’s Amazon grappled with heavy rain.

Experts say the situation is likely to deteriorate as droughts become more regular in future.

“Studies indicate that severe drought periods will become more frequent in all regions of Brazil,” Norte Energia, the company which operates Belo Monte, told the Thomson Reuters Foundation.

A 2015 report commissioned by the government predicted that energy potential from natural river flows in Brazil will fall between 7% and 30% by 2030.

Brazil’s Ministry of Mines and Energy declined the Thomson Reuters Foundation’s request for a comment.

History of underperforming

Hydropower accounts for 47% of Brazil’s energy capacity, making it the cornerstone of Mr. Lula’s ambition to turn the country into a net exporter of green energy, or as he put it, the “Saudi Arabia of renewable energy in 10 years.” Saudi Arabia is the world’s largest crude oil exporter.

Mr. Lula’s bet on “run-of-river” dams was aimed at securing cheap energy that would have less impact on the environment than traditional dams that create large reservoirs.

But the underperformance of the Amazon’s mega dams is not new, raising into question the government’s green strategy, experts say.

Santo Antônio, Jirau, and Belo Monte have not delivered on the “minimum assured energy” output written into contracts between hydropower companies and the federal government in any year since they began producing in the 2010s, according to a Thomson Reuters Foundation analysis of data from the National Electric System Operator.

The “minimum assured energy” refers to the minimum amount of electricity power plants commit to deliver to the national electricity system based on historical river flow patterns.

But history has not been very indicative of future river levels as the climate has been changing, said Celio Bermann, professor at Universidade de São Paulo’s Institute for Energy and the Environment.

Eletrobras, the company that operates Santo Antônio, told the Thomson Reuters Foundation that Santo Antônio’s minimum assured energy output of 2.31 Gigawatts was based on historical river levels that “did not reflect the extreme alterations observed over the last years.”

As the river levels fall, hydropower companies are being forced to buy electricity from other producers in the spot market, often at heavy financial cost, to meet their contractual obligations.

If water levels do not rise in the following years, “those [Amazon] power plants will go bankrupt,” said Mário Daher, a consultant in the energy sector.

Jirau has a minimal assured energy output of 2.1 Gigawatts, and Belo Monte’s is 4.41 Gigawatts, according to data from the Brazilian Electricity Regulatory Agency.

Alternatives?

As electricity output from the Amazon’s mega dams has dropped, authorities have turned to polluting and costly fossil fuels.

The government is currently building 15 additional gas-powered plants, which nonprofit Arayara International Institute says should boost Brazil’s natural gas generation capacity by at least 30%, thereby increasing the country’s carbon emissions.

Meanwhile, an August report co-authored by the nonprofit Institute for Energy and the Environment (IEMA) proposes using solar and wind energy to help convert smaller hydropower dams into “pumped storage hydropower dams.”

The idea is to use solar and wind energy when it is sunny and windy to help fill water reservoirs that could later be used to generate electricity when the sun goes down and the wind eases.

Solar and wind electricity has been growing rapidly over the past five years in Brazil and now accounts for 29.4% of the country’s energy capacity, according to data from Brazil’s Energy Research Office.

The output of Santo Antônio, Jirau, and Belo Monte could also be boosted by building more dams along the river as was originally planned, said Vinícius Oliveira da Silva, researcher at the non-profit Institute for Energy and the Environment.

But this would be controversial given the opposition to the original dams and their disappointing track record.

Environmentalists say their construction has contributed to deforestation, the loss of biodiversity, and dislocation of tens of thousands of Brazilians.

“What good did it do to kill the river, the forest ... and animals?” asked Ana Barbosa, coordinator at the Xingu Vivo movement, which opposes Belo Monte and other dams in the Xingu river.

“You just have a monument in the middle of the river so men can say they were able to build it, even though it doesn’t produce anything but blood and disaster.”

Mr. Lula’s new government has, however, reignited talks with Bolivia to build a new mega dam in the Madeira river, on the border between the two countries, since he returned to power in 2023.

This would be a win-win for his government as it would help boost output at Jirau and Santo Antônio, both located on the Madeira river, while the environmental impact is expected to be greater on Bolivia, according to Mr. Oliveira da Silva.

“It seems to be the right moment to make that dam happen,” he said.

This story was reported by the Thomson Reuters Foundation.