One of the world’s largest rivers and a major tributary of the Amazon, the yawning Rio Negro is a pillar of the rainforest ecosystem that is crucial to the stability of the global climate. But vast sections of the waterway are currently dry.
For weeks, an unprecedented drought has pummelled the region, reducing water levels in key Amazonian arteries to record lows and wreaking havoc on local communities and the unique wildlife of the biome.
The immediate victims of the drought are more than half a million people in Brazil’s Amazonas state, who are suffering an unfolding humanitarian emergency as the region’s river-borne transportation is choked by the lack of water.
But the drought also has far-reaching implications for the Earth’s climate. As the extreme heat and water shortage kills trees and sparks fires, the forest begins to release its enormous stocks of carbon dioxide, fuelling the process of global warming that scientists say was an important factor behind the drought in the first place.
“It is starting a vicious circle that will destroy forest,” said Philip Fearnside, a scientist at the National Institute for Amazonian Research in Manaus.
“Because of this huge stock of carbon in the forest, the Amazon is at the centre of this question of global warming escaping from human control. If just a fraction comes out, it would be the straw that breaks the camel’s back. And there is an increasing risk of that happening.”
In Manaus, a port city in the heart of the rainforest, the watermark of the river has fallen as low as 12.7m — more than 6m below the historic average for October — leaving the docks barren as the region’s rivers lose much of their transport function.
More than 60 municipalities in Amazonas, the state that includes Manaus, are officially in a state of emergency, with the government rushing in basic supplies including food, water and medicines.
“Rivers are our roads, so it has become impossible to go anywhere,” said Fredson Farias, who sells boat tickets at Manaus port. He estimated that footfall had dropped by 70 per cent.
“There are parts of the river that are 95 per cent dry. In 100 years we’ve never seen anything like this,” he said.
The immediate cause of the drought is a combination of the ongoing El Niño weather event, which warms the eastern equatorial Pacific Ocean’s surface, and an unusual patch of warm water in the Atlantic Ocean above the equator.
The two phenomena have inhibited the formation of clouds and caused rainfall to drop sharply. In Belém, a city in the eastern Amazon, rainfall in September was a quarter of typical levels.
In addition to the Rio Negro, which is one of the world’s largest rivers by discharge levels, the huge Amazon, Solimões and Madeira rivers have all hit record lows and are, in parts, dry.
Experts say the intensity of the events in the Pacific and Atlantic — not in themselves caused by human activity — has been worsened by climate change.
“Global warming is clearly making a contribution to this exceptional drought,” said Tim Lenton, chair in climate change and Earth system science at the University of Exeter.
“It has added to the warmth in the Eastern Equatorial Pacific where El Niño is creating its usual warm water pool. It has also contributed to unprecedented warm sea surface temperatures in the north Atlantic. Both patterns of ocean heating are contributing to the current drought.”
Further complicating the situation are exceptionally high temperatures. On October 10, the national meteorology institute reported a reading of 40C in Manaus, the highest since records began almost a century ago.
The heat and lack of rain have created prime conditions for fires, which — like the drought itself — can kill trees, damage the ecosystem and cause the release of more carbon into the atmosphere.
A UK-Brazil study from 2021 found that droughts and fires resulting from the 2015-16 El Niño caused the death of more than 2.5bn trees and woody vines and the release of almost 500mn tonnes of carbon dioxide emissions.
Last month was the worst October for fires in Amazonas state since records began 25 years ago, with more than 3,400 blazes reported, according to the state government.
The events have fuelled concerns that parts of the world’s largest rainforest are being pushed towards so-called “tipping points”, where the mass mortality of trees means the rainforest can no longer sustain its water recycling ecosystem. This would fuel more droughts, more tree mortality and potentially sharp climate fluctuations across Latin America and the world.
“The forest is succumbing,” said Marcio Astrini, executive secretary of the Climate Observatory, a Brazilian non-profit group. “It doesn’t happen as a whole or all at once, but in some regions you’re already experiencing these inflection points.”
Following rampant deforestation in recent years, several parts of the Amazon, notably in the south-eastern section in Pará state, are already emitting more carbon than they absorb, according to several studies.
“You can expect more droughts like this one to happen. That is what the models show,” said Fearnside.
At the docks in Manaus, the impact of the drought is stark. The rapidly retreating river is being replaced by rubbish-strewn sandbanks. Health officials have warned of an increased risk of disease, including hepatitis A and cholera from contaminated water supplies.
Just outside the city, where the black Rio Negro meets the murky brown Solimões to form the Amazon river, the drought has exposed a rocky outcrop with human faces carved into the stone. Archaeologists believe the markings could be up to 2,000 years old.
A pontoon dock in the Rio Negro was crowded with cargo, including Honda motorbikes, cleaning products, clothes and grains, after vessel departures were reduced. The port is a hub for supplying remote villages deep in the rainforest.
“We are trapped in the city,” said Marilene Bonilia, who sat on the dock struggling to sell trinkets to a trickle of arrivals. “We are suffering.”
Ebido Santos, who was supervising the loading of riverboats, said: “It has been bad before, but never like this.”
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