Brazil is reeling from catastrophic floods. What went wrong – and what does the future hold?
When the torrential rain began to swallow her city block, Cristiane Batista, 34, grabbed her three children, a couple of backpacks and her smartphone and waited at the door, hoping to be picked up by the municipal trucks preparing to evacuate the population of Muçum, in the state of Rio Grande do Sul, Brazil.
“I was terrified. The house was about to flood. We had to get out of there,” she says.
Batista, her husband, Jeferson, 34, and their children – who range in age from one to eight – had already been victims of the extreme weather of Brazil’s southernmost state twice last year. In September 2023, Muçum and its nearly 5,000 inhabitants were at the centre of the devastation caused by floods, which left scores of people – including 15 people in a single Muçum house.
“We lost everything,” she says.
Two months later, the city was hit by another fierce bout of rain. The storm destroyed furniture and appliances and left walls stained with mud. After losing everything for the third time, she says she no longer has the strength to live in the city.
Rio Grande do Sul, a state home to almost 11 million people, has witnessed the most extensive climate catastrophe in its history and one of the greatest in Brazil’s recent history.
Over the course of 10 days at the end of April and beginning of May, the region recorded between a third and almost half of the yearly rainfall predicted – between 500 and 700 millimetres, depending on the area, according to measurements by Metsul Meteorologia.
The storm caused the Taquari, Caí, Pardo, Jacuí, Sinos, and Gravataí rivers – tributaries of the Guaíba – to overflow.
According to the Civil Defence, there are more than 100 people dead, more than a 130 missing, and nearly 400 people injured in 425 affected municipalities.
At least 232,125 people have left their homes: 67,542 are in shelters, and 164,583 are homeless or temporarily staying with family or friends. Cities such as Eldorado do Sul, Roca Sales, and Canoas were partly flooded, and villages such as Cruzeiro do Sul were devastated in what the state governor, Eduardo Leite, described as “the greatest catastrophe of all”.
Porto Alegre, the state capital and one of Brazil’s largest urban centres, is one of the worst-affected cities. On 5 May, the level of the Guaíba River, which runs through the city, reached a record of 5.35 meters, surpassing the 4.76 meters reached during the historic floods of 1941.
Neighbourhoods close to the river were submerged. The airport closed, and power and water-treatment plants went down, causing electricity and drinking water shortages in several areas. A dam in a northern suburb failed and flooded a large portion of the city.
Viewed from an army helicopter, the neighbouring city of Eldorado do Sul looks like a set of canals stretching along narrow strips of land and buildings. About 90% of the city is underwater. Along the BR-290 highway, one of the most critical roads in the country’s south, hundreds of people are waiting for transport to shelters.
“We knew it would be a unique event, and the river would overflow within a few days. We did simulations with the data we recorded, and the result was terrifying. So we alerted the authorities,” says Joel Goldenfum, the director of the Institute of Hydraulic Research at the Federal University of Rio Grande do Sul, who is leading research on the unfolding catastrophe in Porto Alegre.
Infrastructure is key to understanding what happened in the state capital, says Goldenfum, explaining that an extended network of 42 miles (68 kilometres) of dykes, gates, a containment wall at the dock, and more than 20 drainage pumps prevented a more severe situation. However, the lack of maintenance of the flood protection system over the years may have been a factor.
“This system has worked well, but it has already shown sealing problems,” he says. “The gates and pump houses have already shown weaknesses. There have been maintenance problems, so the system hasn’t held up.”
Extreme floods were relatively uncommon in Rio Grande do Sul. However, scientists believe that climate factors are now accelerating such events.
These include an intense wind current in the region, which destabilised the climate; an atmospheric block, which emerged after a heatwave that made the centre of Brazil drier, concentrating the rain in the country’s northern and southern extremes; and a moisture corridor from the Amazon, which strengthened the torrential rain.
Twenty years ago, a study produced by the climate researchers José Antonio Marengo and Wagner Rodrigues Soares identified a significant increase in precipitation in southern Brazil and warned of its consequences.
A more recent study published by the National Institute of Meteorology (Inmet) indicated that the number of days Porto Alegre suffers “extreme precipitation” – rainfall above 50 millimetres – has more than doubled since the 1960s. From 1961 to 1970, there were 29 days a year. This number increased to 44 days between 2001 and 2010 and rose to 66 days from 2011 to 2020.
“These climate events gain power as we have El Niño and La Niña periods. Over time, we have seen that the rainfall regime and temperatures are different,” s Marcelo Dutra da Silva, a professor of ecology at the Federal University of Rio Grande and one of the country’s leading figures warning about climate effects. “This is creating climate and ecological troubles and an economic problem.”
In June 2022, Dutra warned public authorities that cities in the southern region were not prepared for natural disasters. “There is no planning for risk areas, for flood areas. There is absolutely no environmental planning to consider the climate changes and events happening,” he said.
Carlos Nobre, a renowned climatologist, principal investigator at the Institute of Advanced Studies (IEA) of the University of São Paulo, and the co-chair of the Science Panel for the Amazon, says climate models had already indicated the risk of increased rainfall in southern Brazil.
The higher the average temperature, the more intense the ocean’s evaporation, bringing more water into the atmosphere and thus facilitating the occurrence and increasing the frequency of extreme weather events, he says.
“What we have seen happen is absolutely devastating,” Nobre says. “We have data on this in Brazil: due to climate change, the forecast is for increased rainfall [in the southern regions].”
For Nobre, a critical problem for regions suffering climate events such as extreme floods is that “the infrastructures were built for a climate that no longer exists”. He says it is time for governments to reconsider planning better adaptation to avoid future catastrophes.
Another study, produced in 2015 during the administration of President Dilma Rousseff, showed projections that now seem closer to our climate reality: heatwaves, water scarcity in south-east Brazil and intense rainfall in the south.
Natalie Unterstell, an expert in climate change policy and negotiations and one of the study’s authors, says the extreme floods in the Rio Grande do Sul are precisely what she has been warning about for years. “What is happening today in Rio Grande do Sul is our new reality and not a ‘sad exception’,” she posted on Instagram.
Brazil’s presidency says that it is not possible to estimate the exact extent of the current damage and how much reconstruction will cost as the water has not receded.
“The country will spare no effort to assist in the reconstruction and resettlement of people who have lost their homes,” itsaid in a statement. “It’s likely that there will be properties that cannot be rebuilt in the same location due to the risk of new floods.”
However, on Thursday the state governor announced his first estimate of the damage : about 19bn reals (£2.9bn), which is expected to rise in the coming days and weeks.
Leite – who has relaxed nearly 500 environmental protection regulations since 2019 when he took office – says his administration will develop a housing plan for people affected by the flood. He had previously said that the state would need “a Marshall plan” to recover, referring to the American programme to rebuild after the second world war.
The mayor of Porto Alegre, Sebastião Melo, says his administration has carried out maintenance but acknowledged that the flood prevention system “is old”.
Amid increasing public pressure for political leaders to be held accountable for their indifference to adapting to the climate crisis, Melo says his efforts are focused on the rescue operations and the displaced shelter. “It’s not time to look for culprits,” he ,says. “It’s time to seek solutions.”