Climate change doubled the risk of historic flooding in southern Brazil and intensified the intense rainfall caused by the El Nino weather phenomenon, scientists said Monday.
Three months of rain was dumped in the southern state of Rio Grande do Sul in two weeks in an “extremely rare event, expected to occur only once every 100 to 250 years,” according to a study published by the World Weather Attribution. WWA) group.
Floods in late April and early May inundated towns, farms and an international airport, affecting more than 90 percent of the vast state, an area comparable to that of Britain.
The disaster killed 172 people and displaced approximately 600,000 people.
“The researchers estimate that climate change made the event more than twice as likely and about six to nine percent more intense,” the WWA said in a statement.
In addition, the El Nino phenomenon has made rainfall between three and ten percent more intense, according to the global network of scientists that assesses the link between extreme weather events and climate change.
“The scary thing about these floods is that they show us that the world needs to be prepared for such extreme events that they are unlike anything we have seen before,” said Maja Vahlberg, climate risk advisor at the Red Cross Red Crescent Climate Center.
Regina Rodrigues, a researcher at the Federal University of Santa Catarina, said the disaster showed that even when El Nino was in a weakening phase, as it is now, it could be extremely dangerous.
“Climate change is amplifying the impact of El Nino in southern Brazil by making an extremely rare event more frequent and intense,” she said.
Of the four worst-ever floods in the regional capital Porto Alegre, “three occurred in the last nine months,” Rodrigues told a news conference.
“This is very rare.”
– False sense of security –
Rio Grande do Sul is particularly vulnerable to flooding, with a vein-like network of river systems covering the region.
Porto Alegre is located on the shores of Lake Guaiba, where five rivers meet before emptying into South America’s largest freshwater lagoon, Lagoa dos Patos.
However, until 2023, the city had not experienced a major flood for sixty years.
This may have given residents a false sense of security, says Maja Vahlberg, climate risk consultant at the Red Cross Red Crescent Climate Center.
An extensive flood protection system in Porto Alegre, built after the 1941 and 1967 floods, was designed to withstand water levels of up to six meters (20 feet). However, Vahlberg said it started to fail at 15 feet due to a lack of maintenance.
The system was criticized by residents for being ugly and blocking their view of the lake. In recent years the system has faced pressure to have it completely dismantled.
– ‘Buffer the impact’ –
Warnings had been issued a week before the flood, but these may not have reached everyone and “the public may not have understood the severity of the expected impact,” Vahlberg said.
The scientists said deforestation to make way for agriculture and the rapid urbanization of cities like Porto Alegre also “exacerbated the impacts”.
The study cited data showing that 22 percent of the state’s native vegetation has been lost in less than forty years; much of it has been converted into soy plantations.
It also highlighted that at least 240 informal settlements, 80 indigenous villages and 40 communities where descendants of enslaved Africans live have been severely affected.
“Implementing policies that make people less vulnerable, increasing flood protection and restoring natural ecosystems to buffer the impact of heavy rainfall are some of the ways governments can prevent human deaths and reduce the damage caused by these events limit,” says Vahlberg.
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