Historic floods in southern Brazil have been returned “twice as likely » by climate change, which has “ intensified » torrential rains caused by the El Niño phenomenon, according to a study made public Monday June 3.
In two weeks, the equivalent of three months of precipitation fell on the state of Rio Grande do Sul, “an extremely rare episode, which should only occur once every 100 to 250 years”, according to the study by the scientific network World Weather Attribution (WWA).
“Researchers estimated that climate change has made this episode twice as likely and 6 to 9% more intense », Explained the scientific network World Weather Attribution (WWA) in a press release.
At least 172 dead
Dantean floods have submerged entire towns and devastated fields as far as the eye can see in this agricultural state as vast as the United Kingdom. The latest official report shows 172 dead and 42 missing. Nearly 600,000 people had to leave their homes. “Researchers estimated that climate change has made this episode twice as likely and 6 to 9% more intense”explains WWA in a press release.
El Niño, a natural meteorological phenomenon associated with warming of the ocean surface, exacerbated precipitation by 3 to 10% in southern Brazil, according to this network which analyzes the link between this type of disaster and climate change.
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“Climate change is amplifying the impact of El Niño in southern Brazil, making an extremely rare episode more frequent and more intense,” says Regina Rodrigues, one of the authors of the study. According to this researcher from the University of Santa Catarina, in southern Brazil, three of the four worst floods in the history of Porto Alegre, capital of Rio Grande do Sul, took place “over the last nine months”, which is ” very rare “.
This is despite the fact that El Niño has weakened in recent months, with the current cycle appearing to be coming to an end, paving the way for the likely return of the opposite phenomenon, La Niña, synonymous with cooler global temperatures.
Faulty protection system
Before last year, when three major floods, one of which was caused by a cyclone, had already caused several dozen deaths, the south of Brazil had been relatively spared for around sixty years.
Enough to give a false sense of security to residents, even if it is a region particularly vulnerable to flooding, because it is crossed by numerous rivers, estimates Maja Vahlberg, consultant from the Croix-Climate Center. Red and Red Crescent.
Porto Alegre, a metropolis of 1.4 million inhabitants, is located on the shores of Lake Guaiba, fed by five rivers. The city had a protection system based on dikes and floodgates after major floods in 1941 and 1967.
This device was supposed to contain a rise in the water level of the Guaiba of up to six meters. But it began to be exceeded as soon as the level of 4.5 meters was reached. The system was criticized by many residents who complained of having the view of the lake obscured by the dikes. So much so that some wanted to see it completely dismantled.
“The world must prepare”
“The frightening thing is that these floods show that the world needs to prepare for events so extreme that they are unlike anything we have seen before,” insists Ms. Vahlberg. WWA researchers also believe that deforestation and the rampant urbanization of cities like Porto Alegre have “aggravated the impacts” of this unprecedented climate catastrophe.
The study cites in particular the loss of 22% of the region’s native vegetation in less than four decades, to make way in particular for soya fields. Maja Vahlberg advocates “put in place policies that make the population less vulnerable, by increasing protection against floods and restoring ecosystems”, in order to “avoid deaths and limit material damage”.
