Destructive floods in Brazil made twice as likely by burning fossil fuels and trees

A study has shown that the unusually intense, long and extensive floods that devastated southern Brazil were at least twice as likely to have been caused by the burning of fossil fuels and trees.

The worst disaster on record has killed 169 people, destroyed homes and destroyed crops, and exacerbated deforestation, investment cuts and human incompetence.

The international team of scientists behind the study predicted that disasters of this scale – the worst to hit the region – would become more common in the future unless the planet’s greenhouse gas emissions were sharply reduced.

Hundreds of thousands of people in the state of Rio Grande do Sul and neighboring Uruguay are still trying to rebuild their lives after a month of continuous flooding that has displaced 80,000 people and left more than a million without essential services such as electricity and potable water.

During the peak of the rain on May 1, the city of Santa Maria set a 24-hour rainfall record of 213.6mm. In three days, the state capital, Porto Alegre, was inundated with two months’ worth of rain, turning roads into rivers, a football stadium into lakes and damaging the city’s international airport so badly that it is closed.

The economic cost is expected to exceed $1bn (£780m) and the adverse impact on agriculture is expected to increase prices of rice – Rio Grande do Sul normally produces 90% of Brazil’s crop – and dairy products across the country.

The region’s focus on agriculture has come at a high cost. The authors of the study said that in recent years, natural flood defenses such as riparian forests and marshes have been cleared for parks, often in violation of weakly enforced environmental regulations.

The disaster in Porto Alegre was made worse by weak flood defenses, which were supposed to withstand 6 meters of water but reportedly began to fail at 4.5 meters.

In recent years, municipal governments have cut investment in these defenses despite warnings that this low-lying, deforested region at the intersection of five major rivers would be increasingly vulnerable to flooding as a result of man-made climate interference. In addition to being unable to stop the rising waters, the state capital’s flood barriers were caught in the floodwaters, slowing down the drying and recovery process.

Scientists from the World Weather Attribution group confirmed the powerful human impact on the flood disaster, the fourth to hit Brazil’s southernmost state in the past year and a half.

They analyzed four-day and 10-day periods of the floods by combining weather observations with results from computer climate models. They found that human-driven climate change made extreme rainfall two to three times more likely and about 6% to 9% more intense. This impact was similar to the natural effect of the El Niño phenomenon.

In addition to increasing the frequency and intensity of heavy rains, global warming is pushing the tropical belt further south, which acts as a wall across central Brazil that blocks cold fronts coming from Antarctica. As a result, flooding is now more likely in Rio Grande do Sul than was more common further north in Santa Catarina. More than 90% of the state was affected, covering an area the size of the UK.

The authors said global warming was also increasing the frequency of El Niño and La Niña events, which are associated with extreme weather. There hasn’t been a neutral year without either of them in the last ten years.

Looking ahead to a world that will become warmer as a result of emissions from cars, factories and deforestation, they found that such a disaster would be 1.3 to 2.7 times more likely in Rio Grande do Sul if global warming increased from current levels of 1.2. C to 2C, which is increasingly likely. “These events will become more frequent and more intense,” the paper concludes.

Lincoln Alves, a researcher at Brazil’s National Institute for Space Research, said that Brazil’s climate had already changed: “This allocation study confirms that human activities have contributed to more intense and frequent extreme events, emphasizing vulnerability the country in relation to climate change. It is essential for decision-makers and society to recognize this new normal.”

To minimize the potential impact of future disasters, the authors recommend more comprehensive urban planning, greater investment in flood defenses and closer attention to equitable social development as floods can create a “poverty trap” in low income communities are in the most vulnerable areas. .

Priority should be given to protecting and reinforcing natural barriers such as forests and marshes, said Regina Rodrigues, a researcher at the Federal University of Santa Catarina. “Land-use changes have directly contributed to widespread flooding by removing natural protection and can exacerbate climate change by increasing emissions.”

As always, however, the most important step is to quickly reduce the burning of trees and fossil fuels that are causing more killing around the world.

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