Climate Change

Climate change was partly responsible for May floods, landslides in Brazil

7-day average rainfall had 1-in-500 chance, finds study; Current climate warmer by 1.2°C

 
By Rohini Krishnamurthy
Published: Friday 08 July 2022
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Climate change has partly contributed to the intensity and probability of heavy rainfall in Brazil in May 2022, a report has found. 

Very heavy rainfall beginning on May 23 had lashed parts of north-east Brazil, including the states of Pernambuco, Sergipe, Alagoas, Rio Grande do Norte and Paraíba. The rain triggered widespread landslides and floods and reports suggested that about 130 people were killed, while 25,000 others were displaced.

The seven-day average rainfall of May 25-31 had roughly a 1-in-500 chance and the 15-day average had a 1-in-1,000 chance of occurring any year. The current climate has warmed by 1.2°C due to human activities, found the report released July 5.

If such rare rainfall events had occurred in a 1.2°C cooler climate, the study estimated, its intensity would have been lesser by 20 per cent.

“Although events like these are still very unusual, they are now more likely, compared to a climate not warmed by human activities,” the study said. The team comprised researchers from Brazil, Netherlands, France, United States and United Kingdom.

The scientists said that between May 27 and 28, in less than 24 hours, Pernambuco received more than 70 per cent of all of May’s rainfall. 

The researchers used data from 75 stations that recorded consistent data from the 1970s.

Natural variability such as the La Niña event over the Pacific could have exacerbated the average rainfall in the region, said the experts.

However, easterly waves were the primary driver of this event. The waves disturb the current that moves from east to west, which is typical this season. 

Easterly waves can potentially cause heavy and widespread rainfall, including thunderstorms.

Anomalously warm tropical Atlantic and a humid and unstable atmosphere near the east coast of Northeast Brazil also played a role, according to the researchers. Still, the rainfall was very rare.

“Combining observations with our physical understanding of the climate system, we conclude that human-caused climate change is, at least in part, responsible for the observed increases in likelihood and intensity of heavy rainfall events as observed in May 2022,” the researchers wrote.

They warned that these trends would continue increasing as greenhouse gas concentrations grow.

Climate change-induced rise in the sea level and higher tides could increase the vulnerability to heavy rainfall, leading to more urban floods.

Further, increased unplanned urbanisation in low-lying flood-prone areas and steep hillsides puts the community at risk.

“As new infrastructure is built, there is an opportunity to increase resilience by accounting for increasing risks in the design and location, instead of reverting to outdated design standards,” the study said.

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