Extreme rainfall in metropolitan São Paulo quadruples in 70 years, Brazil

Researchers at the National Center for Disaster Management and Early Warning (CEMADEN) have found that extreme rainfall in the São Paulo area of ​​Brazil has quadrupled in 70 years.

The study also showed an increase in the number of consecutive dry days, which indicates that intense rainfall is concentrated on shorter and wider spaced periods.

A CEMADEN study showed that both the total rainfall and the frequency of extreme rainfall in the metropolitan area of ​​São Paulo have increased significantly over the past seven decades.

“Intense rains lasting several hours with a huge amount of water reaching 80 mm or 100 mm are no longer sporadic events. They are happening more and more often,” said CEMADEN senior researcher Antonio Marengo, also a research lead researcher.
 
Researchers studied the information received by the INMET weather stations at IAG-USO and Santana Lookout in the northern part of the city. The analysis showed an increase in the number of days with heavy rains, as well as the frequency of extreme rainfall, especially in the spring-summer season or the rainy season.

The dry season usually took place between April and September in most areas of the state, but in recent decades it lasted until October. The number of consecutive days without precipitation has also increased, indicating that heavy precipitation occurs on fewer days, interrupted by longer periods of dry weather.

Convective precipitation is likely to occur, with shorter, colder nights and hotter days, increasing the frequency and intensity of heavy rainfall.

“We observed a long-term trend in this type of weather event, with very strong indications that climate change is occurring,” Marengo explained.

Records from weather stations showed a fourfold increase in the number of days with rains exceeding 100 mm between 2000 and 2018, compared with the 1940s or 1960s.

He also showed an increase in total rainfall, the frequency and intensity of heavy rains, as well as the frequency of consecutive dry days in the period 1931-2017.

“This suggests that the increase in total rainfall in São Paulo in recent decades has been associated with an increase in” heavy “rainfall concentrated in fewer days and with longer dry periods between them,” Marengo said.

“Extreme precipitation is not in itself a natural disaster. The so-called natural disasters are actually the result of a combination of various factors, ranging from climate and weather to urban, economic and social phenomena,” said Marengo.

“In other words, it is also anthropogenic disasters that are the result of human actions, not just climate.”

Most states in the country suffer from floods, but São Paulo sees the worst of it, accounting for 33.36 percent of cases, followed by Santa Catarina with 11.25 percent of cases.

Between 2014 and 2018, about 170 floods and floods on rivers were recorded, as a result of which the number of victims and serious injuries increased, and then landslides followed.

“Landslides, for example, kill people only because they have to live in high-risk areas where no one needs to build a house. The streets are only filled with water because the rivers were directed and buried, and city surfaces are sealed with asphalt and concrete.”

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