RIO DE JANEIRO — Firefighters and desperate residents searched for victims Wednesday after powerful mudslides and flooding swept through a mountainous region north of Rio de Janeiro, dumping a month’s worth of rain overnight and killing at least 78 people.
The mayor of Petrópolis, a historic city nestled in mountains some 70 miles from Rio de Janeiro’s beaches, said the death toll could still rise. A similar disaster killed more than 900 people in the area in 2011. Many experts say such extreme weather events are becoming more common with global warming.
Intense rainfall starting on Tuesday evening caused mudslides that tore down dozens of homes on the hillsides above Petrópolis and caused flooding that did more damage in the streets below. Images and videos on social media showed rivers of mud rushing through the city’s streets, sweeping everything along the way: cars, trees, and sometimes people.
The rains that caused the devastation were the heaviest the city had seen since 1952, Brazil’s National Meteorological Institute said.
“What we saw was a really extreme event,” said Cássia de Castro Martins Ferreira, a researcher at the Federal University of Juiz de Fora, who studies extreme weather events in the region. “It didn’t rain — it was an extraordinary amount of water that poured down.”
For many of Petrópolis’s residents, the disaster was a painful reminder of 2011, when similar mudslides killed more than 900 people in the region — the worst natural disaster in Brazil’s history.
Petrópolis is part of a picturesque region with a major national park and sheer, forested mountains that have become a getaway for people fleeing the coast’s searing temperatures. It was established in the mid-19th century by the Brazilian emperor Pedro II, who held court there during the sweltering summer months.
But its unique geography also makes it vulnerable to extreme rainfall, Ms. Castro said. The region is often where hot-air masses coming from the coast clash with the colder temperatures common at higher altitudes, which can cause storms.
“We have an enormous number of extreme weather events in Petrópolis, related exactly to its location,” she said. But another risk, she said, “is the way that the city has grown.”
As Petrópolis has expanded, residents have moved into the hills, clearing forests that once acted as a buffer against mudslides and building homes on terrain that is often too steep and unsuitable for development.
After the 2011 mudslides, officials created plans to prevent a similar tragedy in the region. But those plans have advanced slowly amid a lack of funding and shifts in political power.
Ms. Castro said that, in Brazil, the top priority should be creating more robust systems to alert residents ahead of extreme weather events. In Petrópolis, only a few neighborhoods are equipped with sirens that warn of weather risks, while state and local governments still have not installed such systems in other vulnerable places.
The governor of the state of Rio de Janeiro, Cláudio Castro, said at a news conference on Wednesday afternoon that preventive action was needed to keep these tragedies from recurring.
“We are doing this prevention,” he said. “It takes time, it can’t be done all at once.”
Heavy rains are not uncommon during Brazil’s summer months. But most experts agree extreme weather events are becoming more common. In December, floods killed at least 20 people and displaced some 50,000 in the country’s northeast. And last month, dozens were killed in São Paulo and Minas Gerais when torrential rains swept through the two states.
Jack Nicas contributed reporting.