Torrential Rain in Brazil Kills at Least 13, With More Missing

At least 13 people have been killed and 21 are missing after heavy rains drenched southern Brazil, prompting a state government to send rescue helicopters in search of stranded residents, the authorities said on Thursday.

The torrential rains that poured over the state of Rio Grande do Sul in recent days were well above normal for this time of year, according to experts.

In the last four days of April, the state received about 70 percent of the precipitation it typically records for the entire month, according to National Institute of Meteorology data analyzed by The New York Times.

The rains swelled rivers across the state’s low-lying central valley region, flooding towns, causing a bridge to collapse, blocking roads and triggering mudslides. One town, Canudos do Vale, was left isolated with no electricity or communication. In the town of Candelária, residents awaited rescue helicopters on the roofs of their flooded homes.

Nearly 10,000 people have been forced to flee their homes, the civil defense agency in Rio Grande do Sul said in a statement. The crisis prompted Grande do Sul’s governor, Eduardo Leite, to declare a state of emergency late on Wednesday.

“We are experiencing, in Rio Grande do Sul, the worst moment — the worst disaster in our history,” Mr. Leite said at a news conference on Wednesday. “And unfortunately, it will get worse.”

Authorities have struggled to reach isolated residents, with search-and-rescue teams unable to travel to some areas because of high river levels and heavy flooding. With nowhere to land, some helicopters have used winches to pull up residents from flooded areas.

“We will not be able to make all the rescues,” Mr. Leite said on Wednesday.

Meteorologists warned that more rain was likely on the way in the coming days, which could further complicate rescue efforts.

The country’s president, Luiz Inácio Lula da Silva, who was to visit the region on Thursday, promised that federal agencies would “join the efforts of state government and municipalities to get through this difficult time.’’

Last year, 37 people were killed in the same region of Brazil by torrential rains and punishing winds caused by a cyclone.

The national weather institute said the region was reeling from the effects of a natural weather phenomenon known as El Niño, which can trigger heavy rains in Brazil’s southern regions, while at same time causing drought in the Amazon rainforest.