Dozens of people died in multiple states this week as Hurricane Helene barreled through parts of the southeastern United States, bringing heavy rain and 15-foot storm surge.

Coastal cities and towns in Florida were devastated as the Category 4 hurricane made landfall, but inland communities felt a similar burden as the storm barreled through North Carolina, South Carolina, Georgia and Tennessee.

“Turn around and don’t drown,” North Carolina Gov. Roy Cooper urged at a news conference.

At least 42 people died as a result of the storm. As of Friday, Florida had reported seven deaths. Meanwhile, Georgia reported 15 and South Carolina 17. In both states, most of the known fatalities were from falling trees and debris. North Carolina reported two fatalities, including a car crash that killed a 4-year-old girl after a road flooded.

Atlanta received 3.12 inches of rain in 48 hours, breaking its previous record of 9.59 inches for the same period dating back to 1886, according to Bill Murphey, Georgia state climatologist. More than a million Georgians also lost power as a result of the storm, especially in the southern and eastern parts of the state.

In western North Carolina, officials sounded the alarm and went door-to-door, evacuating residents south of the Lake Lure Dam in Rutherford County after the National Weather Service warned that a dam failure was “imminent.” Emergency crews also conducted more than 50 quick water rescues across the region, and one sheriff’s department warned it could not respond to all 911 calls because of flooded roads. The North Carolina Department of Transportation warned on social media that “all roads in western North Carolina should be considered closed” due to flooding that affected Helene.

In Tennessee, more than 50 people were stranded on a hospital roof due to heavy flooding and had to be rescued by helicopter. Residents of Cocke County, Tennessee, were also asked to evacuate after reports of a possible failure of a separate dam, although officials later said the dam failure was a false alarm. In South Carolina, the National Weather Service said the storm was “one of the most significant weather events… in the modern era.”

Scientists told Grist that the extensive flooding caused by the hurricane has been made worse by climate change. Hurricane Helene was an unusually large storm with a widespread impact. After forming in the Caribbean, it moved over unusually warm ocean waters in the Gulf of Mexico, which allowed the storm to intensify more quickly than it otherwise would have. In fact, Helene went from a relatively weak tropical storm to a Category 4 in just two days. Warmer air also holds more moisture, increasing the storm’s water content, leading to faster rainfall and intense flooding.

“When this increased moisture comes in and hits an area like the Appalachians,” said University of Hawaii meteorology professor Steve Businger: “this results in very, very high rainfall, extremely high rainfall, which unfortunately results in a lot of flash flooding.”

Shel Winkley, a meteorologist with the science group Climate Central, said research has shown that current exceptionally high ocean temperatures in the Gulf are as much as 500 times more likely to be the result of climate change. “One of the things we’re seeing with these big storms, especially as they seem to be getting more frequent, is that they’re no longer natural disasters, but unnatural disasters,” Winkley said. “This is no longer an ordinary weather system.”

Hurricanes, of course, occur naturally, but the conditions that led to the severity of Helene – its rapid intensification and heavy rainfall – were partly caused by higher ocean and atmospheric temperatures resulting from the burning of fossil fuels. “You can see the fingerprint of climate change in this process,” Winkley said.

“This summer was record warm around the world, and there was a record amount of water vapor in the global atmosphere,” said Daniel Swain, a climate scientist at the University of California, Los Angeles (UCLA). Both factors contributed to what the southeastern United States experienced this week. “This is one of the most significant U.S. floods in recent memory.”

According to the New York Times, initial estimates of the storm’s damage to homes, businesses and infrastructure range from $15 billion to $26 billion. Businger said he expected the huge loss to spark more conversation about the uncertainties of the existing property-casualty insurance system. “The costs to society are becoming extravagant,” he said.

Scientists noted that the fact that the storm’s winds increased by 55 miles per hour in the 24 hours before it made landfall also made the storm deadlier.

“It was so strong and moving so fast that it didn’t have time to weaken significantly before it got far inland,” Swain said. Rapid storm intensification is particularly dangerous, he said, because people often make decisions about how to prepare for storms and whether to evacuate based on how severe they initially appear.

“It was one of the fastest-growing storms on record,” Swain said. “This is not a coincidence. In a warming climate, we should expect hurricanes to intensify more quickly.”