'Brown Ocean Effect' May Have Made Helene Worse

Scientists believe hurricane gained strength from soil waterlogged from days of rain
By Rob Quinn,  Newser Staff
Posted Oct 1, 2024 7:36 PM CDT
Days of Rain Made Helene More Devastating in 2 Ways
Search crews look for victims in the aftermath of Hurricane Helene, Tuesday, Oct. 1, 2024, in Swannanoa, NC.   (AP Photo/Mike Stewart)

Hurricane Helene left scenes of utter devastation in places that don't normally have much to fear from hurricanes. One of the worst-hit communities was Asheville in western North Carolina, once seen as a "haven" from extreme weather, the Guardian reports. Scientists tell the New York Times that heavy rain in the Southeast from storm systems in the days before the hurricane likely made it more destructive in two ways: The soil was too saturated to absorb much more water, and the hurricane could have gained strength from what's known as the "brown ocean effect." Hurricanes usually gain strength from warm water, but warm, wet soil can have the same effect, researchers say.

"If you have wet and hot soil, then we are really priming the land" to give a hurricane strength, Dev Niyogi, an earth and planetary sciences professor at the University of Texas at Austin, tells the Times. He likens Helene to "2024's Katrina."

  • Meteorologist Ryan Maue, a former NOAA chief scientist, estimates that some 40 trillion gallons of water fell on the Southeast in the week to Sunday, with 20 trillion gallons from Helene falling on Georgia, Tennessee, the Carolinas, and Florida, the AP reports.
  • "It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain," Maue says. "That collected at high elevation, we're talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down." Ed Clark, head of the National Oceanic and Atmospheric Administration's National Water Center in Alabama, says the "astronomical amount of precipitation" over such a large area is unlike anything he's seen in his career.

  • Janey Camp, a civil engineer at the University of Memphis, tells Scientific American that in the Appalachians, historic flooding hit "an area where the terrain is not conducive to being able to withstand those levels of precipitation." Camp calls it "a perfect storm for one of the worst-case situations you could have." Another factor, Camp says, is that the storm hit rural, low-income areas. "These are not areas that get a lot of attention and investment for resilience and planning and improved infrastructure."
  • Warmer air holds more moisture, and scientists at the Department of Energy's Lawrence Berkeley National Lab says climate change made Helene's rainfall roughly 50% heavier in parts of Georgia and the Carolinas, the AP reports. "We've seen tropical storm impacts in western North Carolina," says state climatologist Kathie Dello. "But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction."
(More Hurricane Helene stories.)

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