### The Science Behind How a Florida Hurricane Devastated North Carolina
**Summary**
– The devastation in western North Carolina was caused by a combination of climate change and the region’s mountainous terrain.
– Mountains block weather systems, squeezing out more rain, while steep slopes increase flood risk. At the same time, climate change is making storms stronger and wetter.
– The Asheville area was already saturated from previous heavy rain before the remnants of Hurricane Helene made landfall in Florida.
Asheville and surrounding towns in western North Carolina had just experienced a significant storm when the remnants of Hurricane Helene slammed into the Blue Ridge Mountains. This event triggered a well-known atmospheric phenomenon that unfolded from Wednesday evening through the weekend.
“As weather approaches mountains, the clouds rise up and over the terrain, creating the ‘upslope effect,’” said Doug Outlaw, a meteorologist with the National Weather Service in Greenville-Spartanburg, South Carolina. “This effect squeezes out more rainfall, and in this case, it led to extreme flash flooding that devastated communities. It was an overwhelming amount of water channeled through the valleys all at once.”
The severe flooding that struck North Carolina’s inland mountain towns, located thousands of feet above sea level and hundreds of miles from the coast, highlights an unexpected consequence of climate change. Experts warn that these far-reaching impacts will only become more common in the future.
Hurricane Helene dumped over two feet of rain across parts of southern Appalachia. The resulting floodwaters carried away homes, washed out highways, and cut off access to several towns.
“That’s nearly half a year’s worth of rain in just four days,” Outlaw explained. “This was one of the most severe weather events in the area’s history.”
At least 20 locations in western North Carolina, including Asheville, saw flood levels expected only once every 1,000 years. Shel Winkley, a meteorologist with Climate Central, explained that climate change intensifies storms by heating the oceans and warming the atmosphere, which allows for more moisture to be held and eventually released as rain. For every 1 degree Fahrenheit increase in temperature, the atmosphere can hold about 4% more moisture. This significantly raises the likelihood of catastrophic flooding.
In May, Climate Central released a report warning of the increased risk of inland flooding due to global warming. The areas hit hardest by Helene were among those identified in the report as being most vulnerable.
“Appalachia was named as an area facing a growing threat of extreme flooding,” Winkley said. “This region has a known risk for increased flood events, and unfortunately, we saw that play out this weekend.”
More than 120 storm-related deaths were recorded across six states, with at least 44 in North Carolina. The region’s mountainous terrain was partly to blame for the destruction, but the area was also hit by a “double whammy”: days of heavy rain followed by the remnants of Hurricane Helene bringing more rain and wind to southern Appalachia.
“It was two compounding events clashing together,” Winkley noted.
The National Weather Service accurately predicted the extreme weather.
“This will be one of the most significant weather events to affect the region in modern history,” warned officials from the Greenville-Spartanburg office on X (formerly Twitter). “Record flooding is forecasted, comparable to the 1916 floods in Asheville.”
In 1916, 25 people died when floodwaters destroyed buildings, wiped out the local power plant, and cut Asheville off from the rest of the country, according to the Asheville Museum of History. The parallels to the current flood event are striking.
“The forecast was exceptionally accurate,” said Christopher Godfrey, chair of the atmospheric sciences department at the University of North Carolina Asheville. “The National Weather Service did an outstanding job. They used strong and appropriate language to convey the seriousness of the situation.”
Given the warnings and his own expertise, Godfrey was not surprised by the catastrophic outcome.
“The topography around here is steep. Houses and roads are built on steep terrain,” Godfrey explained. “This was such a catastrophic flood that even well-constructed bridges were destroyed.”
Scientists are investigating the role climate change played in intensifying Hurricane Helene. Preliminary studies suggest that global warming made the storm up to 20% wetter in parts of the Southeast. Some estimates also suggest that climate change caused parts of Georgia and the Carolinas to receive up to 50% more rain, making extreme rainfall up to 20 times more likely.
Godfrey recorded 13.37 inches of rain at his home in Arden, North Carolina, over three days. Nearby Hendersonville received over 21 inches in the same period, according to the National Weather Service. The flood damage in his area corresponded with FEMA maps showing what would happen during a flood expected once every 500 years.
Despite warnings, some residents were caught off guard by the severity of the event. “A neighbor told me, ‘I heard the warnings but didn’t think it would be that bad,’” Godfrey said.
One of the surprising consequences of the storm was the amount of tree damage, which created additional challenges for first responders.
“I don’t think anyone expected this much tree fall,” said Godfrey, who researches wind storms and tree falls. Most trees were likely uprooted due to the oversaturated soil. During the storm, Godfrey could hear a pattern of trees falling one after another.
“You could hear the roots snapping—snap, snap, snap—and then the crash as the trees fell,” he recalled. Two towering walnut trees fell just a few dozen feet from his house, and another tree crushed a neighbor’s car.
Communication systems were also severely impacted, making it difficult to assess the full extent of the damage.
“We have no idea what’s happening out there,” Godfrey said in a phone interview from a weather station he manages at UNC Asheville. “I’m only reachable because I’m on top of a hill looking out over Asheville. Down in the valley, there’s no internet, no Wi-Fi, no cellular service, and not even texting.”
Asheville has often been touted as a climate haven due to its distance from the coast and high elevation, which shields it from rising sea levels and extreme temperatures. However, no area is immune to the growing impacts of climate change.
Places like Seattle, once considered safe from extreme weather, saw temperatures soar to 108°F during the 2021 heatwave, and parts of the Midwest that were once seen as climate refuges have experienced record rainfall.
“Climate change affects different areas in different ways,” Winkley said. “While mountain regions were once considered a refuge from extreme heat, we’ve now seen that they’re not immune to devastating floods.”
Winkley emphasized that these far-reaching consequences of climate change are a reminder of how unpredictable the future may be.
“Hurricanes used to be seen as a coastal problem,” Winkley said. “But now we’re seeing that climate-driven events can intensify weather far beyond the areas we typically associate with storms.”
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