Tropical Storm Debby tests severe-weather readiness

Like the alligator spotted this week swimming through a flooded suburban neighborhood in Bluffton, South Carolina, Tropical Storm Debby posed real danger as it slammed the U.S. Southeast, causing floods and seven deaths as of Wednesday afternoon.

“Debby was a mean girl,” Savannah, Georgia, Mayor Van Johnson said at a Wednesday press conference after Debby dropped 13 inches of rain on parts of Georgia’s coast and drenched large swaths of the Southeast. “She ... just stayed there and just rained and rained and rained.”

If warming temperatures mean larger, more dangerous storms, Debby isn’t the most severe example. But its impacts have been  significant as the storm has swept inland. The trend has already been pushing storm-prone states to respond with safety and readiness efforts that helped to mitigate the current storm’s damage.

The rise of “sponge storms”

Weather experts say the “sponge storm” now soaking the rest of the East Coast embodies a profound weather shift: Big storms are behaving in wetter ways. A warmer ocean, for one, likely fueled Debby’s impact, loading it with up to 20% more rain than a similar storm 100 years ago would have had, climate scientists say. Debby dropped nearly 18 inches on Summerville, South Carolina, just to the northwest of Charleston by the time rains largely subsided there on Wednesday.  

In turn, such supersoaker storms create a reckoning in affected states – exposing deep gaps in flood insurance, forcing building code upgrades, and exacerbating income inequities, all of which will impact the resilience of American communities.

“Storms like Debby, these slow-movers that have copious amounts of rainfall, have significant impacts,” says Thomas Graziano, director of the National Oceanic and Atmospheric Administration’s Office of Water Prediction, in Silver Spring, Maryland. “As our population grows and we continue to build infrastructure [near water], there’s more opportunity to be impacted by these floods.”

Tropical Storm Allison in 2001 provided an early clue of a shift toward the new soaker syndrome. Allison hit southeast Texas, rained for four days, and left 38 inches of water in some places, killing 22.

Hurricane Harvey in 2017 drove the point home. After rapidly intensifying to a Category 4 storm, Harvey dropped 51 inches of rain over five days on some parts of Texas. Perhaps as many as 80% of flood victims weren’t insured, meaning they had to rely on relatively small Federal Emergency Management Agency (FEMA) grants to rebuild. Most homes in flood plains are not insured. Federal flood insurance costs an average of $700 a year – which for some owners is a budget-breaker.

Marco Bello/Reuters

A youth driveway-surfs on floodwater as Tropical Storm Debby moves off Georgia to the North Atlantic, in Isle of Palms, South Carolina, Aug. 6, 2024.

Powerful Hurricane Ida in 2021 was followed in 2022 by Hurricane Ian, which bulldozed parts of Fort Myers, caused historic river crests, and left floodwaters in central Florida for a month. 

The trend continues. According to Colorado State University’s Department of Atmospheric Science, early-season storm activity in 2024 is already topping records set in 1933 and 2005.

Effects in hurricane region and beyond

While citizens, officials, and academics can argue about the causes and solutions, there is no question that climate change is upon us. And physical science steers effects. Storms can absorb up to 7% more moisture for each degree Fahrenheit of extra heat. Warmer temperatures also “increase updrafts, where the wind in the middle of the storm is flying upward at a faster rate, so ... that faster wind wrings the sponge out over a region,” says Daniel Gilford, a cyclone expert at Climate Central, a nonpartisan research group.

Total precipitation on the heaviest rainfall days is going up across the United States, according to the National Weather Service’s Office of Water Prediction. Flood losses have gone from approximately $4 billion a year in the 1980s to $17 billion per year between 2010 and 2018, according to FEMA testimony to Congress.  

“No matter how you slice the information, we’re seeing increases in the number of extreme rainfall events,” says Mr. Graziano.

Rising efforts on adaptation and safety

In some ways, Debby’s relative lack of destruction showed that communities may be adjusting to a new normal around climate and extreme weather events. 

Long accustomed to urban flooding, low-lying Charleston instituted an effective curfew earlier this week as residents hunkered down. Water rescue crews were staged, but no rescues were required, although rescues occurred elsewhere in the Southeast.

In Raleigh, North Carolina, new granular city maps show likely flood spots, helping residents prepare. In recent years, homeowners on Tybee Island have used FEMA grants to raise their low-lying homes above Debby’s flood level.

Changes in construction standards and materials are also making a difference. The State University of New York survey of post-Ian photos of Fort Myers showed 18 homes built before 1981 were completely swept away by Hurricane Ian. But a house in the same area built in 2020 remained standing, its roof largely undamaged.

When Hurricane Ida struck the Gulf Coast, the insurance industry found that the $14 billion spent on New Orleans’ levees after Hurricane Katrina had paid off.

“We are seeing some good actions on the community and government side, but [we still need] to be more responsive and more proactive,” says Nicholas Mesa, a graduate research assistant with Colorado State University’s Tropical Weather and Climate Change Group, in Fort Collins, Colorado.

Resources for citizens

Former FEMA director Pete Gaynor cites the National Risk Index as a good source for citizens to gauge disaster risks in their own neighborhoods. “I would tell anyone living anywhere, if you understand your risk, then we have empowered you to do something about it,” he says.

The Saffir-Simpson Hurricane Wind Scale, which provides a 1-to-5 rating based on hurricane wind speed, has long been part of U.S. storm response. But scientists have traditionally struggled to detail the impact of future flooding. Making plans was based mostly on past experiences and conjecture.

This year, however, the Office of Water Prediction began rolling out new flood inundation maps.

“It’s truly transformative to be able to show  – down to the street level  – where the water is going to be, when it’s going to be there, how long it’s going to be there, and what infrastructure is going to be impacted,” says Mr. Graziano. “With that information you can take action.”

Mr. Gilford at Climate Central says debate and tough decision-making lie ahead, to determine how better data will guide building codes, insurance rules, and development patterns. 

“There are a lot of people who are acutely vulnerable to the impacts of flooding, a lot of communities in harm’s way that don’t have the resources to brace for a hurricane’s impact,” he says. “Are we making policies and decisions that serve everyone? That’s an important thing to consider.”