Right now, the chances of back-to-back damaging hurricanes striking the same location within weeks is quite small. But that could change, according to a study published in Nature Climate Change. As climate change strengthens hurricanes and sea level rise makes hazards such as flooding more common, coastal regions could one day see vicious storms strike even as they’re still recovering from the last one.
By 2100, two hurricanes may strike the same region within 15 days of each other every 2–3 years in some locations, researchers say.
The takeaway is clear, said Dazhi Xi, a postdoctoral research associate at Princeton University and study coauthor.
Not only should the United States be able to weather extreme storms, “the community also needs to be able to recover faster,” he said.
Even one hurricane can devastate regions. By some measures, New Orleans is still recovering from Hurricane Katrina, which struck nearly 20 years ago, and Puerto Rico has yet to fully rebuild after Hurricane Maria pummeled the island in 2017, leaving large areas without electricity for nearly a year.
A second hurricane on the heels of the first could devastate already vulnerable areas. Sodden soils would soak up far less rainwater than normal, worsening flooding. Downed power lines might mean there’s no electricity for emergency workers, and flooding could prevent evacuations and storm preparations.
Though two storms are unlikely to occur just days apart, 15 days is a plausible time span, said Colin Zarzycki, an atmospheric scientist at Pennsylvania State University who was not involved with the study.
“You don’t have unlimited time after one of these storms to bounce back,” he said. “If that time keeps getting more and more compressed, that becomes a problem for society.”
Simulating a Stormier World
To arrive at their estimates, Xi and his colleagues first looked back through the historical record to find out how common consecutive hurricanes have been at nine locations along the U.S. East and Gulf coasts. Because this event is so rare and because records have gaps, the group used a computer model to extrapolate between existing data and estimate the odds of back-to-back hurricanes over time.
There’s no official definition for a sequential hurricane, so the authors chose 15 days between storms as the cutoff. Critical infrastructure such as power and transportation systems often can’t fully recover in less than 2 weeks, Xi said, meaning a second hurricane within that span is more likely to be damaging.
They also looked only at two damaging storms that produce hazards such as flooding, high winds, and storm surge and excluded storms that didn’t produce much damage.
The historical data showed that consecutive damaging hurricanes have become slightly more common over the past 60 years, Xi said. That includes recent storms such as Hurricanes Ida and Nicholas, which struck the Gulf coast just 2 weeks apart in 2021. In Louisiana, Ida left soils waterlogged, contributing to extensive flooding throughout the southern part of the state.
To look forward in time, the researchers fed statistical hurricane models data from six Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models. They also simulated storm tides, rainfall, and 10-minute sustained winds for future hurricanes and combined the results with sea level rise predictions from the Intergovernmental Panel on Climate Change’s Sixth Assessment Report.
“Even if you take the exact same hurricane and you move it forward 100 years, but you put that sea level up 6 inches, you’re obviously going to get more inundation,” Zarzycki said.
The researchers found that for most locations, the odds of consecutive damaging hurricanes increase significantly by the year 2100. Currently, they strike every 10–92 years, depending on the location.
In the future, two hazardous hurricanes could hit the same place within 15 days of each other every 1–2 years under the highest greenhouse gas emissions scenario. (Greenhouse gases are a major contributor to climate change.) Under a moderate-emissions scenario, it could happen every 1–3 years.
Worse, the model showed that under a high-emissions scenario, two consecutive category 4 or 5 hurricanes hitting the same region would become a 1-in-85-year event.
The researchers also ran their simulations without sea level rise to estimate what might happen if humanity adapts to it. If communities move buildings inland and build seawalls—a situation the group said is akin to removing the effects of a rising sea level—damaging sequential hurricanes occur every 2 to 5 years under the high-emissions scenario. That’s still far more frequent than today, but less than half as often as a scenario in which no preparation happens.
Preparing for Consecutive Storms
The risks that come with back-to-back hurricanes vary by location, and there is uncertainty about the extent the world will curtail climate-warming emissions. But it’s important that we begin thinking about how climate change will alter the weather no matter what happens, said Kerry Emanuel, a retired atmospheric scientist from the Massachusetts Institute of Technology.
The warming climate means that using the historic record to estimate future risks “just doesn’t work anymore—not for the important stuff,” he said. Research such as Xi and his colleagues’ is just now beginning to explore what Kerry called a “brave new world” of climate-driven hazards, including stronger and more frequent hurricanes and compound disasters.
Modeling a warmer, stormier future could reveal critical information for emergency planners from agencies such as the Federal Emergency Management Agency (FEMA), which have been caught off guard by hurricanes before. In 2017, the agency drew criticism for its slow response to Hurricane Maria, which caused heavy damage in Puerto Rico. An internal report released after the event showed the agency was slow to deploy staffers to the island after the hurricane, in part because many responders were already working in Florida and Texas, which had also recently experienced damaging hurricanes.
Federal agencies will need to increasingly account for the possibility of multiple major storms hitting the United States in the future, Xi said, and prepare accordingly.
“If you were the FEMA chief and you read that [new study], you’re probably thinking ‘Jeez, are we really prepared?’” Kerry said.
—Nathaniel Scharping (@nathanielscharp), Science Writer