Wetter storms drive need for resilient infrastructure as hurricane season opens

North Carolina DOT via Wikimedia

With the Atlantic hurricane season underway, this is the third in a three-part series looking at how engineers are making communities safer and infrastructure more resilient as storms grow stronger and more frequent. Read part 1, here, and part 2 here.

As the Atlantic hurricane season opens, what will happen over the next six months remains uncertain, but we know that wetter storms are a growing threat to communities and infrastructure.

The National Oceanic and Atmospheric Administration’s annual outlook is the gold standard for prognostication. This year, NOAA’s National Weather Service forecast calls for a below-normal season: eight to 14 named storms, including three to six hurricanes. An average season produces 14 named storms, including seven hurricanes.

Further reading:

• Engineering for hurricanes: Modeling bolsters mitigation as Atlantic season begins
• Inside Hurricane Harvey: ASCE president-elect recalls navigating Houston crisis
• How Florida’s Babcock Ranch survived Hurricane Ian

But even defining an average season is complicated, which presents a conundrum for civil engineers trying to find solutions to mitigate hurricane damage.

Anecdotally, the last three decades seem especially destructive, with powerful hurricanes such as Harvey, Helene, Ike, Floyd, Florence, and Katrina standing out. These storms all brought catastrophic amounts of rain during landfall, flooded communities, and caused widespread damage. Helene, the most recent storm from this list, caused nearly $79 billion in damage in 2024.

Official records of the intense storms that threaten the U.S. during hurricane season, which runs from June 1 to Nov. 30, have been kept for 175 years, with some historical accounts of hurricanes swamping armadas as far back as the 1500s. Over the past century, there have been a few decades of clearly increased hurricane activity.

“The 1930s were actually really strong in terms of seasonal intensity, what we call Accumulated Cyclone Energy,” said Carl Schreck, Ph.D., a senior research scholar at the North Carolina Institute for Climate Studies at North Carolina State University. “The most active season on record (for ACE) is still 1933.”

There has been a big change in collecting robust weather data over the past 100 years.

Before the 1950s, some coastlines were sparsely populated, essentially making them black holes for weather data. Additionally, unless a ship just happened to intersect with a storm, no information on hurricanes was collected in ocean waters. Monitoring changed in the 1960s and 1970s, when new satellites provided a bird’s-eye view, allowing scientists to see and track storm systems from space. Considering this jump in data collection and quality, it’s difficult to compare today’s hurricane season to pre-satellite seasons.

Currently, Schreck said, the U.S. is in an active period of hurricanes that began in the mid-1990s. Even with this increase in storms, he and other scientists are hesitant to declare an overall increasing trend in hurricanes. After all, 30 years is “a relatively short period to draw a trend line on,” he noted.

“I like to tell people, ‘Hurricanes aren’t necessarily the best poster child for climate change in a lot of ways. Climate change is very real; it’s warming. But hurricanes are complicated, and there’s more to this story.’

“All that said, we are really confident that storms are getting wetter,” he added, noting that as the atmosphere warms, it can hold more water. “Any rainstorm today is going to drop more rain than it would have 100 years ago.”

Many of the hurricanes that the U.S. deals with start as storm systems that form along the west coast of Africa. As they make their way across the Atlantic Ocean, they sometimes fizzle out. But sometimes they consolidate, growing into epic, rotating hurricanes that eventually make landfall.

The unpredictability of the systems is magnified by their complexity and by interactions between ocean temperatures, ocean circulation patterns, and even the influences of the jet stream.

With the ocean in a warming pattern, it remains unclear how storms might increase in frequency or intensity. However, the warming atmosphere reinforces what Schreck noted: Hurricanes are bringing increased rainfall as temperatures rise.

This is forcing engineers to address more frequent flooding in their communities. In Virginia, for example, stormwater managers and resiliency experts are working hard to redesign infrastructure and prepare residents for future hurricane seasons.

Ingredients for a storm

The formation of hurricanes requires several key ingredients, chief among them warm ocean waters and moisture in the atmosphere. They also need to be off the equator so winds can start to spin. Low wind shear also must be present to keep forming storms upright (not tilted) so that strong eyewalls can form. But like any cook will tell you, the ingredients are only one part of the story; how you combine them can make or break your creation.

The science of prediction is complicated, and researchers are constantly refining their technique with new information and technology. Some of the key inputs they consider are decadal cycles of ocean circulation patterns as well as yearly variations between El Niño and La Niña events in the Pacific Ocean. They also consider conditions that might amplify or dampen the formation of extreme storm events.

The Madden-Julian Oscillation is one of these conditions. The MJO makes its circumnavigation path several times a year, sometimes strongly contributing to extreme weather events in the U.S.

“That’s something that you can’t predict a year or month, even more than a few weeks in advance,” Schreck explained. Depending on when the MJO swings by a hurricane, it can boost or dampen the number and behavior of storms. Because of this effect, Schreck said NOAA’s Climate Prediction Center monitors the MJO and other systems and puts out a global tropical hazards outlook each week.

Staff Sgt. James L. Harper Jr., U.S. Air Force

Even when all signs point to an active hurricane season, nature can be unpredictable. In 2024, the Atlantic Ocean was very hot, much warmer than anything scientists had seen before, recalled Schreck. On top of steamy temperatures, forecasters anticipated a La Niña year with reduced wind shear.

Hurricane experts were preparing for the worst. In June and early July, Hurricane Beryl became the earliest hurricane on record in the Atlantic Ocean to reach Category 4 and then Category 5 status, and it served as a harbinger for the rest of the season.

But immediately after Beryl, “it was crickets – there was almost nothing,” Schreck said. July and August passed without much ado, but in late August and September, scientists noticed a new development in the atmosphere.

“We could see in early September the MJO was going to come back around,” Schreck said. Toward the end of September, a storm system was forming in the Caribbean, but forecasters were uncertain where it might head. The system organized and intensified, developing into Helene.

During Helene, the Appalachian Mountains in North Carolina received up to 31 inches of rain in some locations, causing devastating flooding and triggering landslides. Rainfall was significant along the southeastern U.S., and increased rainfall even stretched as far inland as Illinois.

Schreck, who happens to live in Asheville, North Carolina, got a front-row seat to the extreme rainfall. “Before my experience with Helene, I would always say when a storm is over the ocean, the stories are all about the wind and the storm surge,” he said. “After the storm comes through, the headlines are all about the rainfall.”

He said that even before Helene, more than half of the deaths from hurricanes over the past decade were associated with inland rainfall. “That’s something that just doesn’t get enough attention in general,” he said. “And that is something – again, we’re more confident than (we are about) other things – that is getting worse.”

Designing for future stormwater management

In the wake of increased flooding around the U.S., stormwater management is taking center stage in many communities. For instance, in 2018, a series of storms hit Alexandria, Virginia, flooding areas of the city that normally stayed dry. Soon after, Daniel Medina, Ph.D., P.E., became Alexandria’s stormwater program manager and head of its Flood Action program to help deal with increased flooding in the city.

Alexandria’s stormwater infrastructure system is a case study for other well-established cities on the East Coast: a city settled hundreds of years ago with water infrastructure systems that reflect that antiquity.

“We’ve been putting impervious, or compacted, surfaces in the region ever since the 1700s,” Medina explained. He added that increased stormwater volume can eventually overtake the established drainage systems and cause flooding.

Medina said some of Alexandria’s stormwater pipes are 50-plus years old. It is this outdated infrastructure that can fail sooner, even with smaller storm events. The pipes are no match for today’s rainfall. “They’re just not sized for the kinds of storms we’re seeing right now,” he said.

Medina is seeing firsthand what scientists like Schreck have pointed out: Warmer temperatures are producing wetter conditions. “I like to say that climate change is an amplifier of problems,” Medina said. “We’ve got aging infrastructure, and it was designed with different standards, not as we would today. Then climate change starts operating – all the storms become worse.”

Aileen Devlin, Virginia Sea Grant via Flickr

Updating this aging infrastructure is crucial for stormwater management, but the process requires extensive preparation to evaluate, design, plan, and implement. “I tell people it’s like a soccer free kick,” Medina explained. “You put the ball on the ground, the goalie is organizing the defense, the kicker is talking to other people … then you kick. All that preparation for seconds of action.” He added that stormwater infrastructure is very complex and expensive. “To do it right, it takes time.”

In the wake of severe storms over recent decades, there has been a push to design stormwater infrastructure systems with an eye to the future. Today, most engineering design standards and floodplain regulations are based on precipitation frequency estimates published in NOAA Atlas 14. But Atlas 14 only makes its predictions using historical rainfall data up to the year 2000.

“We know rainfall has changed since then,” said Nora Jackson, a resiliency planner for the Northern Virginia Regional Commission. “So not only do we have extremely undersized and old infrastructure, we’re dealing with more rainfall than what it was originally designed for.”

NOAA’s new Atlas 15 precipitation estimates, which are in the works, will provide an important update, projecting precipitation trends into the future, through the year 2100. NOAA said Atlas 15 “can help communities nationwide become more resilient when planning and designing new infrastructure.”

Indeed, Jackson noted that when precipitation estimates are calculated using a 4.5-degree Celsius warming scenario (8.1 degrees Fahrenheit) over the upcoming decades, rainfall is projected to increase 18% to 20%. While the number hasn’t officially been published in the Atlas 15 report, Virginia communities are taking note of these rainfall estimates.

“We’re used to building systems that are based on this rear view of what happened in the past,” Medina said, adding that teams now must consider future predictions in their designs. Engineers and planners will now have to design systems that can handle predicted precipitation without overdesigning and overspending.