US communities struggle to prepare for growing rainstorm threat

‘The take-home message is that infrastructure in most parts of the country is no longer performing at the level that it’s supposed to because of the big changes that we’ve seen in extreme rainfall’

Design standards for roads and construction regulations are based on often outdated precipitation estimates (Getty Images)

When then-Wisconsin governor Scott Walker, a Republican, announced plans in 2017 for a sprawling Foxconn electronics plant, he touted the 13,000 promised jobs and $10 billion (£7 billion) investment spread across 1,000 acres, much of it farmland. Downstream across the border in Lake County, Illinois, officials focused on a more sinister byproduct: water.

Earlier that summer, more than seven inches of rain drenched the county, setting off flash flooding. Six days later, swollen rivers flowing south from Wisconsin crested at record heights. Families fled. More than 3,000 structures flooded. Damage exceeded $12 million (£9 million).

Where Wisconsin saw jobs and tax revenue, Illinois saw a rising threat. “We realised there were significant storm-water concerns,” said Kurt Woolford, the interim executive director of the Lake County Stormwater Management Commission. “Water doesn’t follow political boundaries, it doesn’t follow state boundaries.”

But rainfall estimates used to design storm-water systems do. As they analysed whether the plans for Foxconn could handle extreme rain, officials in each state reached different conclusions. In Illinois, they relied on a 2020 state study that predicted that as much as 8.57 inches of rain would fall, causing floods. But Wisconsin officials disagreed, citing a 2013 study by the National Oceanic and Atmospheric Administration (NOAA) that forecast 5.84 inches.

The conflict highlights the lack of a comprehensive, national precipitation database as climate change brings more frequent “rain bombs” that can dump up to seven inches of water in hours. Design standards for roads, storm-water systems, dams and construction regulations - even whether a home is in a flood plain and requires flood insurance - are based on precipitation estimates. In many states, those standards no longer accurately portray the risk to infrastructure intended to last decades.

“It is foundational to so many decisions that we make,” said Chad Berginnis, executive director of the Association of State Floodplain Managers. “It’s a risk problem that has ripple effects everywhere.”

Last year, the United States saw a record 22 weather events that cost at least $1 billion (£728 million) each in damage. Seven were hurricanes, according to NOAA.

Many states rely on rainfall estimates, known as Atlas 14, that are produced by NOAA. But data for Delaware, Indiana, Kentucky, Maryland, New Jersey, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia, and West Virginia have not been updated since 2006. And Oregon and Washington state have never sought an Atlas 14 estimate; those states are using 1961 data from an earlier study.

Some localities, such as Broward County, Florida, and Virginia Beach, Virginia, have funded rainfall estimates leading to higher design standards. But rural and poorer communities are unable to afford such studies.

“It’s kind of the Wild West out there,” Mr Berginnis said. “Some communities get it, and they’re planning for it. And some communities don’t [get it].”

Illinois is one of those places that gets it. The state’s 2020 rainfall update at the heart of the dispute over the Foxconn project found not only that rainfall had jumped by 13 per cent over the previous study 30 years earlier but that it would continue to increase.

A study commissioned by Lake County concluded that the combination of Wisconsin’s outdated rainfall projections and inadequate storm-water detention for the development of Foxconn in that corridor between Chicago and Milwaukee would mean a two-foot increase in flooding along the Des Plaines River, one of four snaking south from Wisconsin through Lake County. “It was a big eye-opener for us,” Mr Woolford said, “because we usually don’t think about what happens in other states.”

Mark Glaudemans, director of the National Water Center Geo-Intelligence Division at NOAA, does the Atlas studies. He said the rainfall projections for Wisconsin were accurate when they were published in 2013. But, he added, the dispute over Foxconn highlights the need for a comprehensive nationwide survey.

“Any time you stop a climatology-based study at a political boundary that does not reflect the natural conditions, of course you’re going to have boundary issues,” he said. “That’s why we are in favour of a national study.”

In 2019, researchers at the University of Wisconsin found that design guidelines based on Atlas 14 were dangerously inadequate. Looking at records from more than 900 weather stations from 1950 to 2017, they determined that 100-year storms - those with a 1 per cent chance of occurring in a given year - were happening almost twice as often in the eastern half of the country as Atlas 14 predicted.

“The take-home message is that infrastructure in most parts of the country is no longer performing at the level that it’s supposed to because of the big changes that we’ve seen in extreme rainfall,” said Daniel Wright, a hydrologist at the University of Wisconsin at Madison and co-author of the study.

He points to the 2014 National Climate Assessment, which found that heavy downpours increased 71 per cent in the Northeast, 37 per cent in the Upper Midwest, and 27 per cent in the Southeast from 1958 to 2012. It may cost more initially to build for bigger storms, but it’s less expensive than making fixes later, said Constantine Samaras, an associate professor of civil and environmental engineering at Carnegie Mellon University.

“The place that we want to get to is designing for the future rather than designing for the past,” he added.

But the increasing number of extreme storms means the past is not a reliable predictor of the future. “So if you’re building a house to last for 30 years, or a piece of infrastructure to last for 50 to 100 years, you’re basing it on out-of-date data from the get-go,” said Alice Hill, who served in the Obama administration as a special assistant preparing for climate change. “And that’s doomed to failure because these events are accelerating.”

Engineers say it’s well known that Atlas 14 is often outdated. But if it’s required by a state or municipality, it dictates design - even for projects intended to last 50 years or more.

C.J. Bodnar worked in the private sector before becoming a city engineer with Virginia Beach in 2015. “You did what you needed to meet the requirements, which means you used Atlas 14,” Mr Bodnar said. “You were trying to keep your client’s costs to a minimum.”

Not only are the NOAA estimates often outdated, they also do not estimate increasingly extreme storms driven by climate change. NOAA plans to include those projections in future Atlas updates. “We are aware that we need to do this,” Mr Glaudemans said.

Updating rainfall estimates is cheap compared with storm damage. Texas paid NOAA $1 million (£728,000) for a 2018 update that officials say nearly doubled the number of homes at flood risk in Houston and Austin. That came a year after Hurricane Harvey dumped a record 60 inches of rain, leaving more than 100 dead and causing an estimated $125 billion (£100 billion) in damages.

In 2018, an advisory panel of engineers, hydrologists and meteorologists from the Army Corps of Engineers, the Nuclear Regulatory Commission and NOAA recommended federal funding of rainfall estimates every 10 years and the creation of a national extreme precipitation database. “This small investment,” it said, “would result in significant return and benefits for infrastructure design in the United States.”

Bipartisan bills pending in Congress would fund NOAA updates of precipitation frequency at least every five years and estimates of maximum precipitation every 10 years. The House version would also require NOAA to include future fluctuations in precipitation because of climate change.

Armed with better data, some local and state officials have been able to make sweeping - albeit costly - infrastructure design changes to better protect their communities.

The 2018 NOAA update for Texas revealed a drastic rainfall spike in the eastern half of the state. NOAA increased the estimated rainfall for a 100-year storm in Texas from 13 inches to 18 inches. What had been considered a 100-year storm was now a more frequent 25-year storm, NOAA found. And a 500-year storm became the equivalent of a 100-year storm.

“I think that what we’re doing [now] provides a much better understanding and appreciation of the risk that we have here,” said Craig Maske, the chief planning officer for the Harris County Flood Control District, which includes Houston.

The county increased requirements for rainfall detention on sites, raised the elevation standard for new structures by two feet, and increased storm sewer capacity requirements by 10 per cent for storms forecast to occur every two years and by 22 per cent for 100-year storms.

The majority of homes damaged by Harvey were outside designated flood plains. Now, engineers expect the sprawling Harris County, the third-largest in the United States, to add 162 square miles to its flood-plain map.

The updated rainfall estimates led to design changes for road projects already underway in Harris County, increasing their cost by at least $148 million (£108 million). The revised plans elevate roadways by as much as five feet, enlarge detention ponds, increase storm-water pipelines and strengthen bridges. Among them is Interstate 45, a main hurricane evacuation route.

The Houston-Galveston Area Council, which oversees road projects in the county, estimates that the cost to redesign the infrastructure could rise by an additional $100 million (£73 million). “It’s going to be a hard pill to swallow right now, but I think ultimately it’ll be good for the region,” said Adam Beckom, the manager of planning and project development at the council.

Houston is not the only Texas city to see drastic changes in the updated rainfall estimates. Predictions for what is known as the 100-year storm in Austin increased from three inches within 24 hours to 13 inches. Storms previously considered 100-year-events are now 25-year events. The number of homes in Austin’s flood plains increased to 7,200 from 4,000.

“The challenge is the rain in many of these places is getting heavier. And the amount of pavement that rain is falling on, it’s getting bigger,” Mr Samaras said. “So it’s kind of a double whammy. You have less places for the rain to go into the ground, you have more rain, and you have the same old sewer pipes from 30 years ago.”

In Virginia Beach, where sea levels have been rising at twice the global rate, Hurricane Matthew lingered over the area in 2016 to deliver a knockout punch, the third 100-year storm of the year. The rainfall topped 14 inches in some neighborhoods. It followed a storm two weeks earlier that dropped 12 inches. Areas that had never before flooded were submerged. In the Windsor Woods section of the city, about 250 homes were damaged, 85 per cent of them without flood insurance, according to the city manager. Throughout the city, about 2,000 buildings suffered $30 million (£22 million) in damage.

The city hired Dewberry, an engineering consulting firm, to perform a $3.8 million (£2.8 million) study of its storm-water management. The firm found that heavy rainfall had increased at about 7 per cent per decade since 1950, more than doubling the rate of the previous decades. And the city’s design standards, based on outdated Atlas 14 projections used by the state, underestimated the amount of future extreme rainfall by about 20 per cent, the consultants said. 

Last summer, the city council strengthened design standards for building elevations and calculating storm-water runoff. If it did not act, the city could see $271 million (£197 million) annually in flood losses from sea level rise by 2065, according to Dewberry. Some developers objected to the changes, citing increased costs.

“But keeping the same standards will increase risk,” said Mr Bodnar, the Virginia Beach city engineer. “Either way, there is a cost.”

The Washington Post