The US is finally curbing floodplain development, new research shows

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Over the past century, the United States has built millions of homes along coastlines and rivers, developing on land that is all but destined to flood. At the same time that the warming of the planet has raised sea levels and increased rainfall, annual flood damages have surged in recent decades in large part because more homes are in flood-prone areas now than ever before. In coastal cities like Carolina Beach, North Carolina, most homes sit in a federally-designated flood zone, which tees them up for massive flood events like that which dropped more than a foot of rain on the city this week.

Experts have portrayed this widespread risky construction as an intractable problem, alleging that “home sales in flood zones are booming,” that “more Americans are moving into flood … hot spots,” or pointing out “rapid urban growth in flood zones.” News coverage, including that of this publication, has largely followed this lead.

But new research from some of the country’s leading climate adaptation experts, which was published last week in the academic journal Earth’s Future, suggests that academics and journalists may have drawn the wrong lessons from the last few decades of coastal development. A national survey of floodplain development between 2001 and 2019 has found that the U.S. actually built fewer structures in floodplains than might be expected if cities were building at random. This means that, if anything, the average city now actively avoids floodplains, contrary to conventional wisdom. Indeed, in the 21st century most towns and cities in the U.S. built very little or not at all in flood-prone areas. The vast majority of floodplain construction — the kind that grabs headlines and feeds the pessimistic narrative — has taken place in just two states: Louisiana and Florida.

A separate paper just published by the same researchers in the journal Oxford Open Climate Change found that it doesn’t take a sea change for a town or city to effectively limit floodplain development. According to the paper, which is focused on New Jersey, more than three-quarters of Garden State towns reduced floodplain development after the turn of the last century, and around a quarter eliminated it altogether. They did this not by passing any big legislative reforms or climate policies but instead through what the paper calls “routine municipal practices” — things like zoning changes and permit denials.

The researchers argue that the findings should reframe the conversation around floodplain development. While risky construction remains a significant driver of flood damages and disaster recovery costs, it is not the intractable problem that experts and journalists often make it out to be. 

“We are building a lot in floodplains, but it’s not as bad as you think,” said Miyuki Hino, a professor of urban planning at the University of North Carolina, Chapel Hill, and an author on both papers. “Avoiding development in floodplains is doable, and we can do even more of it.”

There are any number of reasons why a developer might want to build near the water. For one thing, many people like living near oceans and lakes, so homes and apartments built near those bodies of water can fetch higher sale prices and rents. Coastal states like Florida also depend on beach tourism to sustain their economies, so it makes sense to cluster housing and shopping near the ocean. Plus, many towns and cities in the United States were built along rivers for navigational purposes, so a disproportionately large share of urban land is likely to be in or near the floodplain.

All those factors might lead one to expect that an outsize share of recent U.S. housing development would be in floodplains. But at least since the turn of the century, the opposite has been the case, according to the new study: Developers have built 844,000 units of housing on 2.1 million acres of floodplain — but if they had chosen available parcels at random, they would have built even more than that. This was true for more than 75 percent of all jurisdictions studied, indicating that most governments make at least some substantive attempt to avoid coastlines and riverbanks.

It also indicates that the overall increase in flood risk is being driven by a few outliers, many of them clustered in Florida and Louisiana. A large share of available land in these states is located in either coastal or riverine floodplains, and both states’ economies largely depend on proximity to the water. A separate report published this week by the nonprofit Natural Resources Defense Council confirms this contention from the study: Of the more than 250,000 properties in the U.S. that have filed multiple flood insurance claims, around half of them are in states along the Gulf of Mexico.

“When we tell the story that the United States is building a ton in the floodplain, we miss out on the fact that that’s not true everywhere,” said A.R. Siders, a professor of public policy at the University of Delaware and an author on both papers. “Some places are actually not building in the floodplain. And then there are some places that are doing so terribly that they make the whole whole country look bad.”

There are two ways of looking at the problem: A county on the Florida coast might build far more homes in the floodplain than a county in the Nevada desert, but the Nevada county may be building a larger share of new homes in the floodplain than the county in Florida. The storm damages, insurance claims, and rebuilding costs in the Florida county will be far higher, but the Nevada county has a lot of work to do as well, because it is placing new homeowners in harm’s way when there is ample other land available.

Politicians, academics, and climate activists have proposed a wide variety of sweeping policy changes that could help cut down on floodplain development. Some have suggested that federal housing finance agencies should no longer securitize mortgages in flood zones, or that the federally-run National Flood Insurance Program should stop insuring them, or that states should ban such development outright. Given that efforts to simply raise flood insurance rates to market levels have generated huge blowback, these strategies would likely create massive political controversy.

But when the researchers zoomed in on New Jersey, which developed most of its coastline in the twentieth century, they found that the solution may be simpler than that. In a survey of 500 towns, they found that more than 120 had eliminated floodplain development without any big policy change. The zoning commission just denied permits to developers, or the mayor told them to build on higher ground, and that was that.

“There are a lot of new and innovative ideas for how to deal with this, but they’re maybe not necessary for the majority [of risky development cases],” said Siders.

“It shows that when you regulate what’s going on in high-risk areas, you do see a perceptible impact on exposure and risk,” added Oliver Wing, the chief scientific officer at Fathom Global, a flood insurance mapping company owned by the reinsurer Swiss Re. “There are some very simple solutions that you can enact locally.”

What about the small share of jurisdictions that account for most floodplain development? The authors argue that these places need targeted intervention. The state or federal government could provide subsidies to encourage less risky construction, helping offset the economic lure of waterfront construction, or a state could just impose penalties on cities that allow for new builds near the water. According to Siders and Hino, the precise solution in any situation needs to be tailored to the reasons a given locality is developing in the floodplain in the first place Some towns may develop in the floodplain because they lack the capacity to plan for a shift to higher ground, as is the case in many rural areas, and others may do it to capture tax revenue from the wealthy owners of vacation homes. While designing such policy solutions might be tricky, the authors argue that the local nature of the solutions should be cause for optimism.

But Wing, who has led previous research that projected a nationwide increase in floodplain development, cautioned that there are limits to the progress that the new papers document. The researchers show that many governments are regulating floodplain development, but most of these regulations only apply to flood zones as delineated by the Federal Emergency Management Agency, which produces flood insurance maps for most of the country. However, these flood maps are old and often inaccurate, and a huge share of flood damage occurs outside of floodplain boundaries. This was the case during 2017’s Hurricane Harvey, when three-quarters of damaged homes in the Houston area were outside the lands that FEMA deems flood-prone.

In other words, while towns and cities may be acting to reduce flood exposure, they will likely have to go even further to eliminate flood risk altogether. This would entail even costlier trade-offs between the economic benefits of development and the economic risks of construction in climate-vulnerable areas.

“We have some excellent evidence here that when you have a flood map, it’s successful in restricting development,” Wing said. “Regulations have worked. But what about all the places that aren’t subject to those regulations?”

Editor’s note: The Natural Resources Defense Council is an advertiser with Grist. Advertisers have no role in Grist’s editorial decisions.