Over the past century, the United States has built millions of houses along coastlines and rivers, developed on land almost destined to flood. At the same time that the warming of the planet raised sea levels and increased rainfall, annual flood damage has increased in recent decades largely because more homes are now in flood-prone areas than ever before. In coastal cities like Carolina Beach, North Carolina, most homes sit in a federally designated flood zone, exposing them to massive flood events like the one that went down more than a foot of rain this week on the city.
Experts portrayed this widespread risky construction as an insoluble problem and claimed that “Home sales in flood zones are booming,” that “more Americans are moving in flood … hot spots,” or point out “rapid urban growth in floodplains.” News coverage, including that of this publicationlargely followed this lead.
But new research from some of the nation’s leading experts on climate adaptation, 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 found that the US actually built fewer structures in floodplains than would be expected if cities built randomly. This means that, if anything, the average city is now active avoid flood plains, contrary to conventional wisdom. Indeed, in the 21st century, most towns and cities in the US have little or no construction in flood-prone areas. The vast majority of floodplain construction — the kind that draws headlines and feeds the pessimistic narrative — has occurred 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 New Jersey-focused paper, more than three-quarters of Garden State towns reduced floodplain development after the turn of the last century and about a quarter eliminated it entirely. They didn’t do this by enacting any major legislative reforms or climate policies, but rather 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 about floodplain development. Although risky construction remains a significant driver of flood damage and disaster recovery costs, it is not the intractable problem that experts and journalists often make it out to be.
“We build 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 floodplain development is achievable, and we can do even more of it.”
There are a number of reasons why a developer might want to build near the water. For one thing, many people like to live near oceans and lakes, so homes and condos built near those bodies of water can command higher sales 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. Additionally, many towns and cities in the United States are built along rivers for navigation purposes, so a disproportionately large portion of urban land is likely to be in or near the floodplain.
All of these factors might lead one to expect that much of recent US housing development will 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 randomly selected available parcels, they would have built even more than that. building. This was true for more than 75 percent of all jurisdictions studied, indicating that most governments are making at least a substantive effort to avoid coastlines and riverbanks.
It also indicates that the overall increase in flood risk is driven by a few outliers, many of which are clustered in Florida and Louisiana. Much of the available land in these states is located in either coastal or river floodplains, and both states’ economies are largely dependent on proximity to water. A separate report published this week by the Natural Resources Defense Council confirms this claim from the study: Of the more than 250,000 properties in the US that have filed various flood insurance claims, about 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 the fact that that’s not true everywhere,” said AR Siders, a professor of public policy at the University of Delaware and an author on both papers. “Some places don’t actually build in the floodplain. And then there are places that do so terribly that they make the whole country look bad.”
There are two ways to look at the problem: A county on the Florida coast may build many more homes in the floodplain than a county in the Nevada desert, but the Nevada county may build a larger part of new homes in the floodplain than the county in Florida. The storm damage, insurance claims and rebuilding costs in the Florida county will be much higher, but the Nevada county also has a lot of work to do because it puts new homeowners at risk when there is enough other land available.
Politicians, academics and climate activists have proposed a wide range of sweeping policy changes that could help reduce 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 altogether. Given that efforts to simply raise flood insurance rates to market levels generated big blow backthese strategies are likely to 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 might be simpler than that. In a survey of 500 towns, they found that more than 120 had eliminated floodplain development without any major 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 many new and innovative ideas on how to deal with this, but they may not be necessary for the majority [of risky development cases],” Siders said.
“It shows that when you regulate what’s going on in high-risk areas, you do see an observable impact on exposure and risk,” said Oliver Wing, the chief scientific officer at Fathom Global, a flood insurance mapping company owned by reinsurer Swiss. added. Re. “There are some very simple solutions that you can apply locally.”
What about the small portion of jurisdictions responsible for most floodplain development? The authors argue that these places need targeted intervention. The state or federal government can provide subsidies to encourage less risky construction, which helps offset the economic lure of building on the waterfront, or a state can simply impose fines on cities that allow for new buildings near the water. According to Siders and Hino, the exact solution in any given situation must be tailored to the reasons why a given location develops into the floodplain in the first place. Some towns may develop in the floodplain because they lack the capacity to plan for a move to higher ground, as is the case in many rural areas, and others may do so to obtain tax revenue from wealthy vacation home owners. Although designing such policy solutions can be difficult, the authors argue that the local nature of the solutions should be cause for optimism.
But Wing, who led previous research that a nationwide increase in floodplain developmentwarned that there are limits to the progress the new papers document. The researchers show that many governments regulate 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. This flood maps are old and often inaccurateand a large proportion of flood damage occurs outside floodplain boundaries. This was the case during 2017’s Hurricane Harvey, then three quarters of damaged houses in the Houston area was outside the lands that FEMA considers flood-prone.
In other words, while towns and cities may be taking steps to reduce flood exposure, they will likely need to go even further to eliminate flood risk altogether. This will involve even more expensive 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 limiting development,” Wing said. “Regulations worked. But what about all the places that are not subject to those regulations?”
Editor’s note: The Natural Resources Defense Council is an advertiser with Grist. Advertisers play no role in Grist’s editorial decisions.
