Study - Building In Floodplains May Not Be As Widespread As Thought - Florida & Louisiana Notable Exceptions

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.

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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.

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https://grist.org/extreme-weather/floodplain-development-study-flood-zones/