Flood risk, a perpetual concern in porous, low-slung South Florida, is far worse here and across the continental U.S. than now projected under Federal Emergency Management Agency flood maps used by homeowners to decide when to buy insurance, according to a new assessment.
Nearly 41 million Americans — more than three times current estimates — could face 100-year flooding, the study found. The amount of property at risk is more than double.
With about $714 billion in property located in a 100-year floodplain, Florida is a national hotspot.
The study’s authors blamed the massive miscalculation on FEMA’s patchwork of maps, which rely on local authorities to plot flood zones. The process is complicated and time consuming, and often fraught with politics. In addition, FEMA has approved maps for less than 60 percent of the U.S. Many of those local maps also use outdated information while global models use unsophisticated technology, said co-author Kris Johnson, associate director for science and planning at the Nature Conservancy, which teamed up with the U.S. Environmental Protection Agency and the University of Bristol to conduct the review.
“No matter how you slice it, when you look at the whole country, a significant part does not have reliable, up-to-date information on where flood risk is present,” he said.
FEMA officials are aware of the models used in the study, and constantly review new science to update maps, Deputy Public Affairs Director Eileen Lainez said in an email. But before they can be used, models must be certified.
“We welcome new models in science, and as the models described in the article mature, we would look forward to reviewing and including the best of this science into our program,” she said.
Johnson said the team alerted FEMA to their findings before they were published late last month in the online peer-reviewed journal Environmental Research Letters and hoped to work with the agency to improve mapping.
“We’re not trying to throw FEMA under the bus,” he said. “It’s really more about correcting a system that is not proactive enough. FEMA is stretched in many, many ways, and not only the National Flood Insurance Program.”
In fact since Hurricane Harvey swamped the Texas coast and Irma swept across Florida, FEMA has upped its warnings to homeowners about not using flood maps as blueprints for risks. Last week, Roy Wright, FEMA’s deputy director in charge of the flood program, visited South Florida and said the maps obscured the risk for too many under-insured Floridians. He’s set a “moonshot” goal of doubling the amount of flood coverage in the U.S. by 2023.
“These maps are intended to inform flood insurance requirements and regulate development standards in high-risk areas — they are not intended to show absolute lines where flooding will and will not occur,” Lainez said. “Anywhere it can rain, it can flood.”
The study is the first of its kind to look at the physics of flooding from rivers and rainfall in combination with population growth and development. It did not include changes driven by climate change, Johnson said, because sea rise — South Florida’s chief threat — has been well-documented in earlier studies. Climate change impacts are also more difficult to project in river and rainfall flooding, he said.
To update flood risks, Johnson said co-author Oliver Wing used faster computers capable of crunching more data at a larger scale. That allowed him to fill in gaps in mapping and assess entire networks of rivers and lakes. The team also used new modeling developed by the EPA in 2017 that maps changes on the landscape based on population growth and the demand for housing and infrastructure that can change flood patterns. Local flood control efforts, like operations by the South Florida Water Management District, were also included.
“You can make a picture of a whole river system and you’re able to do this in a much more comprehensive way,” Johnson said.
Maps in urban areas regularly updated changed little geographically, he said. But population estimates and projections for future development helped provide a more accurate picture of real risk.
Johnson said he’s realistic about expanding the risk and the opposition that might face from local communities. The maps, he said, were never intended to replace the FEMA maps that undergo public hearings and intense vetting.
“There would obviously be huge political blowback,” he said.
But he hopes they will be used to point out weaknesses and sound the alarm about continuing to build in risky areas where populations are projected to increase at an even faster pace. For example, populations in 50-year flood zones are expected to increase by 53 percent compared to 41 percent in safer, 500-year flood areas.
“If we know this is an issue, let’s not dig the hole any deeper,” Johnson said. “Identify areas of risk and work through local ordinances or zoning or more comprehensive planning. But let’s not develop in these places that are going to be at risk.”
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