This story was co-published with The Weather Channel as part of Collateral, a series on climate, data and science.
In flood-prone regions of the country, a growing number of cities have lost confidence in the ability of the federal government's flood maps to recognize the increasing risks that come with global warming.
From Houston to Baltimore to Cedar Falls, Iowa, and now Mexico Beach, Florida, local officials are going beyond the federal standards and have started to require homes in a much wider area—beyond the usual 100-year floodplain—to be built to higher flood-protection standards.
In Mexico Beach, the move was triggered in part by the Federal Emergency Management Agency's decision to reclassify dozens of properties that flooded last year in Hurricane Michael. The homes had been in the high-risk 100-year flood zone, where flood insurance generally is required, but FEMA moved them to the minimal-risk 500-year flood zone, where flood insurance is optional.
The city's goal is to have more homes and businesses higher and drier, so they're less likely to suffer flood damage when the next storm hits.
Hundreds of communities and as many as 22 states already require new construction be elevated higher than federal requirements in the high-risk 100-year floodplain, which is based on a 1 percent chance of flooding in any given year. Now, a small but growing number of cities and counties are also extending the additional building-height standards to the wider 500-year floodplain.
Officially, the 500-year floodplain means a 0.2 percent annual chance of flooding, but climate change may be loading the dice for higher risks.
"We now are seeing this trend start because people are getting these extreme events," said Larry A. Larson, a professional engineer and senior policy advisor for the national Association of State Floodplain Managers.
"We have people outside the high-risk area getting flooded," he said. "If we regulate to the 500-year (risk) we are more apt to get closer what we call the 100-year but really now is more than that."
The threat will only get worse as communities pack more development into low-lying areas and as global warming fuels more extreme weather, said Shana Udvardy, a climate resilience analyst with the Union of Concerned Scientists.
In the newest National Climate Assessment, published last fall, U.S. government scientists warned that global warming was intensifying and increasing the frequency of extreme rainstorms that cause devastating flooding. Hurricane rainfall and intensity are also likely to increase, as are the frequency and severity of "atmospheric rivers" of rain on the West Coast, like the event that drenched California last month, triggering flash floods and mudslides. Sea-level rise also makes storm surges more dangerous.
But FEMA hasn't taken climate change into account when creating flooding maps.
FEMA Plans Risk-Rating Changes, but Mexico Beach Sees Bigger Problem
Floodplains are mapped by FEMA to determine which properties are likely to be inundated under different risk scenarios.
People with federally backed or regulated mortgages on buildings in the 100-year floodplain are required to buy insurance through the National Flood Insurance Program, which has fallen under extreme stress from repeated, major national flooding disasters and is billions of dollars in debt.
On Monday, FEMA announced it was rolling out a new risk-rating system to determine insurance premiums that will use more risk factors to calculate insurance costs for each property. But it still only requires flood insurance for homes in the 100-year floodplain.
Some communities, like Mexico Beach, join a lot of experts in saying those FEMA flood maps are misleading and downplay overall flood risk.
In Mexico Beach, new draft maps reclassify about 40 properties into the 500-year, minimal-risk zone that were severely damaged by Hurricane Michael's surging waters. Twenty of those buildings were completely destroyed, said Katie McDowell Peek, a coastal geologist with Western Carolina University's Program for the Study of Developed Shorelines, which carried out the analysis. Some were once beachfront homes.
"We were shocked they were removed" from the high-risk zone, Peek said, adding that she and her colleagues have seen the same thing happen with other FEMA remapping, including in Dare County, North Carolina.
The FEMA maps are based on a scientific analysis of ground elevations and contours, said Jerrick Saquibal, hydrology and engineering chief with the Northwest Florida Water Management District, which is working with FEMA to develop flood maps for Mexico Beach and other nearby communities.
They are drawn for insurance purposes and are not meant to convey an overall flood risk, especially from a record storm like Michael, he added. Flood-prone communities like Mexico Beach are encouraged to adopt their own, more stringent regulations, in either flood zone, he said.
Mexico Beach Mayor Al Cathey said he didn't understand the new draft FEMA maps, which, when adopted, will mean homes that are rebuilt on those properties will no longer be required to buy flood insurance.
Without the new city ordinance, there also would have been no extra elevation requirements, he said. But now, he said, new construction must be elevated at least a foot and a half higher than FEMA's base-level flood predictions in both the 100-year and 500-year floodplains, which encompass most of the town, which had a population of about 1,200 before Michael.
"As the local government, it is our responsibility to protect our citizens," said Cathey, adding that the decision was made as a direct result of Michael, with its approximately 19-foot storm surge that swept dozens of homes off their foundations and damaged even more.
"I felt we needed to show FEMA that we are going a step beyond what they say is necessary."
Coastal and River Cities Setting Higher Standards
Mexico Beach's new floodplain regulations are part of a shift, floodplain experts said. Houston made similar changes in the aftermath of catastrophic flooding from Hurricane Harvey in 2017. So did Baltimore after multiple floods, including Hurricane Isabel, which made more than 570 homes and 15 businesses uninhabitable because of flooding.
"The (FEMA) maps are based on historical data and in many cases are old and outdated, so communities are seeing flood impacts that are going well beyond the areas that FEMA regulates," said attorney Jessica Grannis, the adaptation program director at the Georgetown Climate Center in Washington, D.C.
The Georgetown program in January issued a report on how Maryland's eastern shore could adapt to increasing concerns about flooding and sea level rise. Regulating the 500-year-floodplain was among the recommendations of the report, which cited rules in Cedar Falls and Baltimore as examples.
Cedar Falls, which has a 1-foot elevation requirement above base flood levels, according to FEMA, is experiencing flooding again this week after a major storm in the region.
Baltimore requires new construction or substantial reconstruction to be elevated 2 feet above a base flood level, providing an extra margin of safety. The city has a long history of flooding. In 2003, its coastal neighborhoods were inundated by tidal flooding from Hurricane Isabel, causing severe damage, said Victor Ukpolo, the city's floodplain manager. In 2014, the city experienced more extreme flooding.
"The severity of these events flood events ... and anticipating more frequent and severe climate threats led to adopting the higher standard," he said.
In Charlotte and Mecklenburg County, North Carolina, local authorities map what they call a future conditions floodplain that's roughly equivalent to a FEMA 500-year floodplain, with 1- to 2-foot building elevation requirements, said Timothy J. Trautman, the area's stormwater services manager. It has taken anticipated land-use changes into account for 15 years, he said.
Those efforts may have spared thousands of homes from flooding during last year's Hurricane Florence, which hammered North Carolina, he said.
After Harvey, Houston Strengthens Building Rules
A FEMA spokeswoman said the agency doesn't track how many of the 22,000 American communities that participate in the National Flood Insurance Program are voluntarily adding flood protection requirements in the 500-year floodplain.
But in April last year, FEMA praised the Houston City Council for "ensuring new construction will meet a higher standard for flood preparedness" by requiring 2 additional feet between expected flood levels and new development in both the 100- and 500-year floodplains.
The remnants of Hurricane Harvey dumped roughly 50 inches of rain on parts of Houston over four days in August 2017, flooding more than 150,000 homes in that city alone, according to a city study. That study concluded that if all of Houston's homes had been compliant with the city's new rules, 84 percent of the city's homes that flooded during Harvey would have been spared.
That study estimated that the new requirements would add $11,000 to $32,000 to the cost of newly constructed homes, while the savings from avoided flooding costs could range from $50,000 to many hundreds of thousands of dollars—not including the value of avoided risk to first responders, emotional trauma and health impacts.
Harris County, surrounding Houston, passed similar floodplain requirements following Harvey.
"It's revolutionary in the sense that we've never really had regulations so tied to the floodplain at that level of protection," said Iris Gonzalez, the coalition director at Coalition for Environment, Equity and Resilience in Houston. In the aftermath of Harvey, Houston has a "bigger appetite" for "making sure we are building a Houston that can withstand these kinds of weather events that are more frequent."
But she also cautioned that adding more expensive building requirements can hurt low-income and minority families, forcing them out of affordable neighborhoods. "It comes down to designing programs with that in mind," she said, such as directing financial help to some of those neighborhoods.
'We Want People to Build Their Houses Safely'
In Dare County, North Carolina, authorities are preparing to regulate building heights in the 500-year-floodplain, said Donna Creef, the county's planning director. The county includes 110 miles of fragile, sand-shifting barrier islands known as the Outer Banks.
As in Mexico Beach, newly drawn draft FEMA maps are putting properties that have been in the high-risk 100-year floodplain into the 500-year floodplain, which would exempt them from insurance requirements and local elevation requirements.
Yet Creef said these properties, which are vulnerable to storm surges from hurricanes, have flooded and will flood again. So the plan is to propose a higher standard across a larger area to include the 500-year floodplain, she said.
"We want people to build their houses safely," and to have insurance, Creef said.