Charleston County's first new flood maps in more than 14 years have been under review since 2016, and even when they're finally published next year, they'll already be out of date.

The Charleston region has seen some of its most damaging storms in the past three years, but none of that flooding data was incorporated into the new maps, according to Carl Simmons, the county's director of building services.

So, it's possible that some areas that were underwater during the historic flood of 2015, Hurricane Matthew in 2016, or Tropical Storm Irma last year, will be left out of the new map's high-risk flood zones.

Another problem is the maps are based on a coastal storm model, meaning they only consider flooding brought on by storm surge from a low-intensity Category 3 hurricane, Simmons said. They won't show how much an area would flood in a torrential downpour such as the one that inundated the area in 2015, or what the conditions would be if storm surge and a heavy rain came at the same time, as was the case with Irma. 

"It's not going to give you all the answers," Simmons said. 

That's because the Federal Emergency Management Agency doesn't have a mapping model to consider the dual forces of storm surge and rainfall on the coast, a combination that's proven to be devastating in recent storms such as Hurricane Florence last month.

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FEMA's mapping method also doesn't consider sea level rise projections, which scientists warn will make storm surges more damaging and more capable of reaching farther inland.

Still, Charleston County's updated maps will have a smaller flood hazard area overall. More than 13,000 properties will be removed from the flood zones, while about 3,000 are being added. 

'We're in denial'

FEMA's flood maps have become more accurate over the past few decades thanks to technology, but even those involved in creating them today recognize that their failure to factor in new climate forces will make them more inadequate as time goes on.

Research shows that a rapidly warming climate allows the atmosphere to hold more water, leading to more intense storms with much more rainfall.

"I don’t think we have done a good job of finding out where a flood from the Atlantic Ocean and stormwater meet. I don’t think we know where that line is," Simmons said. "I think we’re going to have to work on locating that line."

Despite their flaws, the flood maps remain the basis for local building and land-use regulations in flood-prone areas. 

The most protective measures, such as how high buildings have to be elevated, typically only apply to certain high-risk zones, even though experts know floodwaters rarely stay neatly within those boundaries.

More than a third of federal disaster assistance goes to flood victims outside flood hazard areas.

Three-quarters of the flood damages caused by Hurricane Harvey in Houston last year were also outside FEMA's flood zones. But even in the highest-risk areas, where stricter regulations applied, they weren't enough. Homes that were elevated a foot above FEMA's standard still got flooded. 

"Sometimes, the building codes in an area send a false sense of security," said Lynne Yeates McChristian, executive director of the Center for Risk Management Education & Research at Florida State University. "The minimum is the least you can do, not the best you can do."

Charleston County recognized that and has required all new structures in unincorporated areas to be built 2 feet above FEMA's standard level. That's enforced everywhere, not just in flood zones, Simmons said. 

The maps apply countywide, but towns and cities make their own flood protection rules. For instance, the city of Charleston requires buildings in the highest-risk zones to be elevated 1 foot above FEMA's standard. 

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Only people who buy homes in flood zones are required to buy federal flood insurance through the National Flood Insurance Program. It’s optional for everyone else, and while local officials strongly encourage everyone in the Lowcountry to have it, many don't.

About 38 percent of properties in Charleston County have a policy through the NFIP, according to the Insurance Information Institute. 

"We have a huge protection gap when it comes to flood insurance," McChristian said. 

She said many homeowners wrongly assume if they don't have to buy flood insurance, they aren't at risk. Many choose to cut the cost.

"They make a very costly mistake," she said. "Flooding is the No. 1 natural disaster risk, and we're in denial over that." 

The last flood map for the county was issued in 2004. FEMA recommends communities adopt updated maps every five years, but it's not uncommon for communities to use the same ones for decades.

Filling gaps with other maps

Given the number of flooding factors left out of FEMA's maps, some people are turning to other resources to get a fuller sense of the threats in Charleston.

When Sally Newman was ready to buy a house in Charleston in 2015, finding property on high ground was a top priority. She wanted to look beyond the risks reflected in FEMA's maps, which she had a hard time making sense of anyway.

"I didn’t get the sense they were there to help potential homeowners make a decision," she said.

She wanted a house that would hold up if the worst-case sea level rise projections came true. She used an online interactive map from climatecentral.org that incorporated that data to find where she should hunt for houses.

She ended up in the Wagener Terrace neighborhood on the upper Charleston peninsula, on a property that's 11 feet above sea level. Her house's first floor is 3 feet higher than that. It has remained dry during the past three major floods, she said.

Newman's Realtor, Leslie Turner, markets herself as being able to help buyers find the perfect high-elevation home in Charleston. She has a map that she drew herself by driving around in her pickup during major storms and extra high tides.

Her research and firsthand knowledge helps supplement what FEMA's flood maps say, because they don't reflect recent changes. 

"Since 2015, we've had some major, major changes with the flooding. One, I think it's Mother Nature, but two, I think it's growth and development that Charleston has experienced," she said.

Realtors are being asked increasingly for that kind of insight, she said. 

"Four years ago, I mean, flood zones were not on anybody's top five of what they were looking for in a house," she said. "Now, it's the first question they ask."

The National Oceanic and Atmospheric Administration also has a few relevant tools. Its Land Cover Atlas shows land changes over time, such as the acreage of forests and wetlands, as well as increases in pavement — trends that impact the way water behaves in a flood.

In Charleston County, the developed area has increased 18 percent between 1996 and 2010, and impervious surfaces such as pavement have increased 20 percent.

Another online interactive map is NOAA's Sea Level Rise viewer, which shows how much water would inundate a specific area given different levels of sea rise. 

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One study released earlier this year by the Union of Concerned Scientists estimated that more than 16,000 homes in South Carolina, mostly in the Lowcountry, could flood dozens of times a year by 2045. That would displace the roughly 24,000 people living there today, sink property values and possibly lead to large-scale problems for the region's economy.

Climate scientists have pushed FEMA to incorporate their predictions into the maps, with no luck so far.

 

Reach Abigail Darlington at 843-937-5906 and follow her on Twitter @A_Big_Gail.

Abigail Darlington is a local government reporter focusing primarily on the City of Charleston. She previously covered local arts & entertainment, technology, innovation, tourism and retail for the Post and Courier.