Residents of non-participating communities can't buy federally backed flood insurance. They may also struggle to find private flood insurers willing to cover their properties, as some private insurers won't sell flood coverage in areas that don't take part in the NFIP.

Additionally, residents won't be able to use federally backed mortgages, such as loans from the Department of Veterans Affairs, Federal Housing Administration, or Rural Housing Services, to buy or build a home in a Special Flood Hazard Area, or SFHA. And, if disaster strikes—as it did on Sept. 27 for many Western North Carolinians—non-participating communities won't be able to secure financial assistance from the federal government to repair or rebuild structures in SFHAs.

The Tragic Example of North Carolina

Perhaps no state is a better example of the potential consequences of unprotected flood risk than North Carolina. Most of North Carolina's 550 municipalities participate in the NFIP. But 27 don't—including Mills River, which experienced damage in Hurricane Helene.

Helene ripped through the northwestern part of the state on Sept. 27, decimating communities in North Carolina's largely rural Blue Ridge and Appalachian mountain ranges. The storm killed more than 225 people, and about half of those deaths were in North Carolina. As of October, authorities were still unsure how many people remained missing.

Flood damage to homes and businesses in affected communities is extensive. Since many affected communities are participants in the federal program, the NFIP could cover those losses, at least in part. But few property owners in those areas purchased NFIP policies before Helene.

For example, Asheville, with a population of more than 95,500 and 47,606 housing units, saw nearly 10 inches of rainfall that caused devastating flooding. But city residents and businesses had just 447 NFIP policies in force, offering total coverage of just under $152 million. Helene's total cost could range as high as $250 billion, according to AccuWeather.

North Carolina's Non-Participating Communities

At least one Tarheel community that saw damage from Helene doesn't participate in the NFIP.

The town of Mills River in Henderson County lies south of the Asheville Regional Airport—and the Mills River. After Helene, the town's Mills River Park became a distribution point for food, water, and supplies, and offered a mobile shower station, and mobile kitchen serving hot meals for storm victims.

The town was home to more than 7,300 people, according to the North Carolina League of Municipalities. Because the community doesn't participate in the NFIP, most—if not all—homeowners and businesses in the town lack flood insurance and will have to shoulder the cost of rebuilding without federal funding.

Many of the North Carolina communities that don't participate in the NFIP have very small populations of fewer than 1,000 residents. Like Mills River, they also tend to be rural. Many exist in close proximity to a number of waterways, from large rivers and lakes to creeks and streams. With inland waterways comes an elevated risk of inland flooding.

Helene's severe effect on many inland communities across multiple states took many people by surprise. But with climate change driving more frequent and stronger hurricanes and other weather events, it's likely more communities will face situations similar to Helene's effect on Western North Carolina.

Smaller communities may be unaware of the elevated risks they face.

"In counties and rural areas, you need to pick up 10 to 20 square miles of drainage before a FEMA flood map starts picking up on the floodplain area, yet you have flood risk even if there's only a square mile of drainage," Berginnis said. "These small communities way up in the hollows, they have significant flood risk. [But] we've not mapped it, and that's, I think, on us as a country."

Property owners can take steps to protect themselves, even if they're in a non-participating community, he said. The federal government has been working for over a decade to support the development of a private flood insurance market. People in communities where NFIP coverage isn't available may be able to purchase private flood insurance. Homeowners and businesses can also ask their town leaders to begin participating in the NFIP.

Above all, Berginnis cautioned, communities should continue to prepare for flooding—even those that have already experienced a catastrophic flood event.

"Do not delude yourself to think it can't happen again, or it won't happen again. It will," he said. "And it could happen next week, it could happen next month, it could happen a year from now—the same extreme event."