New research published on Monday indicates that the number of structures in the United States vulnerable to flooding may be greater than previously estimated.

A study, published in the Journal’s Future of Earth, revealed that 43% of North Carolina’s flooded buildings from 1996 to 2020 are outside the Federal Emergency Management Agency’s Special Flood Hazard Areas, which FEMA designates as having a 1% chance of flooding in any given year.

Experts and the study’s authors believe these findings may assist more communities in understanding their flood risks and insurance needs. As companies pull back from increasing insurance premiums and insuring homes in certain regions due to more frequent severe weather, obtaining flood insurance is becoming increasingly challenging, leaving property owners more exposed.

According to NBC News, experts stated that having access to reliable data sources could facilitate the creation of nationwide databases like the one outlined in the study.

FEMA’s maps serve as the main reference for identifying flood-prone zones and structures requiring insurance coverage. However, experts argue that this system is outdated and lacks resolution. A 100-year floodplain projection doesn’t fully encompass the areas that could be at risk for flooding, and the authors noted that climate change has compromised the reliability of previously authoritative weather and climate forecasts.

This study enabled researchers to pinpoint specific structures that have experienced multiple flooding incidents by utilizing address-level data. This information could inform property owners on whether to obtain flood insurance, even if they fall outside FEMA’s designated flood hazard zones. In the United States, FEMA reports that 99% of counties have experienced flooding, yet only 4% of homeowners hold flood insurance at least once.

“Detailed information about previously flooded areas can empower individuals to make informed decisions,” expressed Helena Margaret Garcia, the lead author of the study and a doctoral candidate at the University of North Carolina Chapel Hill.

FEMA and the National Flood Insurance Program did not respond to requests for comments.

FEMA is currently working on revamping its flood mapping system through the Future of Flood Risk Data initiative, aimed at employing more efficient, accurate, and consistent technology to assess the country’s flood risks comprehensively.

As global temperatures rise, more intense rainfall events are becoming common since warmer air can hold more moisture. Climate change has also contributed to rising sea levels, increasing vulnerability to flooding even in coastal and some inland areas. Hurricane Helen, the third deadliest hurricane of modern times, inflicted substantial flooding in North Carolina’s mountainous regions. Damage from the storm exceeded a total of $78 billion, according to the National Oceanic and Atmospheric Administration.

The recent severe rainfall has caused flash floods across many U.S. towns over the last two weeks, most recently impacting towns in New Jersey and New York City. In North Carolina alone, six deaths have been reported, while over 100 fatalities have occurred in Texas. Flash floods have historically accounted for the highest number of storm-related deaths in the U.S., averaging 125 deaths per year over recent decades, according to the National Weather Service.

A North Carolina climate scientist noted that the warm seawater feeding the storm could have been a contributing factor to last week’s Tropical Storm Chantal, which set rainfall and river level records in the state.

With the impacts of climate change, having access to up-to-date maps is essential, experts argue.

In their study, researchers mapped 78 flood events using data from 1996 to 2020 from the National Flood Insurance Program, which allows property owners to purchase insurance for potential flood-related losses. They also incorporated emergency service requests and volunteer-based geographic information obtained from social media, creating what they termed the “first of its kind” database. This historical flood data is often inaccessible to the public, which can hinder homeowners’ awareness of prior flood incidents affecting their properties.

Garcia stated that researchers plan to apply the same methodology from their study to create similar historical maps in various regions across the country, identifying areas previously overlooked concerning flood risk.

The research indicated that out of 90,000 structures, only 20,000 experienced flooding, highlighting a significant number that did not file NFIP claims. The study’s authors are now focused on quantifying the human impact, examining outcomes such as healthcare disruptions resulting from floods and the scale of evacuations caused by repeated flooding, as Garcia explained.

Antonia Sebastian, an assistant professor in the Department of Geology at UNC-Chapel Hill, noted that the study aspires to establish a “comprehensive record of past floods” by gathering data on relatively minor flood events that impact homeowners yet do not receive widespread media attention.

“Areas that have previously flooded are likely to flood again; it’s only a matter of time,” Sebastian remarked. “These sites are inherently dangerous.”

Chad Belginis, executive director of the Flood Plains Association who was not involved in the study, stated that FEMA’s maps are intended to implement the NFIP by utilizing 100-year flood plains to delineate zones for flood insurance coverage. He emphasized that analyzing historical flood research highlights the necessity for flood insurance in areas beyond the mapped FEMA flood hazard zones.

“FEMA’s flood map serves as a starting point, not an endpoint,” Berginnis clarified. “The maps present one kind of flood risk, but to fully grasp flood risk, it is crucial to seek out historical flood data.”

He mentioned that the database models illustrated in the study could be adopted in various other regions. A community manager indicated that identifying past flood sites could enhance community awareness regarding flood risks.

“When we consider the history of floods, [like those along the Guadalupe River], it emphasizes the dangers that have persisted over time,” they reflected. “I truly believe that these areas should be acknowledged as perilous, yet awareness of the actual flooding risks is often lacking.”

June Choi, a doctoral student in Earth Systems Science at Stanford University and not involved in the study, noted that the finding regarding many flooded buildings existing outside FEMA-designated risky areas likely applies to all states. She highlighted that while new databases might have limitations regarding changing building densities over time, the application of historical records and address-specific data still provides valuable insights for assessing future flood risks.