North Carolina Flood Risk Maps Inadequate for Protecting People and Nature
A new study finds current FEMA flood hazard maps under predicted flooding by 23 percent.
As the 2020 hurricane season begins, a new study by The Nature Conservancy (TNC) and Arizona State University’s Center for Biodiversity Outcomes shows that FEMA flood hazard maps underpredicted the extent of recent hurricane-induced floods, their effect on vulnerable human communities, and consequential environmental damage. The study published in Environmental Science and Technology used satellite images to map flooding from Hurricane Matthew in 2016 and Hurricane Florence in 2018. The findings can be used to help communities be more resilient to future storms.
“Our research showed that widespread flooding occurred well outside of the boundaries established by the legal definitions of floodplains,” said Danica Shaffer-Smith, lead author on the study. “Florence and Matthew impacted a footprint more than 23 percent greater than the 100-year floodplain, well beyond what current flood hazard maps predicted. We need better maps to better protect our communities.”
Schaffer-Smith said the findings can be used to help communities improve community resilience to future storms.
“These were devastating storms, but you can’t get good measures of the true impacts to water quality during or immediately after the storm,” Schaffer-Smith. “Many sensors that measure water quality were offline due to flooding, and hazardous conditions didn’t allow for manual data collection, so government agencies had to rely on anecdotal reporting or delayed field sampling to assess the impact. Satellite-based radar makes up for those deficiencies; radar can penetrate through clouds and is highly sensitive to the presence of water on the ground, including beneath trees. That allows us to see the extent of flooding and assess impacts.”
Additionally, the study aimed to determine what vulnerable populations were most at risk from future storms. By overlaying the flood mapping with the Centers for Disease Control’s Social Vulnerability Index, which ranks census tracts to predict how well they will respond to disturbances like flooding, the researchers found that communities with senior citizens, people with disabilities, unemployed people, and people living in mobile homes were disproportionately affected by the storms.
The study provides the first assessment of the two storms’ potential impact on water quality in the region. In total, 118 municipal water intakes and 206 public water supply wells lie in the repeatedly flooded areas. Another 40 hazardous waste sites, 339 industrial wastewater facilities, and 218 municipal wastewater treatment plants were likely compromised by the storms. North Carolina environmental regulations don’t allow the construction of Confined Animal Feeding Operations (CAFO) in the “100-year” floodplain, but the study identified 91 swine CAFO and their associated hog waste lagoons in the repeatedly flooded area and another 36 poultry CAFOS where animal waste is dry composted.
The researchers identified areas where community buyouts of vulnerable homes and businesses may be warranted. It also gives conservation groups like TNC a blueprint for their work.
“We identified extensive areas where wetlands and forests could be protected and other places where these landscapes could be restored. Those nature-based solutions reduce flooding, filter pollutants from flood waters, and provide habitat for plants and animals,” says Julie DeMeester, Director of TNC’s North Carolina Water Program and co-author of the study. “That’s a cost-effective win for people and nature.”
Schaffer-Smith is a NatureNet Science Fellow. The NatureNet Science Fellowship program partners TNC with leading universities to bring the best research to real world problems. In addition to Schaffer-Smith and DeMeester, the research team included Arizona State University faculty Soe W. Myint, Rebecca L. Muenich, and Doaqin Tong. Support was provided by The Nature Conservancy and Arizona State University Center for Biodiversity Outcomes, the Ira A. Fulton Schools of Engineering, the School of Geographical Sciences and Urban Planning, and the School of Sustainable Engineering and the Built Environment.
The full study “Repeated Hurricanes Reveal Risks and Opportunities for Social-Ecological Resilience to Flooding and Water Quality Problems” is available here.
Schaffer-Smith has prepared graphics that may be helpful in reporting this story. They are available here.
The Nature Conservancy is a global conservation organization dedicated to conserving the lands and waters on which all life depends. Guided by science, we create innovative, on-the-ground solutions to our world's toughest challenges so that nature and people can thrive together. We are tackling climate change, conserving lands, waters and oceans at an unprecedented scale, providing food and water sustainably and helping make cities more sustainable. Working in 79 countries and territories, we use a collaborative approach that engages local communities, governments, the private sector, and other partners. To learn more, visit www.nature.org or follow @nature_press on Twitter.