Thanks to climate change, extreme weather events will become only more frequent. Rising sea levels and warming waters are an especially dangerous combination, raising the risk of devastating storms and floods. The nation must bolster its defenses against these rising threats. But it cannot do that without good data on who and what is at most risk. The nation’s flood maps — which inform decisions on who needs insurance coverage, where building takes place and who gets evacuated during a crisis — are dangerously outdated.
By the Editorial Board
Flooding is the United States’ most common and costly natural disaster — and among its most deadly. According to Pew, flood-related disasters have cost the United States more than $850 billion since 2000, and the number of lives these calamities claim is rising, likely in part because warmer air and seas encourage unrelenting downpours.
The Federal Emergency Management Agency creates maps that estimate flood risk across the country. State and local governments use these maps to write building codes and site infrastructure such as hospitals, utilities and emergency shelters. When disaster strikes, flood maps can guide where emergency responders rush and which communities are advised to flee. Good maps save lives.
Federal law requires FEMA to review and, if the agency decides it is needed, update flood maps at least once every five years. But when record-breaking downpours turned middle Tennessee’s creeks into rapids last month, FEMA had not updated the hardest-hit counties’ flood maps in more than 10 years. In Humphreys County, where 17 inches of rain fell in less than a day, FEMA’s maps predicted a third of the flood risk that the First Street Foundation, a research group that quantifies climate risk, estimated. In a neighboring county that was also hit hard, First Street predicted that up to 10 times the number of homes FEMA said were in danger were actually at risk. One reason for this vast divergence: The foundation says FEMA leaves smaller creeks and tributaries completely unmapped in its flood risk predictions. Tellingly, Realtor.com relies on First Street, not FEMA, when explaining flood risk to potential home buyers.
Flood maps can overstate as well as understate risk. Federal predictions said Hurricane Ida would pummel Houma, La., with nine feet of storm surge. But the local emergency preparedness director urged skepticism, saying that the flood maps federal authorities used to make these projections failed to account for the 12-to-13-foot levee system surrounding the city, which held. With federal projections telling residents one thing and local officials another, confused Louisianans were caught in the middle.
FEMA says that cities must flag their maps for updating, but the point of FEMA reviewing all maps every five years is for the agency to make its own determination.
Complicating the process is the fact that flood maps can be intensely political, because the boundaries FEMA sets determine the terms on which communities can participate in the subsidized federal flood insurance program. The nation’s success in coping with climate change depends on high-level federal legislation but also on the extent to which government agencies can adapt a range of obscure bureaucratic functions to the new reality. As sea levels rise and climate change-fueled catastrophes become more frequent, the risks communities face will evolve quickly. FEMA must raise its flood map game.
