MAR 2, 2018
41 million Americans—not 13 million—are at risk of experiencing a 100-year flood, according to the study.
Over the past 30 years, the United States has suffered an average of $8.2 billion in annual damage from freshwater flooding. Studies show that the destruction is intensifying every year. The August 2016 floods in Mississippi and Louisiana, for example, inflicted $10 to $15 billion in damages.
The wrath of Hurricane Harvey sparked debate over how the country manages flood insurance and brought fresh scrutiny on incentives for new construction on the country’s precarious floodplains. But meaningful reform faces a hurdle: the Federal Emergency Management Agency’s flood hazard maps. These maps dictate flood risk management in the U.S., and they’ve been widely criticized for being outdated and underestimating the country’s flood risk.
A report released on Wednesday by the University of Bristol, U.K., and the Nature Conservancy concludes that FEMA’s maps only account for one-third of the total population that is exposed to serious flooding. Whereas FEMA estimates that 13 million Americans are currently exposed to the devastation of a “100-year flood,” the report puts that number at 41 million. (A 100-year flood describes an extreme flooding event that has a one-percent chance of occurring in any year; it is a common benchmark for flood risk management.)
“It’s pretty daunting,” said Kris Johnson, a Nature Conservancy scientist and one of the report’s authors.
The simulations run for this study used large amounts of data from the U.S. Geological Survey National Elevation Dataset, and were “much more accurate and much more comprehensive than anything we’ve had available before,” Johnson said. FEMA’s appraisal of flood risk, on the other hand, relies on time-consuming local assessments of various catch basins and floodplains.