Official numbers vastly underestimate US flood danger, researchers find
By Christopher Flavelle, Denise Lu, Veronica Penney, Nadja Popovich and John Schwartz
Across much of the United States, the flood risk may be far greater than government estimates previously have shown, exposing millions of people to a hidden threat — and one that will only grow as climate change worsens.
According to calculations last year that took into account sea-level rise, rainfall and flooding along smaller creeks not included in the federal government’s flood maps, an estimated 14.6 million properties were at risk from what experts call a 100-year flood, far more than the 8.7 million properties shown on federal maps at that time. A 100-year flood is one with a 1% chance of striking in any given year.
The government’s flood maps guide where and how to build, whether homeowners should buy flood insurance, and how much risk mortgage lenders take on. The numbers, which The New York Times mapped and published last year, suggested that homeowners, builders, banks, insurers and government officials nationwide had been making decisions with information that understated true physical and financial risks.
Numerous cities nationwide — as diverse as Fort Lauderdale, Florida; Buffalo, New York; and Chattanooga, Tennessee — showed the startling gap in the risks. And minority communities often face a bigger share of hidden risk.
“Millions of home and property owners have had no way of knowing the significant risk they face,” said Matthew Eby, founder and executive director of the First Street Foundation, a group of academics and experts who compiled the data, creating a website where people can check their own address.