Should we build where it floods?Countries around the world create flood maps to predict the expected height and frequency of flooding. In some countries, like the Netherlands, these flood maps help set policies for development and infrastructure investment. But in the United States, they are primarily used as a tool for mandating flood insurance. Following Hurricane Harvey, Houston became one of a few cities using flood maps to change development practices, requiring developers to build two feet above the 500-year storm. For the most part, cities rely on flood insurance to mitigate climate risk. This has yet to prevent communities from being impacted time and again. Since homeowners pay for flood insurance, developers are shielded from flood risk. We’ve seen this in how developers continue to build more densely in areas most devastated by Superstorm Sandy. Often developers rely on ongoing investment in flood mitigation infrastructure, such as seawalls and dams. But these investments are based on increasingly outdated FEMA flood maps. A CBO report in 2018 found that 50% of counties with the highest flood risk use flood maps more than 5 years old. In 2019, First Street published a new set of flood maps that showed FEMA’s flood maps underestimate flood risk by nearly 67%. The combination of outdated FEMA maps and perverse development incentives continues to lead homeowners to buy homes in vulnerable areas. This has devasting outcomes. Once a house has been damaged by storm surges and flooding, it becomes more difficult for homeowners to sell their houses and move. As a result, recent studies have found a higher rate of mortgage defaults in flood-prone areas. Knowing this, local private mortgage lenders offload loans from flood-prone areas to public mortgage lenders. When these mortgages default, it's up to the American taxpayers to pay. City builders need to implement new policies to protect communities most vulnerable to climate risk. That might look like New Orleans' investment in parks and wetlands to reduce reliance on pumping or China’s sponge city initiative to collect stormwater to offset water demand while reducing strain on city infrastructure. But really, city builders need to be bold and set new standards that change how (and if) we build communities that face climate risk.
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