If you look closely, you will find America’s “climate abandonment areas.”

More than 16 million people in the contiguous US – roughly 5 percent of the population – live in a place with increasing flood risk and a shrinking population, according to new research. It makes clear that “climate abandonment zones” are becoming an increasingly common phenomenon in the US, as people avoid places that are particularly vulnerable to climate-related disasters.

What is a climate abandonment area? It’s a census block where flood risk has become high enough to prompt people to leave. Many of these areas are located along the Texas Gulf Coast, the Florida coast and the mid-Atlantic Ocean.

But it is certainly not limited to these regions, which can be hit repeatedly by storms during the Atlantic hurricane season. Climate abandonment zones are spread across the US in places where heavy rainfall, tropical cyclones, and coastal and river flooding are becoming increasingly serious problems.

“People understand which parts of their community to avoid and which parts of their community are safer, and they act accordingly.”

“People understand which parts of their community to avoid and which parts of their community are safer, and they act accordingly,” said Jeremy Porter, a demographer and head of climate implications research at the First Street Foundation who led the study. “If you look at the housing markets, people are thinking much more carefully about where they should live.”

The phenomenon is even clearer when you zoom in to see how people move from neighborhood to neighborhood. When people think about climate change affecting migration, they might imagine someone moving far from home to another part of the country. But that is only a small part of the overall migration trends. The majority of people move within the same city, state or metropolitan area, Porter points out.

First Street Foundation is a nonprofit research group that has developed tools to help residents assess the risks of flooding, fire and extreme weather events facing individual properties. The latest research was published in the journal Nature communication Today. Researchers from several universities and the nonprofit Environmental Defense Fund also contributed to the study.

They used First Street’s flood risk data and the Census Bureau’s most recent 2020 population count to build a mathematical model that can determine the relationship between flooding and population change, controlling for other factors such as job availability, which can also influence someone’s decision to move.

For example, they found “tipping points” for each Census block, a threshold at which flooding is so bad that people begin to leave the area. The tipping point varies from place to place, showing that people began moving when about 5 to 15 percent of properties in an area were at risk of flooding.

More than 3.2 million people in the US left neighborhoods at high risk of flooding between 2000 and 2020. Climate neglected areas are expected to shrink by a further 16 percent over the next thirty years, losing an additional 2.5 million inhabitants.

There are still people moving to areas where other people have left because of flooding. The study also identifies ‘high-risk growth areas’, where despite increasing flood risk, the population is still growing (although not as fast as without the risk). Nearly 30 percent of the population in the contiguous U.S., 97.2 million people, live in these high-risk growth areas.

“Public exposure over the next 30 years is a serious concern,” Evelyn Shu, senior research analyst at the First Street Foundation and lead author of the paper, said in a press release. “For decades we have chosen to build and develop in areas we thought posed no significant risk, but the impacts of climate change are quickly starting to look like areas we would otherwise have avoided the past.”

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