Hurricane Irma damaged homes in the Florida Keys in 2017. A new study finds buildings in the contiguous U.S. are concentrated in disaster-prone areas. Matt McClain/AP

More than half of the buildings in the contiguous U.S. are in disaster hotspots, a new study finds. Tens of millions of homes, businesses and other buildings are concentrated in areas with the most risk from hurricanes, floods, wildfires, tornadoes and earthquakes.

The findings underscore how development patterns exacerbate damage from climate change.

"We know that every year, we lose billions of dollars [and] we lose lives to natural hazards," says Virginia Iglesias, a researcher at the University of Colorado, Boulder and one of the authors of the new study. "Of course climate change has a lot to do with this because climate change is increasing the probability of extreme events. But at the same time, it also matters what is in harm's way."

Iglesias and her colleagues analyzed records going back to 1945 to see how many buildings are in hotspots for natural hazards. They focused on the riskiest places — areas where the probability or magnitude of a disaster is in the top 10%.

They found that such disaster hotspots account for about 30% of the contiguous U.S., but are home to nearly 60% of buildings in the country.

That means development is concentrated in the most dangerous places. "We're putting more buildings and more people in these risk prone areas," says A.R. Siders, a disaster researcher at the University of Delaware who was not involved in the new study. "In the United States, we have a great deal of control over risk. Through our development, through local land use, through zoning, through where we allow development to occur."

The study found that development in wildfire-prone areas has accelerated the most quickly of any hazard, especially since the 1980s. Most of that building is happening in the western U.S. In the eastern U.S., cities continue to expand development in places that are extremely vulnerable to hurricanes.

About 1.5 million buildings are in hotspots for two or more hazards. For example, parts of the western U.S. that are extremely prone to both wildfire and earthquakes, or parts of the southern U.S. that are at high risk for floods, hurricanes and tornadoes.

Most people who live in flood and fire prone parts of the U.S. are not aware of the risk to their homes, in part because that risk is not disclosed to home buyers or renters.

The study authors used a massive database of building records that was compiled by the research arm of the real estate listing company Zillow. The records go back more than a century, and show where and when buildings were built across the contiguous U.S. In the last few years, climate researchers have increasingly incorporated such data into their work, as it becomes clear that extreme weather and the built environment are inextricably linked.

Such data can help illuminate who is most at risk from climate-driven disasters. "We know from research done by other groups that extreme events and natural disasters increase social inequality," says Iglesias. She says she and her colleagues are working on follow-up studies that examine who is living in disaster hotspots.

She hopes such research can help policymakers and residents make more informed decisions about where to allow new development, and how to make buildings more resilient.

Siders agrees that such research is an important tool, especially for local governments that control zoning laws and enforce building codes. "[Studies like this one] hopefully give an impetus for local governments to sit up and say 'We can address risk in our own communities by taking proactive steps to not allow new development in the most risk prone areas,'" Siders says.

Right now many local authorities are not taking such steps to reduce risk, Siders says. Local governments have an incentive to retain population and tax base by allowing new development, even in areas that are at high risk for disasters. That has led coastal cities to approve waterfront homes even as sea levels rise and floods get more damaging, a 2020 study found.

A similar trend is playing out in the western U.S., where homes continue to be built in places that are likely to burn. About a quarter of Californians live in high-risk wildfire areas, a recent report found.