The United States has grown a tremendous amount in the last couple of decades. This expansion is putting more people in harm’s way when severe thunderstorms pop up. The amount of damage left behind by the recent spate of tornadoes across the central and eastern United States is a stark reminder of the “expanding bull’s-eye effect,” which explains how Americans are steadily building themselves into the paths of natural disasters like tornadoes.
The population of the United States has never been greater than it is right now. All those people need to live somewhere, so developers are steadily paving over farms and open fields to construct the latest neighborhoods and strip malls. Tornadoes that used to traverse rural areas are now hitting newer communities and even plowing into densely populated cities, leaving behind more destruction that we would have seen just a few decades earlier.
Meteorologists from Northern Illinois University have researched the issue of natural disasters affecting more people as American communities continue to expand on previously undeveloped land. The team’s 2014 paper on the “expanding bull’s-eye effect” focused on the tornado threat to the growing Chicago metropolitan area.
We’ve seen the effect play out several times in recent years. Just a couple of days ago, an EF-4 tornado tore through heavily populated suburbs of Dayton, Ohio, coming perilously close to the city center itself. Villanova University professor Stephen Strader tweeted two maps showing housing density in the Dayton area in 1940 and 2019. Many of the homes struck by the recent tornado didn’t exist 80 years ago.
Growth is even more rapid in some areas. Many of the homes struck by the strongest winds of the EF-5 tornado that ripped through Moore, Oklahoma, on May 20, 2013, didn’t exist just 30 years earlier. I went through Google Earth’s aerial view data and compared an aerial view of the Moore area back in 1984 with an updated image in 2014, taken not long after the devastating tornado. The growth of dense housing developments around the region is extremely noticeable, made even more apparent by how many relatively new homes were directly in the path of the devastating tornado.
We’re not just building ourselves into the paths of tornadoes. The geographic expansion of communities puts more people in the path of all natural disasters, including landfalling tropical cyclones. Florida saw a historic period of no hurricane landfalls between Hurricane Wilma in October 2005 and Hurricane Hermine in September 2016. Florida’s population data shows that the state added nearly 2.4 million new residents during that 11-year period, putting more people in the path of dangerous winds and flooding than ever before, including many who had never had to deal with hurricane preparations or evacuations before.
There’s not much we can do about the expanding bull’s-eye effect unless we stop expanding outward—and that’s not likely to happen anytime soon. Tornado preparedness will need to catch up with our growing exposure to severe thunderstorms. Safety education, such as actively seeking out forecasts and warnings, has dramatically improved the outcome of destructive tornadoes in recent years, including the relatively low number of casualties from this month’s long streak of severe weather. Stricter building codes and more prevalent tornado shelters and safe rooms will also help lower the casualty rate when a tornado strikes residential areas.