These U.S. Cities Could Soon See Frequent Flooding As Seas Rise

Floods that are now rare would become frequent by 2050 in places like San Diego and Key West

An emergency water rescue crew in San Diego — REUTERS
Jun 10, 2017 at 10:00 AM ET

Some coastal cities could spend much of the next century dealing with close to constant flooding, while others could find that rare but devastating floods aren’t nearly as rare as they used to be.

That’s according to new research published in Environmental Research Letters on how climate change will affect flooding in the United States. While precise estimates vary depending on location and which climate model you use, global warming figures to cause sea levels to rise anywhere from half a foot to more than six feet by 2100. Any rise makes flooding a more likely and more frequent occurrence, though exactly what that means varies depending on which part of the country the researchers were looking at.

Across the coast of the contiguous United States, the researchers found that so-called 100-year floods — those that used to happen only once every 100 or so years — would be 40 times more common in 2050 than they are today. That sounds bad, but those same floods are projected to occur 3,500 times more frequently in 2100.

By 2050, San Diego and Key West would both deal with more than 10 of these supposedly rare floods every year, while a few Hawaiian communities would see more than 100 each year. By 2100, that kind of extreme frequency would be the norm for several parts of the United States, including Los Angeles, San Diego, and coastal communities in Florida, Georgia, North Carolina, Maryland, New Jersey, and Texas.

Still, more severe 500-year floods — those that, at least in theory, only have a 0.2 percent chance of happening in a given year —would also become far more common, especially along America’s Pacific coast. San Diego, Los Angeles, San Francisco, and Seattle would all regularly deal with such floods. While severe flooding would remain comparatively rare along the Gulf and Atlantic coasts, many communities would deal with around 180 or so 10-year floods. That’s a flood basically every other day.

This doesn’t mean American cities would necessarily be underwater by 2100. But holding back flooding on this sort of scale would require massive investments in the infrastructure necessary to keep water from inundating cities. This is also where understanding what kinds of floods are coming is important: A city that’s going to face a constant barrage of medium-sized floods has to prepare differently than one that is suddenly dealing with largely unprecedented disasters.