The Federal Emergency Management Agency’s “patchwork quilt” of flood maps has coverage gaps and is obsolete in places, according to a recent study by the US Environmental Protection Agency (EPA), the Nature Conservancy charity and the University of Bristol.

FEMA's current flood maps indicate that about 13 million Americans live in areas that face a 1 percent risk of a flood in any given year — a so-called 100-year flood. But the study, which uses high-tech analysis, finds that number is closer to 40 million and will rise to 60 million by the middle of the century unless land use and planning change.

“It's not good news that there are many more people, many more buildings and much more property in harm's way from flooding, but it is useful information,” says Kris Johnson, associate director for science and planning for the Nature Conservancy. “It’s important that people know. It's important that we as a country have a much better picture of where the risk really is and how significant it is.”

The US needs a more comprehensive, proactive and integrated approach to thinking about risk, Johnson believes. Right now, $5.5 trillion of assets are at risk from a 100-year flood, according to their study.

“We need to address that. We need to mitigate that and, more importantly, we need to not put any more people or property or assets in harm's way in the years to come, because that will only make that price tag even bigger,” he says.

There are places in the US with detailed, up-to-date information about where flooding is most likely to happen. But there are also many places, Johnson explains, where there is no mapping at all, or where towns and municipalities are managing their flood risk from paper maps created 20, 30 or 40 years ago.

“From the Nature Conservancy's point of view, this new modeling approach gives us the ability to develop these floodplain maps at a much bigger scale, which helps us think about risk and about managing the environment in a more integrated way,” Johnson says.

Johnson recommends that homeowners and other property owners find out what local city and town floodplain maps show for their area and when the flood map was created. In many cases, he says, floodplain maps and flood risk information for large cities is “probably pretty good.” But that risk is changing as development accelerates and climate change continues — and recent weather events clearly indicate that flooding is becoming increasingly severe. “We don't fully understand all the ways in which that may change everywhere, but we know that this problem is only growing,” Johnson says.

The study does not incorporate future impacts from climate change. Instead, Johnson explains, they used the current understanding of where flood risk exists and looked ahead at areas the EPA believes people might continue to move into and develop property. “We know that even if flooding doesn't change from what it is today, in 2018, people are going to continue to develop in harm's way,” he says. “We project by 2050 there will be upwards of about 60 million people at risk from a 100-year flood event in the US.”

The study makes this projection without including the possibility of greater storm surges in coastal areas that will likely occur as a result of rising seas. The researchers focused on primarily on non-coastal flood risk, although a couple places that were hit hard recently — Houston, for example — “do show up on our maps as places that you might expect to be flooded during a big event," Johnson adds.

The bottom line: If you live near a floodplain or on the edge of a floodplain or if you're not sure, talk to your insurance agent, Johnson says. “Find out what policy options might be available for you. The good news is, if you're not within a current FEMA flood zone, you could probably add a flood risk reduction part onto your policy for probably fairly little expense.”

This article is based on an interview that aired on PRI’s Living on Earth with Steve Curwood.