[water rushing] There's a real science to how floodwaters move.

They begin in the channel and spill into the natural floodplains.

But when that's full, water finds paths across streets, fields, and yards, sometimes sweeping into places that the Federal Emergency Management Agency never accounted for.

But more recently, it's just heavy rain that inundates these areas.

When we picture flooding, we often think of rivers spilling into neighborhoods, pooling in places people never expected.

So typically, when we think about where it can flood, we think about the riverine floodplain.

Imagine that you're standing in a river and you're looking up and down.

You may have some houses out here on the riverbanks, and we consider how high could the river rise during a given flood event.

So perhaps this floods from a riverine flood.

But you can also have really heavy rainfall falling way out here.

And if that rain falls at a rate that's so fast that it can't run off in time, this house can also flood.

In a groundbreaking study, researchers at UNC Chapel Hill went back and analyzed 25 years of floods in North Carolina.

They mapped 78 separate events between 1996 and 2020, and discovered that nearly 90,000 buildings, or almost half, were outside of FEMA's mapped flood zones, places that weren't expected to flood.

The FEMA maps are used to guide planning, and they highlight areas where the odds are higher that water will go over land.

But the research has revealed just how widespread flooding has been across the state.

Like the coast is a really good example of those places where we know it floods a lot, but our study, we found a lot of flooding inland as well.

So kind of unveiling those hidden areas of flood risk and where flooding has happened in the past.

It's important to remember, FEMA's flood maps are probability maps, not historical records.

They reflect only the likelihood of flooding, like a 1% annual chance based on past data.

But flood risks evolve, and those blue lines are not guarantees.

And there's a lot of floods that are bigger and smaller than that 100 year flood.

And this is just a different form of information of where it's flooded in the past.

And that's usually a good indicator of where it might flood again in the future.

So why does it look like these maps miss so much?

One answer lies in what they're designed for and what they're not.

Our objective was really different than what the FEMA maps are doing, right?

The FEMA maps are a regulatory tool that's designed to communicate something about risky places.

And they're also designed to help determine how we use those risky places, like what the land uses of those places are, how we build, what we build, what that looks like.

Our study was really aiming to try to fill gaps in the historical record of floods.

So we have very little data on where it has flooded in the past.

That's something different than what the FEMA maps are doing.

FEMA floodplain maps are meant to guide us, showing us where rivers may rise or where a storm surge may spill over the coast.

But here's what they don't show.

The flooding that comes when extreme rainfall overwhelms communities far beyond those lines on the map.

We've heard about the 1,000 year flood event, for example, or as FEMA says, has a 1% chance of happening.

But as this map of the French Broad River at Asheville shows in blue, the area where flooding can happen is pretty wide.

And it's getting more common.

In the UNC approach, they use machine learning and geographic data to reconstruct flood footprints, even for uninsured homes or events that don't make headlines that expanded their perspective beyond just disasters like hurricanes.

So doctor, you guys work with a lot of different maps that tell us a lot of different things.

What kind of a map is this?

This, what you're looking at right here is the North Carolina Flood Risk Information System.

It is a website or a web tool that any homeowner in the state of North Carolina can go to and see where they are located relative to the regulatory floodplain map.

So you see here a bunch of building locations, and you can see their location relative to the regulatory floodplain.

Importantly, this doesn't tell you what has flooded in the past, but it does give you a sense of what could flood in the future.

So it's important to know that if a property is located inside of a floodplain, it has a federally backed mortgage, they're required to buy flood insurance, but even properties outside the floodplain can flood during a flood event.

So this doesn't tell us anything about where it's flooded in the past, but it gives us a sense of what could flood with a high probability.

So for residents outside FEMA zones, that can create a false sense of safety, but the risk is very real, and when floods hit, families often bear the full cost.

These UNC maps don't discard FEMA maps, they reframe them.

Researchers dug deep.

They went back and looked at insurance claims and damage records all the way back to the 1980s, and with that new information, they were able to lay down exactly what flooded in North Carolina.

I hope it's helpful for property owners, even renters, to kind of figure out their flood risk in their area, and help them make more informed choices about maybe if I'm not in one of these flood zones that requires insurance, maybe I go ahead and purchase it anyways, because that's really the first form of defense for a lot of people.

UNC researchers say the path forward is unmistakable.

Better data, smarter maps, stronger communities, because floods don't wait for updates.

If you're curious about your own risk, head to fris.nc.gov to see how where you live lines up with these FEMA flood zones.