Intense rainfall events are becoming more common due to climate change. With these events, drain systems can get overwhelmed and severe flooding can occur. The Federal Emergency Management Agency declared a state of emergency in Michigan following catastrophic flooding last summer. Water filled streets and basements in areas that aren’t even near a river or waterway.
Some neighborhoods got hit harder than others, and that may be due in part to ghost wetlands and ghost streams.
Jacob Napieralski is a professor of geology at the University of Michigan Dearborn, specializing in flood risk equity. He spoke with Michigan Public's Katheryne Friske on Weekend Edition.
Katheryne Friske: Jacob, you and your team compared Detroit’s historic maps with maps of today. Tell me a little bit about that.
Jacob Napieralski: Our research was interested in understanding if there were particular communities that were bearing a greater brunt of the impact of flooding. And so we kind of focused on the idea of history being a key player in this.
So we have data that shows for every single parcel in southeastern Michigan what the risk is on a scale of 1 to 10. Then we looked at old maps that showed where members were, and we compared rivers now to what was maps back then. And we were able to identify rivers that existed in the '40s but don't exist now. And same with wetlands. And those were identified as our ghost wetlands and our ghost streams. And then we also looked at the amount of green space of vegetation. So when a community has lots of trees and lots of green space, then a lot of the stormwater gets absorbed through natural processes.
And so in places like Detroit, since 1905, we saw, over 85% of the total stream length of rivers have been removed. But the reality is they're still in the landscape, and nature does its thing. And when there's too much water and it doesn't work within our engineered system, then of course they will fill with water because that's where water is going to go. That's the way nature intends it to be.
In other words, our landscape has been sort of picked apart. Rivers and wetlands have been removed. We build houses on top of it. People unknowingly are living on top of what maybe was an old stream valley and are wondering why their property is flooding because they're not actually near a river. And it turns out this may be one of the reasons why.
KF: You also looked at maps of redlining, when Detroit was cut up into A, B, C, and D communities. A and B were good. C and D were deemed hazardous areas to invest in. What did you find about the impact of that label on flood risk for folks living in those communities today?
JN: We're finding that a lot of D communities have been stuck. We see communities that have very little green space, so when it floods out, there is no there is no relief. There is no root system to take water in. The water just simply goes to garages. They go to basements, they go to roads because the water has no place to go.
So in general, if you live, currently live in a community that was redlined, your probability of flood risk is higher than if you live in an A community. So Jefferson Chalmers, which is a great neighborhood in Detroit, their flood risk is almost completely off the charts.
If you throw in buried rivers and wetlands, that also increases flood risk. So if your parcel is located on top of what used to be a wetland but no longer is, your flood risk goes up by 6 or 7 times what it would be if it wasn't on a wetland. Rivers are the same, not as intense, so maybe 2 or 3 times the risk.
KF: Wow, and then add climate change with more intense rainfall — sounds like the perfect storm, so to speak.
JN: That's right. Yes. Yes, absolutely. And I think we're at the stage now where the decision we have to reckon with — the decisions we made 50 or 60 years ago where it was 'develop as fast as possible, it's the ultimate sign of economic strength' — now we're at the stage where residents are upset because they're losing property, they're unable to get to work, the roads are flooded. And so we have to reckon with poor decisions. And so I think it really is important for us to focus on what's been done in the past to guide us going forward.
KF: Jacob, how do we move forward?
JN: I think communities and municipalities can spend a little bit of time and create accessible maps where residents can just say, "Am I on a river? Am I on a wetland, buried river or ghost river or a ghost wetlands?" And I think with that information ... no matter what neighborhood you're in, every single resident has information that can help them become an informed citizen and help them pursue solutions.
But then we can step back and say, well, as a water authority, as a city, as a municipality, what kind of things can we do to protect neighborhoods? So I think a lot of what we need to do is focus on something like "hydro mimicry," where we're mimicking the way water is supposed to go naturally and building our engineering schemes around that. There are plans to sort of rework parts of the Rouge River, outside Detroit, and try to bring back some meandering and getting rid of concrete. So there's bigger projects that have more cost associated with them.
But the reality is the true need would probably be those that were the C and D communities and some of their neighboring communities. They're the ones that struggle. They're the ones that have a lot of concrete. They're really not able to catch up, and that should be a priority for how we start to solve some of the flooding problems in southeastern Michigan, but also in a lot of urban cities and urban areas in the U.S.
Further reading: How ghost streams and redlining’s legacy lead to unfairness in flood risk, in Detroit and elsewhere by Jacob Napieralski for The Conversation.
Editor's note: Some quotes in this article have been edited for length and clarity. You can listen to the full interview near the top of this page.
