The Impact of High Tides, Rising Seas, and Chronic Flooding : Short Wave As sea levels rise from climate change, coastal communities face a greater risk of chronic flooding. Climate scientist Astrid Caldas and her colleagues have looked at where it's happening now and where it could happen in the future as the tides keep getting higher. Follow host Maddie Sofia on Twitter @maddie_sofia. Email the show at

When The Tides Keep Getting Higher

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You're listening to SHORT WAVE from NPR.

The Florida Keys, Annapolis, Miami Beach - all of these communities have been dealing with a big problem - water that comes in with the tides and doesn't leave.


UNIDENTIFIED REPORTER #1: Saltwater seeping up through storm drains and over the seawall...

UNIDENTIFIED REPORTER #2: Another high tide is closing some streets and threatening businesses.

UNIDENTIFIED REPORTER #3: A shocking announcement today that some roads and homes may be surrendered to the sea...

SOFIA: And that's because, in a lot of places, climate change has resulted in higher sea levels.

ASTRID CALDAS: And with the sea level higher, high tide is going to be higher. So it's going to reach farther inland, and it's going to flood areas that it didn't flood before because it's riding on a higher sea.

SOFIA: That's climate scientist Astrid Caldas, and she calls this chronic inundation. You can think of it as the steady, ongoing creep of water into a community primarily from high tides as opposed to flooding from storms.

CALDAS: Chronic inundation is inundation of at least 10% of a community usable land at least 26 times per year...


CALDAS: ...Which is more or less the two highest tides of a month.

SOFIA: So it's when 10% of the community is underwater.

CALDAS: At least 10%. So it can be 50%. It can be 70%. And some communities are already seeing very high numbers of inundation. And inundating some parts either by an inch or by a foot - it doesn't matter because things get deteriorating. Infrastructure starts getting affected. So that is kind of the canary in the coal mine. It's, like, the areas that are inundating first. And these are the areas that are the most vulnerable. And communities - knowing about those areas, they can actually plan their adaptation to that high tide.


SOFIA: So today on the show, we talk tidal flooding and sea level rise with climate scientist Astrid Caldas and take a look at just how many communities are at risk for chronic flooding as high tides keep getting higher.


SOFIA: Astrid Caldas is a senior climate scientist at the Union of Concerned Scientists. Astrid and her team wanted to know which communities are already experiencing chronic inundation and predict who will be at risk in the future.

Give me kind of the highlights of some of the things that you found in that research.

CALDAS: Wow. We found - we were amazed at two things - first, the number of communities that are already being chronically inundated at the very high level and the number of communities that will be chronically inundated in the timeframe of 15 years.

SOFIA: Give me an idea of some of those numbers.

CALDAS: About 170 communities are going to be seeing at least 10% of their land inundated by 2035...


CALDAS: ...Which is kind of crazy.

SOFIA: Yeah.

CALDAS: 2045 is more than numbers. The other thing that we found and that really kind of - whoa - was that how those numbers in 10, 15 years increase dramatically...


CALDAS: ...And how the scenario of emissions, which - emissions drive global warming, which drive sea level rise.

SOFIA: Sure.

CALDAS: So how - depending on how much we pump in the atmosphere, how much the sea rises - what a big difference that makes in the number of communities that are going to be chronically inundated in the near future and particularly towards the end of the century.

SOFIA: Right. So you kind of broke them into, like, three sea level scenarios - high emissions, meaning we haven't really cut our carbon emissions, intermediate and low. Under the high-emissions scenario, how many communities or how many percent of communities are going to be impacted by coastal flooding?

CALDAS: In the high-emissions scenario, towards the end of the century, we'll see about 60% of all oceanfront communities on the east and gulf coast...


CALDAS: ...Being chronically inundated. That's about 670 communities.

SOFIA: Wow. That's a lot.

CALDAS: It is a lot of communities.

SOFIA: What about if we cut our emissions by mid-century - the intermediate level?

CALDAS: In that case, we'll have about 40% of the oceanfront communities being chronically inundated on the east and gulf coast. In the near term, the difference between the intermediate and the high scenarios is not very marked.

SOFIA: Got you.

CALDAS: But if - as you go through the century and - these scenarios play out...

SOFIA: Yeah.

CALDAS: ...Because they're going to be very different towards the end of the century. That's when you see the biggest difference. And that's why we always highlight the importance of now...

SOFIA: Acting quick.

CALDAS: ...Through the middle century, acting quick to reduce emissions so you avoid that higher scenario.

SOFIA: So tell me about the communities that are already being affected by this, communities that - you know, that we might not expect that are being affected right now. And then tell me about some of the communities that you're kind of keeping your eye on for the future. Who are the people that are going to experience this the most significantly?

CALDAS: Well, the Gulf communities for sure - Florida, of course, the mid-Atlantic. If you go to the bayous in southern Louisiana and you talk to people in the Houma tribe, they go through the water, and they say, well, you know, we don't see as many alligators here anymore because they like the freshwater. And the water is getting brackish. The landscape is a landscape of dead trees because of the saltwater intrusion. The wildlife that they relied upon, the crops that they could plant - everything has changed because of sea level rise. The Eastern Shore of Maryland is the same thing.

SOFIA: Yeah.

CALDAS: You drive through the Eastern Shore of Maryland, and it's that field of dead trees. So these - the cascading effects are the immediate effect, which is the flood - the other immediate effect, which is the water getting salinated...

SOFIA: Right.

CALDAS: ...And the - but that cascades into changes in wildlife, changes in plants that animals depend upon that - you know.

SOFIA: Yeah.

CALDAS: So there's all these things that are - people say, oh, 30 years ago, it was a completely different place and a completely different life.

SOFIA: Yeah.

CALDAS: It's really worrisome. And for us, it's kind of a punch in the gut to work with these kinds of things and...

SOFIA: Yeah.

CALDAS: ...To see the results.

SOFIA: Right. So obviously, cities have to deal with this, and they're kind of already dealing with it. Tell me a little bit about how cities are kind of trying to adapt to this.

CALDAS: So cities decide what to do depending on the level of risk that they can take and what is in harm's way. So there are mainly three buckets of adaptation that cities mix and match to try to protect themselves. It is the protection against the water, which is walls, berms, natural defenses, living shorelines.

SOFIA: Sure.

CALDAS: So these are all kind of protections against the water. There is the accommodation of the water. You raise streets. You raise houses. You raise infrastructure so that if the water comes, it can come and go without causing a lot of damage. And, of course, the third bucket is the worst bucket, which is a place gets inundated so often that there is nothing that really - that can be done because you cannot protect it anymore. And you cannot accommodate the water anymore because there's just so much you can adapt to rising seas.

SOFIA: I mean, this is bad news, right?

CALDAS: We have to have the recognition that some of this is going to happen no matter what.

SOFIA: Yeah.

CALDAS: And this is what we say. So some of this is going to happen no matter what, so you better plan for what you cannot avoid and plan even better and try to avoid the worst of it by reducing emissions, obviously...

SOFIA: Sure.

CALDAS: ...Which is the only way that we can...

SOFIA: Yeah.

CALDAS: ...Slow down the rate of sea level rise.

SOFIA: So the message is kind of, if we act soon, we can have smaller changes that won't impact our lives as much. If we wait, then we are going to have to act in a way that will change everybody's lifestyle in a way that's maybe more than we would be comfortable actually doing.

CALDAS: That's the expectation, and that's kind of my personal message that I've been talking whenever I go talk to different audiences. It's like, what would you prefer - to have to use a different type of food or to have to use a different type of fuel but continue to drive a car, continue to do what you want to do, continue to eat what you like to eat, or to have the conditions that are extraneous to you that you don't have any control over decide what you can eat because there's nothing else or you cannot drive because there is no fuel?

SOFIA: What makes you continually work in this area? What gives you hope when you're thinking about this?

CALDAS: Well, in the years that I've been working with this, I noticed that there is a lot more acceptance and there is a lot more concern. And climate change has gotten to a point where it's an important issue for people in elections. So I see hope. My worry is that we're not going to act fast enough. So there is this thing about - yeah, what kind of actions I can take. Well, to reduce your carbon footprint is super-important, you know, because it's people.


SOFIA: Thanks so much to Astrid Caldas, senior climate scientist at the Union of Concerned Scientists.

Today's episode was produced by Brit Hanson and edited by Viet Le. The facts were checked by Emily Vaughn. I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.


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