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[rhythmic music]

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Kriebel: High tide flooding is the leading edge of the sea level rise problem.

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Grieco: We've been following the data for decades. 

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Going back 50 years, we experienced a flooding like that 

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maybe four times a year where a roadway would be totally flooded

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and impassable. Most recently in 2018,

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we had 52 days of flooding. And so the frequency

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is increasing and the severity, the depth of the water is increasing as well.

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Hamlington: Over the past decade or so, we've seen very high rates 

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of sea level rise along all the coasts of the US, so the US West coast, 

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the Gulf coast, and also the East coast.

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And if you look at a global map of the ocean and the satellite altimeter measured sea level trends, 

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the US really stands out as this hot spot 

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with all coastlines going up very rapidly. 

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Sweet: You know, it’s causing disruption in people's lives. Patience is starting to be lost in some of these communities

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and it's, it's a struggle, but it's not just a local problem.

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It's really a national problem as we want to deal with the increased

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risk of coastal flooding due to sea level rise now, 

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and as we move into the future.

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[music builds and fades]

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Hamlington: As sea level continues to increase, 

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as ice melts, the ocean expands due to global warming, 

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we're going to continue to see these effects increase.

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You're going to get more frequent and worse high tide flooding in a lot of locations. And locations that aren't experiencing 

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high tide flooding now, 10, 20, 30 years from now, 

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they will be experiencing high tide flooding on a pretty regular basis. 

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And on top of that, minor meteorological events. So a slightly lowered And on top of that, minor meteorological events. So a slightly

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lowered atmospheric pressure, on-shore winds that might in our case,

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push up the Chesapeake Bay or push in the Severn River. Any of those factors

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can cause a little bit of an additional rise in water level

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on top of the astronomical tides.

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Sweet: And we're not talking about extreme winds. We're talking about the kind of winds that we like when we go sailing. 

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15, 20 knot winds. But it's that kind of variability

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that is causing flooding to happen at record breaking instances.

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Hamlington: So we have seasonal cycles that occur. 

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So over the course of a year, you're going to have a time of the year where sea level is higher than others. 

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You have a, what we call inter-annual to decadal variability. 

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So El Niño would be example of this. So when you have an El Niño that occurs, 

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you have a higher sea level than normal on the US West coast. 

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Then on even longer time scales than that we have melting of ice, we have thermal expansion 

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due to global warming that's causing long-term sea level rise.

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Sweet: The other part is, what’s land doing? 

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On the East coast and Gulf coast, we have a land subsidence issue.

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Some of that’s natural. Compaction of sediments 

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in the Mississippi Delta, you know, glacial isostatic adjustment that’s occurring.

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But there's a part that's unnatural. It's extraction of fresh water for drinking

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and fossil fuels for consumption. That component

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can exacerbate relative sea level rise, almost on the same order of magnitude

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that the ocean is rising itself.

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[gentle wave sounds]

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Hamlington: Yeah, so a lot of times we talk about coastal flooding 

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and sea level rise as a future problem. So you see projections out to the end of the century,

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but in reality, sea level rise and coastal flooding is a problem that we're experiencing now. 

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Kriebel: Right where we’re at right now is a road that flooded 41 times

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times last year. And you can see 

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how the road is so much lower than the top of the sea wall. 

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The storm drains are really the problem that the water can come up freely from 

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from the Severn River and just backflow right through the storm drains.

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Grieco: And when the tides rise to a certain elevation, 

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the water backs up through the storm drain system and comes out through

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the storm drains in parking lots, for example. 

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One particular intersection that floods is a main arterial to the downtown area. 

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And so it gets completely closed. And so, first responders are impacted.

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When the parking lot's flooded, then their clients can’t park there, 

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or they tend not to even come downtown 

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when these days are reported. It's been documented there’s impacts to their revenues 

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upwards of $200,000 a year just due to tidal flooding. 

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Kriebel: I guess you could say it’s sort of a battle between land elevation and water elevation.

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It's what I've been calling the game of inches.

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Of all the hundreds of high tides a year, some are just a few inches higher than others. 

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And those are the ones of course that are causing flooding now. 

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The real problem though, is all the high tide events that are just a few inches below,

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it's only gonna take a few inches of additional sea level rise

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to nudge them upward. So what will happen over time

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is with sea level rise … we're going to end up not with 20 or 40 flood events, 

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but we'll then be into hundreds of flood events per year.

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[music fades and rebuilds]

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Sweet: One of the things that communities are doing

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is they’re preventing water from coming back through the stormwater systems. 

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They’re called backflow preventers. You want to let rain out, 

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but you don’t want to let the ocean in.

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Kriebel: Some places like Charleston are putting large underground 

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water storage facilities, deep underground, where they can direct rainwater and get it off the city streets 

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and try to hold it there until after you know the rainstorm goes.

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If you have low lying areas, you may need pump stations 

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to collect rain water and pump it.

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Hamlington: But then there's these other strategies where coastal communities are trying to reduce 

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the amount of pavement they have for instance, increase the amount of green space they have

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in these different locations, restoring beach front. A lot of these 

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different things can reduce the impact of coastal flooding going forward.

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So NASA has the observations 

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that are really needed to improve our understanding of 

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sea level science. So across the board, 

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we have processes that are contributing to sea level change on a range of timescales

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and the variety of satellite observations that we have available to us now

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really allow us to improve our understanding of these different processes. 

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Sweet: What we're doing at NOAA is really trying to give the 

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data to decision makers so that they can make informed decisions

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that's best for their community. But one thing's for certain,

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is under current flood defenses, these projections suggest that a floodier future

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is going to be here in the next few decades 

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and the way of life is going to have to adapt to this. 

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[music fades]