[rhythmic music]
Kriebel: High tide flooding is the leading edge of the sea level rise problem.
Grieco: We've been following the data for decades.
Going back 50 years, we experienced a flooding like that
maybe four times a year where a roadway would be totally flooded
and impassable. Most recently in 2018,
we had 52 days of flooding. And so the frequency
is increasing and the severity, the depth of the water is increasing as well.
Hamlington: Over the past decade or so, we've seen very high rates
of sea level rise along all the coasts of the US, so the US West coast,
the Gulf coast, and also the East coast.
And if you look at a global map of the ocean and the satellite altimeter measured sea level trends,
the US really stands out as this hot spot
with all coastlines going up very rapidly.
Sweet: You know, it’s causing disruption in people's lives. Patience is starting to be lost in some of these communities
and it's, it's a struggle, but it's not just a local problem.
It's really a national problem as we want to deal with the increased
risk of coastal flooding due to sea level rise now,
and as we move into the future.
[music builds and fades]
Hamlington: As sea level continues to increase,
as ice melts, the ocean expands due to global warming,
we're going to continue to see these effects increase.
You're going to get more frequent and worse high tide flooding in a lot of locations. And locations that aren't experiencing
high tide flooding now, 10, 20, 30 years from now,
they will be experiencing high tide flooding on a pretty regular basis.
And on top of that, minor meteorological events. So a slightly lowered And on top of that, minor meteorological events. So a slightly
lowered atmospheric pressure, on-shore winds that might in our case,
push up the Chesapeake Bay or push in the Severn River. Any of those factors
can cause a little bit of an additional rise in water level
on top of the astronomical tides.
Sweet: And we're not talking about extreme winds. We're talking about the kind of winds that we like when we go sailing.
15, 20 knot winds. But it's that kind of variability
that is causing flooding to happen at record breaking instances.
Hamlington: So we have seasonal cycles that occur.
So over the course of a year, you're going to have a time of the year where sea level is higher than others.
You have a, what we call inter-annual to decadal variability.
So El Niño would be example of this. So when you have an El Niño that occurs,
you have a higher sea level than normal on the US West coast.
Then on even longer time scales than that we have melting of ice, we have thermal expansion
due to global warming that's causing long-term sea level rise.
Sweet: The other part is, what’s land doing?
On the East coast and Gulf coast, we have a land subsidence issue.
Some of that’s natural. Compaction of sediments
in the Mississippi Delta, you know, glacial isostatic adjustment that’s occurring.
But there's a part that's unnatural. It's extraction of fresh water for drinking
and fossil fuels for consumption. That component
can exacerbate relative sea level rise, almost on the same order of magnitude
that the ocean is rising itself.
[gentle wave sounds]
Hamlington: Yeah, so a lot of times we talk about coastal flooding
and sea level rise as a future problem. So you see projections out to the end of the century,
but in reality, sea level rise and coastal flooding is a problem that we're experiencing now.
Kriebel: Right where we’re at right now is a road that flooded 41 times
times last year. And you can see
how the road is so much lower than the top of the sea wall.
The storm drains are really the problem that the water can come up freely from
from the Severn River and just backflow right through the storm drains.
Grieco: And when the tides rise to a certain elevation,
the water backs up through the storm drain system and comes out through
the storm drains in parking lots, for example.
One particular intersection that floods is a main arterial to the downtown area.
And so it gets completely closed. And so, first responders are impacted.
When the parking lot's flooded, then their clients can’t park there,
or they tend not to even come downtown
when these days are reported. It's been documented there’s impacts to their revenues
upwards of $200,000 a year just due to tidal flooding.
Kriebel: I guess you could say it’s sort of a battle between land elevation and water elevation.
It's what I've been calling the game of inches.
Of all the hundreds of high tides a year, some are just a few inches higher than others.
And those are the ones of course that are causing flooding now.
The real problem though, is all the high tide events that are just a few inches below,
it's only gonna take a few inches of additional sea level rise
to nudge them upward. So what will happen over time
is with sea level rise … we're going to end up not with 20 or 40 flood events,
but we'll then be into hundreds of flood events per year.
[music fades and rebuilds]
Sweet: One of the things that communities are doing
is they’re preventing water from coming back through the stormwater systems.
They’re called backflow preventers. You want to let rain out,
but you don’t want to let the ocean in.
Kriebel: Some places like Charleston are putting large underground
water storage facilities, deep underground, where they can direct rainwater and get it off the city streets
and try to hold it there until after you know the rainstorm goes.
If you have low lying areas, you may need pump stations
to collect rain water and pump it.
Hamlington: But then there's these other strategies where coastal communities are trying to reduce
the amount of pavement they have for instance, increase the amount of green space they have
in these different locations, restoring beach front. A lot of these
different things can reduce the impact of coastal flooding going forward.
So NASA has the observations
that are really needed to improve our understanding of
sea level science. So across the board,
we have processes that are contributing to sea level change on a range of timescales
and the variety of satellite observations that we have available to us now
really allow us to improve our understanding of these different processes.
Sweet: What we're doing at NOAA is really trying to give the
data to decision makers so that they can make informed decisions
that's best for their community. But one thing's for certain,
is under current flood defenses, these projections suggest that a floodier future
is going to be here in the next few decades
and the way of life is going to have to adapt to this.
[music fades]