How climate change, location and topography contribute to flood events in Vermont

Last week, the remnants of Hurricane Beryl collided over Vermont with wet, warm air to produce heavy rainfall across much of the northern and central parts of the state. That led to intense flash flooding — and then river flooding — one year to the day after Vermont saw some of its worst flooding in a century. What's the connection between extreme rain and climate change?

Vermont Public climate and environment reporter Abagael Giles spoke with Vermont State Climatologist Lesley-Ann Dupigny-Giroux about the role of climate change in the flooding Vermont saw last week. We highly recommend listening to the audio. We’ve also provided a transcript, which has been edited for length and clarity.

Abagael Giles: Can you speak to some of the mechanics of this storm and just share how it compares to what Vermont saw last summer?

Lesley-Ann Dupigny-Giroux: Absolutely. So one of the interesting things about what we saw this week was the remnants of what by the time it got us it was called “Post-Tropical Storm Beryl.”

It had been a major Category 5 hurricane as it barreled through the Caribbean, and then made landfall in Central America, made landfall again in Texas and then came up towards us.

We had a very large, potent, early-in-the-season hurricane that produced so much precipitation all the way through, and it then merged with some fronts.

Abagael Giles

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Vermont Public File

So you’re getting two sets of weathermakers, two sets of rainmakers coming together, producing even more precipitation than it would have if it was just the tropical or post-tropical system itself.

And we've seen that in the past, we saw that with Hurricane Sandy. We also saw that back in 1927. That's why we had that tremendous flood of record back in November of 1927.

Now, how's that different from last year?

Well, last year, the storm systems that moved over us actually stalled in place, so they rained themselves out, they kept being replenished. We had fronts, we had low pressure systems, we had tropical moisture, but it didn't go anywhere.

And so, when you have a system that stalls in place, it has the ability to sort of literally, like a sponge, wring itself out over that one place, which was central and northern Vermont last year. So either way, you get flood-producing rains.

Abagael Giles: For some people, this is the third time in a year that floodwaters have damaged their homes, their businesses and their communities. So many people have asked us if these floods are happening more often in Vermont because of climate change. And I'm curious how you would answer that question.

Lesley-Ann Dupigny-Giroux: One of the things that we are looking at in terms of climate change is the frequency of [extreme rain], but also the amount of rain that falls in a given storm, and how fast it falls. Because if it falls faster, and it's a larger amount, then the likelihood of having a flooding event goes up. So we are learning about and understanding those changes in how much rain is falling, how that's connected to the fact that the atmosphere is warmer so there's more moisture in the atmosphere to actually fall out.

But also, is it falling out in faster time frames? So are we getting 5, 6, 7 inches of rain an hour? Or even half an hour? Because it's those amounts in that short period of time that will overwhelm our systems. And that's when you see the culverts blowing out, for example. So there are all of these pieces and it has to be [that we see] how they all work together for us to understand why we're seeing flooding so often.

Dmitry Belyakov

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Associated Press

Abagael Giles: We've had a lot of people ask us whether Vermont and New England are being hit harder by the remnants of tropical storms and hurricanes because of climate change. And I'm curious, is there a connection there? And maybe as a follow up, is this a relationship we fully understand at this point?

Lesley-Ann Dupigny-Giroux: So part of the connection with being hit by either a hurricane or tropical storm remnants has to do with understanding where New England sits. If you look at the eastern seaboard, there are some places that literally jut out or stick out into the Atlantic Ocean. And that's one of the reasons why a lot of [weather] systems, as they come up the eastern seaboard, they hit either North Carolina or South Carolina before they keep on moving up northward.

The next thing that's jutting out is New England and the Northeast. If you look at that sweep, we are perpendicular to a lot of those storm tracks. And so it’s, from a location perspective, why we tend to be hit.

So there are maps that show you where there's coastal vulnerability that then extends inland. And a lot of folks are surprised when they realize, “Oh, my goodness me, the Northeast is almost as vulnerable as the Carolinas, as parts of Florida, as parts of Texas, because we're perpendicular to a lot of [storm] tracks."

Abagael Giles: This time around, we really saw communities in Vermont's deep mountain valleys get inundated. Why is that? And is that something we could see more of with climate change?

Peter Hirschfeld

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Vermont Public

Lesley-Ann Dupigny-Giroux: If we think about Vermont's deep valleys — and I think about the physical landscape around Barre — you've got a valley region, and then these almost 90-degree walls around it. And whenever air is forced to rise along any sort of barrier like that, it increases the amount of precipitation and the amount of rain that falls.

But even worse is if the storm system actually stays along that valley itself and rains itself out.

And I think that's perhaps the worst thing that could happen, is to have storm systems either continue to move along a deep valley like that — it's like moving through a canyon — or to just sit and rain itself out because it just got wedged in there.

So anybody who lives in Barre or has driven through Barre or knows Barre, knows that setup and how that then plays into the physical vulnerability of the land and the people who live there.

Abagael Giles: Dr. Dupigny-Giroux, I know I spoke with many people yesterday who told me that every time it rains, they now feel this level of anxiety about another flood. What do we know about how living through a climate-fueled natural disaster affects people?

Lesley-Ann Dupigny-Giroux: That's an awesome question. I think the best example that I could think of to bring this home is: If you've ever been in a car accident, a really serious car accident, every time a car breaks in front of you, you have this visceral reaction, right? Your heart starts to pump. You freeze, right? And I think that's exactly what is happening right now with anyone who's lived through a flood.

And I think we need to speak that. I think we need to appreciate that. Because it's going to call for us to have a different set of skillsets to be able to assist everyone.

Because it's non-trivial. It's something that everybody who's been through any sort of trauma like that has to be able to work through.

And also [we need] to set up what needs to be done longer term, because this is not going to be [just] weeks or months that it takes you to recover from the trauma that you've been exposed to, especially if it's multiple traumas.

So it gives us an opportunity to see where can we make some improvements.

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