As New Hampshire Warms, UNH Studies Effects Of More Freeze-Thaw Cycles | New Hampshire Public Radio

As New Hampshire Warms, UNH Studies Effects Of More Freeze-Thaw Cycles

Apr 21, 2021

An abandoned car sits in the muddy woods in Strafford after a 70-degree day in January 2020.
Credit Sam Evans-Brown / NHPR file

In New Hampshire and much of New England, climate change is already causing a lot more of what's sometimes called winter whiplash -- rapid freeze-thaw cycles, from unusually warm to bitter cold and back again mid-season. 

Researchers at the University of New Hampshire are working to learn more about how this affects ecosystems and people. NHPR's Morning Edition host Rick Ganley spoke with one of those scientists, Alix Contosta, about her work in this area.

This story is part of special coverage for Earth Week from NHPR's By Degrees project, the New England News Collaborative and Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story. Click here to see more from around the region.

Rick Ganley: You know, less than a week ago, we actually had a snowstorm here in the middle of April in New Hampshire. Not necessarily unusual, but by the weekend that snow had disappeared and we were back into spring temperatures, in fact, above average. Are you finding that that's happening more often? And what are the consequences of those big swings?

Alix Contosta: Yes. So these swings between frozen and thawed, we call those winter weather whiplash. And there's some evidence that we are seeing those events happen more frequently and we may see them more frequently into the future.

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Rick Ganley: What are the effects, Alix, of that?

Alix Contosta: Well, there's a lot of potential effects. So one of the things that I think about a lot, because I work in soils, is what are the impacts on soils? In the past, we had cold winters with a lot of snow. And one of the things that people don't maybe realize is that when we have a lot of snow, soil is actually warm. So you can think of snow as like a heavy down comforter. And so once it's sort of on the ground, it protects the soil. So no matter how cold the air is, the soil is actually warm. And one of the questions that we're exploring is whether or not we have actually colder soils in a warmer world.

Some of the impacts of that could be root deaths, you know, as the soil freezes and then thaws again. You could have disruption to soil structure and loss of nutrients. And that can affect forest growth in the next growing season in ways that we don't really understand.

We can also have effects on roads. More freeze thaw cycles can mean more potholes as we have water that expands when it freezes into ice and then contracts with the thaws into water. And when we have lots of midwinter melt events, we don't necessarily know when to post roads. And so we may drive big heavy trucks on them and destroy them. And this can cause us to have to spend a lot more money to fix our roads.

Rick Ganley: Right. And again, it's not that these things haven't happened occasionally in the past. They happen every season, but they're happening, we think more often. And this, of course, has long term implications on how we build roads and how we build systems.

Alix Contosta: Yes.

Rick Ganley: So is this something that you're seeing researchers and planners take more account of? Is there more research going into this?

UNH researcher Alix Contosta
Credit University of New Hampshire

Alix Contosta: Well, that's what we personally, our team at UNH, is working on right now, trying to understand how deep soil frost can be, how it responds to changing air temperatures, how deep the snowpack has to be to protect the soil, or how shallow it might have to get for there to be a response. One of the problems that we've had in the past is that there aren't really great ways for measuring soil frost. And so that's what we're trying to do moving forward is to develop better systems to be able to do that.

Rick Ganley: I want to ask you a little bit more about the volatility of these freeze and thaw cycles. Is this something we should expect more of here in New England? Is this probably one of the biggest impacts of climate change here in our region?

Alix Contosta: Well, we don't know. So we know that winters are getting warmer, and winter is actually the fastest changing season of all four of the seasons. This freeze-thaw can manifest in a few different ways, right? So overall conditions are getting warmer, but we may still have cold nights and so we end up getting a freeze thaw cycle there. That might not be enough to really have a big impact. We also may have these really huge swings between frozen and thawed conditions, especially when we have the polar vortex events where it gets really, really cold and then we return to something that is much more mild. And, you know, what that looks like in the future is not very well understood.

Rick Ganley: What about the extremes of wet and dry? I mean, we're hearing much about a possible drought again this year in New England. Yet at the same time, we're hearing about more flooding events.

Alix Contosta: Yes. So that's a little bit outside of my area of research. But what I am really interested in exploring is how winter conditions, you know, the depth and duration of the snowpack actually affect growing seasons, soil moisture. So we don't necessarily think in New England that snow provides a lot of water. That's something that is really more of an issue in the West. But as we have more years with low snow cover, meaning really shallow snow and then snow not for very long period of time, if that's followed up by a growing season where we also don't have a lot of rainfall, does that set us up for drought? And that's the question. I don't have an answer for that right now.

Rick Ganley: Yeah. And again, as you said, more research and more data is needed, isn't it?

Alix Contosta: Yeah, absolutely. These freeze thaw cycles, you know, play out in lots of different ways across the landscape. We can have lake ice that gets really thin and unreliable. And how does that impact recreation? You know, ice fishing, ice skating, pond hockey. We have snow amount, and how does that affect outdoor recreation on ski trails and snowmobile trails?

You know, the ski industry has developed a lot of adaptation measures to make snow, and that's really great. But I personally like to ski in the woods by my house. And there was only three weeks this winter where I was able to do that because we're losing a lot of our snow cover. These changes have consequences for our ecosystems, for our economy and for our way of life in ways that we don't really understand, not fully, and that we're experiencing on the ground right now.