Vermont is seeing warmer winter temperatures and more and more rain-on-snow events — which has scientists worried about snowpack.
Snowpack plays a key role in storing nutrients, like nitrogen and phosphorus. But a national study suggests rainy winter days are shifting how and when those nutrients are released.
And that’s putting water quality at risk in around 40% of the contiguous U.S, including in Vermont.
Carol Adair directs the Aiken Forestry Science Lab at the University of Vermont, and she was an author on the study.
Adair recently spoke with Vermont Public's Mary Williams Engisch about her work. This interview was produced for the ear. We highly recommend listening to the audio. We’ve also provided a transcript, which has been edited for length and clarity.
Mary Williams Engisch: How does the increase of rain-on-snow events impact snowpack depths?
Carol Adair: So rain is very effective at melting snow. And I think that we've all seen this happen throughout this fairly depressing winter — so far, fingers crossed for more snow. But it's very good at melting snow and decreasing our snowpack pretty quickly, helping that snow melt and run off into rivers, along with the rain that falls during that time period. And then of course, taking things along with that, that water — whether it be what's in the snowpack, and sometimes even what's underneath the snowpack.
Mary Williams Engisch: What is the decrease in snowpack depth mean for streams and rivers and other smaller waterways?
Carol Adair: We're so used to having snowpack and that snowpack really protects our soils and our land cover, actually. And keeps all of the things that we want to stay on land on the land, right? And if we don't have that — that snowpack sort of insulating our soils and keeping things sort of frozen in place, if you will — it's much easier for the rain that falls to kind of drag it along down into the rivers and streams. And that is what we're not used to thinking about and what is sort of new.
Mary Williams Engisch: Why is it so impactful for water quality to have these big rain events happen in the winter, on top of the snow? And why is that a problem that melting snowpack is changing how these nutrients are moving through the waterways?
Carol Adair: There are sort of two issues that the water quality is really affected by. And one is that the snowpack does accumulate some amount of nutrients. And those are things that we're measuring right now in Vermont, sort of how much is how much in terms of nutrients and other things are being stored in the snowpack. And not, of course, when it rains on top of that snowpack, and all this stuff gets transported down into rivers and streams and lakes.
Ultimately, the second problem is when we actually run out of snowpack; then we're just left with the bare soil, the ground. And we've seen a lot of that this winter as well. Without that snowpack to sort of protect that surface, we've got a lot of soil that can run off, or whatever is there that can run off into our water bodies.
Mary Williams Engisch: Where are these nutrients coming from? You mentioned runoff and it's coming from different things in the soil that end up in the waterways. Is that the only place that that it's coming from?
Carol Adair: We have started some research programs here in Vermont to get at this exact thing — trying to figure out where in the landscape, what is moving during the winter, where it's coming from. So it's a fairly open question at this point. The soil of course being a large source of in particular, you know, erosion if you don't have a snowpack. We get these freeze-thaw events that can sort of freeze the soil and then thaw so that it sort of expands and contracts and breaks up and can actually result in increasing erosion during the winter time. And a lot of that if we then have these rainfall events can get swept down into rivers.
Mary Williams Engisch: Vermont just saw another major flooding event last December. Vermont's Climate Assessment predicts the state will continue to see these rain on snow events in the coming decades due to climate change. Is this a problem that you expect to worsen? And is there anything that we can do about it?
Carol Adair: Yeah, well, as you know, the problem of warming winters is a larger-than-Vermont problem to be sure. But how we deal with them — I think we can do quite a bit about that if we start really understanding where in the landscape arin-on-ground events are happening, where the nutrients are coming from. Then we can start to look for solutions to those problems.
One example could be that we're all, again, very used to thinking of winter as this inactive time. So if we choose to put out nutrients on our farms or our lawns in the late winter, that may have been a great practice back before all of this happened. But now that this is happening, if you just put this fertilizer or manure out, it's going to most likely just run into the rivers during these rain-on-snow or rainfall events. So that would be one thing in particular that we might change given that these events are becoming more and more frequent.
I do think that it's really interesting just for folks to know that we really are sort of on the cutting edge of figuring this out in in Vermont. There aren't that many places in the world that are looking at what's going downstream during the wintertime. And we've got about two seasons of year round data now, and some great preliminary data. Well, great, but also sort of, you know, unfortunate, because there is a lot going downstream in the winter.
But it's really critical for us to be able to figure this out. And then we're working on figuring out where in the landscape exactly those nutrients are coming from so that we're better able to address any problem areas.
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