Wildfires are starting to burn more frequently in areas that also get snow. And that’s causing snowpacks to melt earlier than they typically do, especially in the years right after the fire.
The Show talked about why, and what that could mean with Arielle Koshkin. She recently got her Ph.D. in hydrologic science and engineering at the Colorado School of Mines, where she studies how wildfires are affecting snowpacks in the Western U.S. She’s also an author of the paper describing this research and they started with what about this study stands out to her
Full conversation
ARIELLE KOSHKIN: Yeah, I think it's a complex landscape, and not every place seems to have the same response to these wildfires, but I think it's pretty clear that wildfires are causing snow to disappear earlier, and it's really a question of energy balance in terms of how much snow you get and how fast that snow melts out because of the impacts of these burned trees, especially at like mid to high elevations.
And so this first paper that was published in Science Advances really shows that, yes, we see snow disappearing earlier, but that it's way more severe in the Pacific Northwest, in California than it is in Colorado and the Intermountain West.
MARK BRODIE: Do we know exactly why it is the case that the snow melts more quickly in areas that have been affected by wildfires?
KOSHKIN: Yeah, the leading hypothesis on this is that the black carbon from the burned trees gets shed onto the snowpack, which decreases the reflectivity, or we call it the albedo of the snowpack, which allows the snow pack to absorb more energy, and especially in high severity burns, when you burn down the entire canopy, it also lets more sunlight into those areas.
So you have this kind of dual effect of both getting more energy from the sun and absorbing more energy, and that causes the snow to melt earlier.
BRODIE: And what did you find specifically in terms of the impact of maybe, you know, a coastal maybe a more humid forest versus one maybe at a higher elevation kind of thing?
KOSHKIN: Yeah, these warmer snow packs, maritime snow packs in kind of like Northern California, Pacific Northwest, tend to have warmer storms and have what we call less cold content. So cold content is the measure of how much energy it takes to heat up the snow to get to a point where it's going to start to melt.
And so when you have a warm snow pack, it's kind of always hovering around zero degrees C, so always kind of ready to melt. And so these small shifts in energy balance from the black carbon shed onto the snow, decrease in the albedo, increase in sunlight, really can cause kind of a cascading effect in the maritime climate, leading to up to two weeks earlier of snow disappearance.
Whereas in Colorado or the Intermountain West, these are continental snow packs, they tend to have colder storms, higher cold content. It takes more energy to melt them, and so these small shifts in energy balance have less of an impact. We still see it disappearing earlier, but more on a magnitude of maybe like two to five days. So in terms of hydrologic impact, way less than two weeks.
BRODIE: Understanding this might be a bit outside the scope of your research, but given what you said about what you found in forests in the Pacific Northwest and those in Colorado, that would seem to be good news for those of us who kind of rely on water from the Rockies going into the Colorado River, basically for our cities to exist.
KOSHKIN: I mean, potentially that these burned areas are not having as much impact. However, we often see more burned areas in kind of California and the Pacific Northwest have had just like larger amounts of area burn. So it's kind of a trade-off.
But yeah, as the headwaters of the Colorado gets potentially less impact, and some areas even showed that they get more snow, because when you have a forest the snow falls, it can get caught in the canopy, and some of that snow can sublimate out and never reach the forest floor. So go back up into the atmosphere, but when you get rid of that canopy, that snow will fall and land on the ground and actually pile up more. And so in some areas, especially at high elevation, we actually see more snow post-fire.
BRODIE: There's obviously a lot of work that is done in forests after a fire to try to bring the ecosystem back and restore the ecology to what it was. Is it possible? Do you think to have that impact with snowpack also?
KOSHKIN: Yeah, we do see recovery after a fire. In this current study, we saw that snowpack started to recover as early as, like five years after the fire. And by recover, we just mean we started to see more snow in those areas, so it's not a lasting impact.
And some of that, I think, is as time goes by, potentially you're just getting less black carbon shed from those trees, and so it's just impacting the snow less, and they start to mimic a more just open area. And so we saw the fastest recovery at high elevations, the slowest recovery at low elevations, and those mid elevations were kind of in that five- to 10-year range.
BRODIE: As we see wildfires, the number of them increase, the severity increase, the geographic areas where they can happen increase. I'm curious how you see research like this fitting into the overall structure of us thinking about where our water comes from and how much of it we might have.
KOSHKIN: Yeah, I think the other thing that I would add to that is that it's also increasing in elevation. So we're seeing kind of the largest increase in area above 2,500 meters, which is well into the seasonal snow zone. And so we're getting more overlap between where snow falls and where forests burn.
And I think that is going to continue to increase the impact that these wildfires have on long term water supply in the West, knowing that about up to 70% of snow, or 70% of water in the West comes from snow packs.
So I think the future landscape of water in the West is obviously very complex, and wildfire impact on snow is one component of this interconnected, complex system.
BRODIE: How concerning do you think it is that the overlap between where fires burn and where it snows is getting bigger?
KOSHKIN: I think that's a good question, and I don't know if I'm like the expert to answer that in terms of the larger landscape of water in the West. But I think the biggest thing about fire impacts on snow is that we need to be able to model this and predict it, so we can better capture water coming from the snow pack.
So if we're disrupting patterns of snow accumulation and melt, can we adapt to that to still try to capture as much water runoff from the snow packs as possible?
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