Snowmelt and the runoff from it are critical to water supplies in the Valley and across the region. But new research suggests another part of the ecosystem, dust, can have a negative impact on that.
McKenzie Skiles — an associate professor in the School of Environment, Society and Sustainability at the University of Utah and director of the Snow Hydrology Research-to-Operations Laboratory — joined The Show to talk about this research, which looked at more than two decades-worth of satellite data.
Full conversation
MARK BRODIE: McKenzie, when you’re talking about a dust cover on snow, is this the same kind of dust that would accumulate maybe on your back patio from stuff not being moved around? What exactly are we talking about?
MCKENZIE SKILES: Yeah. It’s similar. We’re talking about mineral dust. So dust that comes from arid regions, from disturbed regions. Dust can encompass a number of aerosols, including stuff like soot and biological material. But what we study is really dust from arid regions.
BRODIE: And what is the impact of having this dust landing on top of snow? It seems as though it makes it melt more quickly. But why is that?
SKILES: Yeah. So you can think of it as being something like the difference between wearing a white or black shirt on a sunny day. Snow is really naturally quite bright. It’s the brightest natural surface on Earth. It reflects up to 90% of incoming sunlight, and almost anything is darker than snow.
So when you put this dark mineral dust on top of the snow surface, it absorbs more sunlight. And that additional energy makes the snowmelt faster.
BRODIE: And what are the implications of that? Like why does that matter?
SKILES: One, we don’t know how much dust is going to come every year. We do know that we see dust deposited on the snowpack every year. But the impact of that dust varies from year to year. And it’s not accounted for in snowmelt models. And snowmelt is our primary water resource in the West. And we make a lot of plans about storing and using that snowmelt as it comes out of the mountains.
And so forecasting the timing and magnitude of snowmelt is really critical to using that water resource in an efficient way. And if it melts earlier and faster than we’re expecting it, then we might not use it in the best way. It might come earlier than we expect.
And also when it melts out earlier, that means the landscape dries out earlier and dries out sooner in the summer, and that eventually can lead to less total water yield downstream.
BRODIE: Why is it a problem if the snowmelt happens earlier on? I mean does that not just mean we get the water a little bit earlier than we expected.
SKILES: There are some practical implications of this. We use snowmelt for irrigation. That’s the main use of water is agriculture in the water use. And what we want is that water to be available when we need it for irrigation. But if the water comes too early, the ground is still cold. and it’s not growing season yet.
And so the water is not coming when we need it most. And then it also might be coming too early for reservoir operations. You need to know when the water is coming in or to store it for later use.
BRODIE: Does it matter how much dust is on top of the snow to affect how much it melts and when it melts?
SKILES: Yes. The amount of dust matters, and also the color of the dust matters. So in years when there’s not much dust deposited, the impact is still there. But it’s not as big of magnitude. When there’s frequent dust events that bring a lot of dust to the snow surface, then the impact to snowmelt can be up to two months faster snowmelt.
And in the Colorado Rockies, we get dust from the southern Colorado Plateau. And that dust is very dark and iron rich. It’s red. And so it has a more dramatic impact on snowmelt. In other regions, we see yellow or brown dust. And that won’t have as dramatic of an impact on snowmelt rates.
BRODIE: What can be done about this? You mentioned where the dust comes from in the Rocky Mountains. It’s not like you can go and put a giant sheet over the landscape to prevent dust from flying about. So what do you do about this?
SKILES: Yeah. So we do know that there has been more dust since modern settlement and widespread sort of land use change and surface disturbance of the West. Surface soils can be fragile, and once they’re disturbed, it takes them a long time to heal.
And so one of the things that we know that we can do is to minimize surface disturbance and land use change in regions that are prone to dust emission and transport. And that can be as simple as just knowing which regions are likely to produce dust and minimizing land use change in those areas.
BRODIE: So not maybe developing areas that are more prone to kicking dust up into the air, which eventually lands on snow.
SKILES: Exactly. Yeah, exactly. That sort of land use change and surface disturbance can come in many forms. It can be grazing. It can be building roads for oil and gas development. It can be off-highway vehicle use. It’s any number of things.
And so understanding which areas are most prone to disturbance and dust emission is important, and then targeting those areas for dust mitigation and restoration is also important.
BRODIE: Has your research suggested that we have missed out on water over the past however many years because maybe it melted too early and we just weren’t ready for the runoff?
SKILES: Yeah. So, previous work before this study showed that earlier snowmelt leads to earlier green-up timing across the landscape, and that green-up timing — vegetation blooming earlier — takes up more water. And so the water goes to the landscape or evaporates into the air and doesn’t make it as runoff downstream.
And that can reduce total water yield by about 5% in dramatic dust impact years. And that can be a hard number to interpret, but that’s about half of LA’s water allocation from the Colorado River.
BRODIE: And that seems like a lot.
SKILES: Yeah. It’s a dramatic impact. And it’s not that level of impact every year. But in the years where we see a lot of dust, we might be seeing less total water yield.
BRODIE: Are there particular factors that lead to more dust being in the air and then landing on snow?
SKILES: This is a question that we would like to understand better, and probably the focus of future research. Currently, we can’t predict when we’re going to have a big dust event, or that any given season is going to produce a lot of dust.
There are some obvious factors that lead to dust — high wind speeds, dry surface soils in these emission regions. But in any given year, we can’t actually predict when we’re going to get a dust event. We know when they’re happening, and then we can monitor the impact afterwards. But more research is needed to understand what leads to dust events and then what leads to dust events that are higher magnitude than other dust events.
