Understanding Colorado's Snow Drought with Noah Molotch

0:00Hey, it's Flades, and this is Climate Changers, a podcast where we celebrate the heroes who are on the front lines of creating a new and sustainable resource and energy economy. Today's guest is Noah Mulach, a professor of geography at CU Boulder and a research scientist at NASA's Jet Propulsion Laboratory. Noah and I first met through our work with Protect Our Winners and were neighbors here in Boulder where the view of the Winter Peaks is looking pretty grim, with Colorado facing one of its worst snow years on record. So Noah, give it to us straight. Current data shows us that we are historical lows for late March. What happened to our snow? Well, it started, we didn't get our snow in the first place, and then what little snow we had melted quite quickly or is melting quite quickly, and that is what we call in the drought vernacular, a warm, dry snow drought. So it's both above average temperatures and below normal snowfall.

1:04And then from your perspective, is there anything about this particular season beyond just the lack of flakes that's unique or makes it especially concerning? I think one of the biggest things I'm concerned about is this snow drought coming on the heels of last year's snowpack condition, which in Colorado was also well below average, not as bad as this year, but still well below normal. And so when you start to build up multiple years of snow drought, I think one obviously stresses our water resources significantly, but two makes you wonder if this might be the new normal. And most climate modeling studies have identified these types of conditions as being characteristic of what's likely to occur in the future, and that's why it's particularly concerning. You said drought, but in some of your research, you talk about erudification. What does that mean and what are the implications of this shifting in the baseline?

2:07That's a great question. Erudification, if you think about having below average rainfall or snowfall, and what that means in terms of the quantity of water that is the input to the land surface, erudification is the combination of that with how much the above average temperatures cause more water to evaporate to the atmosphere and the overall system becoming drier and drier. So erudification brings in the concept of what we call the atmospheric demand for water. In other words, how much water are we losing to the atmosphere that would otherwise be entering rivers and streams? And another issue related to that is what you call thirsty soil, right? The last year, even though we had decent snow, the soil soaked up a lot of the runoff before it hit the rivers. What do you expect the runoff to be like this spring?

3:09What we know about these kinds of snow droughts and with earlier snow melt is that less of that water ends up in rivers, lakes, and reservoirs, then would occur under typical conditions. So if you think about the amount of snow you have as being able to go into two different buckets, one being the atmosphere and one being rivers, lakes, and reservoirs, the proportion of the water that goes into rivers, lakes, and reservoirs tends to be lower when we have these early snow melt years because more of it is allocated to the atmospheric demand. And the land is drying out rapidly given this heat wave. And so not only are we losing the snow, but a lot of that snow melt is going back into the atmosphere as evaporation and transpiration from plants and the forests. Sort of related to that, we're seeing a shift from snow to rain in some cases, and you've

4:12written about the snow storage index or the idea of mountains acting as water towers. What is going to be the impact if there's more rain than snow? In many parts of the Western United States, if you think about a storm coming in as shifting from let's say a big snowfall event to then becoming a big rainfall event, which is projected to occur with some frequency under climate warming, when that occurs that that might change the timing of when water goes into a given watershed by several weeks to months. And that's because that water accumulated in the snow pack might persist on the ground, especially if it stays cold for again, several weeks or months, and then released into the system in May or in June. But shifting it into March, like what's happening this year, totally transforms the ecology of the landscape. It increases the water stress on vegetation.

5:14This can enhance wildfire risk later in the spring and summer. And also as I said before, it reduces the amount of water that ends up in our streams, lakes, and reservoirs. And then what happens to downstream infrastructure like Lake Powell in a rain dominant system? This is kind of an interesting question. Lake Powell is so large and it's so far below normal storage that even if you shifted all that snowfall to rainfall, an enormous reservoir like Lake Powell would simply store all of that runoff that was occurring due to rainfall runoff processes. It becomes actually a much more challenging problem for smaller reservoirs like Dylan in the headwaters of the Blue River, for example, or any of the reservoirs that exist in the state of Colorado or in the state of California or in any of these headwater states.

6:15When you have a reservoir that only holds about one or two years worth of runoff, then you're kind of threading the needle and managing that reservoir for both flood control and water supply. And that's where a shift from snowfall to rainfall can really make that management quite challenging in terms of ensuring that you have enough capacity for flood control while also maximizing the storage for water supply. And really that's where you start to lead to greater inefficiencies in the system because you do have to maintain that dual purpose to varying degrees with different reservoir systems around the Western U.S. And we're talking here at the tail end of March, the heat wave this month is being called a one in 500-year event. How does that warmth change the physics of the snowpack we actually do have? Yeah, so in one week, right, from the data that my team pulls together for the water management

7:20community, we release reports on a weekly basis. And from March 15 to March 22 over that one week period, the snowpack in Colorado, which was hovering at around 50% of normal for that time of year. So already really low dropped by about 20% more across the state. So in that one week period, we went from about 50% of average to about 30% of average. Just due to that heat wave and the intense melt that occurred combined with below average snowfall, like typically this time of year, we'd still be getting more snow. We wouldn't necessarily be melting. Here in Colorado, we have some of the highest peaks in the country. Are we seeing it decoupling where the high peaks know holds on while the mid to low elevations completely lose their seasonal snowpacks? I think the answer is yes and no. So it's a useful question. And yes, the highest peaks definitely show more resilience with regard to warming.

8:23And whereas the lower elevations are definitely experiencing that warming in a more acute manner. This particular year with the heat wave that we've had, there isn't anywhere on the landscape that's been immune to that. Our highest elevations, snow monitoring equipment, which goes up to as high as 12,000 feet above sea level, are registering the impacts of this warming event. And we're seeing snow melt across the landscape in more bare ground above 10,000 feet, which is very rare for this time of year. That kind of a warming signal to even see that kind of melt occurring in early April would be rare. But to see it occurring in mid-March is extremely rare. So on the one hand, yes, there's some additional resilience to climate warming at those highest elevations, but it's not an absolute resilience. And the lower elevations, yes, are much more sensitive than the highest elevations.

9:25So if you think about the bare ground and also then these winds that we've had that have been nuts the last couple of months, you've done work on how dust and impurities affect snow albedo. With the dry conditions, are we seeing more dust on snow this year? And what does that do to the melt? The thing about the dust events is they tend to be most abundant in the second half of March and in April. And the impact of that dust because the dust sits on top of the snow and darkens the snow surface, causing it to absorb more sunlight. What we may see this year is that the snows are already gone before the dust impact could even really dramatically impact the snow melt. So I think it's an interesting, I think we're lucky, right, in that these dust events tend to come in the late spring and not in the middle of winter because, man, if we had dust on top of the snow right now while we're getting these warm events and the clear skies and high

10:28solar radiation, we would really be melting the snow abnormally fast. But luckily we don't have a big issue with the dust right now because it tends to be an issue more in April and in May. And when you look at all of these changes like cumulatively, what's going to happen to the ecology of the front range? Well, I think one of the things that we have to look at and I'm not an ecologist, but I collaborate with a lot of ecologists and if we're looking at the front range and the grasslands around the front range as a system that will have less snowfall in the future than it's had in the past, then we should expect that to have some pretty big impacts, especially with regard to the frequency of wildfire. And the presence of snow cover on grasslands, of course, dramatically reduces wildfire risk, not only during the period of snow cover, but in the period immediately afterward in

11:32which the soils remain relatively moist and the grasses are relatively compressed from the burden of the overlying snow that had existed in the prior weeks. So there's a lasting impact that reduces wildfire risk in the presence of snow cover here on the front range that in the future we may live in a world where it's less common. That certainly seems to be the case based on the trajectory that we've been on, particularly over the last several years. So that I think in terms of the lifestyle that we have here on the front range is of the first order concern. And your research includes satellite imagery and other state-of-the-art technology. Could you talk a little bit about this technology and how this high-tech view from above changes how water managers in Colorado can and will make decisions? I'm happy to talk about that. Interestingly, the way that water managers forecast water supply, which are rather eloquent

12:36in a statistical standpoint and from an engineering standpoint, they still rely on the same ground data that have been collected for about a hundred years now. When you look at, say, the water supply for the city of Denver, the snow pack is the primary source of that water supply. And there might only be five or six ground observations across the Southcloth river basin in terms of the area that serves the city of Denver, which is a dramatic under sampling of the water that's needed to sustain a metropolis like Denver. And so the technologies that we've been developing and that NASA has been working on for decades now aim to provide continuous spatial maps of the amount of water that's stored in the snow pack to provide information to water managers that is more robust when the climate is anomalous.

13:37And the way that it works currently is that we just have statistical models where we say, oh, this year, similar to say 1964, the amount of water we got in 1964 was x amount, so our best guess for this year is that same amount. Those kinds of statistical approaches work okay if the climate is not variable and changing, but as we see the climate variability increasing and the average annual temperatures increasing, those kinds of statistical models become less accurate. And this current snow drought here is a prime example of that. And so the technologies, whether they use satellites that are using wavelengths of light that you and I see with our eyes or out in the microwave portion of the electromagnetic spectrum using radars, these can be used to characterize the depth and water equivalent of the amount of water that's stored in the snow pack and improve the estimates of stream

14:41flow that will flow into our reservoirs. So what can we call radons due to have an impact and help protect our winters? The first thing we need to do is move the needle back to a pro science perspective on these problems that we face. And I say that because particularly over the last 14 months, we've seen a real attack on earth science and society's focus on understanding the changes that lie ahead, whether those are on weekly, monthly seasonal or decadal time scales, it's the science that helps us understand the problems that we face and how to solve those problems. So that's kind of an immediate thing we can do. And then the second is to continue to migrate and move the needle forward on our energy

15:42sources. So at the end of the day, right, this has everything to do with our carbon-based economy and our reliance on fossil fuels for our energy source, which from first principles we know warms the atmosphere. And you don't have to be a rocket scientist to project that a warmer atmosphere will have an impact on snow. And so we need to do everything we can to keep the atmosphere as cool as possible by migrating our energy sources away from fossil fuels. And what makes you optimistic about the future? Probably the young people that I work with, you know, there's so many talented individuals out there that are focused on the problems that we've been talking about. And in the last 15 plus years of being professor at the University of Colorado, I've watched so many of our alumni go into important positions and doing amazing work and the new pipeline

16:42of individuals that comes out every day and their ability to dynamically work with AI and machine learning techniques and new data sets. And to be adapted writing code and manipulating large data sets, it's really an explosion of knowledge development that would have been unimaginable at the time when I was a graduate student. So that makes me super optimistic. Well Noah, thank you for helping us make sense of this crazy winter. And thank you for joining this episode of Climate Changers. Thanks for having me, it's been fun. Every episode of Climate Changers has a call to action posted in the show notes. Each call to action has been curated to make it easy for you to help create the changes that we discussed today. Thank you for joining Climate Changers, until next time.