I am Quoted: Dust on Snow Rec Impacts - Mountain Buzz
 



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Old 10-07-2010   #1
 
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I am Quoted: Dust on Snow Rec Impacts

The Crested Butte News is doing a 3 part article covering local and CO Basin wide impacts of the worsening dust on snow problem that is decreasing our snowpack and reducing streamflows. This comes in the wake of recent studies with findings of basin-wide impacts.

Check out the article here: The Crested Butte News - Dust on snow drops a double whammy on local recreation

Concerning the section where I am quoted, note that I specified (to the reporter) that I was discussing impressions and observations (not scientifically quantified findings).

Overall, this article does a great job of summarizing local dust on snow and future water resourceful availability challenges.

Particularly alarming to me is that this dust on snow caused streamflow decrease of 5% will compound with the projected 7 - 20 % decrease in streamflow (due to climate change) that is forecast for the CO River basin.

Part one of the article series is available here: The Crested Butte News - Dust on snow reducing Colorado River flows by accelerating spring snowmelt

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Old 10-07-2010   #2
 
Denver, Colorado
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Chris, could you explain how dust on snow reduces runoff by 5%? I don't understant the loss in volume, maybe I am missing something. My understanding is that dust could accelerate melting which would mean higher flows in a shorter time, but it seems like the overall volume would be the same. My assumption is that the same volume of water would melt from snow to water thus producing the same volume of runoff, just with a changed time and peak.

Is there something to do with increased evaporation or ground water?
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Old 10-07-2010   #3
 
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If its ok, I will just provide you with a link that should be able to answer this question as I don't have Buzz time to spare today...

Desert Dust Reduces Colorado River Flow, Says New Study: Desert Dust Reduces Colorado River Flow, Says New Study | News Center | University of Colorado at Boulder

This paragraph in particular answers your question (generally).

"Snow dusted with dark particles absorbs a greater fraction of the sun's rays and melts faster than white snow, said study co-author and Research Associate Jeffrey Deems of CU-Boulder's National Snow and Ice Data Center and a scientist at WWA. Earlier snowmelt then lets the growing season of snow-covered vegetation start earlier and more water is lost through evaporation and transpiration, he said. That leaves less water for the Colorado River, which supplies water to more than 27 million people in seven U.S. states and Mexico."
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Old 10-07-2010   #4
 
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I'm not convinced that DOS is a worsening phenomenon. From the journal articles I've read, the rate of dust accumulation peaked about 100 years ago, based upon San Juan Mountain alpine lake bed cores. I'm not sure if there's research regarding the timing of DOS events, for example if they are occurring more frequently in the spring than they did in the past.

Anecdotally, 2010 was a huge spring DOS year, but the Arky basin had an average snowpack and runoff was huge.
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Old 10-07-2010   #5
 
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Seems counter intuitive. Seems like the fast melt would put less in the aquifer, and more in the river. If I understand what he is saying is the evaporation from living organic mater is greater due to longer growing season. I guess we can watch it all play out over the coming decades. After the pine beetle kill, the shape and dynamic of the headwaters of the Colorado is certainly seeing dramatic change.
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Old 10-07-2010   #6
 
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I'm skeptical about the 5% number. The article says that they modeled runoff for conditions prior to the dust, which they say started 150 years ago, which is well before they had any accurate flow meausrement.

The article states that earlier melt will allow for snow covered vegetation to start growing earlier... Maybe... Seems like a pretty weak arguement to me. Much of the snowpack is in high elevations where there isn't much vegetation, and the lower elevation stuff where there is snowpack doesn't seem like it would be that significant of a liquid draw.

What they seem to point out is that they got 5% less runoff in "modeled" conditions for water going into the colorado river reservoirs. If it was hotter in those years, you could have had more loss by evaporation due to temperture alone. The last decade has been warmer that the years that they quote as pre dust. I wonder if they were somehow able to control for temperature in the analysis.

All models have uncertainty as well. I wonder how much uncertainty is in the model compared to the modeled differences. For instance is the model has a 10% uncertainty and the model a 5% difference, its in the noise.

My assumption would be that if the snow melts 2-3 weeks earlier that there would be less snow sitting around in june/july when evaporation rates in the mountains should be the highest due to higher temperatures and longer days. My intuition tells me that a shorter and faster runoff that starts earlier will put more total water into the river than a slow melt. My take is that a slower melt allows more water to evaporate becuase it takes longer, and allows more water to recharge aquifers, because the soils is potentially less saturated.


Either way, its an interesting discussion. I do completely agree that high fast runoff can have a negative impact on recreation. Remembering back this year, it seems that we an early heat wave on top of the dust on snow that really got the snowmelt cranking. I think its hard to decouple temperature impacts and dust impacts from the melt equation. Maybe the researchers figured away to do it. I'm a little of skeptical when folks try and paint a simple picture and blame it all on the dust.

Not trying to jab at you Chris, just thinking of the science behind the articles.
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Old 10-07-2010   #7
 
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Quote:
Originally Posted by deepsouthpaddler View Post
All models have uncertainty as well. I wonder how much uncertainty is in the model compared to the modeled differences.
Agreed. Models are models.

Quote:
Originally Posted by deepsouthpaddler View Post
My assumption would be that if the snow melts 2-3 weeks earlier that there would be less snow sitting around in june/july when evaporation rates in the mountains should be the highest due to higher temperatures and longer days. My intuition tells me that a shorter and faster runoff that starts earlier will put more total water into the river than a slow melt. My take is that a slower melt allows more water to evaporate becuase it takes longer, and allows more water to recharge aquifers, because the soils is potentially less saturated.
Interesting and relevant point because we are seeing reduced base flows in local streams because the aquifers were not as amply recharged this year. This could be a part of accounting for direct streamflow reduction impacts (thinking beyond botable runoff to a more full year picture) of dust on snow.

Quote:
Originally Posted by deepsouthpaddler View Post
I'm a little of skeptical when folks try and paint a simple picture and blame it all on the dust
I don't think researchers are blaming it ALL on the dust, they are simply trying understand it's effects and forecast impacts. As you mention, decoupling from other factors could be quite a challenge. I would recommend contacting the researchers directly with questions on methodology and such.

Quote:
Originally Posted by deepsouthpaddler View Post
Not trying to jab at you Chris, just thinking of the science behind the articles.
No worries! I don't take it as a jab. By all means, question the science here. However, I can't answer your questions, you'll have to go to the source for that. Skepticism is great and so is being informed. To me, this is the current best shot at understanding the impacts of this phenom. Again, my part in the referenced story was providing my personal impressions and observations on whats been going on during the past 2 creeking seasons in CB. From these general 'layman' observations, I would attribute the impacts I reference at least partially to the dust. I do feel this issue needs to be addressed seriously.
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Old 10-07-2010   #8
 
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Perhaps one of the mechanisms that reduces the modeled run-off is the increased direct evaporation that occurs from the dust reducing the snow pack’s albedo, (the amount of light reflected). In the case of dust on snow, there would be a new energy balance at the surface of the snow, even if the temperature is constant between model simulations. Water that melts at the surface will have to infiltrate through the snow pack where it could refreeze or reach the soil. However, water at the snow surface can also evaporate directly off and no longer contribute to runoff; more surface melt would allow more water available for direct evaporation. I would also assume that the amount of time the snow was dusty would also control how much water is lost from runoff. However, I have no idea how this was modeled, and am curious as to what model was used. In any case I agree from the other post that vegetation causing the decrease in runoff is a weak argument.
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Old 10-07-2010   #9
 
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nsf.gov - National Science Foundation (NSF) News - Desert Dust Alters Ecology of Colorado Alpine Meadows - US National Science Foundation (NSF)

Follow the link to read another article on the topic. Different take on both dust on snow historical accumulation rates and plant/evapotranspiration losses. No matter how you cut it - dirty snow sucks.
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Old 10-07-2010   #10
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Quote:
Originally Posted by aatchley View Post
Perhaps one of the mechanisms that reduces the modeled run-off is the increased direct evaporation that occurs from the dust reducing the snow packís albedo, (the amount of light reflected). In the case of dust on snow, there would be a new energy balance at the surface of the snow, even if the temperature is constant between model simulations. Water that melts at the surface will have to infiltrate through the snow pack where it could refreeze or reach the soil. However, water at the snow surface can also evaporate directly off and no longer contribute to runoff; more surface melt would allow more water available for direct evaporation. I would also assume that the amount of time the snow was dusty would also control how much water is lost from runoff. However, I have no idea how this was modeled, and am curious as to what model was used. In any case I agree from the other post that vegetation causing the decrease in runoff is a weak argument.
Sublimation: Sublimation is the transition of a substance from the solid phase to the gas phase without passing through an intermediate liquid phase.

I am not brainy in any way about this, but I have heard hydrologists in the area toss this one around, seems to explain the loss in volume to me though
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