Snow melts faster under trees than in open areas in mild climates
It’s a foggy fall morning, and University of Washington researcher Susan Dickerson-Lange pokes her index finger into the damp soil beneath a canopy of second-growth conifers. The tree cover is dense here, and little light seeps in among the understory of the Cedar River Municipal Watershed about 30 miles east of Seattle.
She digs a small hole in the leaf-litter soil, then pushes a thumb-sized device, called an iButton, about an inch beneath the surface. If all goes well, this tiny, battery-powered instrument will collect a temperature reading every hour for 11 months. Researchers hope this tool and a handful of other instruments will help them map winter temperatures throughout the watershed as they track snow accumulation and melt.
This fieldwork piggybacks on a recent finding by Jessica Lundquist, a UW associate professor of civil and environmental engineering, and her lab that shows that tree cover actually causes snow to melt more quickly on the western slopes of the Pacific Northwest’s Cascade Mountains and other warm, Mediterranean-type climates around the world. Alternatively, open, clear gaps in the forests tend to keep snow on the ground longer into the spring and summer. Lundquist and her colleagues published their findings online this fall in Water Resources Research.
Common sense says that the shade of a tree will help retain snow, and snow exposed to sunlight in open areas will melt. This typically is the case in regions where winter temperatures are below freezing, such as the Northeast, Midwest and most of central and eastern Canada. But in Mediterranean climates – where the average winter temperatures usually are above 30 degrees Fahrenheit – a different phenomenon occurs. Snow tends to melt under the tree canopy and stay more intact in open meadows or gaps in a forest.
This happens in part because trees in warmer, maritime forests radiate heat in the form of long-wave radiation to a greater degree than the sky does. Heat radiating from the trees contributes to snow melting under the canopy first.
“Trees melt our snow, but it lasts longer if you open up some gaps in the forest,” Lundquist said. “The hope is that this paper gives us more of a global framework for how we manage our forests to conserve snowpack.”
For the study, Lundquist examined relevant published research the world over that listed paired snow measurements in neighboring forested and open areas; then she plotted those locations and noted their average winter temperatures. Places with similar winter climates – parts of the Swiss Alps, western Oregon and Washington, and the Sierra Nevada range in California – all had similar outcomes: Snow lasted longer in open areas.
“It’s remarkable that, given all the disparities in these studies, it did sort out by climate,” Lundquist said.
Even in the rainy Pacific Northwest, we depend on yearly snowpack for drinking water and healthy river flows for fish, said Rolf Gersonde, who designs and implements forest restoration projects in the Cedar River Watershed. Reservoirs in the western Cascades hold approximately a year’s supply of water. That means when our snowpack is gone – usually by the summer solstice – our water supply depends on often meager summer rainfall to get us through until fall, he said. Snowpack is a key component of the Northwest’s reservoir storage system, so watershed managers care about how forest changes due to management decisions or natural disturbances may impact that melting timetable.
The UW’s research in the watershed has been a beneficial partnership, researchers say. The 90,000-acre watershed is owned by the City of Seattle and provides drinking water to 1.4 million people. The area now is closed to recreation and commercial logging, but more than 80 percent of the land was logged during the early 20th century, and a large swath of dense, second-growth trees grows there now. Watershed managers have tried thinning and cutting gaps in parts of the forest to encourage more tree and plant diversity – that then leads to more diverse animal habitat – offering the UW a variety of sites to monitor.
The UW researchers acknowledge that temperature is a very broad predictor of snowmelt behavior, yet they expect their theory to hold true as they look more closely at the relationship between climate and snowmelt throughout the Pacific Northwest. They are collaborating with researchers at Oregon State University and the University of Idaho, and are ramping up a citizen science project asking hikers and snowshoers to share snow observations.
“This is really just a start,” said Dickerson-Lange, a doctoral student in Lundquist’s lab who is coordinating the citizen-science observations. “The plan is to refine this model. With climate change, a cold forest now might behave more like a warm forest 100 years from now. We want to be able to plan ahead.”
Co-authors of the recent paper are Nicoleta Cristea of UW civil and environmental engineering and James Lutz of Utah State University.
Funding for the research is from the National Science Foundation.
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For more information, contact Lundquist at jdlund@uw.edu or 303-497-8257 and Dickerson-Lange at dickers@uw.edu or 253-225-9909. Lundquist is on sabbatical but is reachable by email or phone.
here is a video of the field work:
Quote “Trees melt our snow, but it lasts longer if you open up some gaps in the forest,” Lundquist said. “The hope is that this paper gives us more of a global framework for how we manage our forests to conserve snowpack.”
So; the new greens want to conserve snow pack, I guess by clearing the forest?
And like Barbee, I would have explained it in my non-scientific term, as compost. Not only does rotting tree litter provide a comfortable place to sleep, it also provides a little extra warmth. But I’m not a scientist, so what would I know?
Warm air escapes through tree cover (slowly through large surface), dragging colder air from the open (smaller) spots – resulting there in sucking colder air directly from sky. As long these open gaps are colder then the air inside forrest, these spots will keeping on freezing up like a fridge. This mechanism stops when summer returns, and open spots getting warmer then inside forrest (due humidity and leaf cover)..
There is a configuration effect from trees that can minimize solar melting and minimize radiant heat melting. The orientation of a chain of trees is ideal when it provides shade at mid-day over a broad area of snow. The spacing of the rows is best when it minimizes shortwave energy delivered to the snow (shadows), and minimizes the longwave energy delivered to the snow surface by radiating a larger fraction of energy to space instead of other trees. These ideas are several years old (some to at least 2004).
Another important loss of water content in snow is sublimation (not discussed).
http://www.webpages.uidaho.edu/watershed/Papers/The%20impact%20of%20coniferous%20forest%20temperature%20on%20incoming%20longwave%20radiation%20to%20melting%20snow.pdf
http://www.webpages.uidaho.edu/watershed/Papers/Ellis%202011.pdf
http://people.duke.edu/~mk176/publications/BijanEtAl_VegDensityVSRadiation_JGR.pdf
Ric Werme
So do I ,remember Roy Spencer’s discussion ? A great toy.
As many have noted & must add my voice to, snowfall penetration to the ground is inversely proportional to the density of the woods. Clearly, these researchers have spent little time in the winter woods (at least that’s the way this reads).
As an avid backcounty skier & the owner of a large tract of conifer woods , I can assure your from observation that snow penetration is way more significant than any IR effects from the trees. How can I say this – just check out the new snow depth in the woods vs an opening during or right after a snow – before any IR effects could take hold – and you will see the there is an easily measurable effect , with the snow being substantially less in the woods compared to the openings.
What I have observed is that the effect is greatest on smaller snows – with smaller snows largely being caught on the tree limbs & a lot less making it to the ground. With bigger snows, the limbs reach a “saturation limit” so to speak , where they are holding all the snow they can, then more makes it the ground as a percentage relative to an open aspect.
It is also worth noting that most snow that is collected on limbs never makes it to the ground / ground water – it sublimates &/or evaporates prior to making to the ground. There are multiple studies on this – I know this based on research I did for a particular back country ski project I was involved in.
I love this:
“yet they expect their theory to hold true as they look more closely at the relationship between climate and snowmelt throughout the Pacific Northwest.”
Yeap nothing like starting off with a good dose of confirmational bias.
So, the people studying forests have no experience of forests? How could you not know that snow does not collect under trees, at least many kinds of trees? Reminds me of my friend who grew up in a high rise in Queens and had not seen a bug inside a building until she moved to St. Louis.
How could you undertake the study and not learn that snow does not collect under trees? Did the investigators not go into a forest? Did they employ the usual method of the Paleo crowd and just find various “number series” on the internet and use them as their data?
How could you be a Phd researcher on forests and not have read Jack London’s “To Build A Fire?” They better read it or they might end up frozen to death, if they go into a forest.
“Funding for the research is from the National Science Foundation.”
No oversight whatsoever. The people at the granting agency are just as clueless as the authors of the article. And the peer reviewers? Just as clueless.
By the way, I had collected my information about snow and trees by the time I was six years old. In fact, at the age of six I had learned to enjoy standing under a nice pine tree and watching the snow collect beyond the branches. The little trickles down through the branches were delightful.
The study seems to have overlooked the most important aspect of the difference in snow depth beneath trees and open fields. Look at any clear-cut, snowy, mountain slope and you will notice immediately that the snow is (1) much deeper in the open fields, (2) persists longer into the melt season, and (3) is often absent altogether around the base of trees (the dreaded ‘tree wells’ well known to skiers). Is this because it is warmer under the trees and that melts the snow? Of course not! Trees are natural umbrellas–in a rainstorm where do you want to hang out, under a tree or out in the open? So in a snowstorm, where does the least snow accumulate? Guess what–in the forest where much less snow reaches the ground (50-70% less, depending on the vegetation) because the trees intercept a lot of the precipitation. Anybody who knows anything about hydrology knows this. And you have to ask the question, where does most of the snow melt take place, from the ground or from the atmosphere? Depending on the altitude and ambient air temperature, the ground is often frozen and not melting much, if any, snow, whereas the surface of the snow is melted by air temperature and solar energy. This study seems to fall in the category of a really dumb analysis.
u.k.(us) says:
November 13, 2013 at 5:31 pm
“This is really just a start,” said Dickerson-Lange, a doctoral student in Lundquist’s lab who is coordinating the citizen-science observations. “The plan is to refine this model. With climate change, a cold forest now might behave more like a warm forest 100 years from now. We want to be able to plan ahead.”
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“Right now I’d plan for winter, surviving that I’d plan for spring/summer, and so on.
It has worked for many a generation, before studies such as these.
A plan helps, but the onset of cold weather really concentrates the mind.”
How about a plan to find a spouse capable and willing to provide all necessary care for his “helpmate?”
Happens here every spring under my pines in MA. My field is snow and ice covered for weeks after the sno melts under the trees.
So, if the snow pack is melting earlier to AGW, then all we need to do is cut down all the forests!
Brilliant! I like it. Complete anathema to the Warmista and Enviromentalist dogma.
Seriously, the key point is we don’t understand the natural cycles and therefore cannot discover the human effects. Oh, it’s all so complicated. I suggest the Crimotologists be sent to the nursery for a few hundred years while real scientists gather data.
Re Skiphil says: November 13, 2013 at 5:09 pm
and Don Easterbrook says: November 13, 2013 at 7:06 pm
You hit the nail(s) on the head(s). The term I learned from a backcountry ski instructor was “tree well”. Check on line for some technical details from the web site devoted to tree well safety:
http://www.deepsnowsafety.org/index.php/
http://www.ravallirepublic.com/lifestyles/recreation/article_ab180874-3012-11e0-9ac6-001cc4c002e0.html
The researchers need to get out more, but stay out of tree wells unless they have a buddy system.
Snow lands on conifer branches and sticks (unless it’s very cold). As long it’s not too cold, it will melt by afternoon and enter the soil as water. This allows the trees to grow slowly in the winter.
It can’t believe researchers on the west coast don’t know such basic information.
Fenbeagle draws a hilarious rendering of Maurice Strong as an Ernest Stavro Bloefeld style super villain. Just scroll down to see his likeness.
http://fenbeagleblog.wordpress.com/2012/02/04/hanging-up-by-the-constables/
Oops! Wrong post.
We get big dumps in the Cascades! It can be 2ft deep in the open and only 6″ under the canopy. Way less snow falls in the woods. When it warms the snow on the trees melts and drips onto the forest floor melting the snow faster than in the open. I doubt LWIR has much of an effect compared to these other factors. It is cooler in the shade and the snow holds up better than in the open on a sunny day. It can be slushy/wet in the open and icy under the trees!
@ROM re your grant application , I mean really thanks that was a great lesson I am starting today!!! Thanks LOL 🙂 Most of you have already exposed this waste of money thanks.
And as far as tree wells in snow country are concerned ALL of you are more than correct, as an ex ski resort worker they were (and in 1 case tragically) the most dangerous spots on a ski hill. BUT they can also be a place you can survive in if used correctly.
Theo Goodwin;
Reminds me of my friend who grew up in a high rise in Queens and had not seen a bug inside a building until she moved to St. Louis.
>>>>>>>>>>>>>
Reminds me of my city slicker cousin who moved out to the prairies, determined to get back to agrarian roots. He called me over one day in mid summer to see if I could figure out what was wrong with his pumpkins. I said they looked great, there was nothing wrong with them that I could see. He looked at me as if I was daft and said, “….but, but… they’re green!”
We who grew up with nature in our back yards frequently forget how privileged we are to have had that opportunity, and that those who have not are coming from a completely different paradigm. Er, meme. Er, uhm….background.
conscious1 says:
November 13, 2013 at 8:48 pm
Cross country skiing on the west side of the Cascades before modern skis in the ’70s & ’80s used to require changing waxes when moving out of the open into trees. Less so on the east side, except when it warmed up.
davidmhoffer says:
November 13, 2013 at 9:15 pm
Reminds me of my East Coast urban American classmate at Oxford who had never seen a swan before. When he saw them in England, his eyes got wide & he blurted out, “Look at the size of those ducks!”
The UW’s research in the watershed has been a beneficial partnership, researchers say.
In other words, “keep the grant money flowing.”
Which is why the “plant millions of trees” to combat global warming train went off the rails about 10 years ago.
Additionally, trees do hold some snow above the ground from where it can sublimate and melt more easily than in a deep layer on the ground.
You all realise of course that those same researcher’s will now apply for another grant and get it it past handout performance of the grants industry which uses OPM is any indication.
Then using all the knowledge of snow conditions in and around forests and trees that all of you have been posting about here for all to see,, they will never need to leave the comforts of their offices, which means lots of grant money left over to go partying on, to write another new paper on “snow holes” and how the concentration of CO2 around tree trunks creates warming and thereby creates the now famous [ lots around the world read this ] snow holes or some such!
OPM = Other People’s Money ie; yours and mine hard earned.
Indeed, wouldn’t that be because less snow is falling under trees than in open areas basically? Though it depends, the trees are as well blocking sunlight from melting the snow, so snow may melt faster away from the trees. But because less snow is falling under the trees (or rather, the snowfall is scattered along the trees height, and it falls to the ground only when it’s melted); it is actually tough to get to any conclusion. From experience, snow melts faster at spring in open areas, even if there’s basically more snow there. So i think sunlight blocking may well be the bigger factor here.
Just crazy thoughts from a dumb man out of shower. 🙂