Using Trees to Guide Water Resource Management

Sept. 8, 2011 | KUOW
Ashley Ahearn


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  • Roughly 400-year-old Alaskan yellow cedars credit: Ashley Ahearn
  • Jeremy Littell cores a 350-year-old mountain hemlock in the Washington Cascades
  • By looking closely at the tree rings in a core sample like this, scientists can identify climate patterns dating back hundreds of years. credit: Ashley Ahearn
  • Jeremy Littell of the University of Washington's Climate Impacts Group is in his element above the snowline. credit: Ashley Ahearn
  • Jeremy Littell's dog, Jasper, loves a good snow adventure. credit: Ashley Ahearn
Roughly 400-year-old Alaskan yellow cedars | credit: Ashley Ahearn | rollover image for more

When Jeremy Littell hikes, his eyes are almost never on the trail in front of him. He’s scanning the surrounding forest, almost like someone scanning the rows of cereal at the grocery store. But instead of that choice box of Cheerios, he’s looking for old trees, the oldest trees around.

“When I’m hiking I’m almost always shopping,” says Littell. He’s with the University of Washington’s Climate Impacts Group. “When 1,000-year-old trees go on sale I’m there. I’m the first in line.”

These trees aren’t actually for sale, nor will they be cut down, but they are valuable for science. When Littell finds those old trees, he cores them.

After hiking 4 miles through stands of Douglas fir, Pacific silver fir and some yellow cedar, Littell stops next to a 350-year-old mountain hemlock. He takes out a long tube with a screw on one end and twists it through the bark. The increment borer (as it’s called) disappears into the trunk (it doesn’t hurt the tree, he swears) and Littell sticks what looks like the dipstick you use to check your oil into the screw and pulls out a long, golden cross-section of the tree.

Picture a really thick milkshake. Now stick a drinking straw into the milkshake, put your finger on one end and pull the straw out, full of deliciousness. But instead of milkshake, Littell is pulling out a chronological timeline of tree rings that map the growth of this tree going back hundreds of years. Each tree ring tells the story of the climate for that year of the tree’s life, Littell explains as he traces his fingers along the tree’s history, growth ring by growth ring. He’s like a boy with a decoder ring.

“2000 is back here, here’s the ‘90s, the ‘80s, the ‘70s or so. See that wide one, and another wide one next to it?”

(Chris Robertson of the Washington Department of Natural Resources takes a core sample of an Alaskan yellow cedar.)

Tree rings like the ones Littell is collecting on this day document both the normal patterns and the extreme climate incidents of the past –- take the massive drought that happened back in 1250 across the western part of the continent. And that information, Littell says, can help water managers plan for the future.

Littell and other researchers have found that in the past 30 years or so, growth rings in trees at high elevations across the West have gotten wider. That tells them that there’s probably been less snow in the mountains. Around here, where an estimated 85 percent of our precipitation comes as snow, that could eventually mean less water in the rivers from snowmelt.

The challenge is connecting the science with the resource managers.

Enter Connie Woodhouse of the laboratory of tree ring research at the University of Arizona. She and Jeff Lukas of the University of Colorado developed the website treeflow to bring together tree ring data from around the country and make it available to the public.

If you’re a policy maker, or even just a curious web surfer, you can go online to where there’s a map where you can click on major watersheds in the U.S. and pull up data, like Jeremy Littell’s in the Pacific Northwest, that would tell you about snowpack from the tree rings. Woodhouse says snowpack is usually an indicator of how much water is in rivers during that year.

“In many areas of the West when there’s big snowpack in the watershed and when that snow melts it contributes to that stream flow and in many cases it’s the major contributor to that stream flow,” she says.

That information is valuable to the folks who make sure water comes out of your faucet. Woodhouse gets calls from public utilities and water resource managers all over the country. She says for some utilities, TreeFlow is helpful in planning for the worst, once they take a look at climate patterns further back in history.

“They’re saying, ‘hey, there was this drought in the 1850s that was worse, maybe we should consider that, or this drought in the medieval period that went on for a long time’” Woodhouse says. “So it’s kind of a reality check for ‘What’s the worst-case drought that we should be planning for?’”

Paul Fleming, head of the climate change program at Seattle Public Utilities, says TreeFlow could come in handy for planning future water management.

“Connie Woodhouse and Jeremy Littell are doing really good work in exploring whether additional forensic information that could help folks like us understand whether there’s some vulnerabilities out there that we’re not aware of,” he says.

However, Fleming says in the Northwest there’s not too much cause for concern right away, in terms of water supply: “I tend to characterize the impacts of climate change as significant but not necessarily imminent.” Climate change models for the Northwest predict less snowfall, and that’s a problem when it comes to water storage.

Snowpack acts like a giant water bank, dispensing water throughout the drier months in the form of snowmelt that flows into depleted rivers. Fleming says planning for climate change around here means expanding reservoir storage capabilities to make up for that lost snow water bank.

“It’s kind of like, lets say you’re in the tub and you fill the bathtub up to the top of your knees and you say lets fill it to the top of my neck, using the same infrastructure, so we’re adapting how we manage our system to reflect those changes.”

Seattle Public Utilities has done some modeling that shows that its reservoirs in the watersheds of the Tolt and Cedar rivers have enough capacity to meet demand through the middle part of the century, factoring in climate change.

“The big question in this climate arena is, do you get information that merits you to act differently than you’re acting now?” Fleming says. “It’s particularly salient with making big new investments in big new infrastructure. And that’s where the ability to take climate science and drive those large scale investments, we’re not quite there yet.”

Seattle’s utilities department has not engaged directly with TreeFlow, but it’s one of the first such municipal water and power agency in the country to create a full-time position to focus on climate change..

Paul Fleming says he looks forward to using the work of researchers like Jeremy Littell and Connie Woodhouse for future planning, joining the ranks of Denver, Boulder and other cities that have already done so.

© 2011 KUOW
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