An Ice Storm in a Teapot: Researchers Spray Trees to Simulate Devastating Winter Storms

Feb 25, 2016

There’s nothing that strikes more fear into the heart of a New England driver than the words "ice storm."

But this pernicious wintery precipitation is not just trouble for cars. Forests, where a thick coating of ice can break limbs or bring down a whole tree, suffer too.

Now, for the first time, researchers are able to study not just the damage these storms do, but also how that could change our forests, by manufacturing their own ice storms.

In nature, ice storms happen when it’s warm at high altitudes and cold down near the ground. If the layer of cold air is too thin, the water that lands is just cold rain; if it’s too thick, it becomes sleet and then snow.

At the Hubbard Brook Experimental Research Forest in the White Mountains, ice storms happen when you take a 20-minute snow machine ride up a forest road, where you’ll find a team of more than a dozen scientists from all over the Northeast with generators, pumps and fire-hoses.

The hoses are mounted on ATVs and run at super-high pressure to spray a fine mist over the trees in a square of forest about the size of a basketball court. There are ten such squares, eight of which will be sprayed with different thicknesses of ice; two will remain untouched as controls.

John Campbell, a research ecologist with the USDA Forest Service, looking a little frosty after spraying some forests.
Credit Courtesy Photo

“In the forest, there are these orange buckets - see there and there,” explains Paul Schaberg, a forest service plant physiologist and one of six principal investigators on the study. “Those help us monitor how much water we’re putting into the canopy.

"And then there are these baskets that look like laundry baskets. Those are to capture debris that falls down.”

Collecting data while the spraying goes on is no easy task
Credit Sam Evans-Brown / NHPR

(When I point out the baskets are, indeed, actual laundry baskets, Schaberg laughs and says, “Science!”)

As these scientists spray trees way up in the White Mountains, remember it’s freezing cold. The day I visited, the temperature was in the teens, but other times the spraying was done when it was in the single digits in the middle of the night.

“It’s fun for about twenty minutes and then you’re like, 'Yeah, I don’t want to do this anymore,'” says research technician Chris Hansen, from the University of Vermont, who mans one of the hoses.

Hansen is wearing marine-grade foul weather gear on top of his winter clothing, and he’s coated with a thin layer of ice. Though today’s icing is mild compared to some of the more extreme excursions, “Previous times I did this I was always on the side where the wind was blowing into your face so you go pretty soaked," he says. "Despite the ice that’s on my face right now, this was actually really quite easy.”

On this day, they spray just a half inch of ice on the trees. One night, they sprayed three quarters of an inch, which took five hours.

But while the spraying might be the most complicated step logistically, it’s just a tiny part of the science. Underneath the trees there are tiny sensors dug into the ground to monitor soil temperature and moisture.

Lindsey Rustad, another Forest Service researcher and the lead scientist on this project, says that, in the seasons to come, the team will measure what broke off the plants during their simulated ice storms.

“We’ll be measuring the diameter, the length, the width. We will know to the gram what came down from this," Rustad says. "And because we know exactly what came down before, we’ll know exactly what came down in the ice storm."

Rustad says researchers will study these forest plots as well as following up on plots that were studied after the 1998 ice storm. They will also take the data they glean from scouring the forest floor and plug it into ecosystem modeling software to game out the kinds of impacts they think the storms will have.

Nothing’s been published yet, but she has some ideas of what they might find.

"Look at the canopy,” she says, pointing to a research plot that was sprayed most heavily and saw whole tops of trees breaking off under the weight of the ice. “One of the things we’re going to be looking at next summer is there’s going to be a lot more light coming down here. And that means the soils are going to be a lot hotter and a lot drier.”

The trees are sprayed from the back of a UTVs retrofitted with fire-fighting equipment and high pressure pumps.
Credit Courtesy Photo

But these ice storms don’t just affect forests. The most expensive power outage in New Hampshire history was the 2008 ice storm, and it cost more than twice as much as the next most damaging storm to restore power to the state.

So another part of this research is modeling how often - and where - these storms are likely to occur in the future.

Right now, there’s an ice-storm belt that stretches from northern Texas all the way up into New England and Canada where ice-storms are more common.

Katherine Hayhoe, a climate scientist at Texas Tech University and another of the principal investigators, says the time of year ice storms occur and maybe even where they occur is likely to change “So it’s this huge band," Hayhoe explains, "and it’s true that at the very southern-most part of this band, we’re probably going to see less ice-storms, because it’s simply going to be warmer. And at the northern-most end of the band we’re probably going to see more ice storms.”

But at this point, that’s all conjecture – Hayhoe says it will take her two years to finish the modeling.

Up here in New Hampshire, the icing is done for this year. The researchers scraped the windshields of the ATVs and huddled up in a warming tent to get the feeling back in their fingers.

It will take months and years to fully analyze all the data. But as a preview Rustad says she noticed clear tipping points as the ice accumulated – “where all of the sudden the branches, you know big branches start, kaboom kaboom kaboom, crashing down.”

The first of those tipping points occurred at .4 inches - below the half-inch level the National Weather Service uses for issuing an ice storm warning.

That’s a criterion that Rustad thinks maybe should get revisited.

The researchers found that around .4 inches of ice, limbs began to break in large numbers, around .7 inches, whole tops of trees started to fall.
Credit Courtesy Photo