The question biologist Heidi Steltzer is trying to answer is this: How much water does the tiny prairie smoke – a diaphanous pink mountain flower – send into the sky?
The answer could say a lot about how much water cities from Denver to Los Angeles will have as a changing climate tampers with the snow and rain falling on the West.
The buildup of man-made greenhouse gas in the atmosphere is raising global temperatures, which are linked to melting ice sheets in Greenland and rising seas eating away at islands like Tuvalu in the South Pacific.
For the West, the prime climate question will be about snow: how much of it will fall on the Sierra Nevada, the Cascade Range and the Rocky Mountains and how much water it will yield.
Scientists are searching for a solution to the conundrum using supercomputers, laser radar, climate data from centuries past, measurements of stream flow and snowpack across the region and, in Steltzer’s case, by dropping a small plastic tent over prairie smoke to measure its breathing out of oxygen and water and its breathing in of carbon dioxide.
Water has always been scarce in the arid West, relying on a cycle of mountain winter snows followed by spring thaws releasing water into streams and rivers, quenching farm fields and filling reservoirs.
The Future of Snow
Climate is changing, Colorado researchers agree. But how will it change snow and water in the West?
- Day 1: The “breath” of tiny flowers growing in a mountain meadow provide critical clues to climate computer data models used around the world.
- Day 2: The “Eagle” supercomputer is doing the math to calculate how climate change will affect Western water, but researchers worry that modeling still shows the extreme, not what is probable.
- Day 3: Measuring the water in snowpack used to be a boots on the ground enterprise, but as the climate changes, more reliable methods like lidar are needed.
While that has been the rhythm of the region for millennia, there are signs that things are changing, with snows coming later and melting earlier, droughts more widespread and, at times, stream flows lower than they have been in centuries.
There is a suite of forces at work. Some are long-standing and natural, such as variations in Pacific Ocean sea-surface temperatures and shifts in the jet stream, the high-speed winds several miles above the Earth that carry moisture to the North American West.
But one big reason, accounting in some studies for as much as 60% of the change, is a warming climate.
“The snow systems on our planet are changing as places are getting warmer,” said Steltzer, a 47-year-old biology professor at Fort Lewis College in Durango, “and the coldest places on Earth are getting warmer faster.”
It isn’t only the water budget that is changing. Forests are turning into shrub lands at lower elevations, forest fires are becoming bigger and more common in tinder-dry lands, and mountain plants are taking advantage of the earlier melt and warmer temperatures to bloom sooner.
As those plants, like the prairie smoke, grow, they absorb more water, which they release into the atmosphere along with oxygen through small openings in their leaves called stomata while they take in carbon dioxide.
The process, known as evapotranspiration (ET), is not trivial. In the Colorado River Basin, 75% of the water comes from snow and nearly 80% of that ends up being soaked up by plants and released through leaves and evergreen needles.
This is where Steltzer’s work comes in. To better understand how much water will be lost to the air in a warmer world, she is creating an early snowmelt on plots of mountain meadows outside of Crested Butte – at elevations between 9,100 and 11,400 feet – and measuring how the plants behave and how much water they send skyward.
Steltzer’s work is part of a multimillion-dollar project sponsored by the U.S. Department of Energy and overseen by the Lawrence Berkeley National Laboratory called the Watershed Function Scientific Focus Area.
To understand the area’s hydrology, some researchers are drilling wells, some are making detailed snowpack measurements, while still others have installed gauges in the East River to record when and how much water makes it to the waterway as it heads to the Gunnison River and then on to the Colorado River.
“An overarching question is how mountain systems retain and release water,” said Kenneth Hurst Williams, who oversees the project for the Berkeley lab. “The East River watershed is emblematic of many Colorado River watersheds.”
The goal is to develop a model that can tell water managers how much water they can expect in a river based on snow depth, temperatures, groundwater hydrology, ET and stream flow – a tool that can be used on a year-to-year basis.
While in the first instance the project is focused on the here and now, Steltzer’s work to better understand how plants move water to the atmosphere has broader implications.
To peer into that future of a warming planet, scientists use earth system models (ESM), computer simulations that try to replicate the world’s physical, chemical and biological systems. One thing the models have trouble doing is simulating evapotranspiration.
“In an ideal world one would model every patch of dirt and every shrub or tree separately, with lots of details like soil properties, processes controlling stomata of leaves,” said Flavio Lehner, a research scientist at the Boulder-based National Center for Atmospheric Research, where he works on the center’s climate model.
“Evapotranspiration is also difficult to observe in the real world,” Lehner said. “The point is, we don’t have very good data to vet our models with.”
Steltzer’s findings might help calibrate climate models around the world, she said. “This is the coolest experiment I’ve ever been asked to do.”
Not suited for the sea or the jungle
As an undergraduate at Duke University, Steltzer thought she wanted to be a marine biologist. “I went to the Duke Marine Lab for a semester, and I got seasick every time I went on one of the cruises,” she said.
After her junior year, she worked on a research project in Costa Rica. “I could overcome the fear of insects and snakes that could kill me and the depth and darkness of the forest, but I couldn’t manage the heat,” she said.
Her next internship was at the Rocky Mountain Biological Laboratory in Crested Butte. There she found her scientific home. “I love the mountains, and I’m built for the cold,” Steltzer said.
Since earning a Ph.D. from the University of Colorado, Steltzer has done research in a string of cold places, always with the goal of prodding natural systems to see how they react.
In Northern Greenland, she was part of a team that took a cold, polar desert and warmed and wet it to see how much more willow, sedge and Arctic rose would grow and how much extra carbon the plants could pull from the atmosphere. The answer was not much.
On the Wyoming grasslands, she worked on a five-year project that heated test plots and released carbon dioxide through a series of pipes to see the impact of a warmer, more carbon-rich environment.
What the research team saw was a longer growing season, in large part because in the enriched carbon environment, plants did not need to open their stomata as much to get the necessary carbon dioxide and as result were able to conserve water.
And along a remote stretch of Imnavait Creek on the North Slope of the Brooks Range in Alaska, she conducted a three-year study using dark cloth spread over snow-covered areas to create an early snowmelt and measured, through a battery of sensors, the effects on the soils and plants, such as lingonberry, sedges and mosses.
Steltzer found that while the growing season begins earlier when tundra is snow-free and warmer, plant growth also ends earlier for at least some species, affecting tundra greenness in fall.
She is now working with researchers at Beijing Normal University to develop a snow experiment on the Tibetan Plateau.
Steltzer has taken her oldest son — she has boys ages 12 and 10 — with her to Alaska and says she hopes to take them both out into the field. “They are champions,” she said. “They have a mom who runs up mountains, and they come with me.”
Telling a good scientific story
On a late autumn day, Steltzer took a couple of her Fort Lewis students to check out her test sites along the East River. The lowest elevation plot sits at 9,100-feet, a few hundred yards from the East River in a broad-shouldered valley fringed with aspens and evergreen beneath the gray rock dome of Gothic Mountain.
At each elevation, there are three control plots and 32 foot-by-46 foot test plots, which get the black-cloth treatment Steltzer used in Alaska to generate an early snowmelt.
In March, when Steltzer and her crew unfurled the black fabric to absorb the sun’s heat and speed the melt, the low-elevation plots were under more than 4½ feet of snow.
At the lowest elevation there are about 35 different species of plants in the plots – lupine, sunflowers, yarrow and prairie smoke, although sagebrush dominates.
The test plots are tricked out with solar panels that power sensors, cameras and data loggers. Measurements are taken on soil moisture and temperature and on when the plots start to green and brown.
Crested Butte-based field staff also do almost weekly monitoring for the height, cover and biomass of the plants, as well as how much light they absorb and reflect.
Periodically, Steltzer places a “flux tent,” a clear, plastic cube, 2½ feet on a side, over patches to measure the moisture coming out of the soil and the plants, as well as the oxygen and carbon.
It takes five years of data to “tell a good scientific story,” Steltzer said. She has just finished the third year of her experiment, but already there are some signs.
The plants in these mountain ecosystems have evolved to accommodate the short growing season. “Some plants are genetically programmed to grow for a certain amount of time,” Steltzer said. “A bigger window means they’ve lost their niche. A lower elevation plant will come in that can take advantage of the longer growing season, and that could lead to more water being taken up by plants.”
Not far from her lowest elevation plots, the Rocky Mountain Biological Laboratory is finishing up a 30-year experiment in which electric heaters were suspended over an area of wildflowers and shrubs. The patch was transformed from meadow to sagebrush.
“We want to push the system to see how it moves,” Steltzer said. “But what I am doing is a tiny nudge … Now we have years with more extreme climate than I could ever create experimentally.”
“In each of these climate years we’re getting, we are learning so much,” she said. “Every year, it’s a roll of the dice, but it isn’t a six-side die anymore. It’s more like a 20-sided Dungeons & Dragon die.”
“But we can’t wait for 20 years of data to find out what the future holds,” Steltzer said. “That’s why we need models.”
The challenge for the modelers, like NCAR’s Lehner, is getting their creations to faithfully represent the real world, to reflect in equations what Steltzer documents prairie smoke is really doing in a meadow.
“For temperature, the story is now pretty clear: The big part of the warming we’ve seen over the last 50 years can be attributed to greenhouse gases,” Lehner said. “When it comes to precipitation, it becomes a little more difficult, and mountains and snowpack make it even more complicated.”
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