Measuring the mountain tap

As the world increasingly comes to grips with the realities of climate change, American scientists are setting up a first-of-its-kind research project to examine in detail how climate change will affect rain, snow, streamflow, and groundwater recharge in regions dependent on mountain snow and rain to provide water to farms and cities.

The project, called SAIL (Surface Atmosphere Integrated Field Laboratory), is located in the headwaters of the Colorado River, near the ski town of Crested Butte, Colorado.

Its specific purpose is to study the hydrology of the Colorado River, which provides water to parts of seven states and Mexico. But worldwide, says Lawrence Berkeley National Laboratory (LBNL), one of the agencies involved in the project, it isn’t limited to one river.

“It’s broadly applicable to locations that are dependent on mountain snowpack for water,” says Ken Williams, a geologist at LBNL who is the project’s lead on-site researcher.

It should, in fact, be particularly useful for Australians. “The Snowy Mountains Scheme in New South Wales is very, very analogous,” Williams says.

In fact, he says, “our base of operations is emblematic of Cabramurra,” one of the focal points of the Snowy Mountains Scheme. (Much as the Colorado River supplies water and hydroelectric power to seven states and parts of Mexico, the Snowy Mountains Scheme sends water to the Murray-Darling basin and provides hydroelectric power for the Australian Capital Territory, New South Wales, and Victoria.) 

The primary impetus for SAIL was the drought that has been afflicting California—which is also dependent on mountain rain and snow to water its lowlands. “That was a wake-up call,” says Daniel Feldman, the project’s principal investigator, also of LBNL. “It was clear that climate change is here and now.”

Also important was that long-term data have shown that the Colorado River has, on average, experienced a 10 percent reduction in water flow for every 1°C of warming. “We want to see if that holds [for the future],” Feldman says.

The result is an attempt to amass as much data as possible about a few thousand square kilometres of its headwaters, studying them in unprecedented detail over the course of two falls, two winters, two springs, and a summer, stretching from this month (the project officially began on 1 September) until mid-June 2023.

LBNL boasts of it as a “bedrock-to-atmosphere” project, and that doesn’t appear to be hype.

At the atmospheric level, says team member Alejandro Flores, a hydrologist at Boise State University,  Idaho, SAIL will use weather radar to monitor minute-by minute snow and rain patterns to see not only where, exactly, precipitation is falling, but how it is affected by the local terrain.

“We think of the mountains as gradually accumulating snow, but it’s really a half-dozen or a dozen large events,” he says. These large events, he says, are driven not just by things like the effect of sea-surface temperature on the amounts of moisture coming in from far away, but also by elevation, vegetation cover, and other location-specific factors.

“We can’t think of the atmosphere as being independent from the land,” he says. “SAIL is going to be a game-changer in terms of getting us the data we need. The radar system is going to enable us to see how individual events interact with landscapes.”

Feldman agrees. “One thing we don’t know,” he says, “is why does it rain or snow over this location, and not another. The ski resort [near Crested Butte] gets good snow. But ten miles north, the mountains receive twice as much at the same altitude. Why is that?”

Another part of the puzzle, says Jessie Creamean, an atmospheric scientist at Colorado State University, Fort Collins, who is also part of the team, is making on-site measurements of atmospheric aerosols—tiny particles that can be anything from pollen or dust to air pollution from upwind agriculture, cars and trucks, or industry.

These, she says, are important for three reasons: (1) they can absorb or scatter sunlight, thereby warming or cooling the atmosphere; (2) they can settle onto snow, dirtying it and increasing the amount of sunlight it absorbs, speeding up the rate at which it melts; or (3) they can serve as nuclei onto which water condenses to fall as rain or snow.

It’s the last of these that she’s most interested in, in the context of SAIL. “We are looking for insight as to how precipitation forms in the mountains,” she says. “It requires a seed to grow and form on, [and] these tiny aerosols can act as seeds.” Scientists have a general idea of how this works, she says, “but there are a lot of uncertainties.”

Much, she adds, seems to be unique to any given mountainous region: how the right combination of terrain, atmospheric moisture, and aerosols create “the perfect recipe for clouds and precipitation.” Figuring out how this works, and applying it to other mountain regions, is part of what SAIL seeks to puzzle out.

Also important, says Feldman, is learning how snow melts, and why it does so faster in some locations than others. “We are measuring the water going in, the water coming out, and all the things going on in the middle,” he says.

Williams compares it to monitoring your bank account. Snow in the mountains is like money invested in savings. Snow melting and running off is like withdrawing from that account. The goal is to know how much is left at the end of the water year, when winter arrives and the account starts to replenish. Without that knowledge, he says, water managers might allow people to do the equivalent of going on a “spending binge without having any concept of how much money is in your account.”

Related to this is a hidden part of this particular bank account: soil moisture and groundwater. That, Williams says, has been “one of the biggest issues we’ve seen in predicting water supply.”

One of the goals of the SAIL project, Feldman says, is to figure out how soil moisture, snowfall, snowmelt, and all the other factors that might affect the mountain-water “bank account” help determine the amount of water in the rivers so vital to those living downstream.

Puzzling this out is vital to figuring out what people across the world will need to do to brace themselves to contend with as the climate continues to change.

“Mountain watersheds provide 60 to 90% of water resources worldwide,” LBNL wrote in a press release announcing the project. “[B]ut … the best Earth system computer models struggle to predict the timing and availability of [their] water resources.”

The goal, the press release added, in an obvious pun, is to produce “mountains of data” that might help fill this gap.

But at the moment, Feldman says, hydrologists and other climate modelers don’t really know what they need in order to build better models to contend with a globally warming future.

“How much detail do we really need?” he asks. “Maybe we don’t need that much, but we’re trying to go overboard, not underboard.”