It begins at the height of winter in the mountains, when the landscape is particularly inhospitable. The surveyors arrive on skis, snowshoes, and snowmobiles. Some fly in by helicopter. Others travel the backcountry for days. When they arrive at their destination, there’s critical information to collect: the depth of the snowpack and how much water it holds. For regions confronting the effects of climate change, more and more hinges on the results.
“It all boils down to how much water makes it down into the reservoir,” said Sean de Guzman, chief of snow surveys and water supply forecasting at the California Department of Water Resources. De Guzman has it easier than some. Between February and May, around the first of each month, he drives to the Phillips Station snow course—a designated site for measuring the snowpack—located at around 6,800 feet (2,100 meters) of elevation in the Sierra Nevada. Once there, he manually inserts a tube into the snowpack, an instrument and method developed in the early 20th century by James Church, a professor at the University of Nevada, Reno who wanted to help put an end to local water wars by finding a way to estimate how much Lake Tahoe would rise in springtime. With the tube, de Guzman is able to measure the snowpack’s snow water equivalent, or the amount of water the snowpack contains at that location.
Today there are approximately 1,600 snow courses in the United States, with around 260 in California, primarily in the Sierra Nevada and the southern Cascades. Some date back more than a hundred years. Data from these locations, said de Guzman, represent the longest-running climate record in the Sierra Nevada. In the West, manual snow surveys are augmented by data from an automated snow telemetry (SNOTEL) network maintained by the Department of Agriculture’s Natural Resources Conservation Service that provides hourly snowpack measurements.
What these collective data tell snow surveyors, water resources managers, policymakers, and millions of people enduring water shortages, drought, flooding, and wildfires is that the snowball effect of climate change often begins, appropriately enough, with snow. And snow—how much falls, where and when, how much accumulates, and how quickly it melts—is changing.
“As a whole, over the last 70 years, we’ve seen a decline in snowpack,” de Guzman said. “With the warming temperatures and a warming climate, you can expect the snow-line—basically where that snow transitions into rain, and vice versa—to increase,” or climb in elevation.
Even when the snow survey data are relatively promising, other climate factors can inhibit a favorable outcome. At 59% of average on 1 April, California’s 2021 winter snowpack had more snow than was measured in any of the state’s 2012–2016 drought years. At the height of that drought in 2014, the snowpack on 1 April was at only 5% of average. And yet, de Guzman said, the 2021 snowpack yielded about the same amount of runoff as during those very dry years. “If you have more snow, you expect more [runoff], but that didn’t happen this year,” he said. The reason in part was that another low-rainfall year resulted in dry soil, which soaked up more of the runoff. “The snowpack was melting,” de Guzman said, “but the rivers weren’t rising.”
A Shrinking Season
There are different contexts and consequences across the United States, but all regions are struggling with rapid change. While the West grapples with water shortages amid severe drought, other parts of the country have become more vulnerable to extreme thunderstorms and flooding as more precipitation falls as rain rather than snow and as snowmelt occurs earlier in the spring. Increasingly, snow will also accumulate later in the season. An analysis by Climate Central showed that between 1970 and 2019, snowfall measured in 116 U.S. locations had decreased by 80% before December, and at 96 locations it had decreased by 66% after 1 March. But though historical data can reveal broad regional trends and patterns, they are becoming a less reliable forecasting tool as the warming climate throws snowfall patterns into disarray.
“The snow season is shrinking,” said Hans-Peter Marshall, an associate professor in the Cryosphere Geophysics and Remote Sensing group at Boise State University. But how much snow falls within that shortened seasonal window, he said, is difficult to predict. “The main thing we know is there’s going to be larger fluctuations, and the year-to-year variability is likely to increase.”
That variability includes the possibility of heavier snowstorms even as temperature averages trend upward. There’s no consensus on why warming has what appears to be a counterintuitive impact. According to Marshall, one reason the western United States might experience bigger storms is that a heated atmosphere can hold more water. In a warmer climate, water from the ocean could potentially make its way to the mountains, and more of that water might fall as heavy snow or torrential rain.
Meanwhile, warming Arctic temperatures may contribute to the kind of frigid blasts that reached as far south as Texas in 2021 (with catastrophic results) by disrupting the polar vortex, weakening the Northern Hemisphere’s polar jet stream and causing Arctic temperatures to dip south and warmer air to move north.
In the West, as the snow season shortens and the snowpack shrinks, so too does the water supply. In August, the federal government for the first time declared a water shortage on the Colorado River, a move that will reduce the amount of water allocated to Arizona and Nevada in 2022. (Mexico will also see a reduction in its share of the Colorado.) A continued water shortage will reduce water allocated to California.
“If you’re living in the West, you’re going to feel it,” said Amato Evan, an associate professor of climate sciences at the University of California, San Diego’s Scripps Institution of Oceanography. “In regions where the snowcap is vulnerable, like California, we’ve had year after year of 46 drought already,” demonstrating that the consequences are real.
The mountain snowpack, Evans said, acts as the state’s water bank for the year, melting slowly over the course of the summer and refilling depleted reservoirs. But snow that melts too early overwhelms reservoirs and can’t be captured and stored for use later in the year. And runoff that evaporates in warm, dry conditions or, as de Guzman described, gets absorbed into the earth before it reaches reservoirs, results in low water supply early on in the season.
A Recipe for Disaster
Both scenarios may have far-reaching consequences. In California, 2021’s lower than forecast runoff contributed to drought emergency proclamations being declared in May, for 50 of the state’s 58 counties, with state agencies directed to instigate a series of measures to conserve the water supply.
According to Marshall, the entities that decide how much water to release from dams must constantly estimate how much remains in the seasonal snowpack—decisions made more challenging by unpredictable snowfall. Though snow surveys and telemetry data provide accurate measurements for the area immediately surrounding snow courses and sensors, the data aren’t necessarily indicative of what’s happening between the sites. Currently, Marshall said, water managers might take a survey site’s 30-year average, compare it with streamflow over 30 years, and find the statistical correlation between the two. But that approach depends on a stationary climate, and these days, Marshall said, the current year is rarely representative of the past 30.
“As predictions get harder and harder in a changing climate,” he said, “we’re at this point where we need to make a paradigm shift, [and go] from just looking at individual sites and correlating them over the last 30 years to actually being able to estimate how much snow is everywhere on the landscape.”
Marshall and his group at Boise State are helping to fill in the data gaps by supporting NASA’s SnowEx campaign, which uses coordinated airborne and field experiments to determine the best combination of sensors for measuring snow globally from space. Current monitoring from space can tell scientists where snow cover is located but not how much of it there is.
“That’s one of the largest components of the water cycle that we just don’t have a very good handle on,” Marshall said.
When Marshall first began his work in Idaho in 2008, water managers showed less interest in new approaches than they do today. As the climate changes, weather events are altering the snowpack in unique ways, making reliable forecasting technology crucial for implementing decisions that affect water allocation for agriculture, water supply for communities, and flood forecasting.
According to de Guzman, incorporating forecasts into infrastructure operations, rather than relying on historical data, would enable water managers to better determine when to release water from reservoirs.
“A lot of the regulations and operations and maintenance manuals on how we operate reservoirs are built off old historical data,” de Guzman said. “So we’re operating old infrastructure in a changing climate, and that is a recipe for disaster.”
All Over the Map
In the Midwest and Northeast, less snowfall and more rain affect everything from agriculture, as farmers struggle with soil erosion, to the recreation industry, as the snow sport season shortens. In both cities and rural areas, increased rainfall and more frequent severe snowstorms will strain critical infrastructure systems and put vulnerable populations at risk.
In the Great Lakes region, warmer temperatures reduce ice cover on lake surfaces, leaving water open for lake-effect snowstorms. Increases in these storms in the short term could overwhelm snow and ice removal systems and affect roadways, buildings, and power lines. In the long term, as temperatures continue to climb, the air moving over the lakes will be warmer, and rain will fall instead of snow.
Abigail McHugh-Grifa is a founding member and executive director of Climate Solutions Accelerator of New York’s Genesee-Finger Lakes Region, which includes the city of Rochester where the nonprofit is based. McHugh-Grifa sees signs that the climate is changing. “Certainly we are already seeing the impacts of the weather just getting weirder and more unpredictable at all times of the year,” she said, adding that in the past few years, heavy snowfalls have quickly melted rather than accumulating. “It will dump a lot of snow on us and then melt and then dump a lot of snow on us and melt again. It’s just all over the map.”
Patterns can be difficult to tease out in an area like Rochester, where winter is the fastest warming season. The city has experienced a slight downward trend in snowfall over the past 50 years, with a more dramatic decline expected in the next 20–30 years, according to Climate Central meteorologist Sean Sublette in an interview for Rochester’s WROC TV. But in the short term, Rochester, like other Great Lakes communities, will likely see more lake-effect snowstorms, followed by warming springtime temperatures that can hasten snowmelt and lead to, among other changes, disruptions to the growing season.
For McHugh-Grifa, whose organization seeks to engage the community and public officials in mapping out solutions for adapting to climate change, getting leaders to recognize the urgency of the task can be the biggest challenge. “I wouldn’t say that any municipality around here is being bold enough or ambitious enough in their approach,” she said. “Even though we are seeing extreme weather conditions and other impacts of climate change, most local municipalities and community members aren’t making the connection yet.”
New York is a home rule state, meaning in short that municipalities have the autonomy to pass local laws. McHugh-Grifa believes that for public policies to shift toward climate adaptation planning, multiple municipalities must get on board. “If one municipality wants to go above and beyond, it’s challenging for them because there’s a real fear that, for example, if they…demand higher standards for building efficiency, then the developer is just going to go to the next town over.”
Without increased regional cooperation and collaboration on land use, transportation, and building codes, McHugh-Grifa said, policy planning for climate change adaptation will continue to stall. In part to respond to this challenge, Climate Solutions Accelerator uses a collective impact approach, working to convene partners, ensure that the voices of those most affected are represented, and develop a shared regional plan. “No one organization or one individual or one solution can possibly meaningfully address this problem, so we need this kind of massive coordinated response,” she said.
In many urban areas where snow, and winters in general, are predicted to transform in the decades ahead, climate action plans have been developed to set goals for reducing greenhouse gas emissions. Chicago, Boston, and Philadelphia are among the U.S. cities that have joined C40 cities; a global network of so-called megacities whose mayors have pledged to deliver on climate change goals. Ultimately, with sharply divided political positions among top elected officials, local leaders may have the largest influence on whether their cities can adapt quickly enough to meet the changing climate.
A Climate to Reckon With
In Alaska, one of the fastest warming regions on the planet, the effects of changing winter patterns—including snowfall, snowmelt, and permafrost thaw—will have wide-ranging ramifications for the state’s human and wildlife inhabitants. Many animals and native or migrating fish depend on snow, ice, and streamflow for habitat. Communities rely on snow for transportation and recreation and on snowmelt for hydropower. Uncertainties for such key industries as timber and fisheries contribute to economic vulnerability.
In northern coastal areas, Alaska Native communities that hunt for subsistence or migrate to work depend on the sea ice and permafrost—a layer of frozen ground—for survival. As the ice melts and the permafrost thaws and becomes less stable, villages may lose homes and other structures to flooding or erosion. Diminished mobility cuts off access to hunting and fishing grounds and isolates residents from emergency services. In some cases, the thaw has proven fatal.
“In the last couple of years, we’ve had at least a dozen people go through unstable ice,” said Amy Lauren Lovecraft, director of the Center for Arctic Policy Studies and a professor of political science at the University of Alaska Fairbanks. “It’s unimaginably tragic,” she said. “It’s the people who don’t produce or produce very little carbon emissions who are most impacted.”
And yet, Lovecraft said, current and past governors have been careful to avoid politically charged policies that directly address climate change, leaving it to villages and boroughs to take on the role of strengthening their communities. “In the absence of federal or state direction, it’s happening at the local scale,” Lovecraft said, adding that, in fact, these communities know best about how changes in snow affect them. “It’s not an entirely negative thing that it has to happen from the bottom up.”
Still, there is a role for the state to play, Lovecraft said, including setting parameters, spreading information, and backing local-scale projects that address mobility, housing, hunting, and other concerns. “It’s a matter of how smooth that transition could be,” she said.
As scientists continue climate research and refine technologies for accurate forecasts and measurements, communities will need to find support for applying new methods and data and implementing policies that address specific changes in their regions. But for some areas already deeply affected by changing winters, paradoxical weather events and the vagaries of snowfall patterns, winter storms, and snowmelt may hinder efforts to communicate the urgency of taking action.
Ultimately, the question for Alaska, Lovecraft said, isn’t whether the science on climate change is correct but, rather, whether it’s a message that anyone wants to hear.
“Does Alaska really want to face the pain of doing a transition that’s conscious, or do we ignore it? Eventually, we’re going to have to reckon with it.”
Korena Di Roma Howley (firstname.lastname@example.org), Science Writer
Howley, K. D. R. (2021), The changing climate’s snowball effect, Eos, 102, https://doi.org/10.1029/2021EO163185. Published on 24 September 2021.
Text © 2021. The authors. CC BY-NC-ND 3.0
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