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Snow study: Researchers examine factors impacting Sierra Nevada snowpack

Claire McArthur / Tahoe Daily Tribune
The Sierra Nevada snowpack is a “water tower” for much of California and Nevada.
Provided/Claire McArthur

Eight of the top 10 warmest years on record occurred in the last decade. The snowline where rain turns to powder continues to move uphill. The dry season is longer than ever as wildfires ravage forests and communities. It’s a bleak outlook for the state of the Sierra Nevada snowpack, not to mention our planet as a whole. 

But for scientists in California and Nevada, it’s about digging in and uncovering the unknowns of the climate change crisis impacting the mountains that are responsible for a third of the Golden State’s water and, in conjunction with the Rocky Mountains-fed Colorado River, 85% of the Silver State’s supply. In knowledge, they say, there is hope.

RAINY WINTERS



For over 75 years, the Central Sierra Snow Laboratory, perched 7,000 feet atop Donner Pass, has been studying the Sierra Nevada snowpack. Established in 1946 by the U.S. Weather Bureau and Army Corps of Engineers, snow scientists have been manning the station collecting data on precipitation, snowfall, snow depth and air temperature ever since.

The current scientist responsible for the 2-acre property with instrumentation measuring wind speed, solar radiation, snow temperature and relative humidity, to name a few metrics, is Dr. Andrew Schwartz. Though the technology has progressed, Schwartz still treks out after each storm to take core samples just as his predecessors would have since the lab’s inception. 



“There’s always going to be planet and climate variability. There’s always going to be cyclical trends, especially with things like El Niño and La Niña that switch on the order every three to four years and do affect our weather a little bit. With that being said, we are seeing broader trends for sure,” says Schwartz. 

Most notably, says Schwartz, is that more precipitation is falling as rain instead of snow. October and May have already changed from being predominantly snow months to rain months, and November and April are following that trend. 

“The snowpack that we have is very beneficial because it is another means of storage, another reservoir or water tower on top of the mountain, that affords us the luxury of storage without needing any additional infrastructure,” notes Schwartz. “It really helps to have it in that frozen snow form rather than rain because it slowly trickles down in our streams. It allows for summer and fall usage in deep years.”

Scientists are studying a range of factors impacting the snowpack melt in the Sierra, from watermelon snow to wildfires.
Provided/Desert Research Institute

At the snow lab, and across California and Nevada, scientists are working to better understand the factors that lead to earlier and faster snowmelt in the Sierra, including rain on snow events that can lead to rapid melting and flash flooding down the Truckee River.

“We’ve had instances when there has been massive flash flooding in Reno after these types of rain on snow events because it can melt the snowpack very, very quickly,” explains Schwartz. “With the increase of rain in the winter months, these events are going to become more frequent so we really want to understand how rain affects the snowpack and why sometimes we get these massive flooding events and other times we don’t.”

WARMING HABITATS

Dwindling snowpack is taking its toll on the ecosystems of the Sierra Nevada that have evolved to survive with the same amount of snow year after year. Between 2002 and 2011, the snowpack in the Sierra was 100% or more of the historic average for six winter seasons. But in the last decade, it has only reached that marker twice. 

Like a canary in the coal mine, the American pika has disappeared from a 165-square-mile area of habitat in North Lake Tahoe, the largest pika die-off in the modern age. Warmer temperatures and a declining snowpack are to blame, according to a 2017 study. 

The snowline, where rain turns to snow, continues to move uphill in the Sierra Nevada.
Provided/Claire McArthur

A relative of the rabbit, the rodent-like mammal has adapted to survive in cold, snowy winters during which, unlike other high-elevation species such as the marmot, it does not hiberature. With a thick coat of fur and a furnace-like metabolic rate, the pika are vulnerable to overheating in warm weather.

The research team behind the study, led by biologist Joseph Stewart, searched for six years in the former habitat surrounding Mt. Pluto, finding old scat but no pikas. They believe the pika population died from hyperthermia or did not collect enough food due to the warmer temperatures and ended up starving or not reproducing.

Other studies have documented the disappearance of pika from the Black Rock Range in Nevada and Zion National Park in Utah.

By 2050, Stewart predicts that 97 percent of the habitat suitable for pikas in Lake Tahoe will become too warm for the rodents.

“It’s indicative of a very worrying trend. If we don’t reign in global warming pollution, about a million species or 15% of species on earth are vulnerable to extinction from climate change,” said Stewart at the time of the study’s publication. “I think the pika can be an ambassador species for species that are vulnerable to climate change.” 

STRESSED FORESTS

The forests of the Sierra Nevada are feeling the strain of a disappearing snowpack, too. 

“This is not just happening in the Sierra Nevada, but places all over the west,” says Dr. Anne Nolin, a professor in the Geography Department at the University of Nevada, Reno, with three decades of experience researching snow hydrology, climate change and mountain ecosystems. “As snowpacks continue to decline and the summer dry season now extends into November, we see that the forests are really moisture-stressed and that makes them vulnerable to a lot of things like insect infestations and, of course, fire.”

Using satellite images from NASA, Nolin has documented the “browning of forests” in areas where snow has disappeared.

A dwindling snowpack is affecting the health of the trees in the Sierra Nevada.
Provided/Claire McArthur

“When the snow is all melted from a certain pixel on the satellite image, you can really see the statistically significant relationship between that and the forests in those locations becoming browner over the last 25 years. Those are also places where we see the fires happening,” explains Nolin. 

These fires are bigger, more severe and burning into watersheds and seasonal snow zones, which is a new development. Case in point: The Caldor Fire in 2021, which burned its way up the Western Slope, cresting Echo Summit and entering the Tahoe Basin, leaving 221,835 acres scorched in its wake. 

In the burn scar of Caldor Fire, as well as previously torched forests around the west, Nolin and other scientists are studying the impact of wildfires on snow. The loss of the tree canopy exposes the snow to more sunlight. The snow, which usually reflects the sunlight, absorbs more of the solar radiation due to the black carbon falling from the charred trees. And as a result, the snowpack melts earlier and faster in these areas. 

“There’s a significant impact after the fire and that goes on for years,” says Nolin. 

The early melt-off is exacerbated by longer dry spells during the winter, which historically used to last 4-5 days but now stretch on for weeks. 

“We’re seeing mid-winter melt happening in places we wouldn’t expect it and at times when we wouldn’t expect it. The more winters we have with dry spells, the more the snowpack is going to melt earlier and disappear faster,” adds Nolin. 

CITIZEN SCIENCE 

Though the escalating climate crisis — and its impacts reaching far beyond the dwindling Sierra Nevada snowpack — feels overwhelming, the average citizen can make a difference. 

“One way that we can see hope is we can try to affect change through collective action. I always tell people that it’s good to do what you can do individually but you can only change so many lightbulbs,” says Nolin. “Collective action as it affects policy on a larger scale really does affect positive change when it comes to identifying strategies to reduce the impacts of climate change.” 

Supporting research projects that seek to better understand the changing environment in a warming world is another actionable way to support the planet. 

Last winter, an ongoing citizen science project examining pink algae blooms on snow branched out from the Cascade Range to the Sierra Nevada. The Living Snow Project studies the biodiversity of the algae that causes patches of snow to turn shades of red or pink, often referred to as watermelon snow, in an effort to understand its impact on snowmelt dynamics. 

“When the algae grows on snow, it darkens the snow surface, which increases the amount of solar radiation that’s absorbed and increases the rate of snowmelt,” explains Dr. Robin Kodner, an associate professor at Western Washington University where the project originated. “As we get concerned about rapid loss of snowpack, we may be seeing increases in snow algae blooms, which are this added threat to snowpack melt and glacier melt as we see the climate warm.”

Through The Living Snow Project’s smartphone app, people out skiing or snowshoeing can document the algae blooms they come across in their excursions by inputting its size, color and location. Kits to collect samples of the snow are also available for people at Alpenglow Sports in Tahoe City, Tahoe Mountain Sports in Truckee and Patagonia Downtown Outlet in Reno. The samples are mailed back to Washington for processing where the researchers hope to better understand how the algae is dispersed, among other questions. 

“When we sequence the DNA, it lets us know what algae species are present, which algae species coexist, and what other organisms are living with the algae,” says Kodner. “Do we see blooms at the same time each year? How long-lived are these blooms? Do we see them in the same places? A lot of this data that we get from observations from volunteers can help us address some of those questions in addition to the other work that we’re doing in our labs.”

Though watermelon snow is not an urgent concern in the Sierra Nevada like it is for the rapidly-melting glaciers in Greenland, it could be in the future as the snowpack melts faster and earlier than ever. 

“We are hoping for at least 10 years of data in order to see the signal through the noise,” says Kodner. “The environment is changing so rapidly, so even when we look back 5 years ago, some of the changes we’re seeing year to year are even more extreme now.”

Editor’s note: This article appears in the 2022-23 winter edition of Tahoe Magazine.


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