As the climate continues to warm, more and more of the snow falling on California’s mountains will be replaced by rain. Already in recent decades, the snow season has shrunk by a month, according to one estimate, while snow levels have moved upward by 1,200 feet, according to another.
Scientists and water managers say that at some point California’s snowpack could simply disappear. This would leave the state without the crucial spring and summer melt-off that fills rivers and streams, nourishes plants and animals, and provides a huge chunk of the water supply. It would also be devastating for the ski industry.
This snowless future, according to a new study led by researchers at Lawrence Berkeley National Laboratory, could arrive in California’s Sierra Nevada in as soon as 25 years. The study is among many to detail the decline in snow, but it’s unique in synthesizing decades of research to nail down exactly when the snow might be gone. And it offers a timeline that is alarmingly short.
“Warming just doesn’t allow for snow to persist,” said Alan Rhoades, a hydroclimate research scientist at Lawrence Berkeley Lab and one of the lead authors of the paper. “Our one major goal was to identify how much time we have to roll out adaption strategies.”
Experts say that preparing for a Sierra with less snow won’t be easy, or cheap, but they agree it must be done.
The new study, published last month in the journal Nature Reviews Earth & Environment, projects that by the late 2040s, half of the area historically covered by snow in the Sierra will likely have “low or no” snow for five straight years, given current warming trends. By the late 2050s, it could be 10 straight years that the same area sees low or no snow.
The paper defines “low snow” as when snowpack — technically, the snow-water equivalent, or how much water the snow releases when it melts — falls within the lower 30th percentile of its historical peak. “No snow” is defined as when snowpack falls to or below the 10th percentile.
“It’s always shocking when I see the numbers,” said Rhoades, who grew up in California. “Snow has always been part of my life, since childhood.”
The study’s findings are based on a review of hundreds of scientific papers on snowpack, 18 of which contain quantitative projections. The authors looked not only at the Sierra Nevada but at the Cascades in the Pacific Northwest and parts of the Rockies.
In all of these mountain ranges, the study finds that at least half of the historically snow-covered spots will see low or no snow for five straight years by the 2060s, at the current rate of warming. By the 2070s, the same amount of area will see 10 straight years of low or no snow.
The Sierra Nevada is the first to be hit. The California mountains are more vulnerable because storm temperatures, moderated by the Pacific Ocean, are generally warmer.
Already, the Sierra has seen a glimpse of its future. In 2015, at the height of a five-year drought, state snow surveyors marched into the mountains on April 1, when snow is historically at its peak, and found mostly dry ground. Their gauges measured the snowpack at 5% of average, the lowest ever recorded in decades of surveying.
This year marked another grim milestone. While the April snowpack was greater, 59% of average, the melt-off from the snow was extraordinarily low because of how much water was absorbed by parched soils amid the current drought or lost to evaporation amid extreme heat. State officials said runoff efficiency, essentially a measure of how much snow makes it to rivers and reservoirs, was 20% compared to the usual 60%.
A primary concern about snow loss is the dent it puts in the water supply.
Much of the infrastructure that collects and delivers water in the state is conditioned upon having snow on mountaintops well into summer. Hundreds of reservoirs, including such giants as Shasta Lake and Lake Oroville, rely not only on storms for water during the wet winter months, but melting snow to provide another boost once the weather dries out in spring.
Without this spring and summer bump, as much as much as 30% of the state’s water supply could be lost.
“It’s hard to picture: thinking about a future where our kids and grandkids have little or no snow and what that means for our water resource,” said Erica Siirila-Woodburn, a research scientist at Lawrence Berkeley Lab and the other lead author of the new paper. “Our part in all of this is to put our science out there … to inform some of the policy.”
The authors framed their paper as a “call to action.”
While state water managers are generally aware of the problem, their response has been slow, especially relative to the new, more dire timetable for snow loss.
Some want to expand or even build new reservoirs so that more of the winter runoff can be captured in the face of the decline in spring and summer. One of the biggest proposals is Sites Reservoir, an off-stream storage project in Colusa County that would collect surplus water from the Sacramento River. Its estimated cost has varied from $3 billion to $5 billion.
The high price of these projects, as well as the need to protect fish and wildlife, have made them difficult to get off the ground. Also, most of the good spots for reservoirs have been taken.
Ellen Hanak, director of the Water Policy Center at the Public Policy Institute of California, who was not part of the study, said the state will have to pursue a range of initiatives to maintain adequate water supplies as the snowpack decreases.
One of the best investments, she said, is storing more winter runoff not just in reservoirs but underground.
“California is really well positioned to use aquifers in an active way by recharging them,” she said. “Some of our systems have been doing it for decades … and there’s a lot of interest in expanding groundwater recharge.”
Karla Nemeth, the director of the California Department of Water Resources, speaking at a virtual conference held by the Water Policy Center this month about water infrastructure, also advocated a multiprong approach to the future. Among the most important strategies, she said, is doing a better job both projecting California’s runoff and managing it.
“DWR is really redoubling efforts to improve our forecasting,” Nemeth said. “Foundationally, we need better information.”
In September, Gov. Gavin Newsom announced that several billion dollars of state money would go to drought resilience, including expanding water supplies.
A ballot measure proposed for next year, which supporters are still trying to gather qualifying signatures for, calls for even more money for water projects: 2% of the state’s entire general fund budget. Voters in 2014 approved a $7.5 billion water bond, much of which is still being spent on new supplies and storage.
Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@
sfchronicle.com Twitter: @kurtisalexander
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