A record-breaking heat wave is heating up California, with major consequences for the state’s most important reservoir: its snowpack.
Providing nearly one-third of the region’s water, the Sierra Nevada snowpack is an important source of spring and summer runoff that refills the lakes when the state is most in need of water.
But a warm wet storm followed February’s snow, and now, March temperatures are breaking records – prompting warnings of rapid snowmelt and rushing rivers.
Historically, the snowpack is the deepest in April. But climate change is altering the previous flow, leaving less water coming down the mountains in warmer months for homes, farms, fish, electricity and forests.
“In an ideal world, you could have your lake full right now, and this huge lake of ice that we know will help fill and provide more water,” said Levi Johnson, operations manager for the Central Valley Project, a large water project that connects Northern California’s river water to the Central Valley and parts of the Bay Area.
This year, he said, “we won’t have that.”
California’s lakes are in good shape, full above historical averages with many nearby powers. But that summer snow bank on the slopes of the Sierra Nevada is disappearing early, and fast — down to 38% of average by mid-March across the country.
It’s still not the worst snowpack on record: That distinction is from 2015, when Gov. Jerry Brown stood on the brown, barren slopes of the Sierra Nevada to watch scientists measure the smallest ice pack in history.
But this year’s snowpack is quickly approaching the five worst on record for April 1, meteorologist Michael Anderson said — and it’s likely to get worse as temperatures rise. From early to mid-March, the snowpack has been disappearing at a rate of about 1% per day.
A quick departure from last year’s near-term conditions, it also presents both a challenge and a vision for the future of pool workers in the state.
Conflicting roles of dams
Most of California’s dams have a dual role: to hold back flood flows and to store water for future dry periods.
Those roles sometimes conflict — as they did in Lake Mendocino, which dried up to the point of mud during the 2012-16 drought. Strict federal operating rules forced the US Army Corps of Engineers to release critical water supplies from the dam to make way for the winter floods that never came.
The subsequent severe water shortages inspired a pilot partnership called Forecast Informed Reservoir Operations, between the Scripps Institution of Oceanography at UC San Diego’s Center for Western Weather and Water Extremes and state, federal and local agencies.
The program incorporates advanced forecasting and climate monitoring into lake discharge decisions in Lake Mendocino. It prevented the lake from drying up during the recent drought, according to Don Seymour, deputy director of engineering for Sonoma Water, which co-manages the dam.
Now, 100 miles away in the Sierra mountains, the Yuba Water Agency is looking to adopt a similar plan for New Bullards Bar, a lake about eight times the size of Lake Mendocino that is fed by Sierra snowmelt in the North Yuba River.
The reservoir supplies water to more than 60,000 acres of farmland in Yuba County and to users in the southern Delta. But the early melting of the snow complicates efforts to conserve that water.
“We’re seeing snowmelt conditions in mid-March that we don’t normally see until mid-May,” general manager Willie Whittlesey said. “It’s clear that the water flow – this is the melting of the ice – and it happened about two months in advance.”
The lake is almost full at 114% of the average for the day and 84% of the total capacity.
But when the snowmelt comes early, the agency can’t catch it once the reservoir reaches a certain level — even if there are no storms in the forecast at the time. Federal regulations require Yuba Water to maintain a certain amount of empty space until June to absorb potential flooding, according to Whittlesey.
Yuba Water is working with the US Army Corps of Engineers to revise the decades-old rulebook, Whittlesey said, but until then it must request a special permit to store more water.
Although the organization has received permission in the past, this year it is also faced with the rupture of the main pipe leading to one of the hydroelectric power plants, which forced the organization to store a lot of water behind the dam.
Whittlesey said he suspects that the combination of flood control and damage control needs after the pipeline failure could have cost tens of thousands of acres of snow to melting snow.
The California Department of Water, which manages Lake Oroville – the state’s second-largest reservoir – told CalMatters it is storing water above its normal flood control limits, with permission from the US Army Corps of Engineers.
In the Bay Area, the East Bay Municipal Utility District, California Municipal Utility District, which is the second largest urban water supply district in California, owns the Camanche and Pardee watersheds in the Central Sierra foothills.
“We’re working to save every drop in light from the warm temperatures we’re having right now, and because of all the subzeros we’re seeing in terms of rain or snow,” spokeswoman Andrea Pook said. “The last time we exit early is in 2015.”
Pook said the county is releasing less water from its lakes now, to save some for the fall when salmon migrate up the river to spawn.
“We’re tracking that we’re not going to be in a drought situation. But I’m not sure we’re going to fill our reservoirs by July 1, which is our general goal,” Pook said.
Improved predictions after big misses
Even as California suffers from record heat and premature snowmelt, the state is better prepared than ever.
For the past five years, state forecasters have been woefully short of predicting runoff — overestimating the amount of snowmelt expected to refill reservoirs by as much as 68%. Dry soil and dry air absorb runoff water before it flows into storage. Farms and towns were devastated during the drought as supplies fell far below expectations.
This year is different. Major reservoirs are already above historic averages, and early-season storms soaked the soil beneath the ice pack, making it less likely to absorb runoff.
The state was also working for better forecasts.
“Things have gotten a lot better,” said Andrew Schwartz, director of UC Berkeley’s Central Sierra Snow Laboratory, in an email to CalMatters.
Johnson, of the Central Valley Project, said the federal and state water supply systems are in a better place than they were five years ago, and that forecasts have not been more wrong since then.
But an early season thaw could still leave a gap.
“It’s going to be a good finish to the year,” said Johnson. “But it’s not as good as having an extra ice bucket ready to go in the summer, and fill it up to take it out.”
Advanced snowpack modeling and soil moisture measurements, experimental temperature measurements at various snow depths, university collaboration and weather forecast integration are helping, according to the Department of Water Resources.
Still, between the federal budget deficit and state cuts, challenges remain, Anderson said.
Efforts to install soil moisture sensors in national forests have led to the downsizing of the US Forest Service, which has laid off thousands of workers under President Trump.
“You wait in line for a long time,” Anderson said. “That was the biggest restriction of late. There’s nobody there.”
Rachel Becker writes for CalMatters.
