Topic: Water Supply

Overview

Water Supply

California’s climate, characterized by warm, dry summers and mild winters, makes the state’s water supply unpredictable. For instance, runoff and precipitation in California can be quite variable. The northwestern part of the state can receive more than 140 inches per year while the inland deserts bordering Mexico can receive less than 4 inches.

By the Numbers:

  • Precipitation averages about 193 million acre-feet per year.
  • In a normal precipitation year, about half of the state’s available surface water – 35 million acre-feet – is collected in local, state and federal reservoirs.
  • California is home to more than 1,300 reservoirs.
  • About two-thirds of annual runoff evaporates, percolates into the ground or is absorbed by plants, leaving about 71 million acre-feet in average annual runoff.
Aquafornia news Los Angeles Times

State will deliver more water to Southern California this year via State Water Project

Southern California cities can expect to receive 50% of their full water allotments this year from the aqueducts of the State Water Project, up from 40% last month, as runoff from this year’s ample snowpack continues to fill reservoirs in Northern California. … Lake Oroville, the largest reservoir that feeds the State Water Project, is now 95% full and is expected to continue rising as snowmelt runs off the Sierra Nevada. The state Department of Water Resources said the reservoir could reach full capacity this spring for a third straight year. The state’s snowpack in the Sierra reached exactly 100% of average for the season April 4, the department said.

Other California water supply news:

Aquafornia news GV Wire (Fresno, Calif.)

Feds again bump up water allocation for many Fresno County farmers

The Federal Bureau of Reclamation is increasing the amount of water available for Fresno County farmers through the Central Valley Project dam and canal system. On Monday, the bureau said it would boost the allocation for south-of-Delta water users, including the Westlands Water District, to 50%, up from the 40% announced in March. Acting California-Great Basin Regional Director Adam Nickels said the increased allocation abides with President Donald Trump’s executive order increasing water for Central Valley farmers. 

Other California water supply news:

Aquafornia news NASA

News release: NASA tracks snowmelt to improve water management

As part of a science mission tracking one of Earth’s most precious resources – water – NASA’s C-20A aircraft conducted a series of seven research flights in March that can help researchers track the process and timeline as snow melts and transforms into a freshwater resource. The agency’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) installed on the aircraft collected measurements of seasonal snow cover and estimate the freshwater contained in it. … The Dense UAVSAR Snow Time (DUST) mission mapped snow accumulation over the Sierra Nevada mountains in California and the Rocky Mountains in Idaho. Mission scientists can use these observations to estimate the amount of water stored in that snow. 

Aquafornia news San Francisco Chronicle

Surprise atmospheric rivers, toxic seafood: How NOAA cuts could impact California

Coast Guard rescue missions failing after running into unexpected currents. Surprise atmospheric river storms flooding downtown San Francisco. Seafood contaminated by unseen algal blooms. California scientists fear these scenarios, and more, are possible under the Trump administration’s recommendation to reduce the National Oceanic and Atmospheric Administration’s budget by $1.7 billion. Several scientific programs in California are slated for significant reductions or elimination if the budget proposal is pushed through Congress. Scientists say the cuts would hamper weather forecasting, disrupt critical ocean data collection and decimate climate research.

Other NOAA news:

Aquafornia news Action News Now (Chico, Calif.)

New analysis shows Sites Reservoir’s water-capturing potential

The Sites Project Authority revealed that the Sites Reservoir could have captured more than 550,000 acre-feet of water from late November 2024 through early April 2025. According to officials, this amount of water capture could have benefited more than three million people. Fritz Durst, Chair of the Sites Project Authority Board of Directors, emphasized the reservoir’s potential. “Once again, we’re seeing how well Sites Reservoir would perform during wet periods if it were operational today, by capturing and storing water for drier periods,” Durst said. The analysis showed that the reservoir is designed to capture and store water during wet periods. It aims to increase water flexibility, reliability, and resiliency during drier times. In February 2025 alone, Sites could have diverted over 150,000 acre-feet of water. These diversions would add to the 850,000 acre-feet captured last season, nearly reaching the reservoir’s full capacity.

Aquafornia news Fox Weather

Mapped: What a barrage of 56 West Coast atmospheric river events looks like

… According to data from the Scripps Institution of Oceanography, 56 atmospheric rivers impacted the western U.S. during late 2024 and early 2025, with the majority affecting Oregon and Northern California. … Forecasters note that Northern California typically experiences about six strong atmospheric rivers every year, but by April 1, that number had already reached nine. This increase in storm system intensity and frequency led to above-normal precipitation levels, particularly in critical watershed zones, but, in contrast, Southern California saw very few significant storms, receiving only a handful of weak systems. As a result, precipitation totals in Southern California dropped to 70% or less of average levels through early March, setting the stage for an increasingly dangerous fire season. 

Aquafornia news Science News

Earth’s landmasses lost trillions of tons of water this century

Earth’s landmasses are holding onto a lot less water than they used to — and this loss is not just due to melting ice sheets. Terrestrial water storage, which includes water in underground aquifers, lakes, rivers and the tiny pore spaces within soil, declined by trillions of metric tons in the early 21st century, researchers report in the March 28 Science. This sharp decrease in freshwater stores is driven by rising temperatures on land and in the oceans, which in turn are linked to an increased global incidence of drought. And given the projected warming of the planet, this trend isn’t likely to change any time soon, say geophysicist Ki-Weon Seo of Seoul National University and colleagues.

Aquafornia news SFGate

Officials warn of ‘urgent invasive species threat’ in Northern California

Last October, an invasive species never before seen in North America was discovered in the deep waters of the Port of Stockton, about 92 miles east of San Francisco. No larger than the size of a paperclip, the seemingly innocuous, caramel-colored shells of golden mussels clinging to buoys and monitoring equipment in the Sacramento-San Joaquin Delta — and subsequently found at O’Neill Forebay in the San Luis Reservoir near Los Banos — have left California officials scrambling to stop the spread. On Wednesday, the California Department of Fish and Wildlife released its plan to address what it’s calling an “urgent invasive species threat,” with strategies to prevent further distribution of golden mussels and to minimize their impact on the environment, recreation, agriculture and, notably, drinking water infrastructure.

Related article:

Aquafornia news KSL (Salt Lake City, Utah)

Wintery weather makes a return, advisories issued

At least one more dose of winter is headed to Utah’s mountains while the state’s snowpack melts. After previously issuing a winter storm watch, the National Weather Service issued a winter weather advisory for Utah’s central and southern ranges, which could receive up to a foot of snow at its highest points by Friday night, as an incoming storm will likely impact those regions the most. Still, other mountain ranges in the state could pick up decent totals over the next few days. “(It’ll be) a good dose of water for our state,” said KSL meteorologist Matt Johnson.

Other snowpack news:

Aquafornia news KTLA (Los Angeles)

L.A. County remains ‘critically short’ on rainfall despite recent storms

It may feel like it rained a lot last year – and it did – but not enough to satisfy L.A. County’s critical shortage of rainfall, officials say. A news release issued Tuesday by Water for L.A. County indicates that the county captured nearly 12 billion gallons of stormwater over the past several months. Tuesday was the last official day of the storm season, which begins on Oct. 15 every year. But the 11.9 billion gallons of stormwater received are still not enough. … A “stark contrast” provided by officials was the fact that the 2023-24 storm season brought 21.2 billion gallons of stormwater to the region, which was enough to meet the water needs of 2.9 million people for an entire year, officials explained. The drop in rainfall highlights L.A. County’s water management challenges that are exacerbated by persistent drought conditions; thus, local legislators are looking to improve the system that supplies water to more than 9.7 million residents countywide. 

Aquafornia news Fox Weather

California reservoirs near capacity amid peak snowmelt season

A barrage of atmospheric river events that swept across California during the winter and spring has left the state well-positioned when it comes to water storage. As the peak of the snowmelt season begins to slow down, the majority of California’s major reservoirs are at least 90% full – a promising sign for a state that frequently battles drought and associated wildfires. Shasta Lake, California’s largest reservoir, was last reported to be at around 95% capacity, surpassing its historical average by 117%. The reservoir affects 35 California counties and plays a crucial role in managing water for the Sacramento and San Joaquin River watersheds. … Just as notable is Diamond Valley Lake, located about 80 miles southeast of Los Angeles in Southern California. According to data from the California Department of Water Resources, the water basin was at 97% of capacity and 128% above its historical average.  

Other water supply and snowmelt news around the West:

Aquafornia news KCRA (Sacramento, Calif.)

What the 8-Station Index tells us about California’s water situation

The 8-Station Index is compiled by the California Department of Water Resources as a tool to measure the amount of water that has fallen in the Northern Sierra. Measurements from the eight stations cover the watersheds of the Sacramento, Feather and American rivers during the rain season, which begins Oct. 1 and ends Sept. 30 the following year. During a dry season, the average precipitation can be as little as 20 inches, while the wettest season ever recorded was 2016-17 when 94.7 inches fell. This year, the index is at 53.6 inches, which is 118% of the season average to date and 101% of the season total. While the chance for additional rain or snow decreases through the rest of the season, more rain should add to these totals before the season ends. This is good news, considering most Valley spots are running below the average this season.

Other snowpack, water supply and drought news around the West:

Aquafornia news The Eyewall

Blog: Let’s talk about the Western U.S. and their water situation in 2025

It’s been a late season bonanza up north, with snowpack levels sitting at 120 percent of average north of Lake Tahoe. The central Sierra are a little less well-off but still close to normal. The southern Sierra have not had their best winter ever, but even still snow water equivalent is around 85 percent of normal. There have certainly been worse years in California. It’s when you get into the interior West that the problems start. Take Colorado. Their peak snowpack is likely to be the lowest since 2018. The northern part of the state has done well with near average snowfall this year. The Colorado River headwaters are also running near average, but southern Colorado, particularly the San Juan and Upper Rio Grande basins are in bad shape. Snow water equivalents are running about 60 percent of the median right now, or well, well below average. The story improves some in Utah, where the basins are a little noisier, but in general not in bad shape outside of southern Utah. Similar story in Wyoming and Idaho. Not great, not terrible. Oregon? Fantastic winter. Washington? Less so. But for Arizona and New Mexico, it was a dreadful winter.

Other snowpack and water supply news around the West:

Aquafornia news The Salt Lake Tribune (Utah)

Wednesday Top of the Scroll: Here’s why 3 decent winters in a row still isn’t enough to fill Lake Powell

Over the last three years, the Colorado River Basin has experienced three relatively healthy winters. But that decent snowpack, after melting, hasn’t filled reservoirs like Lake Mead and Lake Powell as much as water users across the West might like, due to years of drought and overuse. Recent forecasts show Lake Mead and Lake Powell will remain roughly one-third full after snow melts down from the mountains across the West into the Colorado River and its tributaries this year. … This year’s lackluster forecasted runoff into Lake Powell coincides with tense political negotiations between the seven states that use Colorado River water: Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming. 

Other water supply and snowpack news around the West:

Aquafornia news SFGate

Tuesday Top of the Scroll: Calif. reservoir levels are ‘well-above average’ before dry spring

Nearly all of California’s major reservoirs are fuller than they were in previous years after a wet and stormy winter. … The state’s largest reservoir, Lake Shasta, is at 92% capacity as of Sunday, which amounts to 115% of its historical capacity for this time of year, according to data from the California Department of Water Resources. The lake is at a surface elevation of 1,055 feet, according to data from the U.S. Bureau of Reclamation, a continuation of rising water levels since the holiday season’s heavy downpours. (Shasta Lake is considered full at 1,067 feet, according to Lakes Online, a website that records lake data.) The season’s rains also have filled California’s other large reservoirs, including Lake Oroville and Trinity Lake, which are now at at 90% and 87% capacity, respectively. If Oroville surpasses 100%, it would be the third straight year the reservoir has hit capacity.

Other water supply and snowpack news around the West:

Aquafornia news KLAS (Las Vegas, Nev.)

Snowpack at 90% of normal as ‘lean’ year projected for Southern Nevada

… Current snowpack levels in the Upper Colorado River Basin hit 90% of normal on Friday. The region includes parts of Colorado, New Mexico, Utah and Wyoming, providing the runoff that collects in reservoirs along the river and eventually reaches Lake Powell and Lake Mead. And 90% is better than where snowpack stood on Monday, when it had declined to 86%. It’s been a volatile end to winter, with big swings rather than a steady increase to peak levels. Snowpack measurements — SWE, or snow water equivalent — generally peak the first week of April, when temperatures warm and more snow melts than new accumulation from snowfall.

Other snowpack and runoff news around the West:

Aquafornia news ABC10 (Sacramento, Calif.)

California snowpacks reach 99% of April 1 average

Water years in California can be all over the place with massive years immediately followed by major droughts. It’s been described as hit and miss, but rarely do you get a hit-hit-hit situation in one key metric for water in the state: snowpack. Snowpack is highly variable since it’s a component of water and temperature. You can have big snowfalls followed up by warm and dry conditions, then by early spring when snow melt and runoff is most important, some of the snowpack may be already gone. … This water year is unique since most of the snow has yet to melt and already California reservoirs as a whole are well above average at 115%. … Many lakes are nearly 90% full with many months of runoff and inflows to come. Reservoirs in the Central and Southern Region are not quite as full, but still remain above average or at least close bringing more good water news to the rest of the state.

Other snowpack and water supply news around the West:

Aquafornia news SJV Water

Order that had kept water in the Kern River reversed by 5th District Court of Appeal

In a wide-ranging ruling that could have larger implications for public interest lawsuits throughout California, the 5th District Court of Appeal reversed a preliminary injunction that had required water in the Kern River through the heart of Bakersfield. … Bring Back the Kern, Water Audit California and several other public interest groups sued the City of Bakersfield in 2022 for dewatering the river. They are demanding the city study the environmental impacts of its river operations. That lawsuit is set for trial in December. The preliminary injunction was an outgrowth of that 2022 lawsuit. It was an attempt to keep water in the river for fish that had come teeming back with high flows in 2023. The 5th District’s ruling, issued Wednesday, reversed the injunction but didn’t close the door to a possible future injunction and, in fact, gave lengthy direction for how that could be done.

Related article:

Aquafornia news Record Searchlight (Redding, Calif.)

Thursday Top of the Scroll: Lake Shasta level goes up 18 feet in March after strong rain year

California is only halfway through the rain year, and in Redding’s case, the rainfall and snowfall amounts exceed what the area typically receives in total precipitation, making 2025 one of the wettest years since 2019. …Wet winter storms left waters in California’s largest reservoir, Lake Shasta, less than 16 feet from the top on Tuesday. Precipitation in March pushed the lake level more than 18 feet, according to data from the California Department of Water Resources, boosting the top almost as high as Shasta Dam was after torrential rains in early February. It is expected the lake may be full by end of May.

Other snowpack and water supply news:

Aquafornia news The Mercury News

Wednesday Top of the Scroll: Sierra Nevada snowpack sees most bountiful three years in a row in 25 years

In a much-needed break after multiple years of severe droughts over the past two decades, California’s statewide Sierra Nevada snowpack, which provides nearly one-third of the state’s water supply, was at 96% of its historical average on Tuesday, up from 83% a month before. The April 1 reading, considered the most important of the year by water managers because it comes at the end of the winter season, follows two previous years when the snowpack reached 111% of normal on April 1 last year and 237% in 2023. Although Tuesday fell just short of a third year in a row above 100%, together the past three years represent most bountiful three-year period for the Sierra snowpack in 25 years. The last time there was this much snow three years in a row came in 1998, 1999 and 2000.

Other California snowpack and water supply news:

Aquafornia news The New York Times

‘Robust’ storm brings snow to Sierra Nevada

Significant snow falling in the Sierra Nevada over the next few days could be the region’s last big snow dump of the season, showcasing a dramatic rebound for the snowpack that provides a significant portion of California’s water reserves through the rest of the year. Snow started falling in the Sierra Nevada, the California mountain range that straddles the state’s border with Nevada, on Sunday, and plenty more is expected through Tuesday. Elevations above 4,000 feet are expected to record one to four feet of snow, while the highest peaks over 8,000 feet could pick up five feet.

Other California snowpack and water supply news:

Aquafornia news CalMatters

Monday Top of the Scroll: CA’s snowpack is near-average — what this means for water supply

Despite some heavy rainstorms and squalls of snow in recent months, the Sierra Nevada snowpack today stands at 90% of average, according to state officials. This year’s measurements mark the first below-average snowpack since 2022, when it dropped to a dismal 38% of the historical average. Last year at this time, the statewide calculation reached 110% of the average, and in 2023, the snowpack was one of the largest ever, measuring more than twice the average. More snow is on the way, however, which could make this year right around average.

Other snowpack and water supply news:

Aquafornia news Action News Now (Chico, Calif.)

PG&E conducts snow survey in Lassen Volcanic National Park to determine snow melt potential for hydroelectricity

On Tuesday, a crew from Pacific Gas & Electric took to the skies in a helicopter to access a remote part of the Lassen Volcanic National Park for their snow survey. PG&E, which is dependent on the snow melt to help generate hydroelectricity around the state of California, conducted the survey to help predict just how much snow melt is expected in the coming months. … At the conclusion of the survey, PG&E says that crews measured 119 inches of water content at the measurement location in Lassen Volcanic National Park, which is 11 percent above average for this time of the year.

Other snowpack and water supply news:

Aquafornia news The Colorado Sun (Denver)

Southern Colorado faces “dismal” snowpack ahead of spring runoff

The pressure is on: Colorado’s average snowpack statewide masks worrisome water conditions in the south, where water providers are banking on more storms to boost water supplies before snowmelt begins in April. Much of Colorado’s annual water supply is stored in its winter snowpack, which builds up until early April when it melts and flows into soils, streams and reservoirs. Statewide, Colorado is headed toward that April 8 peak with 92% of its normal snowpack for this time of year. … The Colorado Headwaters Basin, where the Colorado River begins; the Yampa-White-Little Snake combined basin, which supplies Western Slope communities in the northwestern corner of the state; and the South Platte Basin, which feeds rivers on the Front Range, are all in good condition.

Other snowpack news around the West:

Aquafornia news Action News Now (Chico, Calif.)

Wednesday Top of the Scroll: California Department of Water Resources announces increase to State Water Project allocation

The California Department of Water Resources announced Tuesday that the wet and cold storms that moved through California during March have allowed for another increase for the State Water Project allocation forecast for 2025. Officials with the DWR say that the allocation has been increased to 40 percent of the requested water supplies, which is a 5 percent increase for the 35 percent allocation in February. The latest allocation forecast is based on increases in precipitation, snowpack, and reservoir storage in the past month. The DWR says that the allocation increase comes ahead of the April 1 snow surveys taking place (this) week, when the snowpack in the Sierra Nevada typically peaks.

Other California water supply news:

Aquafornia news Los Angeles Times

Southern California is heating up. How long will the high temperatures last?

… Despite some recent rainstorms, the majority of Southern California remains in “severe” or “extreme” drought conditions, as of the latest report from the U.S. Drought Monitor. Precipitation for this water year, which begins Oct. 1, is still well below average for the southern third of the state. In coastal areas, rainfall amounts are about 40% to 60% of average for this time of year; in the state’s most southwestern corner, it’s even lower, according to California Water Watch. While Northern California’s precipitation and snowpack are above average for the year, the Southern Sierra still remains at about 87% of average for this time of year, according to the California Department of Water Resources. 

Other drought and snowpack news:

Aquafornia news KLAS (Las Vegas, Nev.)

Snowpack reaches 97% of normal, but drought hanging on in desert Southwest

Recent snowstorms in the Colorado Rockies have helped elevate snowpack levels as the calendar turns to spring. About two weeks remain to build up snowpack ahead of what climate experts say will be another dry year in the desert Southwest. A report released on Thursday by the National Oceanic and Atmospheric Administration (NOAA) forecasts a greater-than-50% chance that the drought will persist through the end of June. The affected area includes Southern Nevada, Southern California, Southern Utah, all of Arizona, and southwest Colorado.

Other snowpack and water supply news:

Aquafornia news San Francisco Chronicle

Where California reservoir levels stand after recent storms

Steady storms continued to benefit California in March, with reservoirs across the state gaining 200,000 acre-feet of water from the beginning of the month to Tuesday — that’s enough  to fill 100,000 Olympic-size swimming pools. Across California, reservoir storage is well above average for this time of year, according to the Department of Water Resources. Statewide storage was 115% of normal, as of Tuesday. … California’s largest reservoir, Shasta Lake, was at 86% of its total capacity on Thursday, or 113% of normal for this time of year. … Lake Oroville, the state’s second-largest reservoir, received some 30 billion gallons of water, with water levels rising by more than 6 feet. … The statewide snowpack is 93% of normal for this time of year, as of Monday.

Other water supply and snowpack news around the West:

Aquafornia news Ventura County Star

Water spills from Lake Casitas for first time since 1998

A steady stream of water spilled from Lake Casitas Friday, a few days after officials declared the Ojai Valley reservoir had reached capacity for the first time in a quarter century. Just two years earlier, the drought-stressed reservoir, which provides drinking water for the Ojai Valley and parts of Ventura, had dropped under 30%. The Casitas Municipal Water District was looking at emergency measures if conditions didn’t improve, board President Richard Hajas said. Now, the lake is full, holding roughly 20 years of water.

Related article: 

Aquafornia news The Associated Press

Tuesday Top of the Scroll: Study says California’s 2023 snowy rescue from megadrought was a freak event. Don’t get used to it

Last year’s snow deluge in California, which quickly erased a two decade long megadrought, was essentially a once-in-a-lifetime rescue from above, a new study found. Don’t get used to it because with climate change the 2023 California snow bonanza —a record for snow on the ground on April 1 — will be less likely in the future, said the study in Monday’s journal Proceedings of the National Academy of Sciences. … UCLA climate scientist Daniel Swain, who wasn’t part of the study but specializes in weather in the U.S. West, said, “I would not be surprised if 2023 was the coldest, snowiest winter for the rest of my own lifetime in California.”

Related snowpack articles: 

Aquafornia news The Salt Lake Tribune

Opinion: Moab unites to fight a floodplain development

Moab is a growing town of 5,300 that up to 5 million people visit each year to hike nearby Arches and Canyonlands national parks, ride mountain bikes and all-terrain vehicles, or raft the Colorado River. Like any western resort town, it desperately needs affordable housing. What locals say it doesn’t need is a high-end development on a sandbar projecting into the Colorado River, where groves of cottonwoods, willows and hackberries flourish. “Delusional,” shameful” or “outrageous” is what many locals call this Kane Creek Preservation and Development project.
- Written by Mary Moran, a contributor to Writers on the Range

Aquafornia news The Sacramento Bee

Wednesday Top of the Scroll: Red alert sounding on California drought, as farmers get less water

A government agency that controls much of California’s water supply released its initial allocation for 2021, and the numbers reinforced fears that the state is falling into another drought. The U.S. Bureau of Reclamation said Tuesday that most of the water agencies that rely on the Central Valley Project will get just 5% of their contract supply, a dismally low number. Although the figure could grow if California gets more rain and snow, the allocation comes amid fresh weather forecasts suggesting the dry winter is continuing. The National Weather Service says the Sacramento Valley will be warm and windy the next few days, with no rain in the forecast.

Related articles: