Molly Samuel

In January of this year, snow was still sparse at high elevations in the Sierra Nevada.

Researchers from the Department of Water Resources conducted their April manual snow survey today. It’s the most important snow survey of the season, because it’s supposed to capture the Sierra snowpack at its peak. The DWR found that statewide, snow water content is 55% of average for this time of year.

Still, it could have been worse. The previous manual snow survey, which took place on February 28, measured snow water content at only 30% of normal for that date. So the rain in March did help.

“This was certainly a moderately good March at least,” Jeanine Jones, the Interstate Water Resources Manager at the DWR told me. “But the downside is that we are now getting outside of our peak precipitation window. On average about 75% of statewide precipitation comes between November and March.”

In November, the DWR estimated it would be able to deliver 60% of the water the State Water Project requested. But once the dry winter set in, the DWR brought the allocation down to 50%. A press release (PDF) from the DWR says a 50% allocation is “not severely low.”

“So actually what this wet March really did was save the larger water projects from having to lower their allocations even further,” Jones said.

And, thanks to last year’s very wet winter, the state’s reservoirs are in good shape. But Jones warns they’re not in such good shape that the state will be able to fend off water-supply problems if next winter is anything like this one.

“So really the message for people now is to think about planning for what if 2013 is dry.”

There’s one more manual snow survey, at the beginning of May. Following that one, the DWR will release its final runoff forecasts for the year.

John Huseby

Heavy rain flooded the parking lot at San Francisco's Ocean Beach over the weekend.

California’s water supply is in better shape after this weekend’s storms and the wet weather earlier in the month (though the parking lot at San Francisco’s Ocean Beach is in worse shape). The water content of California’s snowpack is hovering around fifty percent of what’s considered “normal” for this time of year — not quite cause for celebration but much better than it had been; on February 28, the date of the most recent manual snow survey, water content was only 30% of normal.

So this winter isn’t going to be the driest on record, or even the second-driest, but it’s bound to be on the dry side, regardless of what happens now. It’s just too late in the year to catch up, even with more storms heading our way this week.

Department of Water Resources

In Northern California, this year, shown in pink, was dragging along near the driest years on record, but precipitation has been better in the last month.

So far, Northern California’s had more precipitation than the Southland but the National Weather Service is forecasting more widespread rain and snow beginning tonight.

California Department of Water Resources

In Southern California, precipitation is at 55% of normal for this time of year.

Most of the state’s reservoirs are near normal levels for this time of year — some are even above normal — thanks to the very wet winter last year.

The upcoming “April 1st” snow survey (actually scheduled for next Monday, the 2nd), is closely watched, as this is the time when the Sierra snowpack generally reaches its peak.

Craig Miller

Frank Gehrke conducts a manual snow survey using a "Mt. Rose gauge," essentially a hollow aluminum tube shoved into the snow at predetermined locations.

In California, where most of our water comes from the mountains, being able to accurately measure the snow pack is vital. And it is in outlier years like this — very dry years, though the same goes for very wet ones — when water managers have the hardest time making accurate predictions.

“Knowing the water content of the snow in an entire watershed is the holy grail for snow scientists,” survey guru Frank Gehrke told me.

During the winter, Gehrke trudges into the woods on a monthly basis to do manual snow surveys for the state Department of Water Resources. DWR uses remote snow sensors, too. But even with all that data we don’t get an exact picture of the snow pack. So scientists from National Center for Atmospheric Research (NCAR) and NASA Jet Propulsion Laboratory (JPL) are developing tools to measure snow with lasers. This new technology has the potential to be that holy grail that Gehrke’s looking for.

At NCAR, scientist Ethan Gutmann is working on a stationary laser instrument. His prototype in the Rocky Mountains is installed on a pole in a snowfield. It sends out light pulses, which bounce off the snow and back to the instrument, which then measures the depth of the snow based on the time it takes for the light to come back. The tool isn’t measuring snow on a watershed-scale yet, but Gutmann says that’s a matter of cost, not of technology.

Ethan Gutmann, NCAR

Gutmann's laser tool reveals the features of a snow field above the treeline of a mountain in Colorado.

“The laser system is expensive, but easy to use,” he told me. He’s hoping as the technology improves, these kinds of tools will become more affordable; water agencies will be able to install the stationary instrument in snow fields and get results in real time.

Here in California, DWR is working with JPL on developing the technology to measure snow with lasers from airplanes. These airborne surveys don’t provide the accuracy and continuous data that the stationary tool provides, but they will be able to measure a much larger area. There’s preliminary work now on the Upper Tuolumne River Watershed, which feeds the Hetch Hetchy reservoir. Gehrke says the need baseline measurements without snow, so they’re planning prototype flights in late-July, then plan to fly over the snow beginning in 2013.

There are drawbacks to lasers. They can’t see through most trees, so the technology is most effective above the treeline (the highest elevation where large trees grow). And lasers can only measure the depth, not the water content, of snow. Gutmann said that’s not a deal-breaker, since depth measurements will be so much more accurate than they are now, over a larger area. The key for Gehrke will be combining the technologies. He told me the stationary and airborne lasers complement each other, and when combined with the tools he’s already using, he’ll get a better picture of the snow pack than ever before.

NOAA

How do you define a "drought?"

As state surveyors trudge into the mountains this week for the season’s second official survey of the Sierra snowpack, the auspices aren’t good. Remote sensors currently show that statewide, water content is averaging just 38% of the average for this date, and less than a quarter of what water managers would hope to see on April first — just two months away.

Consequently, the “D-word” is being nervously bandied about. Are we in a drought?

The state’s newly revamped Current Water Conditions website takes on the question with a definitive “Yes and no.” Drought status, it says “can be very different depending on your location.”

Matthew Heberger agrees. An analyst for the Oakland-based Pacific Institute and co-author of The World’s Water (Vol. 7), Heberger told me in a recent interview that it “absolutely depends on your perspective.” And that perspective is ruled by more than geography.

“I’m a hydrologist by training, so for a hydrologist, a drought would be reflected in changes in the natural environment,” he explained. “So, changes in ground water levels, lake levels, stream flows, things like that.”

Heberger went on to offer some other perspectives:

• “You have a different perspective if you’re a water manager; you care really about what’s the water level in the reservoir.”
• “An aerologist [atmospheric scientist] might define it based on rainfall levels.”
• “An agronomist interested in agriculture would say a drought is when soil moisture levels are below what you need to grow healthy crops.”

I’ll add that suburban homeowners might say it’s a drought when they’re told they can’t water their lawns. “So yeah,” agreed Heberger. “There are a bunch of different definitions for drought out there.”

It is perhaps because experts agree on the highly subjective nature of drought, that few of them seem willing to commit and say if we’re in one (or not). But most seem to agree that time is running out on the catch-up clock.

According to the Department of Water Resources, “the three-storm series that began January 19 added nearly seven inches to the northern Sierra precipitation for the year.” That brought average precipitation for the season from a dismal 30% of “normal” to more than half the average. Snow pack catapulted from 10% to 33% of average, an impressive leap from a few wet days. But there’s been little or nothing to show since then. And as the “wet season” withers, the odds portend another summer of thirsty crops, possible restrictions on urban water use, and a general increase in the number of people declaring a “drought.”

Sasha Khokha

A tree at the Fresno County pilot project adorned with sensors

Researchers at UC Merced are set to open a whole new window on the Sierra Nevada. Using two million dollars from the National Science Foundation, hydrologist Roger Bales and his colleagues can now expand on a pilot project to measure the mountains’ “vital signs.”

Bales says beginning next summer, he, UC Berkeley’s Steven Glaser and their team will start installing a network of 20-to-30 instrument clusters throughout the American River watershed, casting a watchful eye over about 2,000 square kilometers that typically gets snow cover. The instruments record factors that affect the mountain’s hydrology, such as temperature, humidity, soil moisture, stream flow and even how much solar radiation penetrates the tree canopy.

Bales says the pilot phase has taught them how to put together a network of wireless sensors that will endure the extreme alpine conditions and still remain reliable (see Sasha Khokha’s post and slide show from March).

But the work has also produced some meaty data. Bales says the pilot network has already revealed that evapotranspiration (water lost to the atmosphere through evaporation and plants) in the Sierra’s mixed conifer forests is about 20-to-30% larger than previously thought. More evapotranspiration means less runoff for farms, cities and hydropower.

“If we extend the growing season by having a warmer climate, there’s the potential for even more evapotranspiration,” Bales told me. Knowing how to better predict such aspects of the “water balance” should yield better forecasts for how much water we can expect to squeeze out of California’s “frozen reservoir” each summer.

“Part of it is not knowing the physical system out there,” Bales told me in an interview. “My position is that you can’t model your way out of these uncertainties. You need data.”

Bales’ goal is to build more than a “research platform,” but a system that will provide water managers and others with usable real-time information, accessible over the Internet. He’s already teaming up with Sacramento’s municipal utility (SMUD) and the state Department of Water Resources on some of the field installations, and says he’s hopeful that NASA’s Jet Propulsion Lab in Pasadena will provide an additional layer of satellite data to track snow cover.

A new study finds large losses of springtime snow cover in the West in recent years, raising concerns about water supplies.

Spring snowpack in the West is an essential water resource, particularly in Southwestern states that are prone to summer drought, like California, Nevada, Arizona and New Mexico. (Credit: Wolfgang Staudt on Flickr)

Head south across the 40^th parallel, however, and things are dramatically different. While there is still above average snow throughout the Sierra, a relatively snow-less winter and spring has left much of the Southwest in a drought that has fostered record wildfires. Already local officials are worried there won’t be enough water to get through the summer months ahead.

This kind of contrast for the western spring snowpack is not unusual, though. It’s completely normal, and it’s exactly what climate scientists and meteorologists expect during years when the average weather pattern is influenced by La Niña, a climate cycle associated with cooler than average water temperatures in the tropical Pacific Ocean.

But while this north-south dichotomy turns out to be a regular feature of western climate, new research published today in the journal Science shows that, when compared to typical snowfall during the past 1,000 years, snowpack patterns appear to be changing as average temperatures climb. Scientists say that as temperatures continue to rise, this reduced snowpack will lead to more frequent water shortages in increasingly thirsty western states.

“We’re talking about simultaneous snowpack decline in the western watershed that supports 70 million people,” says U.S. Geological Survey (USGS) climatologist Julio Betancourt, who co-authored the new study. “We have to be concerned.”

For several years, scientists have observed that spring snowpack all across the West — in both northern and southern areas — has been decreasing. But now, Betancourt and a group of other climate scientists have found that the recent decline is a departure from patterns of the past 1,000 years. As part of the study published in Science, USGS ecologist Greg Pederson investigated tree ring data to learn how snowpack in the West, on either side of 40^th parallel, changed from year-to-year and from decade-to-decade. Looking back over nearly a millennium, he found that when the north had high snowpack, the south typically experienced low snowpack, and vice versa.

But Pederson and Betancourt noticed a change starting in the mid-1980’s. On average, the amount of snow on the ground at the beginning of April each year was decreasing everywhere across the West. It’s a trend that other scientists studying snowpack have pointed out. This has important consequences for water supplies for drinking water and agriculture, since many areas, including much of interior California, are dependent upon spring runoff for much of their water supplies.

Betancourt says that as average spring temperatures have risen, the snowpack has begun to melt earlier in the year (not the case this year, with record cold weather locking in substantial amounts of snow in many western ranges). Moreover, he says that in many places, the warmer temperatures mean that precipitation falls more as rain than as snow. So while the actual amount of precipitation hasn’t changed dramatically, the amount of rain has.

Snowpack in much of the West remains well above average, thanks to a cold and snowy winter and spring. In the Southwest, however, snowpack was well below average. (Image: NRCS)

“Snowpack is the water resources of the West,” says Greg McCabe, a USGS hydrology expert who was not directly involved in the new study, “and temperature has a dominant impact on the snowpack.” If warming temperatures in the West cause the snowpack to decrease even more, McCabe says, or if the timing of the melt each spring changes, then summer water shortages could happen a lot more often.

McCabe says the research provides valuable evidence about how snowpack has changed historically, and also how unusual the recent patterns appear to be.

According to Pederson and Betancourt’s findings, the way snowpack has changed in the past 30 years isn’t entirely unprecedented. There were two brief periods in the mid-1300’s and early 1400’s where there was less snow built up throughout the West.

“At both those other times in the past, we know it was warm then too,” explains Betancourt.

Now, however, climate scientists are predicting that average temperatures in the West are going to keep rising this century, due in large part to the buildup of greenhouse gases in the atmosphere. Compared to the past, when snowfall returned to normal as temperatures dropped, researchers now expect that warmer spring weather could keep spring snowpack on the decline for years to come.

“What’s happening in the spring for snow is critically important [for water availability] compared to what is happening in the dead of winter,” says Betancourt.

So what do the authors make of a year like this, which has brought frequent snowfall to the Sierra, even into June?

“There isn’t anything that has happened this year that isn’t consistent with what our new findings are,” says Pederson. Even as average temperatures increase in the coming years, there will still be cool years where above average snowpack builds up in parts of the West, particularly during La Niña years. “But these years will tend to be weather noise over top of the larger climate changes we will see over many years,” he says.

NPR’s Richard Harris interviews Pederson in this story for Morning Edition.

A version of this post also appears at Climate Central, a content partner of KQED Climate Watch.

Snow removal near Mt. Lassen. (Photo: KNVN Chico-Redding).

Frank Gehrke summed it up: “Well, it has been a really crazy winter,” said the state’s chief surveyor of the Sierra Nevada snowpack.

Statewide averages from the season’s fourth survey Wednesday, shows water content at 165% of normal for April 1.

The latest survey shows statewide, water content of the Sierra snowpack is 165% of normal. Gehrke says it’s been about 15 years since there’s been this much snow on the ground at this point in the season. Earlier this month, some locations were reporting total seasonal accumulations equivalent to the height of a six-story building.

Key reservoirs are also at above-average levels — to the point where managers are now releasing water downstream. Gehrke says that, “Because of the huge snowpack up above, they’ve got to maintain space for that runoff in the spring.”

As expected, Governor Jerry Brown responded by lifting statewide drought emergencies declared under the Schwarzenegger administration. In doing so, the Governor cautioned that “Drought or no drought, demand for water in California always outstrips supply. Continued conservation is key.”

I heard similar cautions from Jeff Kightlinger, general manager of L.A,’s Municipal Water District. “This isn’t an all-clear to consumers to just say ‘Terrific, let’s just start hosing down the sidewalks again’,” said Kightlinger, who’s district serves about 19 million people in Southern California. “We’re really trying to change a mindset here.”

Kightlinger says his board will now rescind penalties for excessive water use that have been in place for MWD customers, but adds that, “We need to conserve water every year, not just during drought.”

An unusually dry January started some folks thinking that maybe the tap had been shut off for this season. But last month winter came roaring back as Pacific storms brought epic snowfalls to the Sierra. The result: Today’s monthly survey shows the water content of the mountain snowpack at 124% of normal for this date–and even above its normal level for April first.

Check current reservoir levels with our interactive map, below.

Major reservoirs are also above their normal levels for early March. But it still doesn’t mean that contractors on the State Water Project will get all the water they ask for. Officials say they still expect deliveries to come in at about 60% of the volume requested. That’s a number that typically gets adjusted throughout the winter.

We’ve updated our interactive map, showing the status of major reservoirs around the state.

View KQED: California Reservoir Watch in a larger map

Steve Nemeth, a Water resources engineer for DWR, says forecasts for spring runoff are equally cheery for virtually all Sierra watersheds, from the Yuba River south.

And another storm is due in tomorrow.

Of course, no silver lining would do without a dark cloud (that’s a bit confusing since in California, a dark cloud is a silver lining). The snow survey comes on the heels of a new report that suggests the long, long-term outlook for the southwestern US may be one of “periods of aridity lasting centuries to millennia,” if the distant past is prologue. The conclusions, based on studies of sediments from northern New Mexico, appears in the journal Nature.

Lake Tahoe's water level could drop within the century. (Photo: Lauren Sommer)

The average snowpack in the Tahoe Basin could decline 40 to 60% by 2100 and some years could see all rain and no snow. That’s according to climate change forecasts released this week by the UC Davis Tahoe Environmental Research Center.

The decrease in snowpack would be driven by two processes, according to study author Geoffrey Schladow. With warmer temperatures, more precipitation will fall as rain during the winter, instead of snow. And as any skier knows, when rain falls on snow, it melts the snowpack in what scientists call “rain-on-snow” events.

These findings are a concern since the Sierra Nevada snowpack is often called California’s “frozen reservoir.”  That reservoir is critical to the state’s water supply — and it’s free. “What the snowpack affords us is a way to very economically store water,” said Schladow. “If the water is falling as rain, rather than snow, then we have to build more dams and reservoirs to catch it, which is expensive.”

The study also forecasts several climate change impacts on Lake Tahoe itself. Prolonged droughts in California could cause the lake level to fall below out-take valves, which feed the Truckee River. The Truckee supplies water to Pyramid Lake and the city of Reno, Nevada. Output levels have fallen in the past, but under the worst case climate change scenario, those periods could stretch 10 to 20 years.

That would also change the face of the iconic lake. “Suddenly lakefront homes would be hundreds and hundreds of feet from the water. It’s going to be a very different looking lake,” said Schladow.

Lake Tahoe’s unique ecology could also change. Mixing of water from different depths is a critical process for any lake, since it takes oxygen from the surface and makes it available for fish and other species living throughout the water column. Because Lake Tahoe is so deep, today it only mixes fully every three to four years. By the second half of the century, that mixing period will become longer. “At some point, it may not mix for decades at a time,” said Schladow.

Schladow says the study focused on Lake Tahoe as an important case study for changes happening throughout the Sierra Nevada. “These same processes are happening everywhere across the West. Tahoe is the canary in the coal mine.”

Forecasting climate change impacts like these at the regional level has become a Holy Grail for climate scientists. Historically, computer climate models could only scale down to sections of land hundreds of miles across, which made it difficult to predict changes in a landscape as varied as California.

Schladow says newer climate models allow them to see changes at a much more granular level. “What we were able to do is to use grids that were more like one or two miles. That way we could distinguish between effects at the mountain peaks and effects down at the lake level.”

Schladow is hopeful that this study can give land and water managers an early indication of what the future may hold.

Photo: Craig Miller

I don’t know Mark Cowin, the director of the state’s Department of Water Resources. I haven’t even met the man, in person. But after listening to and reading his pronouncements about the state’s water supply, I’d guess he’s a guy who would barely crack a smile if he found himself holding a winning lottery ticket. I hazard that opinion because even after today’s great news about the Sierra snowpack–which is a little like finding out the state has won its annual water lottery–what Cowin emphasizes is that California isn’t out of the woods after the dry spell of 2007-2009. But more about that to follow. First, the details on the DWR’s final Sierra snow survey.

DWR announced on Friday that statewide, the water content stored in the Sierra snow is at 143% of normal for the date; 188% in the northern Sierra, 121% in the central mountains, and 139% in the southern reaches of the range. Up and down the Sierra, those figures are more than double the levels of the past two years, and are up to seven times as much as surveyors found in the bone-dry spring of 2007.

Last week, the Department announced it would increase allocations from the State Water Project to 30% of the amount requested from 29 urban and agricultural customers. Today’s snowpack news prompted the department to say that it’s likely to increase deliveries. How much? “Only marginally,” Cowin said in a phone interview this afternoon. “We’ll have to run the numbers, and we’ll probably make that determination in the next week or two.”

How much water will State Water Project customers get, eventually? Let’s run some numbers of our own.

The main reason the department cites for the very tight supply in the midst of a year of “normal” precipitation is the continuing below-average levels at California’s biggest state-owned reservoir, Lake Oroville. As of Friday afternoon, the lake is at 72% of normal for the date and about 60% full. But the stats that Cowin’s water geeks are crunching aren’t about the level today, but where they guess it will be as runoff begins to pour from the snow-blanketed mountains through the Feather River watershed into Lake Oroville. DWR officials have insisted that it believes runoff will be held down because of dry conditions caused by the last three drought years. You wonder if they’ll still believe that after assessing the impact of an unusually wet April and its impact on the snowpack.

While pondering that, here are some other numbers to consider if you want to play what I’ll call the State Water Project Allocation Game:

• After running far below its 2008-2009 levels all season, the water storage in Lake Oroville caught up and passed year-ago levels this week. The lake’s storage has increased six percent—more than 150,000 acre-feet—since last Friday.
• As noted above, this year’s snowpack is better than double last year’s.
• Last year, the state delivered 40 percent of requested water shipments to its SWP customers. The average allocation for the past 10 years is 68 percent.

Considering all of the above—last year’s deliveries, the snowpack, the sudden late-season surge in Lake Oroville’s levels—it’s a no-brainer that water deliveries will at least match last year’s 40 percent. The question is whether the allocation will go higher. All Cowin would say on that subject today is that he thinks that 45%, the amount DWR described two months ago as the upper limit for shipments this season, is still accurate.

But Cowin did say, as he has more and more frequently of late, that a preoccupation with the this year’s water level misses the point about California’s water reality.

“That’s why we’re so concerned when we get the black and white question, ‘Is the drought over,’” he said. “We are in a period of long scarcity in California. We have no idea what next year’s water supply picture will look like. It’s possible we could have two or three more dry years in a row. So we’re trying to get a message out that we need to have a new attitude about how we use water in California, and it shouldn’t depend on this week’s outlook. We need to conserve water just as a way of life.”

If you want to explore the state’s water supply picture for yourself, check out our California Reservoir Watch map, below:

View KQED: California Reservoir Watch in a larger map
View KQED: California Reservoir Watch in a larger map