Miguel Vieira/Flickr

Scientists found important climate clues hidden away under Fallen Leaf Lake, just south of Lake Tahoe.

Graham Kent wasn’t researching megadroughts when he and a team of scientists began studying Fallen Leaf Lake, just south of Lake Tahoe. They were mapping faults. The little lake is a good place to study West Tahoe Fault, which cuts right through it.

“Little did we know it was a natural lab for droughts, as well,” Kent, director of the Nevada Seismological Lab at University of Nevada, Reno, told me over the phone. “So what started out as a seismic hazard endeavor became both a seismic hazard and climate study.”

There was a handful of trees standing upright on the bottom of the 400-foot-deep lake. Kent and his team from UNR and Scripps Institution of Oceanography decided to look at them a little more closely. “We used a whole bunch of different techniques including side scan sonar, which people are mostly familiar with when people are looking for treasure and sunken ships on the seashore like the Titanic,” Kent said. “We ultimately went down there in a submersible to actually look at these trees.”

They wanted to confirm that the trees had really grown where they were standing, at the bottom of the lake, rather than grown somewhere else, and slid down at some point.

Kent’s team discovered that the trees had grown where the shoreline of Fallen Leaf Lake once was. Clumps of trees of different ages — going back more than a thousand years — showed where the shoreline had been and how it had changed.

“That poor lake changed its level 120, 140 feet, while Tahoe changed maybe ten,” Kent said. The difference is in the geology of the lakes. Fallen Leaf Lake is much more sensitive to changes in precipitation than Tahoe is. “Fallen Leaf Lake probably has the best recorded history of the Medieval Warm Period in all of the Sierra.”

By studying the trees and the ancient shorelines they grew along, Kent learned more specific details than had been previously known about the megadrought that hit California between the 10th and 13th centuries. It lasted for 200 years and during that time, precipitation was 60% of what we now consider “normal.”

“A lot of California, the way that it’s industrialized and grown, is probably in a relatively wetter climate than has happened in the past,” Kent told me. “It [was] kind of like the Dust Bowl era. But again, it’s sustained not over half a decade or a decade. It’s sustained over two centuries.”

And it wasn’t a one-time occurrence. While the two-hundred year-long drought during Medieval times is the best-documented because it’s the most recent, it’s not the only megadrought the ancient trees at the bottom of the lake reveal. “This wasn’t just a one-trick pony where we have relatively normal climate and then the Medieval Dry. We have these kinds of ups and downs throughout the Holocene.”

A host of causes go into climate patterns: tectonic plates can cause changes on the scale of tens of thousands of years, there are the cycles that caused the ice ages, solar variability, different currents in the oceans. So it’s difficult to figure out how human-caused climate change will affect — or be affected by — the possibility of a future megadrought. “You can’t put it on the back of an envelope, you probably have to put it in a big book, it’s so complicated,” Kent said. “But as we look into the future it helps to know what the past was.”

Molly Samuel/KQED

Snow has been sparse in the Sierra Nevada this winter.

There are good years and there are bad years, but overall, snowfall in the Sierra hasn’t declined in the past century. That’s according to a new study by University of Alabama climatologist John Christy (who, it’s worth noting, has come under fire as a climate change denier).

The San Francisco Chronicle had a story about the report, “Searching for information in 133 years of California snowfall observations,” (link is to the abstract; full article is behind a pay wall) in today’s paper:

The analysis of snowfall data in the Sierra going back to 1878 found no more or less snow overall – a result that, on the surface, appears to contradict aspects of recent climate change models.

John Christy, the Alabama state climatologist who authored the study, said the amount of snow in the mountains has not decreased in the past 50 years, a period when greenhouse gases were supposed to have increased the effects of global warming.

Roger Bales, a professor of engineering at UC Merced and director of its Sierra Nevada Research Institute, said this study can’t be used to draw conclusions about climate change.

“(Christy) may have done some appropriate statistical analysis, but the conclusions are stressed beyond what the data will bare. It’s not surprising he didn’t find a trend because he lumped everything together.”

Bales said to detect a change in precipitation patterns from snow to rain, which is an indicator of climate change, the details of the data at specific elevations would be more valuable than all the numbers combined.

The Chronicle also quoted U.S. Geological Survey climatologist Mike Dettinger, who said that water content and density of snow are better measures than snow depth.

Kelly Redmond, a climatologist at the University of Nevada’s Desert Research Institute said he was slightly surprised to see the report, but not floored by it.

“It’s quite natural to say if it’s warming up we’ll see less snow, but in some places because of higher temperatures, we could see more,” he told me. “There’s that famous quote by René Dubos, ‘Trends are not destiny.’ This is a study of what it’s been up to this point. But I’m hesitant to say if it’s been this way, it’s going to stay this way.”

Update:

John Christy got in touch, and I asked him to respond to some of the points in this post. I’m copying his response in here.

Snow Water Equivalent (SWE): my recent paper directly addressed that issue and found snowfall a very good proxy for SWE. SWE is a valuable measure of one thing (amount of liquid water in the snowpack on a particular date, which misses the impact of later snowfalls).  SWE is very useful for its purposes, but only a few measurements go back to around 1930. Snowfall is a different metric (my paper) and goes back another 50 years (thanks to a lot of effort on my part) and so has the high added value of length-of-record as well as a metric of great value to define snow amounts as they fall (for recreation, snow clearing, snow-dependent ecology as well as runoff).

The rate of change of snowfall has been modeled to have already shown decreases (in the models). I addressed issues like temperature (Christy et al. 2006) and runoff/precipitation (Christy and Hnilo 2010 attached) … no changes have been found. Thus, models are not doing well in showing what mother nature is doing. It’s always a nice corner to run to by saying “our predictions can’t be tested because they apply only to the future” — the infamous unfalsifiable hypothesis. I test model results for the time over which we have both observations and model results. (My main work is dealing with global temperatures from satellites where it is more straightforward to show model vs. observation disagreement.)

One critical part of the paper was the handling of “missings as zeros,” where non-reports (i.e. missing) had been filled in with zeros since 1970 by someone down the line for many stations. I had to eliminate as many of these as possible — a very tedious process.

I looked at the elevation dependence in the So. Sierra in the last paper. Note that in the past 60 years, most sites showed positive trends, with no dependence on elevation.

Regarding the Calif. Water Report — the blog commenter was comparing very different apples and oranges: the time frame is different in two ways and the quantity itself is very different. In Fig. 2-13 the quantity is only Apr-Jul runoff for the Sacramento Basin only, not total annual runoff of all of the Sierra. The annual runoff (Fig. 2-14 lower and Fig. 2-16 lower) shows precisely what I found — no trend. The time periods are different too — mine go back 30 years more. It looks to me like California will have roughly the same amount of water it has had for the last 100 years — but I know the demand for water is always rising.

Tyche Hendricks/KQED

After a record dry December, there's finally snow on the ground near Soda Springs, at Lake Tahoe.

This morning’s snow survey (PDF) didn’t turn up any big surprises. As remote sensors foreshadowed, water content in the Sierra snowpack is 37% of normal for this time of year, and less than a quarter of the average for April, which is when the snowpack is usually at its peak before it begins melting and filling up California’s reservoirs.

What’s worrisome about that, according to Jeanine Jones, Interstate Resources Manager at the Department of Water Resources, is that about half of California’s annual precipitation typically falls between December and February, months that are mostly already behind us. “So where we are this year is: November was dry, December was close to record dry, January was maybe half of average,” Jones told me. “And currently the forecast for the first  ten days or so of February is essentially dry.”

The above chart, from the Department of Water Resources, shows that this year — the pink line — isn’t quite the worst on record, but it’s a lot closer to the bottom than it is to boom years like 1982-’83 (the blue dotted line), or even last year (in green). Jones says luckily, last year was wet enough, that we’re still riding its coattails. Most of the state’s reservoirs (PDF) still hover around their averages for the year.

“In terms of impacts to water users this year, the fact that we have good storage conditions courtesy of a wet last year is helpful,” she said. “And a good take-home message here is that we need to think about preparing for the possibility of a dry 2013, because we won’t be going into 2013 with the kind of carryover storage we have now, both in reservoir storage and groundwater basins.”

But, Jones adds, Californians will feel impacts from this dry winter. “The people who rely soley on annual rainfall: the grazing industry, dry-land farming, potential wildfire conditions, and then small water systems in rural areas that are dependent on fractured rock groundwater aquifers that may have very minimal recharge, those are the kinds of typical examples in a year like this.”

And winter’s not over yet. Jones says it’s not likely, but there is the chance that a big storm event could still happen and help catch us up.

Dan Brekke

Highway 120 in Yosemite National Park winds toward Tioga Pass. The road closed Tuesday night after its longest winter opening since at least 1933.

It first captivated me back when I was an adolescent map reader back in the Midwest. I was poring over maps of California for a trip that didn’t happen—then—and took note of the roads across the Sierra Nevada. And the highest of all the mountain routes I could see crossed Tioga Pass, at an altitude that rounds to 10,000 feet. Nearly two miles above sea level.

Eventually I took that trip to California, but it was still a long time before I actually saw the place the map depicted. A good 15 years or so after I moved out here, I managed to scramble up there on a long weekend and spent a single afternoon driving Highway 120, the Tioga Road.

The stark beauty of the Sierra always manages to surprise me, but there’s an extra degree of immediacy to the grandeur along the road to the pass. After rising through a stretch densely lined with conifers, you emerge into a world of granite domes and alpine meadows. It almost seems wrong to be driving through this landscape instead of walking through it (although there’s plenty of opportunity to do that on dozens of trails, if you give yourself time). Approaching from the west, the pass itself is a little anticlimactic. You note the country is getting a little drier, you pass the Tioga Pass entrance sign with the announcement of the spot’s elevation—9,943 feet above sea level—and then you begin a nonstop plummet toward the town of Lee Vining and Mono Lake.

The feeling I came away with, and that I’ve experienced every time I’ve been across the road, is a sense of having been allowed to see a stretch of road that’s a little bit of a secret – it’s much less traveled than most routes into and out of Yosemite – and, without having had to work very hard for it, have been given access to one of California’s greatest treasures.

All of which goes to explain that when high country fanatics began writing about how the road was open in December because of this season’s dry weather, I got the urge to go up there and see what the winter scene looked like. And at the first excuse, I headed up to the pass.

That feeling of being allowed to enter a special world was stronger than ever. I hadn’t planned on doing a radio piece about the trip, but I had brought my little sound kit, which fits into a fanny pack, just in case. When I climbed out of the car at Tenaya Lake, elevation 8,150 feet, I slowly realized that the weird moaning-whale song sound I was hearing was the lake’s thick ice expanding in the sunlight. I just had to record that. And then maybe talk to some people.

Virtually everyone I talked to on the lake and later, on a trail above Tioga Pass, shared the opinion that this was a once-in-a-lifetime opportunity, to be able to drive into the middle of the high country. They talked about the special quality of the winter light on the landscape, the opportunity to change their usual winter routines of snow shoveling and skiing, and the simple amazement they felt in being able to walk and skate and picnic nearly two miles above sea level—in the middle of January.

Dan Brekke

Gaylor Lakes Trail, elevation 10,500 feet, just above Tioga Pass in Yosemite National Park. In the center background, Dana Meadows. This area is typically snowed in by Thanksgiving and the Tioga Road through the area is normally closed until late spring or early summer.

But people also talked about the disturbing part of what they were seeing. Long-time Californians seem to develop an ingrained understanding of the state’s hydrological equations and how important the Sierra Nevada winter snowpack is to maintaining a healthy environment, not to mention delivering water to farms and cities. And looking around, people expressed some worry about the beautiful but mostly snow-free country around them. (A data point here: The daily snow survey summary from the state Department of Water Resources show that the statewide average for snow-water equivalent in the mountains is just 10% of normal. It will be most interesting to see how that changes as the current series of winter storms blows through).

And people have longer term concerns about what they’ve seen along the Tioga Road this season. The person who put it best is someone I did not talk to on my trans-Sierra excursion. Beth Pratt, a California outdoors and environment blogger, made a series of trips across Highway 120 during our weird winter idyll. Her enthusiasm and wonder for the spectacle she’s seen are infectious. But it’s also tempered by thoughts of the future:

“Bottom line: for a Yosemite and Sierra aficionado like me, having access this late is akin to winning the lottery. Of course when I have no drinking water next summer, I might feel differently. The lack of snow is alarming and the landscape is more reminiscent of spring than winter. Although it’s difficult to associate any one weather event or season to climate change, welcome to the Sierra Nevada of the future. I have seen predictions under the best case warming scenarios of an 80% reduction in snowpack. The Sierra can often deliver a wallop of a storm anytime of year, and I have no doubt we’ll recover at least some of the snow–this year at least. But this may be a warning from the ghost of the Sierra future.”

“Ghost of Sierra future?” Those words will stick with me. But for today, I’m glad to know that the snow’s flying again across the Tioga Road.

Some atmospheric scientists think that could change soon.

By Andrew Freedman

While some may be cheering the lack of snow as welcome relief, the widespread lack of it spells trouble for the ski industry, which pumps billions into the wintertime economy in states from California to Maine, and requires cooperation from Mother Nature to stay in business.

Craig Miller/KQED

Snow from last year's big winter storms could still be seen on the mountains near Lake Tahoe on August 30th. This winter has been one of the driest on record.

Ski area operators across the country are already reporting drops in lift ticket sales, and are hoping for a major change in the weather pattern to bring colder, snowier weather. So far, die-hard skiers have been forced to either ski on man-made snow or travel to one of the few far-flung areas that have benefited from the unusual weather, such as the mountains of New Mexico or Alaska (where one town has had 18 feet of snow).

Compared to last winter, this wimpy winter weather is coming as quite a shock.

Snow was so widespread last winter that at one point in January, every state except Florida had some snow on the ground. But this year, the U.S. had the 11th least extensive December snow cover in the 46-year satellite record, said David Robinson, the director of the Global Snow Lab at Rutgers University.

“Is it fair to call it a snow drought? We’re getting there,” Robinson said. “It’s certainly an early season snow drought.”

Michael Berry, president of the National Ski Areas Association, said this winter is noteworthy for how many ski areas are seeing below average snowfall. “Typically, we have one region or another in the country that might be off to a slow start. But the thing about this year that’s somewhat unique is that it’s kind of an across-the-country problem, at least to date.”

Nowhere is the contrast from last winter so evident as in California’s Sierra Nevada Mountains, home to Lake Tahoe’s ski resorts.

National Oceanic and Atmospheric Administration (NOAA)

Observed snow depth on December 29, 2010 (top) and December 29, 2011 (bottom).

Last year, skiers hit the slopes all the way through July 4th, and several mountains set all-time seasonal snowfall records, with totals surpassing 65 feet. Squaw Valley, for example, received a staggering 810 inches of snow.

This December, at nearby Alpine Meadows, just 1.5 inches of snow fell, well below the average of 72.3 inches, and far below last year’s 134-inch December total.

The lack of snow has allowed Yosemite’s Tioga Pass, a road that would normally be buried in snow by now, to remain open later than at any time since record-keeping began in 1933.

In the Northeast, an October blizzard and other early season snows were followed by warm temperatures that melted the natural snow cover, and prevented ski areas from making snow. With a recent shot of cold air, New England’s ski resorts have finally cranked up their snow making operations, but attendance is down from last year, in part due to the bare ground in major media markets, such as New York and Boston. With just a trace of snow in December, Boston had its second-least snowiest December on record, for example.

“Psychologically, we do better when people see snowfall in their backyards,” said Bonnie MacPherson of Okemo Mountain in Vermont, where skier visits were down about 30 percent compared to last year over the same Christmas holiday week. “We’re fortunate in that we’ve invested pretty heavily in the snow-making system that we have,” she said.

With each passing day of below average snowfall, it becomes more difficult to make up for lost time, especially when spring is arriving earlier on average due in part to global warming. This forces ski area operators to squeeze the same amount of earnings into a shorter time period.

Rutgers’ Robinson said ski areas would have to rely more on the President’s Day school vacation week in February to compensate for lost revenue during the Christmas holiday period. “Many of the ski resorts are going to have to really count on it this year because they were hurt by the holiday week between Christmas and New Year’s,“ he said. A poor turnout during that week could mean ski areas are “going to be running in the red.”

Forecasters are quick to caution, though, that the rest of the winter may not play out the same way that the season has started. Much depends on two key factors that affect winter weather in North America: La Niña and the Arctic Oscillation.

Two Very Different La Niña Winters

La Niña, which is a natural climate cycle characterized by cooler than average water temperatures in the tropical Pacific Ocean, tends to nudge the wintertime storm track to favor heavier snows in the Pacific Northwest, northern Rockies, Ohio Valley, and northern New England.

But this winter has not been behaving like a typical La Niña winter. Instead, storms have moved across southern California, into New Mexico and Colorado, and then on up into the Midwest.

Klaus Wolter, a researcher at NOAA’s Earth System Research Lab in Boulder, CO, said there are indications this will change later this month. “I’m pretty confident that it will probably revert back to more typical La Niña winter weather,” he said.

Part of the reason why this winter has departed so dramatically from La Niña’s script has to do with the Arctic Oscillation, which is a pattern of atmospheric pressure that helps steer the jet stream in the Northern Hemisphere. When it’s in a “positive phase” as it has been so far this winter, cold air tends to remain bottled up in the Arctic. So far in 2012, 130 daily high-temperature records have been broken in California alone.

Wolter and many other forecasters think the Arctic Oscillation may shift during the next few weeks, making it easier for a more typical La Niña weather pattern to emerge. This would begin to favor ski areas in the Pacific Northwest and northern Rockies, such as Jackson Hole, Wyoming and Big Sky, Montana.

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

Doug Von Gausig

The American pika can only survive within a narrow temperature band and can suffer heat stroke at temperatures as mild as 80 degrees.

The California Fish and Game Commission is asking for public input on the status of the American pika. The small, alpine mammal has been at the center of a prolonged debate over whether to list it under the Endangered Species Act. If the pika ultimately wins endangered status it would be the first species to do so with climate change cited as a major factor contributing to its decline. The Center for Biological Diversity originally petitioned for the pika to receive protected status, considering it to be a bellwether for climate change in California.

Matt Weiser recaps the the pika saga for the Sacramento Bee:

“In 2009, the state Fish and Game Commission considered and rejected protecting the pika under the California Endangered Species Act. At the time, there was limited evidence that pika numbers in the Sierra Nevada and elsewhere were shrinking due to climate change.

Subsequent research, however, provided some clues that, in fact, the pika’s habitat was shrinking upward as lower reaches of its range warmed, resulting in population losses in the Bodie and Lassen regions. The environmental group Center for Biological Diversity argued that the state should conduct a new status review, and then filed suit when it did not.

A San Francisco Superior Court judge agreed in February 2011, leading to the status review now under way. The Department of Fish and Game is now seeking comments from the public and experts on pika ecology, biology, life history, distribution, abundance, threats, essential habitat and recommendations for management.”

Scientists have been divided over whether the critter is a legitimate candidate for listing. Climate Watch has been keeping an eye on the pika’s plight for several years, with blog posts and radio stories dating back to 2009.

Danielle Hougard

Hard to imagine now: A snowed-over road near Lake Tahoe in March.

It was startling to see the state’s lead snow surveyor kneeling on bare grass near Echo Summit, trying to find enough snow to measure the water content. But so it went with the first official survey of the season, conducted by California’s Dept. of Water Resources.

The manual survey affirmed what remote sensors had already relayed — that water content in the Sierra snowpack stands at just 19% of the average reading for this time, right around New Year’s. The readings are just seven percent of where things usually stand on April first, meaning we have a long way to go, to get back to “normal.”

“The other discouraging thing is looking at the long-range weather forecast, that’s not encouraging either,” said Maury Roos, the chief hydrologist at DWR. He says with the season about one-third evaporated and no rain or snow in the forecast, there’s little encouragement on the horizon. “So if we lose half the month, then we’re down to trying to make it up in about half the season,” Roos told me by phone today.

CA Dept. of Water Resources

Key reservoirs are still in good shape, despite the lack of precipitation this winter.

At that particular spot where surveyor Frank Gehrke was scratching around for snow today, he logged a snow depth of four inches. That’s the least since the state started recording surveys of that snow course, in 1964.

The good news is that reservoirs are still rippling with runoff from last year’s epic snows in the Sierra Nevada. Two key Northern California reservoirs, Shasta Lake and Lake Oroville, are at 106% and 114% of historical averages, respectively. Roos says he estimated that this “carry-over” of water storage from last year could perhaps offset as much as 20% of this winter’s shortfalls. But the rest would still have to be made up in additional precipitation with what’s left of the “wet” season. “If it’s a real duster,” Roos told me, “There are still gonna be problems.”

Those problems would present in the form of water shortages during the summer. State water managers say their preliminary estimate is that towns and farms served by the State Water Project can expect 60% of the water they’ve requested to be delivered — but they hasten to add that weather conditions can change that figure dramatically, as they did last year when an initial 25% estimate swelled to 80% by winter’s end.

Hear my companion radio feature on The California Report weekly magazine.

Molly Samuel/KQED

Giant sequoias naturally grow only on the western slope of the Sierra Nevada.

When William Tweed talks about giant sequoias, he doesn’t beat around the bush.

“Sequoias capture human interest because they’re the perfect thing,” says the writer, historian, and former National Park Service ranger. “They’re the world’s largest trees. We humans like big stuff. They’re also exceedingly old, and they also charm us because they’re rare. We humans go chasing around for the big, the old, and the rare.”

He says while other parks have charismatic megafauna, like bears, or bison, or elk, Sequoia-Kings Canyon National Park and the other national parks in the Sierra Nevada have charismatic megaflora: the giant sequoia.

The Sierra parks — Yosemite and the merged Sequoia-Kings Canyon — have some of the nation’s oldest; all three were created in 1890 (the Park Service itself didn’t exist until 1916). The Service’s long history with the giant sequoia is clear even down to the ranger uniform. There are sequoia cones on rangers’ belts and hats, and a giant sequoia on their badges.

But the giant sequoias may not last in the parks where they live now. Climate change threatens to make summers in the Sierra warmer and drier. Under those conditions, sequoia seedlings won’t take root. When a giant sequoia dies — and the recent toppling of two of them reminds us that they eventually do –  there may not be a young one ready to spring up and take its place.

“This was set aside under the premise that it’s pristine. That it could remain intact,” says Tweed. “Well, it may not be possible.” He says it’s unsettling. He came to Sequoia National Park decades ago, with the promise that the park would always be protected, and would never change.

But it turns out that ideal of the parks being preserved in perpetuity was never really possible. There are too many complications. Providing access to the public to enjoy the parks, while also preserving the natural and historical resources is enough of a challenge. Add to that questions about where and when to allow fire, how to handle weeds and non-native animals, and how to protect or reintroduce endangered species. The goal of keeping things natural, or even agreeing on a definition of “natural” is complicated enough, without having to factor in climate change.

So the parks are learning to adapt, and they’ll probably take different approaches in different places, as they already have with fire, weeds, wolves, and construction. Maybe Sequoia National Park will water some of its sequoia groves in the future. Maybe parks further north that end up with a Sierra Nevada-like climate will plant sequoias. Maybe in some places, the park will just let nature, whatever that is, take its course.

Matthew Green

An early snow in the Grouse Lakes area of the Sierra Nevada

By Matthew Green

For months now, I had reserved the second weekend in October for my annual grand finale “summertime” backpacking trip. Culminating an unusually short warm season, this was to be the ceremonial final alpine lake swim, the last mosquito bloodletting until well after next year’s thaw. Which is why, as my partner and I proceeded to pitch our tent in about 10 inches of snow last Friday evening, I couldn’t help but feel I’d been had.

Last week’s storm, which swept across the northern half of California early Wednesday, dumped up to a foot of snow in the Sierra’s high peaks, with accumulation as low as 5,000 feet. According to the Central Sierra Snow Lab, this is the first snowstorm in 96 days – since July 1 – marking the shortest duration between storms in the Sierra since 1969.

Green surrounded by white in the Sierra

Don’t get me wrong. It was absolutely gorgeous. We hiked – or more accurately, trudged – a few miles into the Grouse Lakes Area, a basin in Tahoe National Forest at just over 6,000 feet, where ridges of polished granite cascade into a necklace of shimmering lakes. Add a blanket of white covering the forest duff, dotted with  majestic cedars and pines,  and the scene was downright breathtaking. Not one mosquito, either. And even though the conditions for us over the weekend were gorgeous, with cloudless blue skies and daytime highs reaching into the low seventies, there was still plenty of snow on our way out Sunday afternoon.

Despite the earlier forecasts of blustery conditions in the area, we assumed (with little rationale aside from denial), any frigid weather this time of year would steer clear of anything below, say 7,000 feet. Evidently, not so.

“October is like a half-and-half month; there are dry Octobers and wet Octobers,” said Johnnie Powell, a weather forecaster at the National Weather Service’s Sacramento office. “This was a December-like storm. It’s not rare but it isn’t normal, either.” And by next weekend, he added, after a warm rain system followed by several days of dry weather reaching into the 70’s, most of the wintry evidence will be gone.

And oh, just for the record: as promised, I did take that final swim, a straight dive into a beautiful snow-encrusted lake, and a very swift exit out. I don’t regret it, but I might not recommend it.

Matthew Green is the education outreach specialist for KQED News.

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.