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Effects of La Niña on Tahoe/Truckee Snow Uncertain for Upcoming Winter

While other parts of the United States may be in for some extreme temperatures this winter due to La Niña weather patterns, the effects on Tahoe are uncertain.

La Niña is associated with cooler-than-normal water temperatures in the Equatorial Pacific Ocean and can bring extreme temperatures and precipitation.

While the National Oceanic and Atmospheric Administration reports the Northwest may experience a wetter and colder winter than normal, and the Southwest and South may experience a drier and warmer winter than normal, Lake Tahoe falls into the “equal chances” category.

Climate Change: Forests, wildlife, fire danger all expected to be affected by warming Sierra

By Greyson Howard, Sierra Sun

Many doomsday predictions of climate change focus on rising oceans, flooding coastlines and submerged cities, but some scientists are watching the Sierra to gauge other significant impacts.

Looking into the future it isn’t hard for researchers to picture the many different Sierra ecosystems — wrapped like bands around different elevations — retreating rapidly upward, squeezing each other and eventually running out of elevation to climb.

As future temperatures rise, predictions are for snow to melt faster and streams to swell earlier, out of sync with the breading cycles of aquatic species like fish and frogs. Dry summers would leave entire forests more susceptible to fire and pests than ever before.

And, many experts agree, the changes become amplified as they move up the food chain, throwing the Sierra Nevada’s entire ecosystem, meticulously established over millennia, out of balance in a matter of decades. The bottom line, some scientists conclude, is the extinction of vulnerable mountain species and increased fire risk for the Sierra’s human inhabitants.

“Our concern is with the rapidity of change — most species can evolve over time and the planet has always been in flux — but it’s the rate of change, which is really unlike anything we’ve been able to study,” said Josh Viers, assistant research ecologist at UC Davis.

The Sierra Nevada has been characterized as the “canary in the coal mine,” according to the U.S. Forest Service, an early alarm for the deleterious effects of rising temperatures. But all parts of the Sierra won’t be treated equal. Despite Truckee-Tahoe’s more northern latitude, the area will likely be hit harder than the taller mountains to the south.

“The area around Tahoe and Donner Summit, for example, would be more affected then Kings Canyon,” Viers said.
And so Tahoe National Forest has been picked as an open-air laboratory for climate change — a focal point in a global issue — with researchers from academic bodies, conservation groups and the U.S. Forest Service gleaning whatever they can learn from the surrounding woods.

“When I started I was a naysayer, ready to poke holes in global warming,” said Carol Kennedy, the watershed project manager for Tahoe National Forest. “I don’t poke holes anymore.”

Retreating trees
Perhaps easiest to predict and already in progress in some cases is the steady retreat of vegetation away from rising low-elevation temperatures and towards ever-shrinking snow melt, said UC Davis’ Viers.
The water problem
While rising temperatures will directly affect many species, indirect affects through changing water availability may be even more drastic.

“Between 7,000 and 9,000 feet the rain/snow mix line will be most severely affected,” Josh Viers said.
This means the timing and flow of streams and river could change, possibly three to seven weeks earlier, he said.

“Everything from what’s in the streams — frogs breeding to vegetation along the side of the streams — a whole series of affects, will come from just the timing,” Viers said. The breeding cycles of both the mountain red- and yellow-legged frogs of the Sierra may no longer match with stream flows he said.

Trout require cold water, no more than 20 to 21 degrees Celsius, meaning many streams could become too warm, Viers said. Flowering plants may bloom with high flows before pollinators like bees and mosquitoes emerge.

Aspen trees, already diminishing in the West, are at risk because of drying stream habitat, Nechadom said.

And moisture could be dropping on the order of 40 to 60 percent by the year 2100, Kennedy said.

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Experts say stream runoff has peaked

By Jeff DeLong • jdelong@rgj.com • May 24, 2008

Runoff in area streams and rivers has peaked, and Lake Tahoe probably won't rise more than another inch or so before it starts dropping in the summer heat, experts said Friday.

That spate of high heat that broke many records a week ago quickly melted the snowpack, causing streams to rise and the Truckee River to turn a muddy brown. Highs in Reno exceeded 90 degrees four consecutive days, ending Monday.

"It pretty much came off in one big flush," said Dan Greenlee, a hydrologist with the National Resource Conservation Service in Reno. "I think we've peaked. Once it warms back up again if it doesn't come back up, we'll know for sure."

Chad Blanchard, chief deputy of the Federal Water Master's Office in Reno, agreed that this year's runoff has hit its peak and will be on a diminishing trend. Natural runoff of the Truckee River peaked May 17 while the Carson River peaked the next day, Blanchard said.

On Friday, Lake Tahoe's level was measured at 6,225.39 feet. While thunderstorms forecast through the weekend could change things if they produce sufficient rain, Blanchard said he doesn't expect Tahoe's level to rise more than an inch or two beyond current levels.

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Snowpack fine for now, but more winter weather needed to increase water levels

Posted: 2/17/2008

January produced a real winter for the region, but more storms will be needed for the season to end with enough snow in the mountains.

The Sierra snowpack, which provides the water needed in the arid valleys of Western Nevada and the cities of Reno, Sparks and Carson City, remains at above-average levels but the cushion isn't a big one.

Last week, the snowpack in the Lake Tahoe Basin sat at 117 percent of average for the date. The Truckee River Basin's snowpack was measured at 101 percent.

That's good news after a slow start to the winter. In late December, the snowpack measured less than half of what it should have been. Then came the back-to-back storms of January, which deposited nearly 20 feet of snow near Donner Summit and beefed up the snowpack to healthy levels.

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Snowpack levels healthy, but Lake Lahontan low

While winter precipitation has reached a healthy level, Lahontan Reservoir remains low due to the breach in the Truckee Canal that is preventing diversions from the Truckee River.

The Natural Resources Conservation Service released its February 2008 water supply outlook report Friday, which forecasts the Carson River to flow 110 percent above normal at Fort Churchill from April to July, the months when the runoff from the higher-elevation snowpack feeds the river.

The snow-water content in the Carson River Basin skyrocketed in early January, climbing from 57 percent on Jan. 1 to 113 percent of average by Jan. 7. The February report states January's precipitation was 146 percent of average - much higher than last year's average of only 49 percent.

"We're in excellent shape now with the snowpack coming back," said Dan Greenlee, water supply specialist with NRCS. "January was just incredibly, phenomenally wet. It helped us recoup on that."

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Power seeds: Spray iodide in the sky and let it snow

Power seeds: Spray iodide in the sky and let it snow

Source: Sierra Sun
December 24, 2007

Lake Tahoe is well-known as a winter recreation paradise, outdoors enthusiasts taking advantage of its ample winter snowfall.

But few who take advantage of the bountiful snowpack realize that researchers have been artificially boosting the Sierra Nevada’s snowfall for more than half a century.

Cloud seeding, as the weather-modification process is known, is conducted in the Sierra Nevada mountain range primarily to increase municipal water supplies in Nevada, said Operations Manager Tom Swafford with the Desert Research Institute’s Cloud Seeding Program.

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