Climate change

Climate change disrupts the natural cycles of drier Lake Tahoe


TAHOE CITY, Calif .– Drought fueled by climate change has caused Lake Tahoe to fall below its natural edge and interrupt flows in the Truckee River, a historically cyclical event that occurs earlier and more often than before – raising fears of what might be in store for the famous alpine lake.

Scientists fear that the increasing frequency of extreme low water will become the new normal.

They point to seasonal changes in weather conditions causing precipitation that historically falls as snow to arrive as rain at the top of the Sierra along the California-Nevada border.

“Our summers last longer. Sources arrive sooner, ”said Gregory Schladow, professor of water resources and environmental engineering and founding director of the UC Davis Tahoe Center for Environmental Research.

“The water level has always gone up and down,” he said this week. “He always sometimes went under the ledge. But the frequency of changes is increasing.

Over the past century, the amount of precipitation falling as snow has increased from 52% in 1910 to 33% in 2020 and is expected to fall below 20% by the end of the century, according to experts at the research center. of Incline Village, Nevada.

Rain trickles down from the mountains instead of collecting as snow on top of the mountains for safe storage until it is needed most in late spring and summer – the high Sierra equivalent of anyone. ‘one leaving the freezer door open at the top of the refrigerator.

Since the summer, the launching ramps have been closed. The docks lie precariously above the dry bottom of the receding lake. Boat and kayak rentals plummeted and rafting operations on the Truckee River had to end earlier.

“Our season has been short and we’re worried there won’t be one next summer,” said Toni Rudnick of the Truckee River Raft Company.

“It all depends on the snowpack,” she said. “In 2015 didn’t open at all when the Truckee River was a series of puddles … In 2016 we had a 15 day season.”

The US Forest Service has canceled this month’s annual Kokanee Salmon Festival in South Lake Tahoe because low water levels virtually cut off their migration route to spawn in Taylor Creek.

Deborah Grant Hanna is no scientist, but she has witnessed decades of highs and lows in water levels for 42 years at the lake. She runs the Gatekeeper Museum / Gift Store next to the dam in Tahoe City, where the dry lake bed now extends 200 meters (183 meters) from the normal shore.

“The water is usually at its lowest in mid-November. It was lower than today in 2015-2016, ”she said. “The problem with rain now is that it moves away from the mountain and causes flooding rather than storing snow. And when it comes to the local economy, rain is falling on the snow at ski resorts.

The lake sank below the natural edge to an elevation of 6,223 feet (1,897 meters) twice in the 1920s after the dam was completed in 1913 and created the capacity to store up to 6 feet (1.8 meter) of water above the natural surface of the lake.

The level fell below the rim half a dozen times during the Dust Bowl in the 1930s, but not until 1961, followed by 1977 and 1988. Since then, it has happened nine times – six since 2004.

Sarah Muskopf, a Forest Service aquatic biologist, said the water drop occurs every year, but with varying degrees of intensity.

“Obviously, climate change is making this problem more serious, as the aquatic habitat starts the season with less water, the system dries out earlier, and water temperatures rise to levels that do not meet the needs of the population. life cycle each year and earlier depending on the year of the water, ”she explained.

Tahoe’s water last peaked in July 2019, but since then it has generally declined. The usual increase from snowmelt in May and June was largely absent in 2021, the Tahoe Environmental Research Center said in a newsletter update this month.

Winter will likely arrive in the next few months and the lake will rise above the natural edge again, he said.

“But if the winter of 2021-2022 turns out to be below average” – as most models predict – “next year the lake will fall below the natural edge much sooner and will probably stay there for most of it. of 2022, “he said.

“This will have an impact on recreation in 2022, as many docks and boat launching ramps will be further from the shore. The growth and leaching of filamentous algae on very wide beaches will increase, ”he said.

In the southwest corner of the lake, silt could accumulate at the 12-foot (3-meter) deep mouth of Emerald Bay, cutting it off from the lake itself for the first time in history, a declared the center. The same could happen at the mouths of many streams, “cutting off spawning access for kokanee salmon next fall.”

Lake Tahoe researchers are better armed than most scientific knowledge since President Bill Clinton and Vice President Al Gore hosted an environmental summit at the lake in 1997. It paved the way for hundreds of millions dollars of investment in new studies out there. the next two decades.

At the time, the focus was on the decline of the famous Tahoe Clarity. Initial concerns were air emissions from increased traffic, fertilizer use, and shoreline development that feeds erosion and sends fine particles into the lake.

Schladow, the director of the research center, said this was followed by a better understanding of invasive species, like the Mysis shrimp, which were introduced to Tahoe in the 1960s as a food source for native trout but have devoured the native zooplankton that historically helped keep the lake clear.

“And while all of this was going on, the planet was changing,” Schladow said. “The dominant processes in the lake are very different from what they were 25 years ago. It doesn’t mix that often. It starts hot earlier. Temperatures are at higher levels.

“It’s a very complex system – a great analogue for all of the other western lakes.”


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