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The Lake that Could Unlock the Mystery of Sierra Nevada Megadroughts
It is the age of mega — megafires, megastorms, and megadroughts lasting hundreds of years, the signs of which are evident worldwide, including in Tahoe over the past 6,000 years. Some of those signs are in Fallen Leaf Lake, where University of Nevada, Reno Professor Emeritus John Kleppe has spent years investigating whether the lake he calls home could unlock the question of whether we are on the cusp of another megadrought. If so, water managers say they have not been preparing for it.
Megadroughts are multi-year droughts that last two decades or more. The historical record is littered with examples of these long periods of parched conditions, and historians suspect that megadroughts contributed to the collapse of numerous ancient civilizations, including the Anasazi in the American Southwest, the Khmer Empire in Cambodia, and the Mayan and Aztec of Mesoamerica.
Fallen Leaf Lake on the south side of Lake Tahoe has recorded the Sierra Nevada’s history of megadroughts with remarkable accuracy because the lake’s dramatic fluctuations have allowed ancient forests to grow during long dry spells, and then be submerged by a resurgent lake.
“Fallen Leaf is very sensitive to drought and begins to fall quickly,” Kleppe said. He said that slight declines in precipitation cause the lake level to fall faster because it drains through porous soil to Lake Tahoe below. He estimates Fallen Leaf leaks 10,500 acre-feet per year, and loses 7,000 acre-feet to evaporation. While that calculation isn’t published, his research on trees left from possibly three megadroughts in the lake were published in Quaternary Science Reviews, Nov. 2011. The report says that during past megadroughts, the lake level dropped and stayed low for up to 200 years, allowing trees to grow for that long. Then, the lake filled fast when the drought ended, drowning and preserving the trees in an ancient underwater forest. At least 90 of those ancient trees, some 100 feet tall, are still standing upright below the lakes’ surface, waiting to be exposed by the next megadrought.
“In 2007 we saw the lake start to drop,” Kleppe said. He theorizes that the megadroughts occur every 800 to 1,000 years, and that is how long it has been since the last megadrought.
The Dramatic Consequences of Megadrought
“If you are talking about a drought of the extreme severity that was shown by the Lake Tahoe cases, you couldn’t sustain a lot of agriculture,” said Jeanine Jones, resource manager for the California Department of Water Resources. “You couldn’t sustain much of the population. You are talking about these geographically extreme droughts that no one plans for. You wouldn’t say, for example, ‘We have one dry year, let’s prepare for another 99.’”
Indeed, drought is not a strong point in the Lahontan Regional Water Quality Control Board’s 2013 Basin Plan, which includes Lake Tahoe. Drought is only mentioned three times in the 148-page document when discussing drought killing trees and stream flow monitoring records that reflect drought conditions in the ’80s and ’90s. But the plan notes that “current consumptive water use in the Lake Tahoe Basin are unknown” because water meters haven’t been installed.
“We are in the 12th year of a fairly prolonged drought in the West,” said Bill Patzert, a climatologist with NASA’s Jet Propulsion Laboratory. “I think that water managers don’t have a 10-year perspective. They certainly don’t have a century perspective. If they did, they would go out and shoot themselves.”
He points to numerous man-made circumstances that complicate drought preparation, let alone a megadrought. “What was a megadrought in 1100 isn’t the same as it is today,” Patzert says. “We are moving water around and tapping aquifers.” In other words, a place where there was once water may not have water anymore. “So you have to be careful when you compare.”
He says the 20th century was one of the wettest. “The simple answer is today’s infrastructure for civilization was built for the climate of the 20th century. As the climate changes on us, that means probably any kind of climate change is not good for civilization.”
In past megadroughts, Patzert points out that nomadic tribes just picked up and left. That’s not the case today. California, Nevada, and Arizona have spent billions developing water delivery systems for tens of millions of people. If the water supply dries up, then what happens to those cities?
Jones points to the northern Sahara Desert, which was wetter in the past, and scientists have detected urban areas buried by dunes. “So what happened to the people who lived there when desertification happened? They moved.”
It would be a lot of people to move. California’s Water Plan under development right now projects California’s population to climb from 38 million to 70 million by 2050. At the same time, the National Center for Atmospheric Research projects “severe and widespread drought” by 2060.
Patzert says population growth, combined with a drying climate and the massive water withdrawal and delivery systems, has built too much risk into civilization. “You risk the danger of being ill prepared for a natural catastrophe, which today would be catastrophic, if not apocalyptic,” Patzert said. “A 100-year drought in the West would wipe out a lot of California, Arizona, and Nevada. We are not going to all get in our Honda Priuses and drive to British Columbia.”
Jones called the idea of evacuating California “outrageous” and said that megadrought is a much slower process. Thirsty residents could get water from desalination plants. A California Environmental Protection Agency panel listed 21 plants either in operation or proposed from Sacramento to San Diego. For landlocked communities, Jones also has what she calls “a much more realistic example.”
“If you are familiar with climate change, one of the projections is that the U.S. Southwest is going to get warmer and drier. Take Phoenix, for example. They had more than 100 days of 100-degree heat. Future climate change says it is going to get worse. Ask yourself how many people will want to move to those conditions in the future?” she asked. “Something on that scale would not be happening to just California, it would have an effect nationwide.”
According to a Yale University newsletter published on June 20, 2013, the current drought is already the fifth most severe since 1,000 AD, and New Mexico is already “a natural experiment in megadrought.”
The National Drought Council That Wasn’t
Progress toward a national response to drought started 13 years ago when a temporary National Drought Policy Commission recommended that the president immediately establish a National Drought Council and that Congress should create a long-term National Drought Council. The proposal was introduced in the 107th Congress but died in subcommittee.
“One of the reasons the bill didn’t pass is because detractors felt it created committees that would prepare a report and further action and that is not a quick way to achieve things,” Jones said.
But the proposal came back in June of this year. USAgNet reported that after Mississippi experienced floods in 2011, drought in 2012, and a violent storm in 2013, Mississippi River mayors successfully amended the Farm Bill to revive the National Drought Council. That bill failed too.
There are also some short-term challenges cropping up that hinder drought planning. “One of the biggest priorities right now is ensuring stream monitoring programs,” Jones said. “That is how we measure what is going on. That is how we know whether it is dry or not and the distribution of dry conditions.” She said the loss of U.S. Geological Survey stream monitoring stations as a result of budget cuts is one of the problems, especially sites with long-term data.
Long-term data is proving invaluable to Kleppe who is trying to use it to find drought patterns that could be used to predict megadrought. He is using long-term snow survey data, covering 100 years at three different Sierra sites, and combining that with the ancient Fallen Leaf Lake trees. He says he has found some possible drought indicators that are “repeatable,” but since his theory is not yet scientifically published, he isn’t ready to go public.
“What is the driver of a megadrought?” Kleppe said. “You look for cyclic things that might occur.”
For now, Kleppe is trying to raise awareness of megadroughts and the signs in Tahoe, giving talks about the issue at Stanford camps. He said it is hard to keep the discussion going because participants then disperse across the nation and Tahoe has a lot of second homeowners.
On the surface, Tahoe residents don’t have a lot to worry about. “They are in good shape in Lake Tahoe because they have a big, deep lake that is fed from the spring melt from the Sierra,” Patzert said. But there is reason for concern when Tahoe has water and all the large communities around it don’t. “Those are called the water wars. People have written about that in our future. We already have it.”
Whether we are on the verge of a megadrought, Kleppe said water managers are becoming more interested and he is writing a proposal to the National Science Foundation for grant money to study the rest of the trees in Fallen Leaf Lake to back up his theories.
Studying the trees involves carbon dating and developing underwater coring techniques to look at the ancient tree rings. Doing that could take years. Meanwhile, the surface of Fallen Leaf is just 25 feet away from exposing the megadrought forest.
“Twenty-five feet would go pretty fast. My guess is it will go down within a decade,” Kleppe said. He doesn’t like to think about that. “You get emotional about it.”
To cope with the welling of all the emotions and issues that come with a megadrought, he makes his own joke about the impact on his lake house: “I would have to get a pier extension, right? You’d walk out your door and it is 150 feet down to your boat dock!”
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