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Drowned Trees Reveal Past Drought

There are ancient trees submerged beneath Lake Tahoe, meaning the region was once much drier than it is now. Those trees are remnants of epic droughts over the centuries that lasted so long, they caused Lake Tahoe and other western lakes to drop 20 feet or more, allowing forests to grow where there is now water. And they could come again. Despite recent heavy rain and snow, should the area start planning for another monster drought?

In 1994, Scott Stines examined tree stumps at the bottom of Mono, Tenaya, Tahoe and other Sierra lakes, using used radiocarbon dating and tree-ring analysis. He discovered the water-logged stumps were holdovers from two extended droughts, that lasted from 900 to 1110 AD and from 1210 to 1350 AD, when the lakes shrank to a fraction of their current size. Analysis of Central Valley oaks shows that major droughts have occurred every century, usually lasting six to 15 years. An epic drought seems unlikely to happen anytime soon, since rain recently soaked the West Coast and the snowpack in the Sierra and other mountains is 139% of the average for this time of year. But California is extremely vulnerable to drought that lasts as little as four or five winters. Since its last drought, from 1987 to 1992, California has added millions more people, along with more yards, orchards, golf courses and other water-dependent businesses. "The picture doesn't look good," says Steve Hall of the California Association of Water Agencies. "Since the last drought, we've added 6 million people. We have not added significant new supplies."

Families are also moving into the drier, hotter parts of the west. Phoenix, which is predicted to have major water supply problems in the future, is one of the fastest-growing cities in America. The Las Vegas area is still growing quickly, and it?s water-challenged as well. One reason people move west is to get more property, which they use water to convert from a desert into a lush lawn. Per capita water use in California has risen to 200 gallons daily, up from 160 gallons during 1992, the final year of the last drought. "The fact is, we don't use water very efficiently in California," says Peter Gleick of the Pacific Institute. "It is only during droughts that people start to pay attention to the proper use of water."

Jeanine Jones, drought preparedness manager for the California Department of Water Resources, says things could get tough if California undergoes a dry spell lasting more than six or seven years. "You know those tree stumps in Lake Tahoe? They represent a dry period that lasted centuries," she says. "Obviously, we have developed in conditions that are much wetter than that."

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