Sierra lake’s submerged trees unlock keys to past, future mega droughts

Retired Reno professor says no way now to say when next one will strike
By: Gus Thomson, Journal Staff Writer
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John Kleppe’s curiosity coupled with a love for fishing led to an underwater discovery in a Sierra lake that continues to help us know more about a lengthy drought in the Middle Ages that hit the area and could return.

Speaking Friday in Auburn, the University of Nevada, Reno professor emeritus told a regional meeting of water suppliers that submerged trees 100 feet high that died in a drought around 1215 have provided a real-time look at how climate change affected the area during the Middle Ages.

Rings from the trees were studied to determine how a prolonged drought swept through the area around Fallen Leaf Lake, where the 100-foot juniper was found 25 feet below the surface. Carbon dating backed up the age of the trees, which had died around the time of the 1215 signing of the Magna Carta.

When rings are narrow, they signal that water is scarce and growth is minimal. When they are wide, precipitation is high.

Kleppe, who bought a second home on the lake adjacent to Lake Tahoe 30 years ago, first encountered the ancient tree while trolling for fish. He eventually he sent a diver down to determine what was causing his line to snag in the water.

That led to the discovery of the tree and a reading of the rings that showed drought had struck the area hard over more than 220 years.

“The droughts we’ve had over the past 200 years are small compared to the mega droughts of medieval times,” Kleppe said.

Kleppe said that the reasons behind any drought are a combination of factors, including increased sunspot activity.

“I wish I could tell you that a mega drought is occurring next Thursday,” Kleppe said. “My mission to you today is to try to be broad-thinking about what is really happening.”

Kleppe, who retired from the Reno university in 2006, said his work on the lake continues. Friday’s speech in Auburn was at a forum sponsored by the Mountain Counties Regional Water Resources Association and the Association of California Water Agencies.

“There are 88 more trees (still submerged) that haven’t been examined that can more closely tell us when the drought may come again,” Kleppe said.