An ancient forest at the bottom of Fallen Leaf Lake might reveal evidence mega droughts return cyclically to the Lake Tahoe Basin.
John Kleppe, professor emeritus at University of Nevada, Reno, authored an article in 2005 after he discovered 200-year-old trees rooted 120 feet below the surface of Fallen Leaf Lake had all died simultaneously.
“(For) these trees to be rooted below the surface of the lake, the lake must have been down at least 36.5 meters (120 feet) for over two hundred years. This would indicate that a ‘mega drought’ had occurred, since several of these trees have been carbon dated to have ‘drowned’ in 1215 A.D.” the report stated.
The extreme dry conditions would have persisted during the medieval period from 850 to 1150 A.D., and would have been followed by a wet period with enough precipitation to raise lake level by more than 100 feet, according to the study.
This summer, Kleppe will carbon date 80 additional submerged ancient trees in Fallen Leaf Lake to test if these mega droughts return periodically to the basin. If Kleppe can prove the trees died at the same time during another period in the basin’s history, it will indicate that extreme droughts have occurred multiple times and could happen again.
“People are convinced now that the mega drought occurred, and it appears to be a cycle,” Kleppe said Friday. “I feel that the cycles aren’t based on one single driver.”
From preliminary work at Lake Lucille located southwest of Fallen Leaf Lake in Desolation Wilderness, Kleppe hypothesizes the cycle is caused by a combination of both orbital and solar factors. He recorded an interesting frequency in the historic annual snowpack at Lake Lucille and Ward Creek in the basin and a similar frequency near Mammoth Peak. He believes the clue to the cyclic nature of the mega droughts may be found at Lucille. He’s working on a paper with his new findings, Kleppe said.
If a mega drought is coming again, what can we do about it? According to Kleppe, the answer might mean how the state manages its water. When an atmospheric river occurs, such as the storm that rolled through the basin late last year, that water should be collected and stored, Kleppe said.
Predicting the duration and timing of the next extreme drought is an imperfect science, and infrastructure changes that would allow more water to be collected are the best ways to prepare for those events, he said.
“You can’t warn people to clear out before an earthquake, but what you can do is change the constriction requirements. And you can do the same thing for water,” Kleppe said.