PITTSBURGH, Feb. 22 (UPI) -- America's Pacific Northwest, known for abundant rainfall, could face longer dry seasons after a wet 20th century not likely to be repeated soon, scientists say.
Researchers led by University of Pittsburgh scientists say the prediction is supported by a 6,000-year climate record extracted from the bed of a Washington lake that suggests Western states likely will suffer severe water shortages as El Nino/La Nina patterns wield greater influence on the region, a university release reported Tuesday.
When the patterns became more intense, wet and dry cycles in the Pacific Northwest become more erratic and last longer, they say.
Scientists say a sediment core from Castor Lake in north-central Washington showed the region's drought history since around 4,000 BC and indicated wet and dry cycles during the past millennium have grown longer, affected by the strong pressure and temperature changes of the El Nino/La Nina cycles.
The sample showed the wet cycle stretching from the 1940s to approximately 2000 was the dampest in 350 years.
Those unusually wet years coincide with the period when western U.S. states developed their present water-use policies, Mark Abbott, a Pitt professor of geology and planetary science, says.
"Western states happened to build dams and water systems during a period that was unusually wet compared to the past 6,000 years," he says. "Now the cycle has changed and is trending drier, which is actually normal. It will shift back to wet eventually, but probably not to the extremes seen during most of the 20th century."