Scientists find patterns in Utah's wet-dry cycles
Environment » USU researchers say Pacific Ocean temps echo, years later, across the northern part of the state.
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Charlie Black has seen the Great Salt Lake rise some years in the wetlands just below his family farm. He's also known years so dry, the farmer has had to cut back on irrigation.

"That's about all I know," he said, "the lake rises and falls."

It would be a big help, he readily agreed, to have some sort of crystal ball to know when the dry and the wet years are coming.

At Utah State University, researchers have been watching the cycles, too. And they have found a predictable rhythm to wet-dry cycles, a pattern that holds promise for helping manage everything from Black's crops to reservoirs and homeowner water conservation.

Rob Gillies, the climate center's director and an author of the report, calls the findings exciting and potentially useful. His team's work has been published in the peer-reviewed journals, Geophysical Research Letters and Journal of Climate .

"It's giving you a telescope," said Gillies, "and allowing you to see into the future."

His team studied long-suspected patterns against temperature measurements, precipitation readings, tree-ring data and Great Salt Lake levels.

They looked at data that goes back nearly 1,000 years, discovering a powerful relationship between sea-surface temperatures in a specific area of the Pacific Ocean and the rainfall and snowfall in northern Utah.

The 12-year cycle is like an echo with a 3-year-delay: just as the Pacific temperatures head toward their lowest, the precipitation in northern Utah begins to increase. And when the ocean temperatures approach their warmest, a drought begins digging in. The pattern does not apply for southern Utah and its distinct climate pattern.

Gillies called this long-distance relationship "an amazing coherence."

The USU team also found two more important precipitation cycles that function simultaneously. One is about 40 years long. The other is 150 years. And, when the cycles coincide, the rhythm is especially powerful.

Remember the wet patch northern Utah experienced in the early-1980s? That's a time period when the 12-year, 40-year and 150-year cycles fell in line at the same time, the USU researchers found.

It resulted in record precipitation. And, a few years later, shoreline levels at the Great Salt Lake were higher than ever measured and a river ran through the streets of downtown Salt Lake City.

In addition, Gillies team noticed another important pattern: droughts like few Utahns have ever seen.

The team found that, in the past 60 years or so, northern Utah has not experienced the profound droughts that have been typical in the region: patches of very long, extremely dry periods when below-normal precipitation parched the landscape for around 100 years at a time.

"What is amazing," said Gillies, "is not only the depth of the drought but the duration."

Richard Bay, general manager of the Jordan Valley Water Conservancy District, said the findings roughly follow a wet-dry pattern his district has seen over the years. He added that the scientific findings potentially will aid in managing the resources relied on by his more than 600,000 customers.

"It's not a total answer," Bay said. "But it would be a big help in predicting water supplies."

If the link between sea-surface temperatures and precipitation cycles holds true, he noted, the district will have another tool for deciding how to juggle its surface water and groundwater supplies and when to step up conservation programs.

Brian McInerney, a hydrologist for the National Weather Service in Salt Lake City, said the scientific findings can help guide behavior. He points to the USU findings about past droughts.

"The future is looking rough for water supplies," he said, noting that Utah is dealing with a fast-growing population and the prospect of drier periods that could come with a changing climate. "If you can plan for what's coming, you can make it easier."

Black, whose family has been farming in Syracuse for a half-century, agreed that the findings could help him decide what to plant and even when a forecast of severe drought might make it smarter not to plant at all.

"If [USU's study] proved to be true," he said, "it would be a good planning tool."

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