Researchers analyzed more than 20 years of satellite and climate data from five major areas: the Upper and Lower Colorado River basins, the Great Basin, California and the Pacific Northwest, including parts of Mexico and Canada.
Together, those areas provide water to more than 60 million people and vast stretches of farmland.
The researchers found some of the strongest connections between California and the Great Basin — which includes most of Nevada and much of Utah. Runoff conditions in the two areas were synchronized 65% of the time, while soil moisture moved together 67% of the time.
Overall, six major watershed pairings had runoff conditions that were synchronized more than half the time.
“That can create a real challenge, actually, for water managers,” said Tom Piechota, a water resources researcher at Chapman University in California and co-author of the study. “Because that could mean if you have large droughts, they could all be in a drought at the same time.”
The researchers also found widespread hydrologic extremes were relatively common. Multiple watersheds experienced unusually wet or dry conditions at the same time in about 25% of the months analyzed, with major synchronized extremes occurring roughly every three to four years.
For water managers, Piechota said those connections can limit options during drought. If nearby areas are also struggling with shortages, there may be less water available to provide relief.
He pointed to California and the Great Basin as an example.
“If the Great Basin’s dry, it’s not going to be able to be bailed out by California, because California’s likely dry also, and vice versa,” Piechota said.
Researchers also found that changes sometimes happened at different times. Water anomalies in the Pacific Northwest preceded those in the Lower Colorado River Basin by about five months. Changes in the Upper Colorado tended to lead California, the Lower Colorado and Great Basin by about a month.
Piechota cautioned that those relationships aren’t necessarily a forecasting tool. Instead, they offer another way to understand how water conditions are connected throughout the West and could eventually inform how managers prepare for widespread shortages.
The researchers also examined what they call “hydrologic whiplash” — rapid swings between unusually wet and unusually dry conditions. The coastal Pacific Northwest and arid Southwest stood out as hotspots, experiencing those abrupt shifts in about 20% of years.
The findings suggest Western watersheds shouldn’t always be viewed in isolation, Piechota said. Understanding which areas tend to get wet or dry together — and which don’t — could give water managers a broader picture as they plan for drought and other extremes.
This story was produced by the Mountain West News Bureau, a collaboration between Boise State Public Radio, Wyoming Public Media, Nevada Public Radio, KUNR in Nevada, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio and KJZZ in Arizona as well as NPR, with support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
