Ocean conditions likely to reduce Colorado River flows during this winter's drought

Meg Sullivan in the UCLA Newsroom: The convergence in the coming year of three cyclical conditions affecting ocean temperatures and weather is likely to create unprecedented challenges for states that depend on water from the Colorado River, a new UCLA study suggests. "If I were concocting a recipe for a perfect drought, this would be it," said Glen MacDonald, co-author of the study and director of UCLA's Institute of the Environment and Sustainability.

Along with a former graduate student, MacDonald has found that the combination of La Niña with two less commonly known ocean conditions — the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation — tends to result in drought in the upper reaches of the Colorado River. The ocean conditions have been known to diminish precipitation in the Southwest but, examined separately, have proven to be poor indicators of drought conditions in the upper reaches of the river.

"It's the combination that's key," said lead author Abbie Tingstad, who conducted the research as a graduate student in geography at UCLA. She is now an associate physical scientist at the RAND Corp. The convergence of these patterns in the Pacific and Atlantic oceans may well drive water levels in the Lake Mead reservoir below a critical threshold and could potentially result in reduced water allocations for Arizona and Nevada, the researchers say.

Essentially all of the Colorado River water used by Southern California passes through the reservoir, which is the largest in the nation. Fed primarily by snowpack melt from its upper reaches, the river is Southern California's chief source of water. "Declines in water availability of this magnitude during the coming winter could be devastating for states that depend on the Colorado River for their water," Tingstad said…..

Desert Shore in Lake Mead National Recreation Area, National Park Service