Drought Return Forecast

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The Colorado River watershed may face a dry winter — and water rationing, according to several recent, unsettling studies.

In fact, Lake Mead may soon fall below the mark that will trigger a reduction in the supply of water for Arizona and Nevada, according to an alarming study by researchers from the University of California at Los Angeles published in the October issue of the Journal of the American Water Resources Association.

The researchers said that the overlap of ocean currents and temperatures in the Atlantic and Pacific Oceans will deliver a dry winter, with Lake Mead already just half full and only nine feet above the level that will trigger rationing.

Most of the studies suggesting a dry winter and serious drought have focused on the upper Colorado River watershed, rather than Rim Country. Fortunately, a wet winter last season filled Roosevelt Lake, which will give the Valley a cushion if drought results in a cutoff of water through the Central Arizona Project.

The worsening water forecasts for the region underscore the value of Payson’s agreement to double its water supply with 3,000 acre-feet annually from the Blue Ridge Reservoir — although that water won’t arrive for three or four years.

A flood of recent research has delivered potentially bad news for the region, including a showing that the Southwest is heating up twice as fast as the rest of the planet as greenhouse gas levels rise in the atmosphere.

Already, a cooling of surface waters in the Eastern Pacific has flipped the atmosphere from an El Niño pattern that often brings lots of rain to the Southwest to the opposite La Niña pattern, associated with below-average rainfall in this region.

Climate experts from NASA’s Jet Propulsion Laboratory reported the shift in September.

Climatologist Bill Patzert said the La Niña pattern will most likely push the region back into drought, and fuel another upsurge in big wildfires next spring. A strong La Niña can result in an 18-degree drop in the temperature of surface waters at the equator in the Pacific.

And that’s not even the worst news, according to the UCLA study, which looked at the link between ocean currents and temperatures and rainfall on a watershed that feeds into the Colorado River.

Climate experts have long struggled to understand the link between both ocean temperatures in the Pacific and rainfall patterns in the Southwest — since the cyclical warming of the Pacific doesn’t always affect rainfall here.

However, the UCLA researchers did an analysis that included two less well-known ocean circulation patterns. One is the Pacific Decadal Oscillation (PDO), which affects sea-surface temperatures off the Pacific Coast of North America. The other is the Atlantic Multidecadal Oscillation, which has to do with temperature changes in the North Atlantic — which can persist for decades.

Researchers used computers and tree-ring growth patterns in pinyon pines going back 1,000 years to search for a link between rainfall on the Colorado River watershed and these three ocean temperature patterns.

Turns out, average rainfall drops by 50 percent for 5 to 18 months throughout the Southwest when those three patterns line up wrong. That has happened five times between 1945 and 1965.

Not only have those patterns kicked in now, they’re also unusually strong. Such a strong lineup played a role in bringing on the disastrous Dust Bowl of the 1920s, the researchers concluded.

The region can expect a roughly 10-percent decline in snowpack on the Colorado River watershed and an 18-percent decline in the river’s flow, the researchers warned.

Some 30 million people get water from the Colorado River, whose waters are divided among seven states, with the lion’s share going to California. If Lake Mead falls another nine feet to an elevation of 1,084 feet above sea level, it would trigger a 12-percent reduction in CAP water going to Arizona — a loss of about 300,000 acre-feet. More reductions would follow as the reservoir drops.

Based on the strong La Niña already in place, the Southwest should have above-average temperatures and below average rainfall this winter, according to seasonal forecasters for the National Oceanic and Atmospheric Administration.

That prediction comes on top of disquieting studies showing that between 2003 and 2007, average temperatures in the Colorado River Basin rose by 2.2 degrees — more than double the global increase of about 1 degree.

That unsettling news was reported by the Rocky Mountain Climate Organization, based on measurements gathered by NOAA.

Study author Stephen Saunders said the temperature rise in the region has contributed to $2.7 billion in crop loss claims related to the drought.

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