Scientists say 10-year or longer drought possible

Friday, Nov. 8, 2002 | 10:01 a.m.

New research indicates the Southwest, which is in a fourth year of drought, could be in for a decade or more of dry weather, similar to a 10-year drought that parched the region in the 1950s.

Scientists have found a climate system that can bring extremely dry weather for 20 to 30 years at a time, in the same way that the climate trend El Nino can bring heavy rains from the Pacific Ocean to the West every few years.

A good snowpack in the Colorado Rockies, which feeds the Colorado River, and steady rain this year could help, but it won't stop the drought, climatologists say -- not even with the help of the moderate El Nino trend that is expected this winter.

"El Nino is not necessarily a savior on a white horse," said climatologist Kelly Redmond of the Western Regional Climate Center in Reno.

The newly discovered system, called the Pacific Decadal Oscillation, could stunt the effect of El Nino in bringing relief.

"We may be entering a period where El Nino is not as effective in bringing winter precipitation to the Southwest," Redmond said. "Such periods might last decades."

With that long-term forecast in mind, climatologists nationwide have been looking at historical trends as far back as the 16th century to see what the drought could mean to the Colorado River and the Western economy that depends on it.

Half a century ago the Southwest suffered a drought that lasted for most of the 1950s, when Las Vegas was a backwater desert vacation spot with only a handful of resorts.

Today, with the population in the Las Vegas Valley at 1.5 million, a drought of that magnitude would be far more severe, National Weather Service meteorologist Ron McQueen said.

It should change the way residents think about water as the drought progresses, said Barbara Morehouse, associate research scientist at the University of Arizona's Climate Assessment Project for the Southwest.

"The region has experienced considerable growth and changes over several decades, a time when conditions have been relatively wet," she said. "Assuming these conditions will continue into the indefinite future flies in the face of everything we have learned about the ancient and recent climate history of the Southwest."

Researchers have continued going back in time to study climate changes that could shed light on current conditions.

Scientists at the University of Arizona, studying cores from old trees, believe they have found an extensive drought in North America during the 16th century that devastated early settlers and Native Americans over several decades.

They think the drought may have been created from a shift in ocean currents, though they do not yet know if it was connected to the Pacific Decadal Oscillation.

But they have asked themselves: What would happen if a similar extended drought occurs today? What if it is occurring?

While most water experts say it is too soon to tell how extensive this drought will be, the U.S. Geological Survey has studied the implications that an extended drought would have in the Western states.

At its worst, they concluded, an extended drought won't drain the Colorado River, but it will drain the West's economy.

In 1995 USGS researchers, using tree ring data, created a computer model that simulated a modern drought similar to the one that occurred in the 16th century.

The historic drought, from 1579 to 1598, accounted about a four-year loss of water in the Colorado River's flow.

The computer model showed that under similar conditions, the river would fall well below the 15 million acre-feet a year that the seven Western states along the Colorado count on each year under the Law of the River.

California by law receives 4.4 million acre-feet per year, the largest share of the Colorado, while Nevada gets the least at 300,000 acre-feet a year.

In the model the artificially harsh scenario showed that a drought lasting of about 19 years would affect California, Nevada and Arizona's water supply for only two years, the USGS study said.

There would still be water behind Hoover Dam even during the drought's worst years.

Economic damages are another story.

"A severe sustained drought would result in economic costs in all parts of the Colorado River basin," the report said.

It would cost consumers in Western states as much as $750 million a year in the final years of drought, but for municipal and energy water users the losses soar to $2 billion a year in the same period, the USGS study said.

The loss of hydropower produced by dams such as Hoover and Davis and the extra salt concentrated in river water could add another $750-million-a-year loss to the economy, the study said, because replacement electricity would be more expensive and salt could make some river water useless for people to drink or water crops.

Las Vegas water officials have been planning for such a scenario for more than a decade.

In 1989 the Southern Nevada Water Authority began pumping 250,000 acre-feet of extra Lake Mead water underground for a future dry spell, Southern Nevada Water Authority Resources Director Kay Brothers said.

That provides Las Vegas residents with a cushion against drought for a while, but the water authority is still nervous.

"When we've had three years like we've had -- the lowest Colorado River flows on record -- we're worried too," Brothers said.