U.S. Southwest Drought Could Be Start of New Dust Bowl

Anne Minard
for National Geographic News
April 5, 2007
The unprecedented drought that has gripped the southwestern United States isn't almost over, researchers say, it may have only just begun.

That's the consensus of all but 1 of the 19 climate models used as the basis for this week's upcoming report from the Intergovernmental Panel on Climate Change (IPCC), according to a new analysis.

Richard Seager, a senior research scientist with the Lamont Doherty Earth Observatory, and co-authors report their findings today in the online advance version of the journal Science.

Based on the climate models, the U.S. Southwest and parts of northern Mexico could become as arid as the North American Dust Bowl conditions of the 1930s, the study authors report.

"If these models are correct, the levels of aridity of the recent multiyear drought … [will] become the new climatology of the American Southwest," the team writes.

Persistent Drought

In general the computer models all predict decreasing precipitation in the subtropics in both hemispheres.

The long-term drying of southwestern North America is part of that pattern. Changes in atmospheric circulation and water-vapor transport are expected to alter the region's climate as the planet warms.

Seager said the most surprising finding is that "this drying trend in the subtropics becomes so clear very early in the current century."

In fact, long-term drying may have already begun, the authors say.

Persistent La Niña-induced temperature fluctuations in the Pacific Ocean caused a drought between 1998 and 2002 that was much like earlier droughts during the 1930s and '50s.

La Niña, the cold-water cousin of El Niño, is a phenomenon in which the Equatorial Pacific experiences unusually cold sea-surface temperatures. The event is associated with drier winters in the U.S. Southwest.

"What is unusual is that after the La Niña ended in 2002, the drought persisted with only brief interruptions," Seager said.

The new paper suggests that the ongoing aridity is linked to broader changes that are causing the drier regions of the subtropics to expand toward the poles—a likely consequence of global warming.

Alarming Consensus

Kenneth Cole is a climate researcher with the U.S. Geological Survey's Southwestern Biological Science Center, who was not a co-author on the new study.

He acknowledges that the paper relies solely on computer models to reach its conclusions about the impacts of climate change.

"One could take a skeptical stance that it is not really possible to model something so complex as climate in a computer," he said.

But Cole isn't skeptical about the latest results.

"The fact that only 1 of the 19 climate models reviewed did not show drier conditions over the next century is alarming," he said. "These types of comparisons rarely show that much of a consensus."

Furthermore, he said, the models match what he and other researchers in the Southwest have been documenting for a decade.

Exorbitant Lifestyle

Continued drought in the Southwest is likely to reduce freshwater supplies and increase wildfire potential, the experts note.

(Related: "Warming Climate Fueling Wildfires, Study Says" [July 6, 2006].)

In addition, plants and the animals that depend on them will likely migrate to higher elevations. Species that can't migrate quickly enough won't survive.

Thomas Whitham, who directs the Merriam-Powell Center for Environmental Research at Northern Arizona University, hopes the new study will serve as a wake-up call to residents of the Southwest.

"If we continue to draw down water to maintain our lifestyle with its exorbitant use of water," he said, "we can effectively turn a hundred-year drought into a millennium-level drought, which far worsens the community and ecosystem consequences."

And because this is a global trend, the U.S. won't be the only country affected.

For USGS's Cole, the new paper also suggests "a spread of global drought into many of the [developing] countries least prepared to deal with it."

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