SCIENCE:

Dust Bowl, 1988 both eclipse 2012 drought, scientists say

For Midwest farmers and ranchers whose parched lands are gasping for rain, the 2012 drought is utterly devastating. For the scientists who take the long view of history, it's merely a climatological blip.

On-the-ground reports sent to the National Drought Mitigation Center tell of stunted corn, dry ponds and dead cattle that have left farmers and ranchers across the central United States reeling. And with more than 40 percent of the country's agricultural land now in "extreme" or "exceptional" drought, the Agriculture Department warned last week that food prices are likely to jump 2.5 to 3.5 percent this year, with further increases through 2013.

But despite the havoc wreaked on one of the nation's richest agricultural regions, scientists say this drought is practically embryonic compared with the severity and extent of others in America's past.

The process of understanding the severity of the current drought begins with the 117-year record maintained by the National Oceanic and Atmospheric Administration. It's based on the Palmer Drought Index, a formula devised in the 1960s that combines information about temperature, precipitation and ground cover to monitor drought throughout the country on a weekly basis.

The latest update, released last week, shows 59.6 percent of the United States in drought. It's the largest dry spell, by area covered, since 1954, when 60.4 percent of the country was in drought. It's also fourth on the all-time list, behind 1954 and two Dust Bowl years, 1934 (79.9 percent) and 1939 (62.1 percent).

But those numbers don't tell the whole story. They are snapshots from the week-by-week historical record.

The Dust Bowl held on for as many as eight years in some parts of the Great Plains, with successive dry spells hitting in 1934, 1936 and 1939-1940. The multiyear drought of the 1950s began in the Southwest but eventually spread to cover 10 states before it ebbed in 1957.

The current drought, in contrast, is just about 2 months old.

Hoping for an '88

On May 15, according to the U.S. Drought Monitor, 33.6 percent of the contiguous United States was experiencing some level of drought, with the worst dryness clustered in parts of Georgia and Florida. Conditions were normal in much of the central United States.

By June 19, the picture had changed dramatically. Hot, dry conditions had rolled into the Plains and worsened in the West and Midwest, with drought covering 46.7 percent of the continental United States. Currently, according to the Drought Monitor, 63.9 percent of the lower 48 states is suffering drought.

The best historical analog is a relatively recent one, said Michael Brewer, a physical scientist at NOAA's National Climatic Data Center.

"This year actually looks a lot like 1988," he said. "A summer-onset drought that hit in the Corn Belt, with conditions that came on and deteriorated rapidly, with big impacts to the agricultural community."

That drought caused an estimated $40 billion in agriculture losses -- $78 billion in today's dollars. But it lasted only a year.

"That's very different than the droughts of the '30s and '50s," Brewer said. "The drought in the '30s was almost 10 years long. In the '50s, depending on where you were, it was anywhere from a few years to six to eight.

"We hope this year is a 1988," he added. But projecting how long the drought might last is a tricky proposition. And understanding what caused it is trickier still.

So far, 2012 has seen record-breaking warmth that shows no signs of ebbing. January to June 2012 were the hottest six months in the lower 48 states since federal records began in the 1880s, according to NOAA.

'Consistent with' climate change

The agency's Climate Prediction Center expects the drought to linger or intensify in the Midwest through the end of October, with temperatures remaining above normal. The Southeast and Southwest could see some improvement, however.

How that forecast plays out will depend in part on the behavior of the natural cycle that produces the El Niño weather pattern and its counterpart, La Niña.

"It's really hard to get a multiyear drought in the same place unless you have a persistent El Niño or La Niña, and it's not like we have that this year," Brewer said.

The two back-to-back, or "double dip," La Niña cycles that ended in May helped create the scorching heat wave that drove Texas' record-breaking drought last year and the drought conditions that still linger in the Southern Plains.

Research by scientists at Columbia University's Lamont-Doherty Earth Observatory suggests La Niña also played a role in the droughts of the 1950s and the Dust Bowl, although the latter was exacerbated by poor grazing practices.

For now, La Niña is gone. Federal forecasters say conditions are likely to transition from neutral to an El Niño sometime this fall. That could bring some relief to the southern United States, which normally sees increased precipitation during El Niño years. But it is unlikely to help the parts of the Midwest and Ohio Valley that are currently suffering from drought.

Though scientists have not fully analyzed the causes of the current drought, Brewer said it is "consistent with what we'd expect under climate change."

"You're going to see more extremes," he said. "When it rains, it rains harder. But it means there is potential to go with longer periods of time between rain."

In its recent special report on extreme weather, the Intergovernmental Panel on Climate Change said it had "medium confidence" that droughts in central North America have been less frequent, less intense or shorter since 1950.

But there is some evidence that suggests climate change increased the odds of at least one drought in the region.

A recent study by researchers at NOAA and the U.K. Meteorological Office concluded that the scorching heat wave that helped produce the recent Texas drought is 20 times more likely to occur during a La Niña event today than it was during a La Niña in the 1960s.