Weather? Climate change? Why the drought is persisting and growing.
Several factors, including La Niña events, have contributed to the expanded drought, meteorologists say. Conditions in the West may be setting up for a 'megadrought' by century's end, researchers warn.
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"It's been kind of a flash drought," says David Miskus, a senior meteorologist specializing in agricultural weather forecasting at NOAA's Climate Prediction Center in Camp Springs, Md. When you look back to February of this year, there was no drought at all in the Midwest Corn Belt area.Skip to next paragraph
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But the winter was unusually warm and dry and was capped by a period in early March when daytime high temperatures in several Midwestern cities ranged from the upper 70s to the mid-80s.
The heat, combined with sparse snow cover, set the stage for drier soils heading into the growing season. Drier soils also meant less evaporation to ease the warmth.
The drought began to spread in April, gathering intensity to strike in force in May, June, and July, Mr. Miskus says. Its timing couldn't have been worse. High temperatures that accompanied the growing drought came as corn and soybeans were set to pollinate.
"When temperatures reach above 95 degrees, corn doesn't pollinate," he says. "We haven't seen a drought like this hit that area since 1988."
The '88 drought triggered congressional hearings on global warming that significantly raised the issue's public profile.
To explain the current drought's persistence, meteorologists point to a dome of high pressure that has been doing a rumba back and forth across the country's midsection.
Storms moving in off the Pacific have moved up over the dome into southern Canada before moving back down the eastern side of the dome to moisten the East Coast.
Given the history of drought in North America – including three decade-long droughts in the 1800s and one in the 12th century that lasted 40 years – it's difficult to spot changing trends that would clearly point to human-triggered climate change as a significant factor, says Richard Seager, a climate researcher at the Lamont-Doherty Earth Observatory in Palisades, N.Y., who focuses his research on multiyear droughts.
"The climate system has a tremendous amount of noise in it," he says. "You're trying to detect an emerging human-induced signal amongst this colossal natural variability. It's very hard to do."
Researchers also note that the Intergovernmental Panel on Climate Change's latest report on global warming and severe weather, released earlier this year, found that for central North America, droughts have become shorter, less frequent, and less severe.
Drought represents the combined effects of high temperature and a shortage of rain or snow. Global warming's fingerprint stands the best chance of showing up in temperatures.
A study published Monday attributes record-smashing summer temperatures in Russia in 2010 and in Texas and Oklahoma last year to global warming, based on a statistical study of global temperature records since 1951.