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Ocean temps signal drought
What are the odds of the drought disaster of 2012 repeating itself in 2013? While Art Douglas won't predict that, he does think there are more droughts in store in the next decade.
Douglas is professor emeritus of atmospheric sciences at Creighton University. He's made extensive studies of global weather patterns, with particular attention to ocean currents and ocean water surface temperatures. Looking back at 2012, a perfect storm of events teamed up to make it one of the driest summers in memory for the Midwest.
The roots of the drought of 2012 involve some events you might not know much about. And those phenomena relate to long-term drought prospects.
Early soil dryness
Douglas says he had a hint of drought last winter, when we were already in the midst of a dry spell that had started the previous fall. It left Midwest soil moisture at low levels going into the summer. “We know that about 40% of the rainfall we get in the summer is recycled soil moisture that evaporates and transpires from the soil surface,” he says. “With very low soil reserves early in the growing season, we didn't have that 40% of normal rainfall to work with. We were in trouble right out of the chute.”
On top of that was the very hot weather that hit the Corn Belt early in the summer. It dried up any remaining moisture. “I thought it would be a warm summer; I saw that coming. But it intensified more than I thought.”
Those events – lack of moisture and extreme early heat – can help form an upper-level high-pressure dome that blocks weather events from moving through the Corn Belt and producing rainfall. It tends to push storm events north toward the Canadian border or farther, which is exactly what happened in 2012.
Ocean temperatures along the equator are well known for their influence on weather patterns and rainfall in North America. Normally, an El Niño pattern (warmer-than-normal water on the equator) would predict good summer rains. We've had an El Niño in place since early summer, and about 80% of the time this would give cooler and wetter conditions as the summer progresses. But not this time.
Higher-than-normal North Atlantic (red) and colder-than-normal Eastern Pacific (blue) ocean surface temperatures point to drought in the U.S. midsection, says climatologist Art Douglas. he expects recurring droughts in coming years.
Douglas knows why. He's been watching the ocean temperatures in two other places: the North Atlantic and the Eastern Pacific (California to Hawaii). He says they are now providing a more dominating influence on Midwest weather than waters on the equator.
In the case of the North Atlantic, it's warmer-than-normal waters. In the Pacific, it's colder. Both of those events are strongly in place right now, by several degrees deviation from normal, and both predict drought in North America, which is exactly what happened. “In the case of the Pacific, it's the coldest water in 60 years,” says Douglas. “It's a very strong influence and has overpowered any effect of El Niño.”
Put together, the soil dryness and the ocean temperatures gave sort of a perfect storm for extreme drought in 2012. It's identical to the pattern that produced historic Great Plains and Midwest droughts in the 1930s and 1950s, says Douglas.
He says those phenomena and the dry weather appear to be persisting into the early fall, despite the El Niño that would normally end a drought. “It just tells me that the North Atlantic and Eastern Pacific water temperatures are more influential right now on our rainfall than what happens on the equator,” he says.
Breaking a drought
Two events may move the high-pressure dome and let more normal rainfall patterns come to the Midwest later this fall. One is shorter days of less sunshine. That reduces the surface soil heating that feeds the dome of high pressure in the Plains. The other is the El Niño on the equator. If it intensifies, it could overpower the other ocean temperature events farther north and change Midwest weather to cooler and wetter by mid-fall 2012.
“Most weather models say we will have a moderate or moderately weak El Niño into early spring. That would predict more moisture in the Plains between now and then,” Douglas says. “El Niño patterns can often create temporary breaks in long-duration drought events.”
In the meantime, he continues to watch the temperatures in the North Atlantic and Eastern Pacific. “Those tend to be longer-term shifts that can often last for decades,” he says. El Niños and La Niñas (cool on the equator) run their course in just a few years, but the Atlantic and Pacific events run in 20- to 25-year cycles. Since we're in the middle of the pattern, Douglas says the next 12 years could be punctuated by periodic droughts, similar to the 1930s and 1950s.
Douglas is confident these patterns are not the result of global warming. “They are oscillations of ocean currents and naturally occurring patterns. Global warming may influence them, but it is not the cause,” he says.
What you can do
You can't make it rain, but you're not powerless, either. “There's nothing you can do about this Atlantic-Pacific thing, it's out of anyone's control,” he says. “But conservation tillage with less soil exposed to water loss is a good practice. That may be a part of the reason that we haven't seen more recurring drought in recent years.
“The other thing you can do is choose your crops and hybrids accordingly. It makes sense to choose crops that have drought-resistance built in,” he says.