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Ocean temps signal drought

11/16/2012 @ 1:51pm

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.

Water temperatures

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.”

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