La Nina return may prolong drought

Sep 9, 2011
by DTN

In the past year, U.S. crop areas have been buffeted by the effects of the strongest La Nina in almost 100 years.

La Nina describes Pacific Ocean equatorial waters having cooler-than-average temperatures. In the U.S., the weather effects of La Nina include drier conditions in the southern Plains and Midwest, and above-average precipitation during winter in the northern states.

La Nina is blamed for helping to cause some outrageous weather since last year: a hot and dry pattern in the Midwest in late summer 2010; the beginning of what has become a historic and devastating drought in the southern Plains that is still in effect; record snow and rain in the northern Plains which contributed to Missouri River basin flooding during winter and spring 2010-11; heavy rain that delayed field work and flooded the eastern Midwest and Delta this past spring; and a catastrophic round of severe weather, which included a record number of tornadoes in April 2010.

On the market side, it’s questionable as to whether a return to La Nina would make much of a difference— even if drought were to continue in the southern Plains wheat areas.

While their pocketbook might be affected by what happens globally, America’s farmers continue to feel the effects of the most recent La Nina on their crops.

La Nina took hold in late summer 2010 and lasted until April 2011. During that time, a Pacific barometric pressure comparison known as the Southern Oscillation Index had the strongest La Nina readings between August and December 2010 since a La Nina event during World War I back in 1917.

A recurrence is not out of the question. One measure of the Pacific temperature and pressure patterns, called the Multivariate ENSO Index, predicts a re-forming of La Nina, based on the historic strength of the 2010-11 pattern.

Telvent DTN Senior Ag Meteorologist Mike Palmerino agrees that such a return of La Nina conditions is possible.

“I think you certainly have to lean towards more of a La Nina characteristic to the pattern coming back into play,” Palmerino said. “It seems like an initial surge of the temperatures to a little bit warmer—which would be a trend toward El Nino— has died out and we’re prob ably going the other way a little bit at this point. I´m not leaning toward this being the magnitude of last year, but certainly leaning neutral to at least a weak La Nina as opposed to more on the side of El Nino.”

Should the Pacific head back into a La Nina direction, the fall weather pattern would be generally beneficial for harvest in the Corn Belt, which is a similar situation to harvest in 2010.

However, the potential for additional drought problems in the southern Plains is a big concern.

“I don’t think trending in that (La Nina) direction is particularly helpful in terms of improving the overall situation,” said Palmerino. “I’m also not a believer that this drought scenario is La Ninadriven, but it’s La Nina- supported, and a La Nina tendency in the fall would continue to support drought in the Texas-southern Plains area.”

Nebraska state climatologist Al Dutcher agrees with Palmerino on the potential for continued dryness issues in the southern Plains if La Nina makes a repeat visit. “A multi-year La Nina would be disastrous,” Dutcher said.

Dutcher is also worried about another year of flood issues in the central and northern Plains and western Midwest if La Nina remains in play during the winter of 2011-2012.

“We’ve already got some areas in the northern Rockies that will not lose snowpack this summer,” he said.

“If there’s another winter with heavy snows, can we manage the reservoirs adequately, to move water around to avoid a repeat of what happened (Missouri Basin flooding) this year?” — DTN