After dealing with widespread drought conditions for nearly a decade, the U.S. as a whole experienced a big-time reprieve in 2009. Yet, as weather experts look toward the 2010 growing season, recovery may be slower in the West than in areas farther east.
“There are still some dry pockets, but we're in a substantial recovery considering where we were just a few months ago,” sums up Brian Fuchs, climatologist with the University of Nebraska's National Drought Mitigation Center (NDMC).
With 75% of the country showing no drought as of late fall, Fuchs notes, the U.S. was in the least amount of drought since the U.S. Drought Monitor was developed 10 years ago. By way of comparison, roughly 72% of the country was in drought at the height of the dry spell in July 2002.
“Heading into the winter, there was very little in the way of drought across the eastern two-thirds of the country,” says USDA staff ag meteorologist Brad Rippey, noting that parts of Wisconsin, Minnesota and Florida were the exceptions. “As we got into the fall, there was even some relief in Texas, the Southwest and California, although there's still a long way to go in those areas before they get back to anything that could be considered normal.”
A cool, wet growing season coupled with a wet fall in many areas played a big role in relieving the overall drought situation. “Nationwide, it was an unusual year,” says Rippey. “In a lot of places, it was a year without a summer. We certainly didn't hear a lot of complaining about heat stress.”
A stubborn polar jet stream that remained locked in place over much of the continental U.S. for longer than usual was a key factor in keeping summer temperatures on the cool side.
“Normally, that jet stream pushes up far into Canada by late May or early June,” he says. “This past year, though, it didn't really break down until September.”
The wet fall, Rippey adds, was likely related to a developing El Niño, an irregular warming in sea surface temperatures from the equatorial waters of the central and eastern Pacific Ocean to the South American coastline. That was seen as good news for areas still struggling with drought.
“With El Niño, you tend to get a strong sub-tropical jet stream across the southern U.S. from California and Arizona through Texas and then along the Gulf Coast to Florida. It increases the likelihood of wet falls, winters and springs in those areas.”
Even so, moisture from El Niño may not be enough to help some drought-stricken areas recover immediately, cautions NDMC's Fuchs. Drought has persisted for several years in parts of Arizona and California.
“In Arizona, they missed out on the late summer-early fall monsoons, and there's been talk of cutbacks for federal grazing allotments. And in California, ranchers with irrigated pastures have seen water allotments cut off.”
Likewise, while any additional precipitation would certainly be welcome news in much of Texas following last year's severe drought episode, the pace of recovery will depend a great deal on how producers managed their grazing and haying lands during the drought.
“We saw the same kind of thing a few years ago following a prolonged drought in South Dakota,” Fuchs says. “Producers who were able to adjust their stocking rates or take other management steps to avoid overgrazing will likely see their pastures and rangelands come back more quickly.”
The good news in Texas, he adds, is that forages in many parts of the state recovered well following a series of rain events last fall.
Fuchs and Rippey also point out that El Niños can lead to drier-than-normal winter/spring weather in parts of Washington, Idaho and Montana. “We'll have to watch those areas closely,” says Fuchs.
Elwynn Taylor, Iowa State University extension climatologist, notes that the Midwest typically benefits from an El Niño.
“You don't get the temperature extremes — cold in winter, heat in summer. You don't see as much moisture in the eastern Corn Belt and Ohio River Valley, maybe a little more in Kansas, Nebraska, Iowa, the Dakotas and western Minnesota.”
Taylor says the Corn Belt generally considers an El Niño a friend, especially if it continues through the growing season. “We haven't had a widespread drought during an El Niño summer.”
There were major questions as winter started about just how persistent this El Niño would be. Taylor notes that, in the 100 years weather records have been kept, El Niños have usually lasted about 14 months. The last two, though, have lasted less than five months on average. If the current El Niño follows that trend, it would end in late spring of 2010.
“It's not uncommon to have hot, dry conditions immediately following the end of an El Niño,” he says. “That's something we really don't need in June and July through the Corn Belt.”
The law of averages also suggests the Midwest is due for a drought within the next couple of years. The historical average between droughts in the region is 19 years, according to Taylor. The longest span between droughts was 23 years. The last drought was in 1988.
On the flip side, wet weather has become much more common in the Corn Belt, Taylor says. In Iowa, during the three to four years immediately following 1893, when the first weather stations were put in place, the state had measurable precipitation 60 days per year. In the past four years, though, the number of days with measurable precipitation has doubled to 120. What's more, flooding events on rivers in the Midwest now occur six times more often than they did before the 1950s, when the 100-year flood benchmark was established.
“Now, 100-year flood levels have to be expected about once every 17 years,” he says.
Weather developments in the Carolinas may also bear watching as a predictor of what lies ahead for the upcoming growing season. Taylor points out that 16 of the last 17 major nationwide droughts started in either North Carolina or South Carolina, then migrated westward over the next 10-12 months. Neither state was in drought in 2009.