Farm News, IA
04-19-07
Climatologist examines trends
By Darcy Dougherty Maulsby, Farm News staff
Elwynn Taylor, a climatologist from Iowa State University, says current
weather indicators should boost the odds of yields above trendline for 2007,
although the risk of drought remains.
LAKE CITY — While there are some indications of increased crop production risk
this year, large-scale weather trends by mid-April appear to favor a good start for
the 2007 crop season.
“When you analyze a number of risk factors, from pre-season moisture to ocean
temperatures, currently it looks like all this should boost our odds of yields above
trendline,” said Elwynn Taylor, a climatologist from Iowa State University who
spoke in Lake City recently. “If we get trendline yields this year, we’ll get 148.4
bushels per acre.î”
Perhaps the biggest wildcard is the phase of the 19-year drought cycle. In the
middle of a continent, serious droughts occur about every 19 years, Taylor said,
and tree-ring studies indicate that the longest drought-free period of the past 800
years in central and eastern North America was only 23 years. The last serious
Midwest drought occurred in 1988.
“I don’t know for sure that we’ll have a serious drought between now and 2011,
but if we do not we’ll break an 800-year-old record.î”
Taylor reported a mix of positive and negative indications for the 2007 crop
season:
n While subsoil moisture was generally low in the central and western Corn Belt
by the end of the 2006 season, fall and winter weather has resulted in a
recharge.
n While the Pacific Decadal Oscillation (PDO) has encouraged drought in the
western Corn Belt during five of the past seven years, there is some indication of
a return to normal for 2007.
n Weak La Nina conditions existed in early 2006 but shifted to El Nino-like
conditions in mid-July. El Nino appeared to end in February 2007. There is a
possibility of La Nina conditions developing during the spring, with a tendency to
be on the dry side of usual west of Interstate 35. In this case, summer
temperatures tend to be more extreme than usual across the Corn Belt. Taylor
said near-normal conditions are most likely, although he added that droughts
tend to be most serious in La Nina.
n Hurricanes and other tropical storms set records in the Atlantic in 2005 and
were gradually diminished in 2006 because of El Nino conditions. “The impacts
on farming and the shipping of produce may be just a wake-up call to what the
next 20-plus years will bring,î” Taylor said. “There is some indication that the
number of tropical Atlantic storms is trending upward, but year-to-year variability
of numbers and severity is substantial.Ӕ
n Conditions as of March 5, 2007, indicated a 2007 U.S. corn yield of 146
bushels per acre. A return of La Nina would bring a 70 percent risk of belowtrend yields in the United States.
Based on data from Feb. 12, 2007, Taylor’s estimate of risk for the 2007 crop
season predicted a 12 percent chance of having above-normal yields with 163
bushels per acre nationwide, putting December corn at $3.10 or lower. He
predicted a 25 percent chance of drought, leading to yields of less than 134
bushels per acre, with corn at $5.19 a bushel. He predicted a 34 percent chance
of 153 bushels per acre, with corn around $3.82.
What about
global warming?
Global warming has a major impact in the Corn Belt, Taylor said. “It seems the
reality of the widespread warming trend is expressed in extreme weather, erratic
yields and volatile markets. This is a condition that doesn’t appear to be
transient, so we may as well plan on improving our risk management as we move
into the coming score of years.î”
Based on weather records, the earth tends to go through 40 years of global
warming, followed by 40 years of global cooling, Taylor said. According to his
data, the planet should hit the global warming peak around 2025 before cooling
starts again.
Ironically, the lowest winter temperatures tend to happen in times of global
warming. Taylor said Iowa may be headed for 20 years of generally colder
winters. The pattern is linked to the North Atlantic Oscillation Index, which
measures how cold the ocean is. “We go through 20- to 30-year periods of cold
winters, followed by 20 to 30 years of warmer winters,î Taylor said. He cited the
negative phase that occurred during the 1950s through 1970s, which contributed
to bitter winters in the Midwest, while the positive phase that ran from the 1980s
through the 1990s led to warmer winters.
If Iowa is heading into a period of cooler winters, the revised plant hardiness
zone map released recently by the National Arbor Day Foundation may offer
misleading advice, since it has nearly all of Iowa classified as a “balmy”î Zone 5.
“During global warming things get extreme, so it only takes one or two cold nights
in the spring to harm plants and trees that aren’t hardy to your zone,”î Taylor
said.
With weather, only one thing can be predicted for sure, Taylor concluded. “The
climate has always changed, and it always will. While we have a lot of weather
variability, this risk can be managed.î”
For more information on current weather forecasts, log onto www.weather.gov.