Farm News, IA
12-27-07
Weather patterns may be pointing to parched conditions
Could it be the perfect drought?
By Darcy Dougherty Maulsby - Farm News staff writer
Spencer—Could a year with record-breaking rainfall events in Iowa segue into a
period of drought? It’s possible, based on the way weather conditions are
shaping up from coast to coast.
“A number of current trends are following what happened in 1987 leading into the
drought of 1988, and that worries me a little bit,” said Elwynn Taylor, an Iowa
State University Extension climatologist who spoke at a recent MaxYield
Cooperative meeting in Spencer.
Drought risk tends to follow a 19-cycle, and the risk of serious drought is doubled
in the phase of the cycle which is now occurring. Taylor noted that many serious,
widespread droughts start in the eastern United States and work their way west,
although they don’t always reach western Iowa. In 2007, many areas of the
southeastern United States were plagued with drought, just as the Carolinas
were in 1987 before a major drought hit in 1988. While this drought did not
decimate the crops of the western Corn Belt, it reduced yields by 30 percent
across much of the central and eastern portions of the region.
Currently, a residual moisture deficiency persists in the southeastern United
States, including South Carolina, said Taylor, who added that more than 90
percent of all major Corn Belt droughts are preceded by drought in South
Carolina.
Droughts can also spread from the western United States and Colorado and
work their way to Iowa, said Taylor, who noted that dry conditions helped feed
the California wildfires this fall. “Both types of droughts can happen at once,” he
added. “Just think of the Dust Bowl in the 1930s.”
Watching the desert
All this comes at a time when Iowa has received the most heavy-rain days in the
history of the state’s recorded weather. In 2007, there were eight days in which 4
inches or more of rain fell at multiple sites in the state, beating the previous
record of six days in 1979. While it’s too early to determine why this is
happening, it does highlight the volatile nature of current weather patterns, Taylor
said.
Climatologists know that Iowa became wetter from 1950 to 1993. “When I was a
college student in the 1960s, the annual precipitation for Iowa totaled 31 to 31.5
inches,” Taylor said. “This has gone up 10 percent since then.”
This wet pattern may be changing, however. The dry conditions of the desert
Southwest may, with some justification, cause concern for Corn Belt weather,
Taylor noted. While droughts originating in the Southwest are not known to
sweep the Midwest, a series of dry years in the Southwest may precede belownormal moisture years developing in the eastern half of the United States. Tree
ring studies from Arizona and Virginia show that wet and dry intervals of
approximately 30 years are not uncommon and do not appear to be random.
During the past 100 years, this wet/dry relationship is discernable in weather
records. The similar pattern seems to lag somewhat moving from west to east,
Taylor said. The “dry” trend in Arizona may be an indication of a 30-year trend
toward more arid conditions here. The trend appears to have initiated about
1980. “It’s possible that much of the Midwest reached the peak of moisture in the
mid-1990s and may experience diminishing annual moisture during the next two
decades,” Taylor said.
Climatologists are also tracking the Pacific Decadal Oscillation, which is detected
as warm or cool surface waters in the Pacific Ocean. When the waters north of
Hawaii have become warmer than normal eight years ago, Colorado experienced
a serious drought in six of those eight years. “Currently the North Pacific is
running warm, which increases the drought risk here,” said Taylor, who added
that there is a positive factor working in Iowa’s favor, however, since soil
moisture across the Corn Belt is about normal.
Expect increased volatility
Due to the cyclical nature of the world’s climate, Iowa may also be heading into a
period of colder winters, Taylor said. From 1880 to 1940, for example, the climate
entered a warming pattern, while conditions began cooling after 1940. “When I
was in college, the big concern was global cooling,” said Taylor, who noted that
global warming returned by the 1970s. “People were worried that this would limit
the amount of crops that could be harvested to feed the world’s growing
population.”
While it’s unclear how much humans are contributing to the current pattern of
global warming, one thing is sure—more erratic weather leads to increased
volatility of both yields and agricultural markets, said Taylor, who has pegged the
most likely 2008 U.S. corn yield at 146 bushels per acre (estimated according to
conditions as of Dec. 4).
The chance of a record high yield (above 165 bushels per acre) in 2008 is 18
percent, he added, while the chance of drought (below 135 bushels per acre) is
33 percent. At 64 percent, there’s an even better chance of being below the trend
(149.8 bushels per acre). Taylor said this estimate considers the above-average
subsoil moisture in much of the Corn Belt, a statistical risk of widespread
drought, the shift to La Nina, sea surface temperatures in the central and North
Pacific and in the Gulf of Mexico, and extended dry conditions in the
southeastern United States.
“The longest time between serious droughts is 23 years,” Taylor noted. “If we
don’t have a serious drought by 2011, we’ll break an 800-year-old record.”
Darcy Dougherty Maulsby can be reached at yettergirl@yahoo.com.