Arid start to 2012 crop season raises concern as heat builds
COLUMBIA, Mo. - An arid spring brought only 4 inches of rain to Missouri in May and June. Normal rainfall is 10 inches, says a University of Missouri climatologist.
We have a 6-inch moisture deficit going into what are normally the hottest and drier months of summer, says Pat Guinan with the MU Extension commercial agriculture program.
In addition to the rain shortage, January-to-June temperatures show the warmest average on record in 118 years. The state continues to set heat records: Third warmest winter, warmest March and warmest spring.
"It's a unique growing season," Guinan says. High heat and lack of rain indicate possible prolonged drought.
"It's beginning to look a lot like 1988," says Bill Wiebold, MU Extension agronomist.
Guinan says 1988 was one of the three worst droughts of the last century. That includes the mid-1950s and the dust bowl days of the 1930s.
"We're not there yet," Guinan says. "But you do have to go back to 1988 to find a drier May and June than we've had this year. Hot, dry weather in the spring isn't a good start."
Normally, May and June are the wettest months of the year in Missouri. "This year, we're short on soil moisture. There's no reserve in the top 12 inches and subsoil is not much better," he says. Soil moisture supports crop growth during hot months, supplemented by normal rainfall.
In many parts of Missouri, a foot of soil is all there is. Below the topsoil lies claypan or rock. Iowa and Illinois cornfields tend to have deeper soils with more water reserves. That can make a difference in plant survival, Guinan says.
A National Weather Service outlook for July issued at the end of June shows below-normal precipitation and above-normal temperatures for the month ahead. Usually, July is the hottest month of the year.
A drought has many facets, Guinan says. There is the lack of precipitation. That is combined this year with high temperatures, an unusual number of sunny days and low relative humidity. Humidity levels run 20 to 30 percent by midafternoon, day in and day out.
"We've already had temperatures in triple digits, most unusual for June," he said. "Strong winds and low humidity boost water evaporation, creating plant stress."
The buildup of solar energy on the soil intensifies drought effects, Guinan says. Sunshine boosts evapotranspiration, the water use by plants combined with evaporation from soil surfaces.
Plant transpiration pulls moisture out of the soil. Evaporation removes water from the surface, including ponds and lakes.