The seasons, they are changing -- whether there is climate change or not. Springs are earlier, wetter and warmer but summer precipitation trends are about the same, according to a 30-year trend-line study at the University of Missouri.
"The change trends have been occurring the last four decades, but have become more pronounced in the last 10 years," says Pat Guinan, climatologist with the MU Extension Commercial Agriculture Program. "In general, weekly precipitation decreases as you progress through the growing season from June to August."
However, the median last frost in spring has occurred two to four days earlier over the past 30 years. Last frosts of spring have moved up three days over much of the state, with a week earlier in places. However, first frosts of fall are not pushing back into winter. Guinan has looked at 120 years of weather data to draw conclusions on the changing weather patterns. The trends will redefine what we consider "normal weather."
The results were presented last month at the MU Crop Clinic at Bradford Research and Extension Center, Columbia. The advanced two-day event is for top farmers and certified crop advisers.
Guinan looked at nine locations around the state that have long-time continuous daily weather observations. He picked three stations across three zones of Missouri. The groupings were north: Conception, Brookfield, and Steffenville; middle: Lee's Summit, Jefferson City and St. Louis; and southwest, Nevada, Lebanon and Neosho. He compared 30 years from 1971-2000 versus 1981-2010.
All three northern locations had frosts an average of three days earlier. Lebanon had its last frost seven days earlier, starting the growing season earlier. Guinan used 32 degrees F as the frost date. Ten of 12 months were wetter, when the recent decade was included. May and June have gained 0.40 and 0.41 inches of precipitation. The only drier months were March and November, at minus 0.18 and 0.17 inches of precipitation.
The 30-year weekly precipitation trend line for north drops about 0.3 inches from June to August. The summer weekly precipitation trend line drops more, going south. In southwest Missouri, the drop is 0.6 inches from May to August.
All of these shifts have implications for crop planting and the growing season.
Bill Wiebold, MU Extension crop specialist, noted that farmers should be thinking about earlier corn planting dates to allow corn to reach tasseling and silking stages ahead of the drier periods of summer. "I think planting dates should be moved earlier," Wiebold said.
However, Ray Massey, MU Extension economist, raises concerns about risk management. Earlier planting plays into the frost dates. Massey's specialty is crop insurance risks.
Last frost dates across north Missouri at Conception moved from April 19 to16; for Kirksville from April 21 to 18; and for Steffenville from March 20 to 17.
Wiebold pointed out that the key factor is not planting date, but date of emergence. Planted corn is not subject to frost. Emerged corn is, however. In Wiebold's date-of-planting studies, corn planted ultra-early in cold soils have not emerged for up to 28 days. Modern seeds have survivability.
The Climate Prediction Center posts long-range forecasts daily on its website: www.cpc.ncep.noaa.gov/
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