Midwestern farm states are experiencing a gradually lengthening growing season, which can have a variety of impacts for agriculture.
Justin Glisan, the Iowa state climatologist, says the trend is showing more time between the last freeze in the spring and the first freeze in the fall.
“What we’ve seen is an expansion of the growing season across the Midwest and Iowa,” he says.
States have weather data going back to the 1800s, but Glisan says looking at the last 30 years can help illustrate the recent trends. He says Iowa is experiencing 1 to 3 days more per decade during its growing season. Overall, Glisan says Iowa is seeing about 8 to 12 days more in its growing season than the historical number. He says the average growing season ranges from 170 to 210 days in Iowa.
Pat Guinan, the Missouri state climatologist, says his state’s data shows a similar trend.
“Missouri air temperatures are trending warmer over the last couple of decades, which is extending the growing season,” he says.
Guinan says statewide averages for spring minimum air temperatures over the last 127 years show a warming of 1.4 degrees per century. Missouri’s autumn air temperatures have trended 0.8 degrees warmer.
When comparing the last 20 years to the 127 years of weather data, Guinan says the most recent decades show the last spring freeze occurring 3 to 6 days earlier than the historical average, and the first autumn freeze is occurring almost one week later than the long-term average.
Illinois state climatologist Trent Ford sees the trend in his state as well.
“In Illinois we’ve seen an increase of the growing season of 10 to 15 days over the last 50 to 60 years,” he says.
Ford says the climate projections indicate this trend will continue.
Despite the trends, growing seasons can see a lot of variation from year to year in the Midwest, so it is difficult for growers to simply plant earlier due to longer growing seasons.
“Missouri weather is still variable, and seemingly random freeze events can and will occur late in spring or earlier in the fall,” Guinan says.
As an example, Ford says central Illinois saw a freeze as late as May 7 in 2020, bucking the recent trend.
“If we go year to year, the variability is really high,” he says.
In general, Ford says very late spring freezes will become more rare.
Warmer winters
Glisan says there are other factors beyond air temperature at play.
“What we also have to think about is the soil temperature,” he says.
He says farmers do think about changes in typical frost and freeze dates, but more so on the end of the growing season.
“Farmers are more keen to look at those during the fall,” Glisan says.
The long weather history shows many extremes, and Glisan mentions the extreme heat in the 1930s as one example.
He says Iowa’s June, July and August temperatures are the same as in 1895, the year the state’s widespread weather records begin. But he says overall the state is 1.3 degrees warmer than 1895, warming about a tenth of a degree per decade on average, with the warmer winters offsetting the fact the summer months have stayed about the same.
“Winter is the fastest warming,” he says.
Ford says Illinois has similarly seen a slight overall temperature increase over the last 125 years, with it being most pronounced in the winter.
Glisan says an increase in temperature increases the amount of water vapor that can be held in the atmosphere, meaning more intense, more infrequent precipitation events. He says an increase of 1 degree in average air temperature means 4% more water vapor can be stored.
Glisan says July is Iowa’s hottest month, but is on average the state’s third-wettest month. A dip in July rainfall in recent years has contributed to a three-year drought for parts of Iowa, triggered in part by years of La Niña conditions in the Pacific.
New strategies
Still, despite drought and challenges from the frequency and duration of rains, Iowa set records for corn and soybean yields in 2021, and came within a few bushels of doing so again last year. Crop technology continues to advance.
Source: agupdate.com
Photo Credit: istock-UrpsPoteko
Categories: Missouri, Crops, Weather