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Air humidity has a big influence on rainfall in the Corn Belt

The US is the largest producer of corn in the world. More than 35 percent of the global production of this important cereal grain comes from the Corn Belt, an agricultural area in the Midwest that stretches from Indiana to Nebraska. 

In the light of changing climate conditions, researchers at Penn State University have conducted a new study on the importance of soil moisture and air humidity for influencing rainfall patterns in this area.

“We were curious about the effect soil moisture has on convective precipitation in the Corn Belt under different atmospheric conditions, such as dry or humid,” said study lead author Connor Chapman. “Plenty of research of this nature has been done for the Great Plains region, but the neighboring Corn Belt – which has a different climate type – has received much less attention.”

According to the Global Climate Observing System, soil moisture is an essential climate variable because it determines the amount of evaporation and cooling of the air near the Earth’s surface. With decreases in soil moisture anticipated as a result of climate change, the consequent reduction in evaporation could have the effect of amplifying warming even further

“This study is important also because Corn Belt agriculture is mainly rainfed, rather than irrigated,” said study co-author Professor Andrew Carleton. “So the Corn Belt is much more susceptible to year-on-year climate variations, like droughts and wet periods, and to the impacts from climate change, which are likely to increase this variability and lead to even greater extremes.”

For the Corn Belt, continued warming is likely to shift crop types northward and with a longer growing season, which could increase climatic and market economic uncertainties going forward, Carleton said.

For this study, Chapman analyzed nine consecutive years of growing-season data in relation to soil moisture, near-surface humidity and low altitude wind velocity.

He also created three sub-seasonal groups: early, middle and late to see how the results might vary because as the growing season progresses in the Corn Belt, the land cover changes from bare to short and then to tall crops with a far greater potential for evapotranspiration. 

“We found that during the early season, when croplands are bare, convective precipitation is more likely to occur with drier soil, high humidity, and strong, humid, low-altitude winds,” said Chapman. “Although soil moisture and wind vary across the growing season, we found that high near-surface humidity consistently was most important for convective precipitation or rain.”

“The most challenging aspect of our study is the low amount of long-term soil data available for the Corn Belt. Compared with the Great Plains region, the Corn Belt does not have as much available, in situ soil data, and only a limited number of soil data stations met the criteria for our study.”

Chapman was surprised by the results, which illustrate how adjacent regions with different land cover experience different climate conditions.

The results are published in the Journal of Applied Meteorology and Climatology.

By Alison Bosman, Staff Writer

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