There’s a saying in the Great Plains: “Rain follows the plow.” Like the suburban legend about rain falling once the cars have been washed, it refers to the way rain always seems to fall once it’s no longer needed, or when it will be most inconvenient.
But is it true? And more importantly, do these myths affect how scientists compile data about rainfall?
In the 1800s, settlers used the “rain follows the plow” myth as impetus to clear the Great Plains. The theory went that turning up the soil would help it collect moisture, and then the moisture would add humidity to the air. That would lead to rain.
No one’s quite sure if it worked, or if the myth itself is making people want to see evidence that it did.
“In addition to, and partly motivated by, the ‘rain follows the plow’ myth, many scientific papers have been published with conflicting results: wet soil would increase, decrease or not change precipitation in different papers. Our goal was to resolve this controversy,” said Dr. Xubin Zeng, a professor at the University of Arizona who worked with doctoral student Josh Welty to examine whether the myth held any truth.
The pair looked at data from June to September of each year from 2002 to 2011, collected by the U.S. Department of Energy’s Southern Great Plains observatory.
They found that the amount of moisture in the soil in the morning can have an effect on afternoon rain on the Great Plains it two different ways. On days when less moisture is carried on the wind, dry morning soil can increase any afternoon rain.
“The dry soils that enhance afternoon rain are acting like conveyor belts for warm air that’s being sent into the upper atmosphere,” Zeng said. “Combine that upward motion with moisture and a water vapor source, and the result is afternoon rain.”
But on days when the wind is damp, moist soil leads to more rainfall, the researchers said.
Human activity – like plowing – may play a role, but so does the climate and how much moisture the wind carries over the Great Plains. Manipulating the moisture content of soil under the right climate conditions could encourage rainfall, the researchers said.
The study has been published in the journal Geophysical Research Letters.
By Kyla Cathey, Earth.com staff writer