ISU Dept. of Geological and Atmospheric Sciences

National Weather Service and Iowa State researchers don't rule out climate change as the cause of the derecho severity.

Derecho was a foreign word to most Iowans before August, now it has become a prevalent part of climate conversations. Weather specialists in Iowa are in the process of researching the cause of the severe derecho and have not ruled out climate change.

The severe winds and rain of the Aug. 10 derecho devastated crops, pushed down trees and damaged power lines. Similar to hurricanes and tornadoes, a severe derecho is not expected in Iowa and Ames residents had no warning of the storm until 20 minutes before it hit.

Atmospheric scientist Russ Schumacher wrote in his article for the Iowa Capital Dispatch, a derecho is a storm with winds “57.5 mph (26 meters per second) or greater – and those intense winds had to extend over a path at least 250 miles (400 kilometers) long, with no more than three hours separating individual severe wind reports.”

Iowa State researchers and the National Weather Service of Des Moines say climate change may be the reason the derecho in August was so severe.

Bill Bunting, chief of forecast operations at the National Weather Service Storm Prediction Center, explained how even if the elements that cause a derecho are present, oftentimes they do not occur. However they are hard to detect on traditional computer models used by the National Weather Service because it presents as a regular thunderstorm.

“Once a cluster of storms gets organized, it can internally change its structure in ways that allow it to do what we saw on August 10th,” Bunting said. “Central and Southern Minnesota, southeast across Iowa and Northern Illinois to the Ohio Valley are areas we typically see [derechos]. Not all of them are as intense as the one August 10th.”

William (Bill) Gallus, professor in geological and atmospheric sciences at Iowa State, has been doing research on severe storms for several years. Gallus said thunderstorms are hard to predict because of their size and the lack of reliable data. Additionally, all weather reports have less access to atmospheric data due to the cancellation of many commercial flights.

“There has been a reduction in [weather] data due to [COVID-19]. Some studies have shown that the weather predictions have become less accurate,” Gallus said.

Contradictory to Bunting, Gallus said it was unusual the derecho this severe did not show up on computer models the day before, but it was still too soon to say if climate change is responsible for the lack of warning.

Gallus and fellow professor Christina Patricola strive to answer that question through future research.

Derechos have been reported several times dating back to the 1870s. In “About Derechos,” the National Weather Service and other weather specialization groups explain in depth how climate change interacts with derechos. While climate change itself will not increase the amount of derechos, it could change the location of them.

This effect is called shifting poleward, and it is seen across different weather systems. In this illustration by Dennis Cain from 2018, Iowa is in the “one derecho every two years” category. As the Earth continues to warm, scientists believe the cloud pattern changes, shifting more toward the poles. In the future, it is possible the high derecho concentration, highlighted in purple, could move toward the north pole, impacting Iowans directly.

Derecho Climatology

Illustrated by Dennis Cain in 2018, this map depicts derecho concentrations across the U.S.

More research is required on derechos and the effects of climate change before a conclusion can be made regarding the interplay of the two.

“There’s room to debate what [humanity] should do, but there is really no logical reason to believe that the Earth is not warming and it is because of human actions,” Gallus said.

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