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Iowa rainfall highlights serious weather variation

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An increase in water discharge is needed because of recent heavy rainfall in the Iowa River Basin and higher water levels on the lake.
Iowa City Press-Citizen

The Iowa City area — much like other areas of the currently waterlogged state — absorbed a dramatic increase in rainfall this autumn, leading to multiple flood events on multiple rivers and forcing people to confront the question of whether this is Iowa’s new normal.

The U.S. Army Corps of Engineers will start releasing 12,000 cubic feet of water per-second (CFS), up from 10,000 CFS, from the Coralville Lake Reservoir to prevent water from reaching the emergency spillway level, beginning Wednesday afternoon. 

An increase in water discharge is needed because of recent heavy rainfall in the Iowa River Basin and higher water levels on the lake.

That discharge rate will remain at 12,000 CFS through Oct. 23 if conditions remain as forecast, officials said. The normal CFS rate in the month of September is around 1,000 CFS.  

Last month, however, wasn’t normal.

The Iowa City area recorded 7.05 inches of rainfall in September, compared to an average of 3.35 inches, according to National Weather Service meteorologist Tim Gross, in the Quad Cities office. 

Interested in understanding just how abnormal this rainfall was, Director of the Iowa Flood Center, Gabriele Villarini, teamed up with his colleagues to review historical rainfall data.

Looking at rainfall in September months from 1948 to present, they found that it did indeed rain much more than usual this past month in eastern Iowa. 

“For large areas of eastern Iowa, the amounts (this past September) are unprecedented,” said Villarini. “For several areas, they were the largest or second largest.” 

The unusual deluge has saturated the soil, which is exacerbating flood control efforts.

“It’s led to the widespread flood conditions we are experiencing,” Villarini said. 

The next question they were interested in was why. 

Villarini said they have identified three potential culprits for the unprecedented precipitation: a low-pressure system in the western part of the United States, a high-pressure system in the East Coast and moisture funneled into the Midwest from the Gulf of Mexico. 

“You have three ingredients for heavy precipitation,” he said. 

Their next question is, “Is this going to be the new norm, or not?” he said. That answer matters, because if they know these will start to be common events, they can invest more time in understanding how they occur and their potential impacts. 

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Water raises out past the beach to surround a play structure on Wednesday, Oct. 10, 2018, at the Coralville Lake dam. (Photo: Joseph Cress/Iowa City Press-Citizen)

Dr. Elwynn Taylor, extension climatologist at Iowa State University, is also reviewing this year’s rainfall data. 

“We have unofficially so far, set records for the wettest summer for a few areas in the state,” he said, noting that records date back to the 1880s.

Specializing in long-term weather variability in the Midwest, Dr. Taylor said considering the data shows not only wetter months, but drier months as well, all of Iowa is projected to experience more extreme weather conditions. 

“We’re moving into a time of extremes,” he said. “We already know this year will be wetter because it’s already wet.” 

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