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Research Links Climate Change to Flooding in Iowa

Posted on March 1st, 2021
Aerial view of muddy brown floodwater submerging Pacific Junction, Iowa, in 2019.

Catastrophic Missouri River flooding engulfed the entire town of Pacific Junction and its residents in 2019.

Climate scientists at the University of Iowa’s IIHR—Hydroscience & Engineering are reporting new research that shows an important link between climate change and flooding in the Midwest. IIHR researchers Gabriele Villarini and Wei Zhang (now at Utah State University) have connected the rising levels of greenhouse gases in the atmosphere with Iowa’s more frequent flooding. Their paper appears in the March 1, 2021, edition of the scientific journal Philosophical Transactions of the Royal Society, Mathematical, Physical, and Engineering Sciences.

This new research shows rising greenhouse gas concentrations caused by human activity are producing an increase in the frequency of a particular weather type that has been linked to flooding in Iowa and surrounding states — the “Midwest Water Hose.” The Midwest Water Hose (MWH) is the weather type that contributes the most to precipitation in the Midwest and that produced more than 70 percent of the total precipitation in the first five months of 2019. The MWH transports moisture from the Gulf of Mexico to the Midwest, Zhang said. “The moist air is then lifted above cold dry air from the north, leading to precipitation across the Midwest.”

Two headshots, Wei Zhang and Gabriele Villarini.

IIHR researchers Wei Zhang and Gabriele Villarini (IIHR director) have published research linking urban sprawl to an increase in rainfall and flooding during Hurricane Harvey.

Iowa’s flood season was especially bad in 2019. The two large rivers that serve as Iowa’s eastern and western borders both rose to major flood stage, causing levees to breach and producing widespread flooding. Small towns such as Hamburg and Pacific Junction were inundated in muddy water, devastating homes and businesses. Larger cities such as Davenport also experienced catastrophic flooding. The MWH, which has been occurring more frequently in the last 40 years, delivered much of the precipitation punch behind this flooding.

Villarini and Zhang said that their results based on CMIP6 climate models show that natural climate variations cannot explain the more frequent occurrence of the MWH. When they accounted for the rising greenhouse gas concentrations caused by human activity, however, the results reproduced the observed increase in the occurrence of the MWH quite well. “This trend cannot be reproduced only in terms of natural variability of the climate system,” said Villarini, who is also director of IIHR—Hydroscience & Engineering. “Therefore, these results led us to attribute the detected trend to greenhouse gases. This means human-induced (anthropogenic) climate change increased the odds of more frequent flooding, including the 2019 floods.”

The IIHR researchers are excited about these novel new results. “All the climate model experiments point in the same direction—the rising trend in the Midwest Water Hose is caused by increasing greenhouse gases,” Zhang said. “It provides a strong piece of evidence that anthropogenic climate change has made flooding, such as what Iowa experienced in 2019, more likely, and this type of flooding in this region is expected to become even more likely in the future if we do not take immediate actions to cut greenhouse gas emissions.”

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