Massive US flooding linked to climate change-driven weather system

March 8, 2021
Homes in floodplains are floating on overvaluation. (AP Photo/Carlos Osorio)

Homes in floodplains are floating on overvaluation. (AP Photo/Carlos Osorio)

Researchers have implicated a climate change-driven weather system known as the Midwest Water Hose in the 2019 floods that devastated large expanses of the U.S. region, noting that it has been accelerated by increasing greenhouse gas emissions over the last 40 years and is only expected to cause more damage as climate change continues.

The study, published March 1 in Philosophical Transactions of the Royal Society A, stated that this powerful weather system contributed to 70% of Midwestern precipitation from January to May of 2019, making it the major cause of the flooding.

The floods affected up to 14 million people in the Midwestern U.S., setting over 100 precipitation records across 16 declared disasters. The National Oceanic and Atmospheric Administration estimates the total economic impact of the flooding to be $10.9 billion, with the disasters ravaging agriculture, infrastructure and ecosystems.

The Midwest Water Hose begins its journey as moisture over the Gulf of Mexico. As it travels north, this moisture condenses into dense rainclouds over the Midwest that douse the region in high levels of concentrated precipitation, like a firehose drenching the landscape.

"People have used other names for it, like 'Maya Express,' referring to the 'Pineapple Express,'" a similar weather system that forms over the Pacific Northwest, said lead author Gabriele Villarini, a professor of civil and environmental engineering at the University of Iowa. "But I think this name describes it better visually. It's a concentrated flux of water that strongly affects a very limited region rather than a widespread phenomenon, like a hose without a nozzle."

Villarini and his colleague Wei Zhang, an assistant professor in the Department of Plants, Soils and Climate at Utah State University, originally uncovered the Midwest Water Hose in a 2019 study. However, they were unsure whether the rising trend in its frequency was a direct consequence of climate change or due to natural cycles in climate.

To answer this question, the team used computer modeling to verify the role of greenhouse gases in the system. Their models attempted to reproduce the increasing frequency of the Midwest Water Hose with and without considering the role of greenhouse gases.

"What we wanted to do in the study was isolate the role of the different forces in this flooding," Villarini said. "And it turns out that if you remove the role of the greenhouse gases and just take into account natural climate variability, you just aren't able to reproduce the increasing trend that we have seen in the data."

The team did not fall into this area of research by chance. Villarini personally experienced the impacts of these types of natural disasters at the start of his career.

"I was finishing my Ph.D. at the University of Iowa in 2008, right around the time of another major flood," Villarini told The Academic Times. "We had to evacuate. The university buildings were closed for some time and we were displaced. That left a really strong imprint on my current research interests. We all have certain events that shape our future and for me, that was the flood."

While that flood was not on the same scale as those that occurred in 2019, the University of Iowa reported that it did cause extensive economic disruption by displacing households, destroying croplands and damaging personal and commercial property, pointing to the continuous and increasingly dire danger posed by Midwestern floods.

While this research clarifies the drivers for these flood events in the continental U.S., the researchers are next interested in extending their analyses beyond that. The team is also interested in applying its analyses toward new projections about what flood events may be expected in the coming years.

However, until that work is complete, the path to mitigating the damage from these events is unclear, requiring expertise beyond the scope of any one study.

"I am wrestling with the question of how my findings should be responded to by policymakers or governments," Villarini said. "It's outside of my comfort zone as a scientist, so my first reaction would be that we haven't done the work yet, so we need expertise from other people, not just what I do."

However, these findings do demonstrate the need to consider the immediate consequences of climate change beyond the nebulous future dangers of global warming.

"These findings contribute to a body of knowledge that moves us away from saying that climate change only affects global temperature," Villarini said. "And in a sense, they bring the issue closer to home. I think more of a storytelling approach will let us convey that the impacts of greenhouse gases are immense — not just in an abstract sense, but in a concrete one."

The study "Greenhouse gases drove the increasing trends in spring precipitation across the central USA," published March 1 in Philosophical Transactions of the Royal Society A, was authored by Wei Zhang, Utah State University; and Gabriele Villarini, University of Iowa.

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