What’s Causing the Devastating Floods in the Midwest?

ST. LOUIS (AP) — Hundreds of Iowans have needed rescue from record-breaking floods that have inundated parts of the state, covered buildings up to their roofs, closed major roads and disrupted basic services such as electricity and drinking water.

Iowa Gov. Kim Reynolds said waters in some areas rose above records set in 1993, a flood that many in the Midwest remember as the worst of their lives. The floods were so powerful that they took down a train bridge connecting North Sioux City, South Dakota, to Sioux City, Iowa.

The water is expected to be at its highest early this week – already passed in some places – and then the top of the river will move south, eventually into the Missouri and Mississippi rivers.

“Businesses are closed and main streets are affected. Hospitals, nursing homes and other healthcare facilities were evacuated,” Reynolds said at a news conference last weekend, calling the expected damage “mind-boggling.”

It is also hot, making the dangerous conditions even worse.

A look at why water levels are so high in the Midwest:

What causes the severe flooding?

Torrential rain. Over a three-day period, Sioux Falls, South Dakota, received approximately 7 inches of rain. Canton, South Dakota, about 30 miles (48 kilometers) to the southeast, saw 18 inches of rain. In Iowa, as much as 38.1 inches of rain has fallen in some areas since Friday.

“It’s been round after round all month. And recently we’ve had a few big rounds,” said Joseph Bauers, meteorologist at AccuWeather.

Hot air in the Northeast has guided the path of storms through the Midwest, according to Shel Winkley, a weather and climate expert at Climate Central, a nonprofit organization focused on climate science.

“With that big high-pressure system over the east, those types of systems are helping to direct and slow down those systems, specifically to where we’ve seen the flooding over the last few days,” he said.

And the most recent heavy rains have fallen on wet ground. When the soil is wet, it cannot absorb as much new moisture, causing more rain to enter rivers and streams.

What is a weapon and why are they important?

A crest is the highest level a river reaches before retreating, and they are closely watched by forecasters. It is essential to know when a ridge is expected to strike, how bad it will be and how fast it is moving down the river.

As recent rains dumped extraordinary amounts of water on the region, rivers were rising rapidly and peaks are expected soon or have already occurred in some places.

Sioux City Fire Marshal Mark Aesoph told reporters that the Big Sioux River stabilized Monday morning at about 45 feet, more than 7 feet higher than the previous record.

“It’s just been hard to predict what’s going to happen when the levels are that high when we have no history with it,” he said.

South Dakota Gov. Kristi Noem said other rivers, the James and Vermillion, will peak on Wednesday. The flooding is “more widespread” than expected, helping to reduce flooding in some populated areas. It will “push up” levels in the Missouri River, but not as much as expected, she said at a news conference Monday.

“The later and lower top levels gave us some time that we needed to upgrade some of the levees that we needed,” Noem said.

While the heaviest rain has been concentrated in northwest Iowa, parts of northeastern Iowa will see up to an inch on Monday, National Weather Service hydrologist Jeff Zogg said. It will take “several days” for rainfall in northern Iowa to work its way through the state.

Because all that water ultimately ends up in the Missouri and Mississippi rivers, flooding is also expected in those major rivers, according to Zogg.

Does this have to do with climate change?

Floods are not new in the Midwest. There is also no heavy rain in June. And linking a particular major rainstorm to climate change is difficult, Winkley said.

But as greenhouse gases warm the planet, the warmer atmosphere can hold more water. This means that large rain showers can cause even more water to flow downhill, overload the sewers and flood the city center. In addition, serious flooding is becoming more common, he said.

“The extremes are becoming more and more extreme,” says Winkley.

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Associated Press reporters Hannah Fingerhut in Des Moines, Iowa, and Margery A. Beck in Omaha, Nebraska, contributed to this report.

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Michael Phillis, The Associated Press