The National Weather Service projects an above-normal risk of flooding this spring in the Missouri and Mississippi River basins, which include western and eastern Iowa, according to a spring flood outlook released Thursday.
Two things are stirring concern and putting the Missouri River from south of Sioux City in western Iowa to Omaha, Neb. at a higher risk for flooding this spring: The soils in the Missouri River Basin are very wet, and river levels and flows are higher than normal.
David Pearson, a hydrologist with the National Weather Service in Omaha, Neb. called the outlook “grim” for people who live along the river below Sioux City. Soils, especially in the Dakotas, are soaked, like a sponge that's dripping wet and can't hold more water.
“The ability for rain to soak in is limited,” Pearson said, “and that just leads to more runoff, more water going into the rivers, which then in turn leads to more flooding potential.”
In 2019, 60.9 million acre-feet of runoff entered into the Upper Missouri River Basin above Sioux City – just short of the record 61 million acre-feet set in 2011. Major to historic flooding devastated some western Iowa communities for months. Some are still recovering, 11 months later.
The U.S. Army Corps of Engineers forecasts 36.3 million acre-feet of runoff could enter the Missouri River above Sioux City this year, which would be in the top 10 runoff years in more than 120 years of records, if reached.
The Mississippi River Basin also has very wet soil conditions, which means that nearly every river across eastern Iowa could reach flood stage this spring, according to the National Weather Service. Jessica Brooks, a hydrologist with the National Weather Service in the Quad Cities, said the entire north-central part of the country has extremely wet soil conditions, including the Dakotas, Minnesota and Wisconsin – the upper parts of the Mississippi and Missouri River watersheds.
“We will continue to see a higher risk for flooding until we are able to dry those soils out,” Brooks said.
Jim Noel with the Ohio River Forecast Center said during an NWS webinar Thursday that scientists expect widespread flooding this spring across the whole Mississippi River Basin, but the eastern two-thirds of the Mississippi drainage system has an above-normal potential for flooding, he said.
“The most significant flooding right now is expected in the Upper Missouri, Red River of the North and portions of the Upper Mississippi Valley,” Noel said.
Parts of northwest Iowa could also face minor, moderate or major flooding from rivers and streams this spring.
There are still some unknowns, like how intense spring rains will be and where that rain will fall. The National Weather Service will release two more spring flood outlooks on Feb. 27 and March 12.