Flooding in the Midwest: Why the Water Is So High

Source: By Adeel Hassan, New York Tmes • Posted: Tuesday, March 19, 2019

Flooding from the Elkhorn River in Omaha, Neb., on Sunday.Kent Sievers/Omaha World-Herald, via Associated Press

A historic snowy winter is turning into record spring flooding across a wide area in the middle of the United States, as major rivers spill over their banks, break levees and inundate towns and farms. The governors of Nebraska, South Dakota, and Wisconsin have declared emergencies, and Iowa’s governor has issued a disaster proclamation. At least two people in Nebraska have died in the floodwaters, and two others are missing.

Hundreds of families have fled their homes, especially in the Mississippi and Missouri flood plains, where levees were breached in many areas. Offutt Air Force Base, outside Omaha, said that one-third of the base was underwater on Sunday. Even the National Weather Service said it had to evacuate its offices in Omaha on Friday because of rising water.

What touched off the flooding?

Rain was the immediate cause. The Weather Service’s Omaha office recorded 1.37 inches last week; more fell to the north and west, with Norfolk, Neb., getting 2.27 inches Tuesday, Wednesday and Thursday.

That isn’t all that much by itself, though it is more than the area usually gets at this time of year: Omaha, which averages less than an inch of rain in all of March, already has had 2.15 inches this month.

How did that cause so much flooding?

The devastating effect came mainly from what the rain fell upon: a snow-covered region that was unable to absorb much of the blow.

“A lot of it stems from the fall flooding in September and October,” said Mindy Beerends, a senior meteorologist at the Des Moines office of the National Weather Service. “The soil was saturated in the fall.”

That moisture stayed in the ground all winter, deep-frozen, while snow piled up on top of it, she said — and then, “on Wednesday and Thursday, warm air moved in, and we got rain, and the snow melted.”

“The higher-than-average precipitation, combined with warm temperatures, snowmelt and the frozen ground, was a perfect storm for flooding,” Ms. Beerends added. “The ingredients were in place.”

The flat, frozen land, unable to soak in much of the water, spread it fast and furious, the way liquid would spread across a tiled floor. And the runoff quickly filled many rivers and streams to overflowing.

Did anyone see this coming?

Forecasters knew that the snowy winter was building up the potential for spring flooding. In February, the Army Corps of Engineers lowered the reservoirsalong the Missouri River to try to make room for excess runoff.

What’s the forecast now?

River levels have peaked in many areas and have started to recede, but parts of Nebraska, Iowa, Minnesota, Wisconsin and South Dakota still face “historic to catastrophic flooding,” the National Weather Service said on Monday. Warm weather will continue to melt snow this week across the vast area drained by the Mississippi and Missouri rivers, from the northern Great Basin to the Northern Rockies, and water levels downstream in Missouri are expected to keep rising for several more days.