Risks of spring flooding decrease in Eastern Iowa

The National Weather Service is anticipating even lower spring flood risks in Eastern Iowa than it predicted in its first outlook two weeks ago.

Timothy Gunkel, meteorologist with the service’s Quad Cities Bureau, said the spring flood risk currently is below normal for the Mississippi River and “near to below normal” for the river’s tributaries across Eastern Iowa.

Two weeks ago, the Mississippi had a 10 to 15 percent chance of a flooding event. Now, Gunkel said that projection is under a 10 percent chance for the same area.

Specifically, the Cedar River has about a 10 percent chance of flooding this spring, according to the prediction. Typically, it has a 30 percent chance.

And Rock Island near Davenport along the Mississippi River has a 15 percent chance of flooding. Historically, it has a 55 percent chance of spring flooding, Gunkel said.

Gunkel said that the current flood risks could increase if Eastern Iowa receives bigger storm systems in March — of either snow or rain.

As of the Weather Service’s second of three spring flood outlook webinars Thursday, Gunkel said there is a system set to come through Eastern Iowa that is predicted to bring 1 to 1 1/2 inches of rain to the region. The next flood outlook report is March 13.

“We are having our eyes in the system, but right now, we're not really too worried about that or having any impacts for our spring flood outlook,” Gunkel said.

If the region does receive significant rainfall in the next few weeks, Gunkel said that there is “plenty of room in our local streams to handle the rain.”

Most of Iowa received several inches of snow — ranging between 6 and 8 inches — in mid-February. But Gunkel said this week’s above-normal temperatures melted most of it, so there is “little to no” snow water equivalent.

“And that’s usually a big factor,” Gunkel said.

In fact, Eastern Iowa received only about 30 to 50 percent of its typical winter snowfall, the service said on Facebook this week.

The Weather Service said only two other winters — 1921 and 1936 — had less snow in the area between the same December and February time frame

Lingering drought

One key factor that could determine if Eastern Iowa sees any spring flooding is when the ground starts to thaw from the winter.

As of Thursday morning, Gunkel said there was an 8-inch frost depth in the Quad Cities. However, he said the top layer of soil has started to thaw due to the warmer temperatures in the 40s and 50s.

“That should continue as we go on, especially since we don't see right now any excessive cold moving in (and) we're generally going to stay above freezing,” Gunkel said. That will “give us some more room for whenever it does rain, let that water infiltrate into the ground, rather than going to the direct runoff and into the rivers.”

This comes as drought conditions across the state have slightly increased.

Within the last week, “moderate drought” increased by 11 percent throughout Iowa since the previous week, according to the U.S. Drought Monitor.

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About 1.3 percent of the state is experiencing “severe drought,” which includes parts of Sioux, Plymouth and Woodbury counties. About 14 percent — most of Iowa’s southern counties — do not have drought or abnormally dry conditions.

“Much of the region still is dry, so (there is) plenty of room once we thaw out our soils to let that spring rain and spring snow to infiltrate into the ground, rather than go right into the rivers and stream flows,” Gunkel said.

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

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Comments: olivia.cohen@thegazette.com