Record winter snowfall across northern Minnesota, which quickly melted in a spell of unprecedented spring heat, is dramatically swelling waterways along the upper Mississippi River basin.
Major flood stages, the second highest on record in some spots, stretch from Minnesota and Wisconsin to Iowa and Illinois. In Stillwater, Minn., the water level along the St. Croix River, which feeds the Mississippi, is forecast to be the seventh highest on record as the city endures persistent floodwaters.
So far, efforts to contain the floods and limit damage are working, Stillwater Mayor Ted Kozlowski said. Hundreds of volunteers piled sandbags 12 feet high to protect the historic logging town from the St. Croix’s surge, the first time they’ve done so in several years.
Still, Kozlowski worries about the toll extended floods will take, and is asking Minnesota officials for $6 million to address damage to shorelines and parks. And with the floods forecast to recede slowly, hope is fading that residents will be able to tear down the levee and reclaim a riverside park before Memorial Day.
“Now I’m like, is it going to be the middle of June?” Kozlowski wondered.
The floods are the latest boom in what has become a boom-and-bust cycle for the “mighty” Mississippi, which drains 41 percent of the contiguous United States. Last fall, the lower Mississippi diminished to such a trickle that it caused major disruptions in barge traffic. Months before that, heavy rains inundated the central Mississippi Valley with deadly floods.
Experts say such dramatic swings are to be expected as global warming triggers intense precipitation and unseasonable heat waves like what occurred in Minnesota this winter and spring — and what the swollen rivers now demonstrate.
“Climate change is affecting all different parts of our climate system. Precipitation is changing, the timing of warming events is changing,” said Jason Knouft, a professor at Saint Louis University who studies large rivers. “It leads to a much greater possibility of these really unexpected events.”
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The year began with a deluge of snowfall in a region familiar with harsh winters. Duluth, Minn., broke a record set nearly three decades ago, with more than 137 inches of snow. In Minneapolis, the 90.3 inches of snowfall ranked as the third most on record.
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Greater-than-average snowfall is common for the Upper Midwest in years when La Niña — the global climate pattern marked by cooler-than-normal waters in the equatorial Pacific — is present. La Niña has influenced global weather for most of the past three years, though it ended in February.
While snowfall has continued into April in parts of Minnesota, though, record-setting heat marked the early days of the Midwestern spring. Temperatures surged into the 80s on four consecutive days at Minneapolis-St. Paul International Airport in mid-April, peaking at a record high of 88 degrees on April 12.
It was enough to melt more than three-quarters of Minnesota’s snowpack — the equivalent of up to 8 inches of rain — in just a few days, said Jordan Wendt, a hydrologist with the National Weather Service in La Crosse, Wis.
“That really kicked off this flooding risk into overdrive,” he said.
As of late Wednesday, the Mississippi had reached 18.24 feet at St. Paul, Minn., and was expected to rise slightly higher Thursday and to not begin receding until the weekend. In Dubuque, Iowa, 200 miles to the southeast, the Mississippi hit major flood stage Sunday, reaching 22.28 feet by Wednesday. It is expected to crest a foot higher than that over the weekend.
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The flooding can cause disruption in river commerce, Knouft said, as the high and fast-moving waters make it harder to move barges upstream.
Communities in Minnesota were largely prepared for the surge, although the inundation has forced the closure of roads and parks along the river.
“Preparation matters,” Sen. Amy Klobuchar (D-Minn.) said at a news conference Monday in front of Army Corps of Engineers-built levees in St. Paul. “If we didn’t have these levees, it would be so much worse.”
Flood risks are expected to dissipate as the waters flow southward, because other major tributaries, such as the Ohio and Missouri rivers, are at lower levels, said Bob Criss, a hydrogeologist at Washington University in St. Louis. Farther downstream, the river is expected to reach moderate flood stage in Hannibal, Mo., around the middle of next week, but no flooding is in the forecast for St. Louis or points south.
“The monster will go away because it’s not being fed downstream,” Criss said.
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But in Stillwater, Kozlowski said, there is growing understanding that flooding will keep returning. At times, the floodwaters even rise up through storm drains that run along the river, he said. In addition to the levees, the town makes use of pumps that redirect that water back into the St. Croix.
While the town once had to worry only about springtime flooding, high water is occurring more often at other times of the year, too, he said.
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