Natural weather patterns triggered March flooding. How much of a role did climate change have?

It had been a long winter, cold and snowy.

When the March warmup came, the frozen landscape melted in a giant swoosh. Runoff poured into frozen rivers, sheets of ice the size of homes crashed together, damming up water.

At Yankton, South Dakota, the Missouri River rose perhaps 35 feet, killing several people. As flooding surged downstream, other towns, including Omaha, flooded, levees broke and residents scrambled to higher ground.

The year was 1881, and the rivers of the Plains were teaching residents a bitter lesson — a lesson that would be repeated nearly 140 years later.

The Great Plains of North America are home to some of the most volatile and destructive weather on the planet. And catastrophic flooding is part of the bargain for living here.

This year has been no different.

Nebraska sustained more than $2 billion in damage in March, its costliest disaster on record, when a powerful storm unleashed a blizzard and widespread flooding. Iowa and other neighboring states were similarly affected.

Predictably, disagreement over the role played by climate change followed in the storm’s wake.

As history shows, unimaginable weather disasters were occurring long before global warming became a concern.

And scientists say human-caused climate change didn’t trigger the March disaster.

It’s tougher to figure out whether global warming magnified the result.

Climate change: Think of it as weather on steroids

Climate scientists often use a baseball analogy to explain the connection between climate change and extreme weather.

Martha Shulski, Nebraska’s state climatologist, describes the analogy this way:

Say you’ve got a home run hitter and you put him on steroids. He still hits home runs, but now he’s hitting the balls farther and getting home runs more frequently.

That’s how climate change influences weather: It can increase the intensity and frequency of extreme events.

“Is our risk going to be greater?” Shulski said. “Yes, because these events (drought, flood, heat waves) are going to become more common. The better question is ‘How prepared are we?’ ”

The March flooding, the region’s history of flooding and projections for increased flooding all point to a need to be realistic about flood risks.

“Overall, people underestimate the frequency of very large floods,” said John Pollock of Omaha, a retired National Weather Service meteorologist. “Disasters are ... made worse when people are unprepared.”

Mark Anderson, who has studied the hydrology of the Missouri River extensively, said it’s past time to be smart about flood vulnerability.

“There should be no question in anyone’s mind that the climate is changing,” said Anderson, retired director of the U.S. Geological Survey Dakota Water Science Center. “The rock to jump on, in all this, is to continue our research into how the climate is changing and to develop adaptive strategies. The amount of damage in the U.S. from flooding, in part, is because we’re not being smart.”

Being smart includes not building in flood plains, providing more robust protection of critical infrastructure in flood plains and using nature to absorb runoff.

“We shouldn’t be lulled into thinking that dams will provide all the protection necessary,” he said.

Or levees for that matter.

“Levees give you a false sense of security,” Pollock said.

More heavy downpours in northern Plains and Midwest

Already, the Northern Plains, which includes Nebraska, has seen about a 30% increase in heavy downpours, according to the National Climate Assessment. The Midwest, which includes Iowa, has seen a 40% increase. That’s based on the period from 1958 to 2016.

Not surprisingly, then, the amount of water pouring into the Missouri River from some of its main eastern tributaries is up, too, according to Anderson. In the 2003-12 period, compared with the 1960-69 period, runoff from the James River in the Dakotas more than tripled, from the Big and Little Sioux Rivers in Iowa it more than doubled, and from the Platte in Nebraska it was up about 25%.

That translates into large volumes of water churning down the Missouri River, Anderson said.

Research by the Iowa Flood Center at the University of Iowa confirms what people anecdotally have been saying: Flooding is on the increase. The center was created by the Iowa Legislature after devastating floods in 2008.

A regional increase in flooding has occurred over the last 50 to 70 years, said Gabriele Villarini, one of the researchers.

“It’s not so much that the largest floods are getting larger, rather we’ve been experiencing a larger number of events,” said Villarini, director of IHR-Hydroscience and Engineering at the University of Iowa.

Villarini said it’s likely that flooding across the Midwest will worsen by the end of the century due to global warming. The biggest increases will likely occur in the spring.

Why? Climate scientists say a well understood aspect of physics is that as the planet warms, its atmosphere contains more moisture. That contributes to flooding, because when there’s more moisture in the air, storms can produce more rain or snow.

The regional increase in downpours and flooding is occurring in lockstep with Earth’s atmosphere becoming wetter. The amount of water vapor in the atmosphere is up about 7% since the 1970s, said Jennifer Francis, a senior scientist at Woods Hole Research Center. It’s expected to increase by half that much again in the next 30 years, she said. That’s because global warming is accelerating.

Iowa center will study March flooding, and feds may, too

Villarini said the Iowa Flood Center will study the 2019 March flooding to see what it can learn about causes.

The U.S. Army Corps of Engineers is in talks with the National Oceanic and Atmospheric Administration about a federal study, said John Remus, chief of the corps’ Missouri River Water Management Division in Omaha.

NOAA scientists analyzed the 2011 flood on the Missouri River for the corps.

That study concluded that naturally occurring weather was the cause. There was “no definitive reason” to connect climate change to the 2011 flood, said Martin Hoerling, a meteorologist who contributed to the analysis.

“Climate change is affecting everything, there can be no question about that,” Hoerling said. But the effect on Missouri River flooding remains an open question, he said.

Part of the problem could be data. Computer simulations are the basis for this type of analysis. Owing to the sporadic nature of precipitation, and thus the smaller set of data, precipitation trends are harder for computers to decipher than temperature. That was clear in March when NOAA’s computer models didn’t predict the severity of the flooding.

Multiple factors led to the flooding in March: widespread, heavy rain on top of a widespread blanket of snow, with runoff streaming across frozen ground and pouring into frozen rivers.

Between the rain, snow and parking-lot like surface of the frozen ground, it was as if the plug was pulled on a 2- to 8-inch-deep lake covering much of northern Nebraska, southeastern South Dakota, southwestern Minnesota and eastern Iowa. The rain and snow drained off the landscape, surged into streams and, with nowhere to go, crashed through levees and spread across valleys.

Februarys are colder, and harsh end to winter favors flooding

Nebraska has seen its winters get colder over the past 30 years, especially in February, Shulski said.

Eastern Nebraska in 2018-2019 had its wettest winter in more than 100 years, capped off by one of the 10 coldest Februarys on record, according to the National Centers for Environmental Information. For Omaha, it was the city’s snowiest February on record and one of its coldest.

A harsh end to winter favors flooding in several ways. Late winter snows tend to be heavier because springlike, moist air is feeding into the region and thus can fuel snowfall. Additionally, when winter’s cold sticks around, snowmelt and the breakup of river ice gets delayed. That sets up the potential for flooding if a quick warmup or heavy rainfall occurs.

The shift to colder winters in the central U.S. isn’t fully understood. Scientists say it could be caused by cyclical changes in weather, could reflect a relatively recent intensification of “stuck” weather patterns that lead to more extremes, or it could be something else.

“It all points, unfortunately, to things we can expect more of in the future,” Shulski said. “I only see the chances of that increasing, given where climate projections are telling us where we are likely to be going.”