Five years ago this week, people living and working along hundreds of miles of the Missouri River were scrambling to evacuate loved ones and possessions as a historic summerlong flood shoved downstream.

When it was over, the Flood of 2011 left more than $1 billion in damage, claimed at least one life and wrecked towns, homes, farm fields and roads from Montana to Missouri.

It was a harrowing summer in the Omaha metro area as an army of volunteers and workers sandbagged, patrolled and plugged sodden levees. Had the levees failed, tens of thousands of homes and critical infrastructure such as Eppley Airfield, Offutt Air Force Base and Omaha’s sewage-treatment plant would have been inundated.

As it was, the river filled the valley wherever it could, swirling around Fort Calhoun Nuclear Station, damaging portions of Interstate 29 and I-680 and closing access to multiple bridges across the river. Travel between Nebraska and its neighboring states was impeded for 100 miles north of Omaha and the 100 miles between Plattsmouth and St. Joseph, Missouri.

Nearly 480 riverside-property owners from six states now are suing the federal government for damages caused by flooding in recent years.

So, could a 2011-level flood happen again?

In a word, yes.

“It’s not a matter of if it’s a matter of when,” said Dennis Todey, South Dakota’s state climatologist. “That’s not meant to scare people. ... (It’s) probably not in our lifetime, but we can’t say that for sure.”

Globally, human-caused climate change is tilting the odds toward more frequent flooding because the increasing warmth is pulling more moisture into the atmosphere, said Jerry Schnoor, co-director for the Center for Global & Regional Environmental Research at the University of Iowa.

Determining whether global warming will make catastrophic flooding more common on one spot of the planet — in this case, the upper Missouri River basin — is harder to predict, he said, because precipitation patterns are vulnerable to the chaos inherent in weather.

What is known about the Missouri River basin is that some parts are becoming drier while other portions are seeing a shift toward more extreme precipitation, Todey and Schnoor said.

The U.S. Army Corps of Engineers, which manages the dams on the Missouri, commissioned three weather studies by the National Oceanic and Atmospheric Administration. Two are complete, and the third will be finished by the end of the year.

One study examined whether the corps could have foreseen the magnitude of the flood. That study concluded that weather forecasting capabilities aren’t advanced enough for the corps to have had an adequate head start.

“With a reservoir system this big,” said Jody Farhat, the corps official who oversees releases from the dams, “we need months of advance notice to make any major muscle moves that would provide additional flood control. Three to six months.”

Another study concluded that the flood likely arose from the normal extremes of weather rather than being juiced up by global warming. NOAA drew that conclusion, in part, by noting that human-caused climate change appears to be reducing runoff in the upper basin, so the record runoff of 2011 is contrary to what is expected with global warming.

However, that study didn’t analyze the extreme swings in runoff seen in recent decades. That is the subject of the final study, due by the end of the year.

“We’re peeling back the onion, trying to figure out what went on in 2011,” Farhat said. “Nine of the 10 wettest years have occurred since 1970, so (NOAA) is looking at what is happening. ... Is that climate change? Are there land-use changes?”

The basin cycles through periods of relative drought and high runoff. It’s this shift that the corps would like to be able to forecast, because it determines whether the agency should hold back or release water.

In the early 2000s the basin went through its deepest drought since the dams were completed in the early 1960s.

In 2008 the watershed began shifting back to a wet period, culminating in 2011’s unprecedented runoff — 20 percent more than the reservoirs were designed to handle.

The cliché “a perfect storm” comes into play with the flood of 2011 because complex factors had to occur to produce runoff of the magnitude that occurred.

These factors included heavy autumn rains; full streams and lakes; plentiful soil moisture; heavy snowpack in the Plains and mountains; prolonged cold weather; and historic spring rains.

Changing climatic patterns are the subject of intensive research.

A team of researchers from Utah State University and the South Dakota School of Mines and Technology thinks that slow changes in the Pacific Ocean could be a key to developing a long-term forecast for the Missouri River basin. The team based its research on a combination of old-school data — soil moisture and stream levels — and high-tech wizardry — satellites that use GPS and microwaves to detect minute changes in Earth’s gravity.

The team’s goal was to see if a novel forecasting approach used in the Great Salt Lake Basin also could be used in the Missouri River watershed.

Simon Wang, associate director of the Utah Climate Center, said he thinks the research holds tantalizing promise. If the team’s results are correct, he even has a rough forecast.

“If ​our reported ​connection of the (Missouri River basin) climate cycle with the Pacific variability ​holds true,” he said, “​then ​the next high-flood potential would be expected during 20​18-202​2​.”

Contact the writer: 402-444-1102, nancy.gaarder@owh.com

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2011 flood by the numbers

Historic runoff

Nearly 250 percent of normal runoff flushed through the Missouri River reservoir system, the most in 114 years of record-keeping. It was enough to cover 95,625 square miles with a foot of water — essentially, all of Nebraska and the western third of Iowa.

Controlled but unstoppable

The amount of water gushing out of Gavins Point Dam, the smallest and southernmost of the corps’ six great dams, was 60 percent more than flows over Niagara Falls in the summer.

Flood stage

The Missouri River at Omaha was at or above flood stage for all but a few hours from May 31 to Sept. 10, 2011. The river crested 7.29 feet above flood stage on July 2 in Omaha — at 36.29 feet.

Expensive fight

More than $52 million was spent by Eppley Airfield, the City of Omaha and the City of Council Bluffs in fighting the flood. The Army Corps of Engineers spent $70 million in its flood fight and $580 million fixing levees and dams.

Lives upended

» 1,245 families qualified for a total of $8.9 million in federal grants to make their homes habitable.

» 294 homes were destroyed and 890 were damaged in Nebraska and Iowa, not including summer cabins.

» 299,000 acres of insured crops were damaged.

Sources: U.S. Army Corps of Engineers; Federal Emergency Management Agency; Omaha Airport Authority; World-Herald archives

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