The nightmare that was June 20th last year in the Omaha area wouldn’t let up. A train of storms moved through, unleashing successive rounds of wind, lightning and rain. Emergency scanners crackled with a surge of frantic calls, especially from areas south of Interstate 80 where up to nearly 8 inches of rain fell.
Bellevue rescuers hurried from one call to another as motorists became stranded in high water. When the night was over, 29-year-old David “Mikey” Farr was dead after his SUV was lifted off the ground by rising water and he was sucked into a culvert and washed downstream.
Asked to describe that night, Bellevue Fire Battalion Chief Steve Wagner grappled for words and said simply, “it was incredible.”
Powerful storms such as the one on June 20 are a part of life in the central U.S., but research is finding that intense precipitation is becoming more common, and with that is coming an increase in flooding in some areas. While scientists know that the planet is becoming warmer and wetter, what is less understood is how that will play out in regional weather patterns.
A University of Iowa report published this spring in Nature Climate Change is the latest to note an increase in flood frequency in the central U.S.
Other studies of specific watersheds within the central U.S. have also detected increases in precipitation or flooding, including research by the U.S. Geological Survey and NOAA’s Earth System Research Laboratory.
The 2014 National Climate Assessment, an exhaustive compilation of climate change research, concluded that the eastern half of the U.S., including Iowa, has seen the greatest increase in downpours, between 27 percent and 71 percent, depending upon the region. The northern Great Plains, including Nebraska, is next, with a 16 percent increase in heavy precipitation, with the northernmost of those states seeing the most significant increases. Most of the rest of the country has seen smaller increases.
For its study, the University of Iowa examined records at 774 USGS stream gauges in 14 states for the years 1962 through 2011. States included were Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, North and South Dakota, Ohio, West Virginia and Wisconsin.
The study found more frequent flooding at 34 percent of the stream gauges and less at 9 percent of gauges.
For the most part, the study found an increase in flooding in eastern Nebraska and areas farther east. Western Nebraska didn’t experience a similar trend in flooding.
The U.S. Army Corps of Engineers also has seen an upward trend in precipitation, be it rain or snow, in the upper Missouri River basin, said Kevin Grode, a civil engineer who leads the team that assesses conditions in the upper Missouri basin and forecasts runoff.
A study for the corps by the Earth System Research Laboratory concluded that nine of the upper Missouri watershed’s 10 highest runoff years have occurred in the past 40 years, he said. Records date back 117 years. The corps has commissioned a study by the research laboratory to examine the causes behind changes in runoff.
Stream levels in the Elkhorn River basin generally are increasing, and flood magnitude has increased in parts of the basin, according to a USGS study that was done in conjunction with the Lower Elkhorn Natural Resources District.
Three of nine Elkhorn basin gauges with at least 50 years of records showed an increase in annual flood peaks, said Ben Dietsch, a hydrologist with the USGS Nebraska Water Science Center. Those gauges are on the Elkhorn at Waterloo and Neligh and on Maple Creek near Nickerson.
At Waterloo, where 95 years of stream flow records are available, the USGS data show a noticeable uptick in the magnitude of the Elkhorn’s peak flows beginning in the 1960s. Since then, 17 of the 20 highest annual peaks have occurred. The data look only at river levels, Dietsch said. Understanding why annual peak flows are increasing on the Elkhorn would require additional study.
Harry Hillaker, state climatologist for Iowa, said precipitation in that state has generally been increasing since the late 1950s. Virtually all of that increase has occurred in the spring and summer, he said. All types of rainfall are occurring more frequently, with heavy rainfall, an inch or more per day, increasing the most.
“We’re getting more small events, more medium-sized ones, and more large ones,” he wrote via email.
Yet-to-be published research into Nebraska’s temperature and precipitation patterns didn’t detect a discernible trend in precipitation, said Natalie Umphlett, climatologist at the High Plains Regional Climate Center.
“We did find that there is an overall increasing number of wet days, but only for small amounts of precipitation (less than 0.10 inches),” she wrote in an email.
Umphlett said the High Plains Center and University of Iowa used different data sets and time periods in their research, which might explain the difference in findings.
Additionally, Nebraska’s climate differs from much of the central U.S., including Iowa, with Nebraska generally being more arid. Eastern Nebraska tends to bridge the two climates.
Last year was extraordinary in terms of rainfall in the Omaha metro area, said Dave Pearson, a hydrologist with the National Weather Service in Valley. Omaha set four precipitation records in 2014. Not included was the June 20 deluge because most of that rain occurred in Sarpy County.
The biggest record was set June 3, when the city had its fifth-rainiest day in more than 130 years of records. The 5.3 inches that fell prompted nighttime water rescues in northeast Omaha.
Pearson said a direct link can’t be made between a single year’s excessive rains and the overall trend noted by the University of Iowa study. Instead, he sees 2014 as a wakeup call.
“Last year showed us it definitely happens here,” he said.
Those who make their living along streams and rivers aren’t surprised by the University of Iowa report.
Glen Stenzl’s voice sags with fatigue when he talks of flooding. The northwest Missouri farmer and levee board member spoke by phone last week from atop a levee that he was inspecting near the Iowa border. Stenzl has been farming along the Missouri for decades and he was among those fighting to save farm homes and communities during the historic Missouri River flood of 2011.
What he and other farmers mostly are seeing, he said, are gully-washers that strip away topsoil and erode terraces. Additionally, levees built decades ago have become silted in, making them less effective in high-flow years.
Bottom line, things aren’t getting better, Stenzl said; they’re getting worse.
While more study is needed to understand what is happening in the central U.S., scientists know that the rapid warming of Earth is making the planet more humid. The reasons are two-fold. With a warmer atmosphere, more water is evaporating from the Earth’s watery surface. Also, as air warms, it’s able to hold more water. Thus, there is more water in the air to “rain out.”
The disruption caused by flooding underscores the need to understand what’s happening, said Gabriele Villarini, professor in civil and environmental engineering who co-authored the University of Iowa report.
“Flood events come with a big price tag, and the price tag is both in terms of fatalities and economic losses,” he said.
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