SAINT PAUL, Minn. (CN) — Minnesota’s capital is playing host to a conference of hydrologists and other water scientists this week, and the importance of their work is plainly visible as flooding ravages the state.
Media and bystanders were transfixed by the rapidly swelling Blue Earth river near the southern Minnesota city of Mankato on Monday as local officials warned that the Rapidan Dam was in imminent danger of breaking. That prediction didn’t come to pass, but relief from downstream residents wasn’t felt upstream; on Tuesday night, the widening river upstream of the dam devoured a recently evacuated home.
Elsewhere in the state, a smaller dam did fail. The 7-foot, 124-year-old dam owned by the U.S. Forest Service in northeastern Minnesota’s Lake County didn’t take any homes with it, but it did take a toll on one of Minnesota’s favorite statistics by draining Sullivan Lake. The Land of 10,000 Lakes’ 11,842 lakes (of 10 acres or more) are down to 11,841.
In the state capital, the Mississippi River rose 15 feet to flood low-lying roads on Monday. That’s increasingly common; it happened last year, too, and the year before.
All this flooding raises questions: Why is this happening, and how can we better prepare for it?
The first question’s answer is brief, if not simple: climate change is responsible. While the exact impacts of climate change on extreme weather are the subject of much study and few definitive answers, warmer air can hold and transport more water than cooler air can. Warmer weather speeds up evaporation in lakes, reservoirs and other surface waters, leading to more water in the clouds and rain.
Between 2010 through 2019, the state saw more 10- and 100-year floods than any previous decade on record, with records extending back about 140 years.
How to prepare for climate change-caused flooding was the topic of a talk at the American Geophysical Union’s WaterSciCon by University of Minnesota PhD student Noah Gallagher on Monday. Gallagher presented findings from his study of stormwater management solutions for extreme weather events in and around Duluth, Minnesota’s fourth-largest city and a major port on Lake Superior.
Those flooding events are typically known by the frequency they can be expected at: 10-year, 50-year, or 100-year floods should be expected in approximately 10%, 2% and 1% of years, respectively. Those names, however, are increasingly inapplicable, Gallagher said.
“These events are becoming more frequent than their names would suggest," he said.
As a result, cities and other stormwater authorities are often underprepared to deal with them.
According to Andy Erickson, who manages the St. Anthony Falls Laboratory at the University of Minnesota, where Gallagher worked on this report in conjunction with outside organizations and the Minnesota Department of Transportation, the majority of U.S. stormwater facilities have been built to accommodate rainwater totals from data collected in a 1961 report. They’re also old; most stormwater pipes have a projected lifespan of 50 to 100 years.
Funding is another challenge. Stormwater is usually managed by local authorities, ranging from city departments to county or multi-county drainage authorities. Those authorities often charge stormwater utility fees to the beneficiaries of their systems, but those fee structures were typically conceived for a lower-rainfall world.
Speaking at a poster session at WaterSciCon, University of Delaware civil and environmental engineering student Rachel Zobel pointed out that in Pennsylvania, a university recently successfully argued in court that it should be exempt from stormwater fees as a tax-exempt institution. That case is now before the Pennsylvania Supreme Court, and likely to be decided this year.
Universities, Zobel said, often obtain permission to operate their own stormwater facilities rather than using those of the municipalities around them — but without charging students a designated “stormwater fee,” the requirement that they actually maintain those systems can become an unfunded mandate.