From the Minneapolis Star Tribune:
The rain that flooded Duluth last week also flushed an unprecedented quantity of dirt, pollution and bacteria into Lake Superior -- enough to make experts worry about the long-term environmental consequences on the largest and clearest of the Great Lakes.
One day after the storm, sediment runoff made the lake opaque for miles along the shore, local researchers say. Satellite photos show a wide swath of mud streaming into the lake from the Duluth harbor almost all the way to the Apostle Islands. "We don't know what's going to happen because we've never seen this," said Elizabeth Austin-Minor, an associate professor of chemistry at the University of Minnesota Duluth's Large Lakes Observatory.
Understanding the lake's new dynamics is important because major rain events are occurring more often...
Between 1958 and 2007, the Upper Midwest saw a 31 percent increase in "intense" rainfalls -- those 1-in-100 storms -- compared to previous decades, according to the National Climatic Data Center.
The rainfall in Duluth last Tuesday and Wednesday, measuring from 7 to more than 10 inches across the city, was in some places nearly twice what is regarded as Duluth's 1 percent-chance rainfall.
Climate scientists say big rainfalls, particularly from intense thunderstorms, are a symptom of ongoing climate warming. (Warm air holds more water vapor than cooler air.)
Brown said his quick review of data from the Minnesota Climatology Working Group shows that rainfalls of more than 2 inches have come and gone in a decades-long cyclical pattern for Duluth. The number was high in the late 1800s, then dropped in the 1930s, but has been rising steadily again since the 1960s.I put a version of this at my Journal Sentinel Purple Wisconsin blog, too.
But, compared to the last century, the landscape around Lake Superior now has far fewer forests and far more farm fields and cities, making it much more vulnerable to erosion, he said.