Sunday, September 21, 2008

From deluge to drought in Minnesota

Winona Daily (Minnesota): … [Germain] Davison, a cooperative observer for the National Weather Service, just last year poured 15.1 inches of rain from the steel canister in his yard — a new state record for 24-hour rainfall. He recorded some heavy precipitation again in June, when more torrential rains fell across the region. But the last significant rainfall was July 18. Since then, there have been only about a dozen rainfalls — most of them measured in hundredths of inches, hardly enough to soak the ground and nourish his corn. The story is the same for most of southeastern Minnesota and western Wisconsin: Though above normal for annual precipitation benchmarks, the region is parched.

…It’s certainly too short to say much, but it is fitting with the trend we’ve observed lately,” said Stephen Vavrus, an atmospheric scientist and interim director of the Center for Climactic Research at the University of Wisconsin in Madison. In an effort to predict how a warming global climate will affect Wisconsin, Vavrus is studying rainfall records for Madison since 1940. What he’s found is a dramatic increase in the occurrence of 2- and 3-inch rains.

The past eight years have seen eight 3-inch, one-day rainfalls, compared with nine in the previous 60 years. The pattern is similar for 2-inch rainfalls, and 1-inch events show a steady increase. That, Vavrus said, is what the future might hold for the area: more floods and more droughts.

…Vavrus said his rainfall study is consistent with others across North America. Though not a “smoking gun” pointing to human-influenced climate change, the trend is consistent with the expected result.

However, other trends don’t follow the expected pattern. Take heat waves: the number of 90-degree or hotter days in Madison has gone down over the past 60 years. This summer, La Crosse has had five; the average is 20. Vavrus suspects Wisconsin’s weather system might be heading into a situation in which the variability exceeds the expected range of variability.

Locator map of Winona, Minnesota, rendered by Arkyan, Wikimedia Commons, under the terms of the GNU Free Documentation License, Version 1.2

No comments: