WEATHER

Minn. floods, early tropical storms fuel questions about changing climate

Before last week, the inland port city of Duluth, Minn., fairly assumed that its greatest weather threat came from periodic gales off Lake Superior, along which the city built its harbor, downtown and gilded lakefront homes with sweeping views.

But the June 19-20 super storm that produced between 8 and 10 inches of rain across the city -- causing an estimated $50 million to $100 million in damage to streets, sewers and other public infrastructure -- had nothing to do with the brooding Great Lake.

Rather, according to weather experts, the rains were spawned by an unusually powerful series of storm cells that drifted across north-central Minnesota overnight on June 19, crescendoing into an earth-scouring torrent that broke 40 years of flooding records for Duluth and surrounding communities.

Meanwhile, in Florida, the fourth named storm of the 2012 hurricane season brought major flooding to portions of the Gulf Coast and north Florida on Monday and Tuesday before finally making landfall and weakening into a tropical depression.

As flood-weary Duluth residents began returning to their homes this week and city engineers began the daunting task of rebuilding the city's damaged streets, bridges and stormwater collection system, the question in the minds of many is whether Duluth is the latest in a string of Midwestern cities being walloped by severe weather-borne damages from climate change.

Informed opinions vary -- from the definitive "yes" to the cautious "maybe" to the conservative "impossible to know."

Minnesota state climatologist Greg Spoden, in a telephone interview, erred toward the latter view, stressing that the Duluth storms were consistent with previous weather events in Minnesota. And their destructive power, while unrivaled in terms of property damage, was aided by the storms' track over the most urbanized sections of Duluth, which is built on a steep hillside overlooking the lake.

"This type of event certainly is consistent with Minnesota's climate," said Spoden, whose State Climatology Office is housed within the Minnesota Department of Natural Resources.

"As long as there have been individuals writing things down in Minnesota, we have heard of such mega-events," he added. "So linking this one event to broader changes in our climate is difficult at best, and it's probably unknowable."

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But other observers, whom Spoden said he respects, are taking a less nuanced view of the Duluth storms, which washed out or buckled an estimated 60 roadways in St. Louis County and turned life in the city of 86,000 upside down.

A National Weather Service report explained that a stationary front that set up just south of Duluth on June 18 conspired with already saturated ground, steep terrain, and swollen creeks and rivers to cause "devastating damage and flooding," including the near complete inundation of the Lake Superior Zoo, where more than a dozen animals died and others were swept by floodwaters from their enclosures into city streets.

Mayor Don Ness, in comments published yesterday in the Duluth News-Tribune, said the cleanup process "will need to continue for many days and months." He requested state and federal disaster relief aid through the Minnesota governor's office in St. Paul. Gov. Mark Dayton (D), after touring the flood-damaged areas last week, said, "It's just terrible devastation, the awesome, destructive power of nature."

Rains 'juiced' by climate?

Experts observing from a greater distance say the intense rainfall and localized flooding may represent a new normal for places like northern Minnesota, where climate change is expressing itself in a variety of ways, including hotter summers, milder winters, a shift in species composition, and a general trend toward more frequent intense storm events.

"This type of storm reminds us that climate is changing in Minnesota. Not only in terms of quantity of precipitation, but in the character of precipitation as well. In recent decades a larger fraction of our annual total precipitation is coming in the form of intense thunderstorms," Mark Seeley, an esteemed meteorologist and climatologist at the University of Minnesota Extension Service, wrote in his weekly "WeatherTalk" newsletter last week.

Meteorologist Paul Huttner, Minnesota Public Radio's resident weather expert, wrote on the network's "Updraft" weather blog that a "rearview mirror" reading of the Duluth storms allows observers "to look back and see how it fits into the overall picture of climate change in Minnesota."

While downplaying any cause-and-effect relationship between climate change and the Duluth storms, Huttner said, "what we can credibly say is the extreme rainfall events are increasing in frequency in Minnesota, and that climate changes favoring a warmer wetter atmosphere may have enhanced or 'juiced' rainfall totals in the flood."

Meanwhile, Paul Douglas, a well-known Twin Cities meteorologist and founder of the online publication "WeatherNation," said in a recent blog post that he had little doubt the record rainfall in northern Minnesota last week was related to climate change.

"The question keeps coming up -- people want to know if a warmer atmosphere somehow contributed to the mega-flood that may ultimately cost Minnesota well over $100 million," Douglas wrote.

"My answer, after teeing this up with climate scientists I trust, is yes," he continued. "People who say 'you can't link any one event with climate change' are missing the point. Climate and weather are now hopelessly intertwined, linked -- flip sides of the same coin. It's basic physics: a warmer atmosphere holds more water vapor. If there's more water floating overhead you increase the potential for these extreme rainfall events. You may argue over how much is 'natural' vs. man-made, but there's no debating the fact that Minnesota is a warmer place than it was 30-40 years ago."

Fla. takes center stage

While memories of Minnesota's flood damage are fresh, residents of northeast Florida feared the worst had yet to arrive yesterday as Tropical Storm Debby finally made landfall on the state's Gulf Coast.

Debby had dumped as much as 26 inches of rain in some areas north of Tampa by yesterday afternoon, and National Hurricane Center forecasters predicted the weakened storm could drop an additional 4 to 8 inches overnight along portions of Interstate 10 between Tallahassee and Jacksonville.

Before making landfall at Steinhatchee, Fla., yesterday afternoon, the storm sat nearly idle in the Gulf of Mexico for four days, exacerbating flooding conditions and triggering evacuations across sections of western peninsular Florida near Tampa Bay.

By midday yesterday, Debby was moving at 6 mph from the Tampa area toward Jacksonville with sustained winds of about 40 mph, according to the hurricane agency. Tropical storm warnings remained in effect for 450 miles of the Gulf Coast from Mexico Beach to areas south of Sarasota.

The 2012 Atlantic hurricane season, which formally began June 1, is on pace to be one of the most active on record, with four named storms -- Alberto, Beryl, Chris and Debby -- occurring within a month of the season's opening. The first two storms of the season formed in mid-May.

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