Climate Change likely ‘juiced’ Duluth flood of 2012

Here’s how the experts characterized the 2012 floods in and around Duluth:

“The most damaging flood in Duluth’s history”

— Minnesota Climate Working Group

“This storm eclipsed a heavy rain event in August 1972 that caused serious damage in the Duluth area.”

— Minnesota Climate Working Group

“The climate record from Duluth shows very few stormy periods that are analogous to what happened there this week.”

— Excerpt from Mark Seeley’s “Weather Talk”

A 500+ year flood — USGS assessing severity of Duluth floods

16.6 feet — New record flood level on the St. Louis River at Scanlon

JayCookeSwingBridge

A 4% increase in atmospheric moisture has been observed, consistent with a warming climate. The increased moisture in the atmosphere is driving the shift to heavier but less frequent rains — ”when it rains, it pours.” In turn, this increases the risk of flooding.

— Trenberth et al.2007 climatenexus.org

“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. A larger fraction of our annual total precipitation is coming in the form of intense thunderstorms.”

— Mark Seeley

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Some perspective:

A year after the devastating Duluth Flood we can look back and see how it fits in the overall picture if climate change in Minnesota.

It is now increasingly clear this type of event “fits” in the overall picture of Minnesota’s changing climate.  The evidence shows 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 delivered in the flood.

We’ve always had active warm fronts that have spawned MCS and heavy nighttime rains in Minnesota. The meteorological set up would have occurred anyway. But CC may have “enhanced” the Duluth flood event.

Now the real question is, how much did a warmer & wetter atmosphere “juice” this particular event to produce more rainfall than would have occurred without CC? That’s an important question. How do you quantify how much “extra” rain fell as a result of a warmer/wetter climate?

We know, and I have blogged/discussed on MPR, that rainfall events of 3 or more inches have doubled in frequency since about 1960.   Trends observed by Mark Seeley and others show Minnesota is getting a larger percent of our annual rainfall through thunderstorms. According to a report from climatenexus.org there has been a 31% increase in extreme rainfall events in the Midwest since 1958.

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The Duluth flood is part of a growing “extreme rainfall” trend in Minnesota. Since 2004 there have been three separate “1,000 year rainfall events” in southern Minnesota.

CC MN flood AEP

The most difficult question may be not if, but how much CC is “enhancing” extreme rainfall events in MN.

With factors such as a warmer atmosphere that can hold (and deliver) more water, and Lake Superior temps warmer than average for June feeding additional moisture into the system we may be able to say climate changes in Minnesota “enhanced” the dramatic Duluth flash flood event. A warmer atmosphere loads the dice in favor of more extreme rainfall.

Would it still have rained heavily in Duluth without climate change given the “synoptic” meteorological set up? You bet.

How much rainfall “enhancement” can we attribute to climate changes? 10% more rain? 50% more rain?

That may be impossible to quantify.

Duluth Flood rewrote flood maps:

The Duluth Flood event rewrote the so called “Annual Excedence Probability” (AEP) maps for northeast Minnesota. NOAA and the USGS have classified the flood as  “500 year” event, and it may have approached a “1,000 year” event in some location on the northeast side of Duluth.

CC Duluth AEP

Seeley weighs in:

My MPR colleague Mark Seeley also elaborated on the storm in Weather Talk. Here’s an excerpt:

Following the devastating flash flooding in Goodhue, Rice, and Dakota Counties last Thursday and Friday (June 14-15) and the hail and wind storms of June 17 and 19 earlier this week (hail up to 1.5 inches in diameter and wind gusts up to 83 mph), another larger flash flood encompassed much of northeastern Minnesota over June 19-21 (Tue-Thu) this week. A slow moving thunderstorm complex brought 3 to 10 inches of rainfall over portions of Cook, Lake, St Louis, Carlton, Itasca, Cass, Crow Wing, and Aitkin Counties. A report filed by a National Weather Service employee in NE Duluth mentioned a measurement of 10.10 inches of rainfall in the northeastern part of Duluth. Officially the National Weather Service in Duluth reported new record daily rainfalls back to back, 4.14 inches on the 19th, followed by 3.11 inches on the 20th, for a total of 7.25 inches. The climate record from Duluth shows very few stormy periods that are analogous to what happened there this week. Arguments can be made that thunderstorms on September 5-6, 1876 (6.48 inches); July 20-22, 1909 (7.83 inches), and August 15-21 (7.91 inches) might be comparable, but of course the Duluth neighborhoods and landscape in general were vastly different in those times. It is expected that damage to infrastructure in Duluth will be considerable this time around.

Some others reported record rainfalls: on June 19th, Grand Rapids with 4.78 inches, Hibbing with 2.57 inches, and Moose Lake with 3.12 inches; on June 20th, Wright with 6.11 inches, Two Harbors with 4.65 inches, Pine River Dam with 4.24 inches, Brainerd with 4.20 inches, Aitkin with 3.86 inches, and Grand Portage with 3.40 inches. Too many other observers reported record rainfall to report here.

Additionally a new statewide daily rainfall record was set on June 20th, with 7.41 inches reported from the Island Lake cooperative observer in St Louis County (about 18 miles north of Duluth). This broke the old statewide record for June 20th of 5.93 inches at Georgetown in 2000. This was the 2nd statewide daily rainfall record broken this month. Last week Cannon Falls set a new statewide rainfall record with 8.83 inches on June 14th, and this was associated with flash flooding over Goodhue, Rice, and Dakota Counties.

The St Louis River near Scanlon reported a new all-time record flood crest near 16.62 feet (flow volume over 45,000 cfs, about 15 times normal volume) beating the old flood crest record of 15.8 ft on May 9, 1950. The Kettle River at Sandstone also set a new record flood crest with1 16.2 feet, surpassing 15.38 feet on July 23, 1972. In fact many watersheds flooded included the Knife River, Crow Wing River, Pigeon River, Cloquet River, and Mississippi River at Aitkin among others. The discharge volume on these watersheds flooded many roads, highways and parks.

 Big picture: What does it mean for Minnesota’s climate?

Two weeks before the flood last June I gave a talk about “Minnesota’s Changing Climate” to a group at The North House Folk School in Grand Marais. One of my taglines summing up climate changes in Minnesota and along the North Shore was…”Expect the Unprecedented.”  I must admit I never expected something so unprecedented … so soon.

CC unprecedented

Of course the flood made national news. People want to know why events like this are happening with more frequency in Minnesota, and what it means in the overall context of climate change. Last fall I was  invited to speak about the flood and extreme rainfall at the MPCA in Duluth. In January I was invited to present a talk on the Duluth Flood at the Annual AMS meeting in Austin, Texas.

My message is simple. It is clear that the great Duluth Flood of 2012 “fits” into the overall pattern of climate changes we’re seeing in Minnesota.  One of the takeaways from the Duluth flood is that we have built our infrastructure under older, outdated perceptions of climate behavior in Minnesota. Extreme rainfall events are increasingly part of the “new normal” in Minnesota’s climate.

CC new normal

We need to adapt accordingly.