https://www.washingtonpost.com/weather/2020/10/17/iowa-derecho-damage-cost/
By Bob Henson
Oct. 17, 2020 at 9:04 a.m. EDT
No single thunderstorm event in modern times — not even a tornado — has wrought as much economic devastation as the derecho that slammed the nation’s Corn Belt on Aug. 10, based on analyses from the public and private sectors.
The storm complex, blamed for four deaths, hit Cedar Rapids, Iowa, particularly hard, cutting power to almost the entire city of 133,000 people, and damaging most of its businesses and homes.
In an October update to its database of billion-dollar weather disasters, the National Oceanic and Atmospheric Administration estimated damages from the August derecho, which raced from Iowa to Indiana, at $7.5 billion. This includes agricultural impacts that are still being analyzed, so the total may be revised, said Adam Smith, who manages the database.
The derecho’s financial toll exceeds that of nine of this year’s record 10 landfalling U.S. hurricanes and tropical storms. The exception is Hurricane Laura, which struck Louisiana in late August and caused an estimated $14 billion in damage.
Including the derecho, the U.S. has been hit by a record-tying 16 billion-dollar weather disasters this year through September.
A derecho is a fast-moving, violent wind event associated with a thunderstorm complex. One common definition specifies that it must produce “continuous or intermittent” damage along a path at least 60 miles wide and 400 miles long, with frequent gusts of at least 58 mph and several well-separated gusts of at least 75 mph.
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Parts of five Iowa counties were struck by wind gusts estimated at 110 to 140 mph.
“To have a Midwest city endure [such] wind speeds, and also see such a devastating impact to a large volume of regional crops, is almost unbelievable,” Bowen said. “I don’t think most of the country truly realizes how severe the event ended up being.”
Derecho winds typically last about 10 to 20 minutes at any one spot. In contrast, the 30- to 60-minute duration of severe gusts in the hardest-hit areas Aug. 10 was much more comparable to the passage of a hurricane eyewall than a tornado, whose winds typically last only a few seconds to a minute or two.
In Cedar Rapids alone, more than 1,000 housing units were deemed unlivable in the week after the storm, according to the Gazette. Hundreds of other homes were damaged.
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Iowa state climatologist Justin Glisan highlighted the scope of agricultural impacts in a September webinar. According to initial estimates, more than 3.5 million acres of corn and 2.5 million acres of soybeans were affected in Iowa, or about 20 percent of the state’s total farmland.
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U.S. derechos typically form along the north edge of a very hot, humid surface air mass with the approach of a strong upper-level impulse. There has been little research on how human-produced climate change might affect derechos, though it’s conceivable that a poleward shift in summer weather patterns might nudge their U.S. distribution northward over time.
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The high cost of this year’s Midwest derecho is in line with a trend toward the highest-end global weather disasters becoming even more costly at a disproportionate pace, especially in midlatitudes. This phenomenon was analyzed in a 2019 paper in the Proceedings of the National Academy of Sciences.
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The authors reported an increasing trend in extreme damages from natural disasters that is generally consistent with a climate change signal.
“Increases in aggregated or mean damages have been modest,” they said, “but evidence for a rightward skewing and tail fattening of the distributions is statistically significant and robust — with most pronounced increases in the largest percentiles (e.g., 95% and 99%), i.e., the catastrophic events.”
tags: severe weather, extreme weather,
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