The 5th most damaging (in terms of dollars of economic and/or property losses) weather event in the U.S. in 2011 was the historic flooding that took place along the Mississippi River and its tributaries during the Spring and Summer months.
During the spring, rainfall amounts averaged as much as 300% of normal across a large portion of the Mississippi and Ohio River Valley area:
150-300% of normal rainfall in purple shaded areas
During the month of April alone, 1300 daily precipitation records were set at observing stations across the Mississippi and Ohio Valley regions. A total of 72 reporting stations observed their wettest day of any April on record:
As if the record rainfall flowing into the Mississippi River and its tributaries was not enough, a melting snowpack containing 4-20 inches of additional water equivalent added fuel to the fire:
Water equivalent of the snow pack as observed on 3-1-11
The result of the two was widespread flooding, of record proportions in some cases. To date it is believed that this event was responsible for 2 deaths and "$3 to $4 billion" in damage across the region. (For purposes of simplicity I split this figure down the middle, which is how I arrived at the $3.5 billion amount).
The following image of the Mississippi and Ohio Rivers in flood was taken by the Landsat 5 satellite in May of this year (image courtesy of NASA):
The magnitude of the flooding was much greater near Memphis, TN this year as compared to last year, as you can see on the close-up Landsat 5 images below:
Mississippi River Flooding in May 2011 near Memphis, TN
Mississippi River Flooding in April 2010 near Memphis, TN
The crest of 47.9 feet in Memphis on May 10th was just shy of the all time record of 48.7 feet which was set on February 10, way back in 1937.
An informative video regarding the Landsat 5 satellite passes over the flooded Mississippi River valley this year can be seen here:
Indeed, the Mississippi River crested anywhere from 4 to 18 feet above flood stage across the middle and lower portions of the valley before the flooding subsided in May:
The image below provided by the U.S. Army Corps of Engineers shows the crest this year (top figure at each station) and the all time record crest level (bottom figure):
Record crests were set this year at Caruthersville, MO (47.6 ft. on 5/7/11 vs. 46.0 ft on 2/5/37), Birds Point, MO (58.3 ft. on 5/2/11 vs. 52.3 ft. on 9/15/97), Vicksburg, MS (57.1 ft. on 5/18/11 vs. 56.2 ft. on 5/4/27), Natchez, MS (61.9 ft. on 5/19/11 vs. 58.0 ft. on 2/21/37) and at Red River Landing, LA (63.4 ft. on 5/18/11 vs. 62.3 ft. on 3/25/97).
The Army Corps of Engineers took some dramatic (and at times controversial) steps in an effort to mitigate potential damage from the flood, as described in this excerpt from a NOAA report:
Despite the best efforts of the Corps and others, the economic losses from this event were staggering (figures are not necessarily final): $500 million in agricultural losses in Arkansas; $320 million in damage in the Memphis, TN area; $800 million in agricultural losses in Mississippi; $317 million in agricultural and property losses in Missouri's Birds Point-New Madrid Spillway region.
The flooding that took place in the Upper-Midwest later in the Summer caused an estimated $2.0 billion in damage, landing it in the #9 spot for billion dollar weather disasters in 2011.
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