14 March 2016 Operational Risk

North American floods a 200-year return period

Flash floods that occurred in parts of North America last week resulted in more than 3,500 evacuations and hundreds of road closures, according to Risk Management Solutions (RMS).

The floods hit Louisiana, Texas, and Arkansas on Monday 7 March. Parts of Louisiana, such as Shreveport, received more than 16 inches of rain since Tuesday (March 8), resembling the 200-year return period (0.5 percent chance of occurring in a given year), according to MetStat.

In Northern Louisiana, rainfall runoff into local water bodies caused a few rivers and lakes to come close to or exceed their highest water levels on record, such as the Bayou Dorcheat at Lake Bistineau and the Sabine River near Burkeville

As of Thursday (March 10) afternoon, 14 United States Geological Survey (USGS) river gauges in Louisiana and Texas were at major flood stage. At the same time, parts of the Northeast experienced temperatures 30 to 40 degrees warmer than normal, breaking many all-time records

Jeff Waters, manager, model product management, RMS, said: "The atmospheric conditions driving this event are extremely rare. A strong upper-level disturbance over Mexico and a high pressure system off the east coast created a narrow convergence zone over the south central US, funnelling significant amounts of tropical moisture from the Eastern Pacific and Gulf of Mexico to parts of Texas, Louisiana, and Arkansas.”

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