16 August 2016 Insurance

Severe flooding from record rainfall hits Southern Louisiana: AIR

Extensive precipitation-induced flooding in southern Louisiana has caused six deaths, tens of thousands of rescues and significant property damage from west of Baton Rouge to Mississippi, according to catastrophe modelling firm AIR Worldwide.

A state of emergency has been declared for Louisiana and the impact counties in Mississippi, as thousands of homes, as well as farmland, highways, and commercial and industrial property have suffered flood damage, with additional rain likely to initiate flash floods.

Hemant Chowdhary, principal scientist at AIR Worldwide, said: “Record rainfall fell across a large portion of southern Louisiana as a slow-moving tropical depression–like system crawled across the region this past week.

“Rainfall amount ranged from 12 to more than 24 inches, with 31.39 inches recorded near Watson and 27.47 inches in Brownfields; 8.49 inches fell at the Baton Rouge Metropolitan Airport in one day.

“Parts of the region received two to four times the average total monthly rainfall for August in just three days.

“The culprit—the tropical depression–like low-pressure system—intensified as it slowly drifted across the state. Although the storm featured a closed warm core low, because it formed and was maintained inland it was technically not considered a tropical depression. Nevertheless, the counter clockwise (southerly) flow off the Gulf of Mexico—where sea surface temperatures are almost at record warmth levels—brought tremendous amounts of moisture inland across southern Louisiana.

“Also, precipitable water amounts in the atmosphere were at near record amounts of 2.50-2.75 inches. The combination of these factors, with a lift from the low-pressure system, resulted in slow-moving torrential rainfall and thunderstorms from Lafayette to Baton Rouge. As the storm trekked westward the heaviest rainfall shifted west, too; however, localized downpours continued to plague the area through the weekend.”

The Louisiana Department of Transportation (DOT) has reported that approximately 200 roadways became impassable due to flooding, and that that as many as 1,400 bridges need to be inspected before they can be reopened.

According to AIR, only 0 to 10 percent of buildings constructed since 1980 in the Gulf States have basements, which increase vulnerability to flood damage.

Buildings in the region are more typically built on slab foundations, which are designed to withstand flotation, collapse, or lateral movement that can be inflicted by floodwaters. Crawl space foundations in residential buildings in the region are required to have flood openings no more than 1 foot above grade.

In Louisiana, more than 80 percent of the residential construction is wood, with an estimated 5% having basements, and over half of the commercial buildings are steel and concrete, according to AIR.

AIR suggests commercial buildings, unlike residential structures, often are engineered and built to stricter standards, and are thus less vulnerable than single-family homes. However, mechanical, electrical, and plumbing (MEP) systems can experience severe damage, which results in high losses.

Chowdhary concluded: “The drenching rain in southern Louisiana during the past week, from west of Baton Rouge to New Orleans and Mississippi, brought historic inland flooding in many communities.”

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