Sep 7, 2017

Texas A&M Expert: Rainfall From Harvey Shattered Every Record

Houston, TX
USA
by
Keith Randall
,
Texas A&M Today
Chris Ginter wades through deep floodwaters on September 6, 2017 in Houston, Texas. Ginter, a Houston resident, has been taking local residents to their flooded homes in his monster truck which can drive through waters up to 4 feet deep. Photo: Justin Sullivan/Getty Images
Chris Ginter wades through deep floodwaters on September 6, 2017 in Houston, Texas. Ginter, a Houston resident, has been taking local residents to their flooded homes in his monster truck which can drive through waters up to 4 feet deep. Photo: Justin Sullivan/Getty Images

Hurricane Harvey was billed as a once-in-every-500-year event, and it more than lived up to its billing. It produced rainfall amounts that will re-write the weather books in Texas and the United States, says a Texas A&M University expert.

John Nielsen-Gammon, who is a Regents Professor of Atmospheric Sciences at Texas A&M and also serves as Texas State Climatologist, says Harvey set new standards for historic rainfall and flooding.

“Harvey is head and shoulders above all previous multi-day storms ever recorded in the continental United States,” says Nielsen-Gammon.

“I examined 18 different combinations of storm lengths and area sizes, from two days long to five days long, and standard areas from 1,000 square miles to 50,000 square miles. According to the preliminary data, Harvey was the worst in all but one.”

Nielsen-Gammon said that the most amazing record is for the five-day total over an area of 10,000 square miles.

“For Harvey to average 34.72 inches over five days across that large an area is ridiculous,” Nielsen-Gammon says. “The previous all-time United States record, set in Texas back in 1899, was estimated at 21.39 inches. Harvey exceeded that record by 62 percent.”

Ten other records were shattered by 20 percent or more, he confirms.

“To examine a storm’s flooding potential, scientists and engineers look at total rainfall over a large area over an extended period of time,” Nielsen-Gammon notes. “Extreme rainfall in one location causes problems, but when that rain falls over a much broader area, you get a disaster.”

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“The rain in Harris County was worse than the previous worst-case scenario. If Houston had gotten the equivalent of the worst storm in history, and if it had targeted Harris County like an expert marksman, it still would have fallen several inches shy of Harvey.”

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Nielsen-Gammon also notes that information like this is essential for understanding the performance of existing flood control plans and infrastructure and for developing new ones.

“There has been lots of commentary about Houston development, disaster planning, and flood control measures in the wake of Harvey,” Nielsen-Gammon adds.

“But even the best urban preparations in the world would not have been designed for an event as extreme as Harvey.

“Now that we know what the atmosphere can do, we can prepare better for the next time,” Nielsen-Gammon added. “Except that because of climate change, we have to prepare for a moving target.”