Harvey’s 5-Day Rainfall in Texas Unprecedented in U.S.

The U.S. has never experienced the amount of rainfall across such a vast area as that brought by Hurricane Harvey when it struck Texas, according to a report released this week.

More rain fell over a five-day period, and on such a broad area, than at any time since records have been kept in the U.S. beginning about 1850, the report by the Harris County Flood Control District said. The area extends roughly from Victoria in South Texas northeast to Houston and over to the Louisiana border – a region approximately the size of Massachusetts.

The report relied on rainfall calculations done by Texas state climatologist John Nielsen-Gammon, who compared Harvey to other storms in terms of duration, amount of rain and spatial coverage.

The National Hurricane Center early this year issued its own report saying it’s “unlikely that the United States has ever seen such a sizable area of excessive tropical cyclone rainfall” as that which fell on the Houston metro area. The report released Monday took a broader, regional look.

Flood Control District officials say rainfall amounts in Harris County, home to Houston, ranged from 26 to 47 inches (660 to 1194 millimeters). Some areas east of metro Houston saw an estimated 55 inches (1397 millimeters).

Sixty-eight people in Texas died in the days after Harvey came ashore Aug. 25. It spawned 57 tornadoes and caused an estimated $125 billion in damage, placing it second in U.S. history behind Katrina’s inflation-adjusted $161 billion.

The name Harvey was retired last month from the National Hurricane Center list of tropical cyclone names and won’t be used again because of its deadly and devastating effects, according to the Flood Control District.

“The takeaway from Harvey is that it expands our understanding of what is possible,” Nielsen-Gammon told The Associated Press on Wednesday. “We have never experienced a storm like Harvey.”

As the earth warms, hurricanes and other storms are absorbing more moisture and are capable of regularly producing more rainfall, he said.

This week’s report contains a host of eye-catching information, including that more than 60,000 people were rescued by government rescue personnel across Harris County. Some 1 trillion gallons of water fell across metro Houston in that final week of August, a volume that would flow down Niagara Falls for 15 days.

For Jeff Lindner, director of hydrologic operations for the district and an author of the report, one remarkable finding was that 64 percent of the more than 154,000 homes that flooded in Harris County did not have flood insurance coverage.

“One of the first things people tell me is that they live outside the 100-year flood plain so they don’t need flood coverage,” Lindner said. “It’s just not true at all. It’s become kind of a myth. Everyone here in Houston and southeast Texas have a flood risk.”