In the weeks and months after Hurricane Harvey, the evidence of its historic scope and intensity trickled out bit by bit: Record rainfall totals. Record reservoir levels. Record destruction.
Now, nine months after the storm, a report by the Harris County Flood Control District combines and analyzes all the available data about Harvey and its aftermath, distilling the numbers into a single message: By every conceivable measure and in every imaginable context, Harvey caused the most disastrous flooding in the nation’s history. And it could have been worse.
“All 4.7 million people in Harris County were impacted directly or indirectly during the flood and after the flood waters receded,” states the 32-page memorandum by two flood control district officials, Jeff Lindner and Steve Fitzgerald.
The compilation of all the data into one document provides a useful backdrop for ongoing policy discussions about recovering from Harvey and strengthening the region’s resilience to future floods. County officials were recently scheduled to host the first of 23 planned public meetings on a $2.5 billion August bond issue for flood control projects.
Lindner, the flood control district’s meteorologist and director of hydrologic operations, said district officials prepare similar reports after every major flood. The documents provide a historical record and make it possible to compare the relative impacts of different events, he said.
In Harris County, the highest total recorded over four days was 47.4 inches at Clear Creek and Interstate 45. (Totals exceeding 51 inches were recorded in Liberty County east of Houston.) The lowest four-day total in Harris County was 26 inches.
According to the report, the Texas state climatologist, John Nielsen-Gammon, examined the largest rainfall events in U.S. history and compared them with Harvey for durations of 48, 72 and 120 hours, and covering areas ranging from 1,000, to 50,000 square miles.
“Harvey exceeded the previous records in all of the 18 different combinations except one,” the report states. “The most astounding statistic is that for the 120-hour duration over 10,000 square miles, Harvey exceeded the previous record from June 1899 by 13.33 inches or 62 percent. The rainfall amounts and spatial coverage of those amounts have never been experienced across the United States since reliable records have been kept.”
Other key points in the report:
— Officials confirmed 36 flood-related deaths across Harris County and 68 statewide. While most deaths in other recent floods were caused by drownings in vehicles, most of the Harvey fatalities involved “people outside in the fast-moving or high water levels,” the report states, adding, “Harvey is one of the only flood events where a few people drowned in their home or workplace.”
— With damage estimated at $125 billion, Harvey was the second-costliest hurricane in U.S. history. Hurricane Katrina, which struck New Orleans in 2005, caused $160 billion in damage.
— Government agencies rescued 60,049 residents in Harris County, most of them from their homes, and 32,000 to 34,000 evacuees stayed in 65 temporary shelters. Civilian volunteers rescued tens of thousands more.
— The Federal Emergency Management Agency has provided $4.8 billion in rental assistance, home repairs and other aid to more than 177,000 households through its individual assistance program.
— Harvey dropped 1 trillion gallons of water on Harris County over four days, enough to fill NRG Stadium 1,472 times and cover Harris County’s 1,777 square miles with an average of 33.7 inches of water. Over a 50,000 square-mile area, Harvey dropped more than 16.6 trillion gallons.
— In Harris County, Harvey flooded 154,170 single-family houses — about 9 percent to 12 percent of all buildings in the county — and 5,000 to 15,000 apartments, condominiums and townhouses, making it “the largest and most devastating house flooding event ever recorded” in the county. In addition, thousands of commercial structures were flooded.
— The Brays Bayou watershed, which includes the hard-hit Meyerland neighborhood, recorded the most flooded houses, 23,810, followed by Buffalo Bayou at 17,090 and Greens Bayou at 12,900. A watershed is the land area that drains into a particular stream. Among jurisdictions, Houston’s 96,410 flooded houses was the highest by far, followed by unincorporated Harris County (34,600) and Pasadena (4,610.)
— As many as 24,000 additional houses might have flooded if not for previous flood control district projects, including the buyouts of more than 2,000 homes deep within floodplains and improvements to Sims, Brays and White Oak bayous. Despite these efforts, “Hurricane Harvey’s relentless and widespread heavy rainfall filled every channel and detention basin in every watershed in Harris County at some point during the four-day historic event,” the report states.
— More than 300,000 vehicles were flooded across the county.