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. On Tuesday night, county officials were scheduled to host the first of 23 planned public meetings on a $2.5 billion August bond issue for flood control projects.
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.”
The Flood Control district puts out a report like this one, which you can find here, after every major flood. For the most part, this is data we’ve seen before, but not all in one place, and not with all of the comparisons this report includes. It’s pretty sobering to read and think about, so by all means go do so. Swamplot has more.