Mapped: In one Houston community, 80 percent of high-water rescue calls were outside of flood plain

High-Water Rescues By Neighborhood

The Houston Fire Department responded to more than 7,000 calls for...

A map of the approximate 7,500 high-water rescues calls that came in during Hurricane Harvey further suggests how ineffective Harris County's flood plain map is when it comes to predicting where Houston neighborhoods will flood during catastrophic storms.

The maps reveal that one neighborhood — East Houston — located in northeast Houston had the most 911 calls for high-water rescue outside of both the 100-year and 500-year flood plains, according to maps created by the Houston Chronicle using data obtained from the Houston Fire Department.

The department kept a log of each call and the location of the caller.

While most of the high-water rescues across Houston were inside flood zones, data show more than 80 percent of the 943 calls for help in East Houston were outside of the flood plain

But calls outside of the flood plains should not be too surprising.

Harvey was a phenomenal storm.

Analysts with the National Weather Service have considered the storm a 1,000-year flood event and current maps do not account for those kinds of storms.

The term "1,000-year flood" means that, statistically speaking, a flood of that magnitude — or greater — has a 1 in 1000 chance of occurring in any given year.

In terms of probability, the 1000-year flood has a 0.1 percent chance of happening in any given year, according to the the United States Geological Survey.

East Houston is a community of about 18,000 residents in northeast Houston, populated primarily by black and Hispanic residents.

Like other Houston communities, East Houston had not seen flooding to that extent since Tropical Storm Allison in 2001. But East Houston resident Juan Antonio Sorto said even Allison does not compare to Harvey.

He added that East Houston did not flood on either the 2015 or 2016 storms in the city. But during Harvey, water was waist deep and families were forced to flee their homes.

"It [is] remarkable that we have not flooded as often since the community runs between Halls and Hunting Bayou," Sorto said.

Sorto, who does freelance work for the Rice Kinder Institute for Urban Research, has been researching and writing about the response and recovery in his community since the storm hit.

On Aug. 29 he wrote on his blog:

"Water levels continue to rise steadily. By this time, most of East Houston is under water. The entire community around Lake Forest Park is flooded as the lake there overflows with rainwater."

The city is working on addressing response in areas most prone to flooding. In fact, HFD has proposed placing its new high-water rescue vehicles across Houston in strategic locations. One of those locations includes Meyerland, Kingwood and the East Houston area.

Meanwhile, since Harvey residents and local leaders have scrutinized the flood plain maps. In October, the Houston Chronicle reported that Houston area flood maps were based on outdated rainfall data and trends.

More than 80 percent of the high-water rescue calls in East Houston...

And even that data, from 2001, is more than 15 years old and doesn't capture severe storms that included Hurricane Ike in 2008, the Memorial Day floods in 2015 and the Tax Day floods of 2016, according to the report.

An analysis by the National Oceanic and Atmospheric Administration suggested the standards used to map flood zones and design flood control projects routinely underestimate the severity of the Houston area's downpours.

That analysis by NOAA, which looked at rainfall data stretching back decades, up to and including Harvey, shows the amount of rain that defines a "100-year storm" - one that has a 1 percent chance of occurring in any given year - has risen by 3 to 5 inches in Harris County since the last estimates were put in place in 2002.

In other words, instead of expecting 12 to 14 inches in a day during a 100-year storm, the data shows the county should expect 15 to 18 inches.

The final NOAA data will be published in May 2018, the first statewide update to the federal agency's rainfall estimates in nearly 50 years.

The Houston Fire Department responded to more than 7,000 calls for...

John D. Harden is a data specialist at the Houston Chronicle, telling the stories behind the numbers. Follow him on Twitter and Facebook. Send him tips at john.harden@chron.com .