‘100-year floods’ every year? New Texas rain data is redefining storms


Highlights

The federal government is updating rainfall frequency estimates for Texas for the first time since the 1970s.

A preliminary version of the new data shows big increases in rain expectations for Houston and Hays County.

The data is used for building standards, flood plain maps and describing which storms are “100-year” events.

Onion Creek on Halloween 2013. Wimberley on Memorial Day weekend 2015. Houston’s Tax Day flood in 2016. Hurricane Harvey.

If you feel like Texas has had a constant stream of 100- or 500-year floods in the past few years, you’re not wrong.

Texas rainfall estimates, the federal data used to describe flooding, were last updated in the 1960s and ’70s, and the National Oceanic and Atmospheric Administration is updating them to reflect the increased frequency of heavy rainstorms documented over the past two decades.

The data are not just for forecasting the weather and describing storms. Once adopted, the new numbers will be used in engineering standards for roads and buildings and in the National Flood Insurance Program’s mapping of flood risk, potentially forcing more people to buy flood insurance or to build their homes to higher elevations.

“A lot of people are anxious about this,” said Nick Fang, an engineering professor and flood expert at the University of Texas at Arlington whom NOAA invited to review the data. “It’s going to change or affect a lot of people’s personal lives and also the design criteria.”

A preliminary version of the estimates has been released for peer review. It shows major increases in expected rainfall for the Houston area, Hays County and the area along the Rio Grande near Del Rio — and huge leaps in how often severe rainfall is expected to hit those areas.

Compared with current data, a 24-hour rainfall in Houston would have to drop an additional 4 to 7 inches for it be considered a 100-year event, meaning it has a 1 percent chance of occurring in any given year. In most of Hays County, the threshold would increase 3 inches, while Austin would see a 2-inch jump.

Despite the big changes, some experts say the maps don’t go far enough in making sure Texas is prepared for flooding because they look only at past events and don’t project forward using emerging trends, especially an increase in storm severity that climate scientists attribute to global warming.

READ: Hurricane Harvey breaks Texas rainfall record

“While (the new data) is an improvement over the statistics we’re using, that does not take into account really the trend lines that we’re seeing within the most recent 15, 20 years,” said Jim Blackburn, an environmental lawyer and Rice University professor. “It’s about human life. It’s about human property. It is a very, very serious public safety issue.”

The Houston area, he noted, has seen four 500-year floods in just the past 23 years.

The Federal Emergency Management Agency, which oversees the flood insurance program, said it will examine the data once completed.

“FEMA is aware of the new preliminary rainfall frequency data and will utilize that data once it is finalized,” FEMA spokeswoman Deanna Frazier said in a statement. “We are evaluating how this data impacts our understanding of the flood hazard, and will discuss with state and local partners the need to update NFIP flood risk data.”

In the aftermath of Hurricane Harvey, Harris County officials are not waiting around for new data to change FEMA’s maps.

The county commissioners on Tuesday voted unanimously to require more people to build to minimum elevations or buy flood insurance if they have federally backed mortgages. Previously, only property owners in FEMA’s 100-year flood plain had to follow those rules. The commissioners applied those regulations to the 500-year flood plain, a broader flood risk designation that is mapped by FEMA but usually does not carry special rules.

Waiting in Wimberley

When the Blanco River jumped its banks and tore through Wimberley’s Flite Acres Road in May 2015, it destroyed one of Phil Collins’ houses and poured four feet of water into another.

The deadly flood convinced many that it was time to rethink how Wimberley handles flooding and development along the river. FEMA, which had already been working on a rewrite of the area’s flood plain maps, pounced on the opportunity, pushing out the new maps on an advisory basis.

Wimberley’s City Council declined to immediately adopt the maps, which would greatly expand the number of property owners required to obtain flood insurance or build to higher elevations. Instead, it established a plan to present the new maps to the public for feedback and, in the meantime, allow owners to rebuild their homes as they were before the flood — so long as they sign affidavits saying they are aware of the coming changes.

Collins, a retiree who owns several properties in Wimberley and rents out some to vacationers, was one of the few who signed the affidavit, according to City Council Member Steve Thurber, who was mayor when the flood occurred.

Collins said he is trying to sell the property where he lost the house. (The other was quickly repaired.) If it doesn’t sell, he will rebuild to the old standards, not the new minimum elevations recommended by FEMA, he said.

“I wish there was just more flexibility for rebuilding in the flood zones,” Collins said. “I’m concerned that if we have an entire neighborhood built up on stilts, it’s not good for the neighborhood property values.”

Two and a half years after the flood, the City Council still has not adopted the new maps. Thurber said he expects that to happen in the fall of 2018.

But the longer governments wait to act after a disaster, the more likely their constituents are to develop what’s known as “disaster amnesia,” as the enthusiasm for safety measures wanes over time and individual concerns take over.

Thurber said that, while he expects the council to adopt the maps, the process might be complicated by Texans’ aversion to regulation and owners’ concerns about their property values.

“It’s the Texas desire for no regulations. It’s money that developers have, a way of lobbying. It’s about population growth in some areas,” Thurber said. “It’s a mixed bag. People that are on the river like to live on the river, and they don’t want to have to build up. And people who don’t live on the river don’t really care.”

Collins said he would prefer the city focus on safety measures such as improving flash flood alarm systems than on regulations aimed at property owners.

“I wish there were more opportunities for people to make decisions on their own,” Collins said.

Onion Creek buyouts

While newer data will likely improve flood plain mapping, it won’t be a panacea for the many problems facing the National Flood Insurance Program, which is nearing $30 billion in debt and has in the past been criticized for subsidizing property owners to rebuild in risky areas over and over.

Bob Gilbert, a UT-Austin engineering professor, said there is a natural incentive for property owners to fight being included in flood-risk zones where they will have to pay more in insurance and could see their values decrease.

“That’s part of the flood insurance being broken, because it’s like a scarlet letter on you,” Gilbert said. “It’s crazy if you think about it: If you’re 1 foot outside that flood plain, you don’t have to do anything. And if you’re 1 foot inside, you have to do everything.”

Relying so heavily on flood plain designations also gives residents the impression that they don’t have to worry about flooding if they’re not in a risk zone, Gilbert said. Because flooding is ultimately unpredictable, he said, everyone needs to be prepared.

One instance of good flood risk management, Gilbert said, is the city of Austin’s handling in recent years of the flood-prone Onion Creek area, much of which has been included in FEMA’s flood plains for years. After the deadly 2013 flood, the city amped up its buyout program to remove families from harm’s way and improved its waterway monitoring system to warn or evacuate residents when flash floods approach.

“They’ve been buying out property in a way that’s working with the community, so you don’t hear a lot of complaints about it. It takes time,” Gilbert said. “A lot of people were impacted when we lost lives on Onion Creek, impacted in a way that they decided we can do better, and they are doing that.”



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