One Year After Texas’ Deadliest Flood, Scientists Have Life-Saving Suggestions

In the wee hours of Independence Day last year, parts of the Guadalupe River rose by 2 feet in five minutes. In an hour, the water had risen more than two stories. Submerged trees toppled under the force of the current. Entire houses were torn from their foundations and floated away. Heavy-duty SUVs crumpled like wads of paper. At least 119 people died.

Halfway across the planet, French climate scientist Davide Faranda was one of the first researchers spurred into action. His colleagues in the U.S. were talking about the floods and images were in the news worldwide. “We were emotionally all affected to see how many kids had lost their lives, so we wanted to contribute to the understanding, for them, for their family,” Faranda told the Chronicle.

Faranda and a team of researchers at ClimaMeter cross-checked conditions of the flood with historical weather records. They didn’t attribute the disaster as a whole to climate change, but they found that the conditions that fueled the flood were more likely due to today’s warmer climate.

ClimaMeter’s climate change attribution study was global news, but at home in Texas, researchers wanted more detail.

This May, a team of flood engineers at UT-San Antonio published the preliminary results of a study that reconstructs the Kerr County floods. One year later, they have a detailed understanding of exactly how weather caused the flood, and how new infrastructure and policies might prevent deaths in a future flood of this size.

“There is a gap between what the science shows and actually what is being built and regulated,” said researcher Hatim Sharif. “I think this gap should be as narrow as possible.”

One of the most alarming findings: Based on decades of weather records in Texas, this flood reached (and may have gone above) the upper limits of what scientists “consider physically plausible” in the region, explained lead author Ayantika Bose. “That does not necessarily mean the laws of hydrology were broken, but it does indicate that this flood was among the most extreme ever documented in Texas.”

Why was this flood so extreme? The team found that it was literally a perfect storm. Several extreme factors happened all at once: The storm was exceptionally intense, and it stayed largely in one spot instead of moving on. The water landed on a steep-sloped area of Central Texas where drought may have hardened the ground, so the rainfall rushed on top of it instead of soaking into it.

Human-driven climate change was a factor threaded through the findings – warmer air holds moisture and makes storms like this one wetter, and hot summers of drought can make dirt act more like pavement, where runoff barrels across it at higher speeds.

Because this flood was at the very upper limits of scientists’ benchmarks for floods in the area, Texas might need to update its flood models, the researchers said. The federal government needs to catch up, too. Many deaths occurred in areas outside of current FEMA maps of flood hazard zones, the study found.

Today, flood-risk planning should consider not just historical records, but climate projections about possible futures, said Mireia Ginesta, an Oxford climate scientist who also worked on the initial study with Faranda.

In this case, the flood wasn’t just stronger and in a bigger area than scientists are used to – it also ballooned faster. “The most surprising finding was the speed of the river response,” Bose said. Because of that, she said investing in monitoring and warning systems is just as important as structural changes.

Having studied Texas floods for decades, Sharif underscored again and again that rainfall records and statistics used in engineering design are outdated. That impacts bridges, culverts, roads, drainage systems, and where housing can safely be developed. 

Forecasts also need to change, he said. Instead of focusing on potential inches of rain or other weather descriptions, they should focus on potential impacts: Which roads will flood? Which neighborhoods will be inundated?

To get to those impacts, he urges specific updates to monitoring systems. He pointed to AI’s ability to analyze radar, satellite images, and security camera footage on roadways. Together, this kind of data could pinpoint unsafe roads, he argued.

That’s important because driving is one of the most fatal decisions during flooding, he said, pointing to research that found that more than half of flood fatalities are road deaths.

Weather and climate scientist James Marshall Shepherd was one of the first American meteorologists to analyze the Texas floods. He echoed the main conclusion of the San Antonio preprint: “Most of our infrastructure is designed for storms of a century gone by, and that will need to be rectified going forward.” That’s true across the U.S., he told the Chronicle. “People need to adjust their benchmarks.”

But in Texas, infrastructure may be changing faster than expectations about extreme weather. Sharif pointed out that many flood-prone areas are adding buildings all the time.

“The Kerr County floods are a reminder,” Ginesta said. “The scientific evidence is clear that climate change is increasing risks. … The biggest challenge remains translating knowledge into action.”

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