The project is part of the UT-City CoLab, a collaborative initiative between UT researchers, Austin city leaders and community members.

AUSTIN, Texas — A new study by University of Texas at Austin researchers is examining the indoor heat vulnerability for single-family homes across the City of Austin.

Researchers found that if power went out during a heatwave, 85% of Austin’s single-family homes would pose a significant risk of death to an elderly person inside. For younger Austinites, the risk is far lower, at about 15%. 

“When we are trying to see something with heat, it is always unclear which areas are going to pop up and which neighborhoods are going to be vulnerable to that,” Dev Niyogi, a professor at the UT Jackson School of Geosciences and CoLab co-lead, said. 

To conduct the study and assess the heat risk for each home, researchers simulated the conditions of a historical three-day heatwave in Austin, during which temperatures exceeded 110 degrees Fahrenheit. At the same time, the energy grid was blacked out. Then they used that to determine the survivability of those conditions for different age groups.

Similar to what is done to protect homes near floodplains or in flood-prone areas, Niyogi said the study could help pinpoint locations that would benefit from heat mitigation efforts.

“This is how you use the best science to try and invest in the most vulnerable, high-impact regions where you can start developing a solution pathway that really matters,” Niyogi said.

According to the study, the Rundberg and St. John neighborhoods are the most vulnerable overall.

Marc Coudert, climate resilience and adaptation manager for Austin Climate Action & Resilience, said places with more freeways and parking lots are hotter than locations in, for example, West Austin, which has more trees and canopy and tends to be cooler.

“There are other places in Austin that are definitely equally as sensitive to heat, but we want to make sure that we’re really focused on the areas that have high heat and ambient sort of in the area,” Coudert said.

The study was published in the journal Building and Environment. The project is part of the UT-City CoLab, a collaborative initiative between UT researchers, Austin city leaders and community members that focuses on climate resilience.

One of the study’s corresponding authors, Zoltan Nagy, said the heat risk for specific buildings can vary depending on factors such as age, materials, and construction. So the outdoor temperature is not a good indicator of what it feels like inside a building during a blackout.

“What happens inside depends very much how your house was built,” said Nagy, who was an assistant professor at UT’s Cockrell School of Engineering. “If you have good windows, and it’s well-constructed, it takes a long time until the heat builds up. But if you have cracks all over the place, and it’s an old house with single-pane windows, then it’s a lot faster for the house to heat up.”

Researchers put together a map showing the risk of death to the elderly population if they stayed in their homes during a heatwave and power outage. The dark red indicates higher risk, and the yellow indicates lower risk.

While the city does a lot of work on heat and its impact on community members, Coudert said they don’t have a good understanding of how heat affects people at home.

“We tend to focus more on outdoor spaces like parks and cooling centers, but we don’t have a good understanding of how people are impacted at home,” Coudert said. “This allowed us to have a look at the whole city and see which houses and which buildings are most impacted by heat, and how we can sort of rethink our approaches to weatherization or public health issues.”

Coudert said the data will allow the city to take a “methodical approach to mitigating risk” and ensure resources reach those that need them most.

“We have rec centers in those places, we have health centers, we have libraries, how can we talk to those groups or to talk to the community members, maybe talk to community organizers and say, talk to your constituents and make sure that people are thinking about heat and make sure people are safe,” Coudert said. 

For example, he said they could add cooling centers, create home weatherization programs, or plant more trees in areas most at risk.

“This is just a starting point,” Coudert said. “We have heat maps for Austin, but this is the next step to look at which structures are impacted by heat and how we should be thinking about sort of next steps.”

In the 1970s, Coudert said Austin averaged 12 days over 100 degrees. Now, the average is around 30 days over 100 degrees. However, he said there have been some big peaks, like in 2011, when there were 90 days over 100 degrees, and in 2023, when there were 80 days over 100 degrees and 40 days over 105 degrees.

“We want to make sure as the world gets hotter and Austin gets hotter, we provide resources to people to ensure that they’re safe,” Coudert said.

In the future, the researchers said nearly every single-family home in Austin could face some level of heat risk. According to the UT-City CoLab, the frequency of heatwaves in Austin could double by 2100.

Most heat-related deaths in the U.S. occur inside, but UT researchers said the issue is rarely studied. Similar to a hot car, heat gets trapped inside homes with nowhere to go, raising temperatures to levels that are not survivable.

“If you have a heat wave and there is no power, your home itself can actually start becoming like an oven,” Niyogi said. “We want people to be aware that heat is a silent killer, and the heat may not be seen like water that is rising, but it is something that affects us.”

While this study focused on Austin, Niyogi said the approach can be replicated in other cities across the country and around the world. He said the findings can be applicable wherever heat is a problem.

“There is a common aspect that we seem to find neighborhoods which have a poor infrastructure in terms of their houses and neighborhoods which have less shade from trees, are essentially the neighborhoods which are going to have heat as a vulnerable part of their ecosystem,” Niyogi said. “As we start looking at what areas we see this vulnerability, we start looking for areas where we have an older habitat and where we have less tree cover as the areas to be considered as vulnerable.”