JOHN YANG: This summer, cities across the United States broke thousands of heat records, but in many of them some areas were hotter than others, what are known as urban heat islands, and that can mean higher energy bills for some and unsafe conditions.

Blair Waltman-Alexin of Austin PBS in conjunction with Austin Vida has this report.

BLAIR WALTMAN-ALEXIN: Bertha Hernandez lives in the dove springs neighborhood of Austin and selling her homemade tamales and propostas (ph) is her main source of income.

But he's making less money this year.

BERTHA HERNANDEZ (through translator): I had to change because of the heat because I no longer go out to sell the same as I did before.

The sun won't that means, it's too hot.

So even if I want to do that, I can't.

BLAIR WALTMAN-ALEXIN: Over the summer Austin saw record breaking heat, but some areas of the city see hotter temperatures than others and that can mean higher energy bills for residents.

Mark Coudert is with the city of Austin's Office of Resilience.

MARK COUDERT, Office of Resilience, City of Austin: We have data that shows heat from satellites, and mostly shows areas like parking lots, the airport and so on.

And that's valuable information but doesn't really tell you what's happening on the ground level.

BLAIR WALTMAN-ALEXIN: So the city of Austin teamed up with researchers at the University of Texas to see exactly what was going on.

What they found was higher temperatures in places with less greenery.

This is called the urban heat island effects.

Dr. Dev Niyogi is a professor of Geosciences and Engineering at the University of Texas at Austin.

DR. DEV NIYOGI, University of Texas at Austin: In the solar radiation that comes in, over this urban areas, it gets absorbed into the streets, into the steel, into all the infrastructure that is required.

And so when you measure the temperatures, you will get that there are blobs, which are much hotter, it will look like an island.

And that's why it gets referred to as an urban heat island.

Those temperatures could be different by anywhere between 5 to 10 degrees.

BLAIR WALTMAN-ALEXIN: This is what Hernandez and others are dealing with.

Areas with impervious cover, absorb and reflect the sun's rays, increasing temperatures.

But not everyone is feeling the heat.

DR. DEV NIYOGI: Some parts of the city, it is much cooler, and other parts of the city are much, much warmer.

BLAIR WALTMAN-ALEXIN: Some of this can be traced back to redlining practices that started in the 1930s when the federal government labeled non-white neighborhoods as risky places to invest home loans.

According to the Environmental Protection Agency, research shows that red line communities have less vegetative cover, higher temperatures, and increased health risks.

MARK COUDERT: If you look at maps that look at health outcomes, or a map or look at race or income, they essentially show the same maps.

And we, through talking to committee members understand that they are the most sensitive to heat, but also cold, better quality, and so on.

BLAIR WALTMAN-ALEXIN: These neighborhoods also often have older homes that can be harder to keep cool.

According to Dr. Zoltan Nagy, he studies architecture and climate change at the University of Texas.

ZOLTAN NAGY, University of Texas at Austin: So older homes are particularly vulnerable today.

So you have, you know, you single pane windows that holds around the windows, where air comes in directly and not just through heat transfer, but mass transfer, so the hot air comes in or the cold air goes out.

Plus, of course over time you deteriorate, right.

So anything build before the 80s is probably not an insulated at this point.

BLAIR WALTMAN-ALEXIN: Many homes in Hernandez' neighborhood were built in 70s.

And older homes plus higher temperatures equals higher energy bills.

BERTHA HERNANDEZ (through translator): It's not well insulated.

It's also old and not well insulated.

ZOLTAN NAGY: There is another thing that happens which is that those who cannot afford it delay energy use and so they turn their age back on a lot later, it's a lot warmer inside.

And so that creates all kinds of adverse like health effects.

And then because due to climate change, it gets worse outside, right?

Maybe you delay turning on the AC but then the conditions lasts longer and longer.

So it's really not good.

MARK COUDERT: So they have to make a decision between not using energy and staying cool.

And that's a very hard conversation ahead.

BLAIR WALTMAN-ALEXIN: It's a conversation Hernandez has had more than once.

BERTHA HERNANDEZ (through translator): Well, it's also difficult if we want to save electricity because it's getting very expensive.

So there are moments when we have to put up with the heat because we can't have the air on all day.

BLAIR WALTMAN-ALEXIN: Heat has pushed electricity bills higher for everyone.

But for lower income households, that increase is harder to deal with DR. DEV NIYOGI: The cost associated, it might seem like it is $50 more, but that $50 would be quite different as against certain neighborhoods where this might be a significant dent in the monthly budget.

BLAIR WALTMAN-ALEXIN: Cities can take steps to turn down the heat.

Coudert and his team are making recommendations to the city council that include adding trees and improving bus stops.

But they agree action needs to be taken and quickly.

MARK COUDERT: We need to be thinking about what we need today.

But also what our strategy needs to be doing in the next year or two years as climate change gets worse.

BLAIR WALTMAN-ALEXIN: For now Hernandez says she'll continue to get out early and get back inside before the temperature rises.

BERTHA HERNANDEZ (through translator): Well, you can't be defeated.

You have to push forward so the heat doesn't impoverish us any more than one hour.

BLAIR WALTMAN-ALEXIN: For "PBS News Weekend," I'm Blair Waltman-Alexin in Austin.