SAN ANTONIO (NYTIMES) - One day last week, Ms Juanita Cruz-Perez poked her head out the back door of her two-bedroom home in San Antonio and shook her head.

It was not quite noon yet, and the heat was already unbearable. She opened the front and back doors, praying for any kind of breeze, and turned on a plastic fan that sputtered hot air. She resisted the temptation to turn on the power-guzzling air conditioner.

"The AC (air conditioner) only goes on at night, no matter how hot it gets," she said.

Ms Cruz-Perez suffers from a slew of health problems that are exacerbated by the stifling heat, including diabetes and high blood pressure, but her monthly budget of US$800 (S$1,111) leaves little room for what she would consider a luxury.

In San Antonio, weathering the second week of a heatwave that has been ferocious even by Texas standards, lower-income residents such as Ms Cruz-Perez are sometimes left with few options to relieve the misery.

Not only can she not afford air conditioning during the hottest part of the day; she lives in the Westside, one of several parts of San Antonio - nearly all of them working-class or poor neighbourhoods - where there are few trees to provide shade.

Simple things such as venturing into the backyard, walking to the store or waiting for a bus can be perilous.

"When you are poor, the sun finds you faster," Ms Cruz-Perez said.

San Antonio has seen at least 46 days where temperatures soar about 38 deg C so far this year, according to the National Weather Service. Through July 25, measurements taken at the city's airport have detected that all but one day in July has surpassed the 38 deg C mark.

The heat wave has been blamed for a series of wildfires, including a blaze that damaged more than 20 homes on Monday (July 25) evening in Balch Springs, a suburb of Dallas.

The heat has also tested the state's beleaguered power grid. The Electric Reliability Council of Texas, which runs the power grid, has pleaded for power conservation from those who can afford air conditioning to avoid rolling blackouts.

High temperatures have afflicted much of the southern and eastern parts of the United States over the past two weeks and have reached this week into the normally temperate Pacific Northwest.

The oppressive impact is particularly visible in places such as the San Antonio metropolitan area, a Latino-majority region where nearly 18 per cent of the population lives in poverty.

The heat is inescapable in the city's historic Westside, where the high ratio of asphalt to green space - along with old structures, freight trains and an abundance of concrete - creates the kind of "heat island effect" that is known to lead to higher energy consumption, more pollution and a greater risk of related health problems.

"It is the poor who usually end up suffering through these heat spells, because they lack the resources," said Ms Kayla Miranda, who heads the Coalition for Tenant Justice, an advocacy group that is pushing for more green spaces in San Antonio.

"We feel forgotten by those in power. The wealthier neighbourhoods have more green spaces, shade."

Ms Miranda knows this personally. She and her four children live in public housing, at the Alazan-Apache Courts, where her door opens onto a landscape of dry lawns and blistering sidewalks. She often struggles to pay the nearly US$350-a-month electric bill to keep her children cool.

San Antonio as a whole is no stranger to scorching temperatures. When the temperature hit 107 deg F on July 11, that was only the sixth hottest day since 1885, according to the weather service; the hottest day on record, reaching a blistering 111 deg F, was 22 years ago.

Even so, scientists are increasingly finding that, as the climate warms across the globe, heat in urban areas is not distributed equitably.

The National Oceanic and Atmospheric Administration is joining other agencies this year in mapping the distribution of heat in 14 cities around the country.

Urban heat islands, often located in the neighbourhoods occupied by lower-income residents and people of colour, can be up to 20 degrees hotter than adjacent areas on summer days, researchers already have found.

Keeping cool

San Antonio officials said the city had created a campaign known as "Beat the Heat" to offer some temporary relief. Cooling centres are open during the hottest days, and residents are reminded through various media to stay indoors as much as possible, drink plenty of fluids and take frequent cool baths if air conditioning is not an option.

But some residents in the Westside have to take a bus to get to the cooling centres. And with little shade, waiting for a bus can often be an excruciating experience.

On a recent day, Mrs Amelia Castillo, 67, walked slowly behind her husband Antonio, 66, struggling with a walker, to reach a bus stop with no roof along Guadalupe Avenue in the Westside.

Mr Castillo settled onto an old wooden bench and winced as the sun baked his skin. His wife tilted a blue umbrella above their heads.

"It feels like the sun is getting hotter every day," Mrs Castillo said. "And we are still in July."

Minutes later, a bus arrived, and Mrs Castillo shared a surprised smile. "Sometimes we have to wait for 40 to 50 minutes," she said.

Ms Susana Segura, who volunteers with a group called Bread and Blankets Mutual Aid, was spending the hottest parts of the week driving around poor neighbourhoods to deliver water, mainly to homeless people, many of whom have disabilities. The homeless are especially vulnerable because they have nowhere to escape the arid streets and hot concrete, she said.

Mr Elpidio Palacios, 56, rolled his wheelchair in her direction. He said he had lost both of his legs years ago when he fell off a train and landed on the tracks. He took a bottle of cold water from Ms Segura and took a sip. He then showed off a straw hat that Ms Segura had given him the day before - his version of shade.

"If it wasn't for her, I don't know what I would do in this heat," Mr Palacios said. "You can't outrun the sun."