The sun was barely up when the three-person medical team pulled into the parking lot of a Phoenix soup kitchen, but the temperature was already around 90 degrees, on its way to 111.

The team starts its rounds at 5 a.m. because the afternoon highs are so dangerous. Perla Puebla, the family nurse practitioner leading the team, took a look at Hawaii Kalawaia and Zephyr Harrell and could tell they were dehydrated from their dry lips and skin. It’s hard for homeless people not to be during Phoenix’s unrelenting summers.

Mr. Kalawaia, 61, said he had passed out a couple weeks earlier. And Ms. Puebla remembered all too well what had happened last year, when Mr. Harrell, 55, got so dehydrated that his kidneys started failing. She offered intravenous fluids, one of many free services provided by Circle the City, the nonprofit that runs the street-medicine teams.

Mr. Kalawaia moved to Phoenix from Pearl Harbor to teach Hawaiian language and dance, but has been homeless off and on for over a decade. Sipping an electrolyte drink with an IV in his arm, he said he was so used to the heat that he hadn’t realized he was dehydrated. But he said he often felt as though he would pass out again.

Phoenix, the hottest city in the United States in the summer, is one of the most extreme examples of a threat that is growing across the country: unrelenting heat.

Summers have always been sweltering there, but climate change has made them worse. In the early 20th century, highs there typically reached 110 degrees fewer than 10 days a year. Last year, it happened 70 times; this year, more than 30 already. Nine of the city’s 10 hottest years on record have come since 2010. Nighttime lows have risen, too, making it harder for heat-stressed bodies to recover.

Everyone is affected, but especially the unsheltered. They are highly vulnerable to dehydration and heatstroke. They sustain burns from sleeping on the scorching asphalt. Some get itchy from sweat and scratch themselves, causing infections. Their hearts and kidneys struggle. Their behavior becomes erratic.

One study published last year found that in the Las Vegas area, a staggering 49 percent of deaths among homeless people from 2015 to 2022 were attributable to heat — far higher than the percentage among the general population.

The climate in Phoenix is similar. Over three days in July, patient after patient described the effects of heat on their bodies to Circle the City teams: lightheadedness, weakness, irritability. Melanie Baragar, 49, said that even in the shade, she had been so hot the previous day that she cried.

“It’s all related to the heat,” Ms. Puebla, 34, said. “Every system we have, it affects.”

Constant dizziness

Later that week, another street team hiked into a bone-dry riverbed west of Phoenix carrying a cooler and dog treats. It was not yet 8 a.m., but the temperature was already 92.

In the riverbed, Leslee Hamadeh, 43, the family nurse practitioner leading the group, found a familiar face: Christi Noe, 58, who has spent 19 months there with her partner and their dog, Biscuit. A food services worker and a retired bar cook, Ms. Noe and her partner lost their home when the rent increased, and a low-cost apartment she is trying to secure isn’t available until November.

She said she felt dizzy and sick from the heat almost every day.

“Even in the middle of the night, it’s stupid hot,” she said. “I cook, and I can’t eat. I’m losing a lot of weight.”

Ms. Hamadeh examined her and prescribed antibiotics for a deep cough. She said she would deliver the prescription herself if Ms. Noe couldn’t get to the pharmacy.

Caring for homeless people has been Ms. Hamadeh’s goal since she was 8, when she wrote in her journal that she wanted to buy a house for homeless people to live in, she said. Through Circle the City, she is able to provide that care.

Founded in 2008, the nonprofit operates medical services including outpatient clinics, mobile offices and temporary residential facilities to recover from illness or injury. It also runs five street teams, which provide medical care along with water, sunscreen, clothes and hygiene items. The street teams see 10 to 15 people a day, often repeat patients, spending considerable time with each to treat acute problems while building trust to address issues such as addiction.

Over time, friendships develop. Ms. Hamadeh said if Ms. Noe’s apartment fell through, she would bring her a Thanksgiving meal. Ms. Noe had told her she hated the prospect of spending a second Thanksgiving in the riverbed.

But that day, Ms. Hamadeh’s team had to see more patients. By the time they left the riverbed, around 8:45 a.m., the temperature had risen to 97.

Bone-deep burns

Traversing Phoenix and its western suburbs with Ms. Puebla’s and Ms. Hamadeh’s teams, it could feel as if every patient had a harrowing heat story. Alexis Bejarano, 38, learned she was close to heatstroke after being hospitalized for dizziness and vomiting last year. Katrina Budnik, 41, got a blistering sunburn after she fell asleep with her shirt askew.

In a parking lot outside a nondescript storefront as a Tuesday morning heated up, Bill Tucker, 48, rolled up his sleeves to show burn scars. These were burns of a different sort, from contact with the ground. The most recent — second and third degree, across many parts of his body — happened just weeks before.

Such injuries are increasingly common, and not just for homeless people. A study led by Dr. Kevin Foster, the director of the Arizona Burn Center at Phoenix’s Valleywise Health hospital, found an association between rising temperatures and the frequency and severity of burns at his center over 16 years, and he said the increase had been especially sharp in the last four. The study identified 105 degrees, common in Phoenix, as a particularly dangerous threshold.

Surfaces like asphalt can reach 180 degrees under searing heat and cloudless skies, causing severe burns almost instantly. Dr. Foster said people passed out from the heat and burned themselves “all the time.” Others trip while walking their dog. Toddlers burn their feet by running out barefoot.

Robert Woolley needed seven surgeries after falling near his pool. Mr. Woolley, 72, put his hands out to catch himself, but the rocks were so scorching that he pulled them away as instinctively as recoiling from a stove, and his body hit the ground. His forearm turned black, his hands peeled “like the skin of an onion” and he left charred skin behind as he dragged himself to the door.

But homeless people have particular vulnerabilities. Beyond sleeping on the ground, they are likelier to become dehydrated enough to pass out. Sweating makes it difficult to keep bandages in place, dehydration interferes with healing and wounds can hasten fluid loss.

By Maricopa County officials’ count, less than 1 percent of Phoenix residents are homeless, but in 2024, 20 percent of deaths at the Arizona Burn Center were homeless people. Others sustain burns but don’t go to that hospital, or sometimes to any, Ms. Hamadeh and Ms. Puebla said.

Recently, a homeless woman approached Ms. Hamadeh for help. She had been walking with her bicycle when a car hit it and she fell, tangled between bike and asphalt.

Ms. Hamadeh said she could see bone through the burn wound on the woman’s foot.

She urged the woman to go to a hospital and said Circle the City could arrange free boarding for her dog. But the woman wasn’t willing to leave the dog. Ms. Hamadeh did what she could, cleaning and bandaging the wound.

Later, she tried to check on the woman. But, as often happens in Ms. Hamadeh’s line of work, she couldn’t find her.

Barriers to safety

Ms. Budnik, the woman with the blistering sunburn, has been kicked out of many air-conditioned stores, where she tries to escape the heat.

“So you walk around most of the day trying to find a spigot to douse yourself in water, and hope you don’t have somebody call the cops on you just for trying to stay cool,” she said.

Homeless people face many such barriers. Some manage to buy supplies like a battery-powered fan, only to have them stolen while they sleep. Mr. Kalawaia, the patient who received intravenous rehydration, said many machines that dispensed water had been shut down. And while the city runs cooling centers, some people can’t find one close enough to reach.

Circle the City tries to address barriers by making appointments, arranging transportation and more, and its providers take wins where they can: a patient addicted to opioids, which are more dangerous in extreme heat, who tries buprenorphine. Another who accepts IV fluids. A patient who agrees to go to a hospital, as Ms. Baragar is edging closer to doing for a kidney abscess, at Ms. Hamadeh’s urging.

On a recent Wednesday, as Ms. Puebla finished with her last patient, the temperature was 104 and still rising. She poured cold water over a cloth, draped it around her neck and sighed.

“I already feel like crap,” she said on the ride back to headquarters. “They’re out in it 24/7.”