As Phoenix swelters, the nights are even worse than the boiling days

After a record-breaking daytime temperature in Phoenix last Friday, the onset of night offered little relief from the sweltering heat. As the clock struck midnight it was still a staggering 100F (38C) outside and just a few degrees cooler inside 60-year-old Sareptha Jackson’s home.

Jackson lay naked and as still as possible on the bed next to an old portable air conditioning unit in the bedroom window, but couldn’t relax or get comfortable. She eventually got up around 2am to make rice and beans for the following day because the air conditioner and electrical appliances won’t run together, so it’s too hot to cook during the day.

“This heat is miserable, my body can’t take it,” said Jackson, who has high blood pressure and diabetes, and last year suffered a stroke after overheating.

The overnight low on Friday was a suffocating 90F – the first time it stayed so hot so early in the season according to the national weather service (NWS) . This broke the previous overnight record for 10 June by a staggering 5F.

Temperature records are being smashed time and time again, said Matthew Hirsch, meteorologist at the NWS in Phoenix. “The changing climate means that every year the records get easier to break. This heat is very dangerous if you can’t get any relief.”

For Jackson – and many others – the daytime heat of the current wave is grueling enough, but it is the nights that are truly intolerable.

The central air conditioning in the poky apartment that she shares with her husband Jerry Stewart, 69, and daughter Zadie, 19, has been broken for three years. A selection of fans are running constantly but it’s still way too hot. Zadie, whose room felt like a sauna over the weekend, slept at a friend’s place to get some relief.

The couple spent a few hours at church on Sunday and visited their grandchildren who have air conditioning, but gas prices are too high to make the trip often. “We just try to keep cool and hope we get through it,” said Jackson.

The temperature has not fallen below 80F (27C) for the past week in the city, breaking several night-time records. The impact of heat is cumulative and the body only begins to recover when temperatures drop below 80F.

In this heat, staying cool and hydrated is a matter of life and death. In the morning, the mockingbirds and flycatchers frolic in the lawn sprinklers to cool down, in the evening, small children do the same.

Phoenix, the capital of Arizona and America’s fifth largest city with 1.6 million people, is accustomed to a hot desert climate, but temperatures are rising due to global heating and urban development which has created a sprawling asphalt and concrete heat island that traps heat especially at night. The city has appointed a heat tsar to coordinate efforts to mitigate and adapt to the extreme heat that is killing record numbers of people.

This was the first extreme heatwave of the season for Phoenix – and large swaths of the US south-west of the country – with the temperature topping 110F on four consecutive days, including two new daily records. Even before this extra-hot spell, the county medical examiner was investigating 30 possible heat-related deaths dating back to April – 60% more than the same time last year. Another excessive heat spell is forecast for later this week.

In downtown Phoenix, high-rise office blocks and hotels provide some shade, but walking even a couple of blocks is draining.

Alexia Gonzales, 26, hosed herself down before leaving home to pick up groceries for her Instacart job. “It’s too hot to work, but this is when people want deliveries.”

In this heat, Gonzales never leaves home without an ice chest filled with cold drinks and orange cups as the air conditioning in her old Buick isn’t great. “I’ll hose myself down again when I’m done, it’s the only way I can cool down.”

Temperatures this high are tough for everyone, but for some staying cool is easier.

Around 7am on Saturday, Roland Arnold, 58, was out meandering on his cart with Valentine, an eight-year-old rescue mini pony, greeting friends and neighbours in Coronado, a leafy middle-class historic neighbourhood. It was already 90F (32F), and the rising sun was piercing but still tolerable.

“In this heat, by 9am my day is done, I’m inside with the aircon on. If I have to do work outside, I’m in my board shorts so I can jump in and out of the pool to keep cool,” said Arnold, an Arizona native who owns a marble and granite business. “But I’m tired of the hot nights, it’s definitely got worse.”

Night-time temperatures have risen twice as fast as daytime highs over the past three decades, according to NWS data.

Plenty of dog walkers were also out early with their pooches, as by 9am or so the ground would be hot enough to burn paws. Some said they were heading for higher, cooler ground – to state parks or the city of Flagstaff where it’s cooler at night, while others planned to spend the day between the aircon and pool like Arnold.

Health experts advise staying inside as much as possible to avoid heat exhaustion and heatstroke, but this isn’t always an option.

A few blocks away from the dog park, landscape gardener Miguel Padilla was shovelling gravel into a wheelbarrow – backbreaking work he started at 4am after a terrible night’s sleep. “For those of us without air conditioning, the summer is hell,” said Padilla, 46, originally from Acapulco in southern Mexico.

By mid-morning on Saturday it was 110F, and in midtown the central library was filling up with folks trying to stay cool. The library is part of the city’s heat relief network but few cooling centres are open outside business hours, even though it remains dangerously hot in the evening. Still, it’s a lifesaver for locals with few other options including the street homeless.

Katie Lavra, 67, came in to cool off for a few minutes, taking a break from registering voters out front where there’s little shade. “I’ve been here all my life but you never get used to this heat, you just learn to tolerate and respect it.”