By Carlos Barria

PHOENIX As the world registered the hottest month of all time in July, the southwestern U.S. city of Phoenix shattered its own 1974 heat-wave record, with temperatures above 110 degrees Fahrenheit (43°C) for 31 straight days.

Heat-sensitive photography in late July reveals an even hotter Phoenix, where concrete on the street registers 150F (66°C), outdoor workers' bodies reach 105F (41°C) and homeless people swelter, surrounded by surfaces as hot as 143F (62°C).

Before 10am at one of the city's favorite sites - the Desert Botanical Garden - the thermometer is already at 111F (44°C), but a Saguaro cactus records a surface temperature of 120F (49°C). A man walks on a road with no shirt and a bottle of water. The camera puts his temperature at 105F.

The summer monsoon rains that historically help Phoenix residents and the vegetation cool down have been scant this year and even the cacti have started to collapse.

Health workers say hospitals have been inundated with patients suffering from heat-stroke, sometimes life-threatening.

"We've had patients that are 111 degrees," said Dr. Frank LoVecchio at Valleywise Health in Phoenix. "Your brain cannot handle that that long."

Patients are put into an ice slurry to bring their temperatures down as quickly as possible.

At noon, the record temperature is 109F but the surface temperature is a furnace-like 150F. A construction worker drinks water and the camera shows his body is at 105F.

Phoenix, the capital of Arizona, is now a city of 1.6 million, the fifth most populous in the United States. It sprang to life over 150 years ago with the arrival of the pioneers, who built irrigation canals to make the land fertile.

Despite its location in the Sonoran Desert - which stretches across the U.S. southwest and into northern Mexico - Phoenix has become a favorite place for retirees, attracted by year-round sun and its ochre mountain backdrop.

For those who can afford it, there is air conditioning. A Major League Baseball game is played early in the afternoon at Chase Field, where a retractable roof and air conditioning keeps the stadium a cool 64.5F (18°C).

But for the homeless population of Phoenix, there is no such respite.

A homeless man sitting on an abandoned microwave oven around 3:30 pm is captured by the heat-sensitive camera and the surface temperature around him is 143F.

"About half of our patients who come in in this comatose state are homeless," said Dr. LoVecchio.

Sometimes people pass out on the scalding pavement, suffering serious burns on their bodies.

With day after day of relentless heat and evenings that remain at 90F (32°C), there is little chance for the homeless to recover and hydrate. The heat also worsens conditions like diabetes, lung disease, and heart issues. And some suffer memory loss and cognitive decline.

Maricopa County, where Phoenix is located, reported 39 confirmed heat-associated deaths by the end of July, with over 300 more under investigation to determine if they were caused by heat.

(Additional reporting by Liliana Salgado in Phoenix; Writing by Mary Milliken; Editing by Rosalba O'Brien)