PHOENIX (AP) — When temperatures soar as they have this week in downtown Phoenix, homeless people ride the air-conditioned light rail to avoid a heat so brutal it killed 155 people in the city and surrounding areas last year. An occasional siren wails as paramedics rush to help people sick from the heat.
Already devilishly hot for being in the Sonoran desert, Arizona's largest city is also an "urban heat island," a phenomenon that pushes up temperatures in areas covered in heat-retaining asphalt and concrete. Phoenix on Wednesday recorded a sweltering 116 degrees (46 Celsius), setting a new high for the date.
Elsewhere, Chicago maintains more than 500,000 trees to offset rising temperatures and is a national leader among cities for so-called green roofs covered with vegetation. Los Angeles adopted an ordinance in 2014 to require reflective "cool roofs" for new homes including rentals, while Seattle is working to restore the city's forested parklands.
But climate specialists like Brian Stone, who runs the Georgia Institute of Technology's Urban Climate Lab, said more is needed.
"We are working against a pronounced warming trend in large cities, and so it will require a substantial resurfacing of urban environments simply to slow the rate of warming," Stone said.
He said the heat island effect prevents a city from peeling off the day's furnace-like heat after the sun sets, driving up temperatures over time. His team's research shows Phoenix temperatures rising nearly 1 degree per decade, consistently placing it alongside Dallas and Louisville, Kentucky, as some of the fastest-warming U.S. cities. He said Phoenix is warming at three times the rate of the planet as a whole.
"If similar numbers of people died from any other type of weather event, "it would be considered a national disaster," noted Phoenix sustainability officer Mark Hartman.
Forecasts now take into consideration the heat island, which in the case of Phoenix stretches some 25 miles (40 kilometers) out from the city's airport, National Weather Service forecaster Marvin Percha said.
To show the difference the effect can make, he noted that in June 2017 the nighttime low at Arizona State University's grassy campus in Tempe was just 69 degrees (21 Celsius). But the nighttime low just 5 ½ miles (9 kilometers) away at Phoenix's Sky Harbor International Airport, where expanses of asphalt cover former farm fields, was 81 degrees (27 degrees Celsius).
Aimee Esposito, executive director of non-governmental Trees Matter, said her Phoenix organization this year plans to give 5,000 small trees to residents across the area's Valley of the Sun, and will plant more at schools through educational programs.
"I really think the community is getting the message about trees," Koetter said. "There's usually a line around the block during the giveaways."
Koetter said Louisville was the first major city to commission a heat management study, which was done by Stone's climate lab. It now offers $2,000 rebates to homeowners for cool roofs.
"A palette of solutions like this is necessary, especially planting shade trees with walkable corridors," said David Sailor, director of Arizona State University's Urban Climate Research Center.
"Just as tree cover and other cooling materials have been lost in cities through a piecemeal process of developing individual lots over time," he said, "we need to restore these materials though a process that requires more green and reflective surfaces with improvements to individual lots over time."
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