More buildings, parking lots, streets, highways and driveways marking the march of urban development across the Valley are expanding what climatologists call the "urban heat island effect."
Its impact is not only the discomfort of longer periods of high summer temperatures but potential long-term economic drawbacks and health risks, experts say.
Arizona State University research programs and the Valley’s major power utilities are stepping up efforts to find ways of abating the heat-island trend.
It’s brought on by all the cement, concrete and asphalt soaking up solar heat during daylight hours and radiating it back at ground levels at night.
The effect has raised average overnight temperatures as much as 10 to 13 degrees over the past four decades in the most intensely developed areas, according to the National Weather Service.
The Valley’s rapid growth has made it a hotbed for microclimates spawned by clusters of hard, heat-absorbing, man-made building materials that hinder nature’s cooling processes, said Doug Green, science officer for the weather service’s Valley headquarters in Tempe.
It’s now often taking hours longer for overnight temperatures to dip back down significantly after those 100-degree-plus summer days.
"Our problem isn’t just global warming but local warming," Green said.
LOSS OF COMFORT
One result: The amount of daily time that temperatures exceed a normal comfort level has grown from about two hours to almost five hours since the Valley began urbanizing in the 1950s, said Anthony Brazel, an ASU geography professor who has studied local climate change.
Today, about 30 percent to 40 percent of the Valley’s urban cores and the growing suburban areas around them are covered in pavement, said environmental engineer Jay Golden.
But he and colleagues at ASU’s International Institute for Sustainability, which opened its doors a few months ago, are not taking an antidevelopment approach to seeking solutions, said Golden, who directs the group’s Sustainable Materials and Renewable Technologies Program.
The focus is on how regions can continue to urbanize without intensifying heat islands.
So researchers are working on alternatives to conventional concrete, cement and asphalt. New materials, such as resins and rubberized composites, won’t absorb and radiate as much solar heat, Golden said.
In addition, they’re looking at ways that architectural design and landscaping, or "urban forestry," can more effectively prevent heat buildup and provide cooling effects, he said.
Arizona Public Service Co. is collaborating with ASU’s programs. The utility company plans to promote new energyefficient materials to developers, said Tom Hines, an APS customer and information programs manager.
The Salt River Project utility company also supports ASU’s studies, said spokesman Jeff Lane.
ESCAPING THE HEAT
The urban heat island effect has long been evident to Grace Schoonover, who lived in central Phoenix from the 1930s through the 1950s.
"When I grew up there, Phoenix was bearable all summer," she said. "We noticed a rise in temperatures as they started paving everywhere."
Schoonover now lives in rural Cave Creek. "We fight against paving here as much as we can," she said.
Fellow Cave Creek resident Bob Moore said a major reason he and his wife moved from Phoenix several years ago was the climate difference.
It’s often 10 degrees cooler in Cave Creek than in the central Phoenix area, plus "there’s an almost constant breeze. . . . You walk outside at night and it’s cool, even during a lot of the summer," Moore said.
Roseann Sweet recalls that when she moved to Phoenix almost 20 years ago, "I was amazed at how hot it was all night long in the summer."
She later relocated to Tempe, then to rural Queen Creek, where she and her husband, Kevin, now live on a 4-acre horse property. On some summer nights, the heat still subsides enough to comfortably wear a sweater, she said.
On the 27-mile drive home from their business near Loop 101 in Tempe, "I really feel a big difference, the temperature just gets cooler the farther away you get," she said.
BIGGER HEAT WAVES
That could begin to change if nothing is done to ensure new development isn’t significantly increasing the heat island effect, said Tony Haffer, chief meteorologist for the National Weather Service’s Valley headquarters.
"It’s a regional effect. . . . Our atmosphere is very fluid, so heat islands tend to shift to some degree, and they can blend into each other," Haffer said.
If localized heat islands combine extensively and consistently, waves of heat emanating from urban and suburban cores would grow strong enough to begin changing temperatures even in outlying Valley areas, he said.
"Overall, things could add up to (the Valley) being one big urban heat island. It would just be more intense in certain spots and weaker in others," he said.
More is at stake than the comfort factor.
Heat islands are extending the peak demand times for energy use. It’s taking more energy to service the typical Valley home than in past decades, and air conditioners are running longer, APS officials said.
That’s putting more strain on power resources, raising power bills and boosting the potential for heat-related illnesses, such as heatstroke, Golden said.
There’s another big potential economic downside. If heat islands continue to grow, the normal span during which the Valley could experience periods of high heat might expand from summertime to late spring and early autumn, Golden said.
"Our hot season might go beyond June, July and August to April through October. We depend on tourism. If people are seeing that it’s 100 degrees here in October, then it doesn’t look like a good place to go," he said.
The research into easing the heat island effect is being cheered by Bill Mundell, a Chandler attorney and member of the Arizona Corporation Commission, which regulates the state’s utilities.
There’s a direct link between the heat island problem and broader energy conservation and quality-of-life issues, said Mundell, an exstate legislator who formerly headed the House environment committee.
Power plants must be built to handle peak demand periods. So when heat islands push peak demand higher for longer stretches of time, it hastens the need for new or expanded power plants, Mundell said.
That means burning more fossil fuels in generating plants and the additional air pollution produced by the process, he said.
Utilities share Mundell’s concern, said APS’ Hines. "APS is in an energy-efficiency mode . . . summer peak demand time is a problem," he said.
The company is significantly increasing funding for programs to educate consumers and businesses about energy conservation, Hines said.
That includes informing developers about the types of environment-friendly building materials ASU’s Sustainability Institute is working on to combat the urban heat island effect. "We think we can bring some market credibility to those products," Hines said.
Giving government policymakers and the development industry good reasons for changing old and environmentally unsound habits is the challenge facing ASU’s program, Golden said.
Beyond making technological advances, researchers have to establish a strong case for the long-range economic viability of building to diminish heat island effects, conserve energy and protect the natural environment.
"It’s hard to do when you have companies with boards of directors pressuring developers to show quick profits," Golden said.