phoenix’s urban heat island
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Phoenix’s Urban Heat Island
May, 2011, Page 28
Phoenix’s urban heat island effect could mean we’re heading for 100-degree nighttime lows. Will scientists step up to help cool us down?
It was a time when parents encouraged their children to wet the bed. In fact, they often did it themselves. In front of their neighbors.
It was Phoenix in the early 1900s, B.A.C. (before air conditioning), when homes sweltered and residents spilled into their comparatively cooler yards every summer evening for some semi-communal grilling. Afterward, Dad put cots on the lawn, setting the legs in cans of kerosene so scorpions wouldn’t crawl up to cuddle, then hosed down the cots and sheets. Mom sprayed the kids with citronella, tucked them into the wet beds, and they’d all sleep under the stars, damp and cool in the 75-degree air.
For this was also a time when summer nights in Phoenix averaged 75 degrees. When longtime Phoenicians wax rhapsodic about how it used to be cooler here, it’s no “I walked five miles uphill to school both ways” story. But those days are gone.
“It’s been getting significantly hotter,” says Harvey Bryan, senior sustainability scientist at ASU’s School of Architecture and Landscape Architecture. “It’s a magnitude now of about 12 degrees above our historical nighttime lows. It was very typical to have summer evenings of 78 degrees back in the 1950s. Today we rarely go below 90. I think we’re headed to conditions where we have 100 degrees as our maximum nighttime low.”
Climate change plays a part – 21st-century Arizona is about 2 degrees hotter than 20th-century Arizona – but that’s nothing compared with the urban heat island effect. The concrete jungle of metro Phoenix is about 10 to 15 degrees hotter than the surrounding rural areas – and it’s getting hotter earlier in the day and staying hot longer. In the 1950s, Phoenix averaged seven days a year over 110 degrees. In the 2000s, it’s 22.
That not only means more mercury-induced misery for residents. It means we’re coughing up tens of millions of dollars more in energy costs, breathing 30 to 45 percent more smog, pumping out more greenhouse gases, risking more heat-related deaths, and suffering untold losses for the many businesses that effectively go into a heat-induced coma during summer.
Thankfully, scientists and city planners offer several savvy solutions, from the futuristic (heat-seeking-missile-proof paint) to the ancient (architecture under which Aristotle ambled). Added together, they could prevent us from surging to three-digit nighttime lows and make Phoenix a more pleasant – and profitable – place to live.
Island in the Sun
In the early 1900s, Phoenicians escaped scorching summer days by putting the top down on the Ford and cruising north. As the wind blew through their hair, many swore they sensed the temperature drop the second they left the sun-baked city, crossed the bridge on North Central and entered the countryside, around Indian School Road.
Imagine that the city of Phoenix is a potato. Put that spud in the oven, and it will absorb the heat. Take it out, and it will cool off by radiating its heat outward, warming the air around it (see that steamy spot on the plate?). Shoestring fries would cool quickly, but a baked potato has so much mass that it retains and radiates its heat much longer.
Photo courtesy Emerald Cities
The world’s first green solar reflective parking lot at Phoenix’s Robert L. Duffy Charter School near 24th and Jefferson streets
That is the urban heat island (UHI) effect. On scorching days, Phoenix’s asphalt, concrete and buildings absorb the oven-like heat. At night, when the atmosphere cools, the pavement and buildings radiate their stored heat, warming the surrounding air. Rural areas with only a few, shoestring fry-like roads cool relatively quickly. But the city’s core, with its huge, dense mass of pavement and buildings that trap escaping heat, is like a baked potato that never cools down before it’s thrown in the oven again the next day.
Metropolises around the world experience UHIs, but Phoenix’s differs in two ways, Bryan says. First, ours is more of a nighttime phenomenon. Cities ringed by a forest or water are significantly steamier than their surroundings during the day. But under the unrelenting sun, our unshaded desert often broils at a higher temperature than the building-shaded city. At night, however, the desert cools off very quickly because heat easily escapes the air- and moisture-permeable dirt, whereas the city’s asphalt is like a heat Alcatraz.
Second, Bryan says, the Valley’s heat island is one of the most extreme and most rapidly increasing in the world. And if you thought a college degree was expensive, it’s peanuts compared with one degree of heat.
Cooling early 1900s Phoenix didn’t take much energy, unless you were one of the street urchins paid to constantly crank the giant fans hanging from restaurant ceilings. The first local “air conditioning” was dreamed up by staff at the Adams Hotel in Downtown Phoenix, who set fans over 300-pound blocks of ice in the lobby. Later, folks who couldn’t afford the new evaporative coolers (made from a fan blowing past water dripping through burlap fastened with chicken wire) fashioned their own with a fan blowing through apple crates, wet sheets, charcoal and wood chips.
Today, for every degree the mercury rises, air conditioners use 2 to 3 percent more electricity, according to Arizona Public Service Co. Officials for the Salt River Project calculated that for every one-degree temperature increase, the utility company’s 610,000 Valley residential customers alone pay $3.2 to $3.8 million more every month in cooling bills.
Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) estimate that Los Angeles’ UHI is responsible for an extra 1 to 1.5 gigawatts of power – about $100,000 per hour, or $100 million per year. (How that corresponds to Phoenix is difficult to pin down: L.A.’s population is higher, but our UHI is worse.)
The same study on L.A. found that for every degree the temperature soars above 70 degrees, smog increases 3 percent. That means that in Phoenix, with a UHI of 10 to 15 degrees, we could be choking on 30 to 45 percent more smog, risking health problems and losing federal money if the city fails to meet EPA pollution level targets.
“For every degree of heat, we use so much more electricity for cooling, which is more carbon-based energy produced, and then the emissions go out in the Valley,” says Phoenix Mayor Phil Gordon. “The reduction of electricity is important for the environment, and it’s important for health.”
The UHI also could lead to more deaths from heat, which is the No. 1 weather-related killer in the country, according to the Centers for Disease Control and Prevention. In this regard, the heat island is not an equal opportunity effect: It hits the poor hardest.
A 2009 study led by ASU geographer Darren Ruddell found that for every $20,000 an area’s average income rises, the temperature drops 1 degree. That’s because poorer ’hoods – generally set in the sparsely landscaped inner city, packed with buildings, houses and pavement – are the hottest pockets in Phoenix. To make matters worse, many residents in these areas cannot afford to crank up the A/C, or even turn it on, making them the most vulnerable to heat-related health problems, such as dehydration and heat stroke.
The UHI also acts as a firewall deterring tourists (and their dollars) from visiting the city. And it means most residents “summer hibernate,” chilling out with the A/C and a pint of Cherry Garcia till the weather cools off around Halloween. Meanwhile, not only do our social lives suffer, but areas of the city turn into temporary ghost towns. One Downtown bar owner says he could have closed between last July and September.
That’s not all attributable to the UHI, but the community’s (understandable) unwillingness to go outside puts a considerable damper on the city’s attempts to create the vibrant cultural, social, retail and entertainment networks that define urban life.
“People want to be outside,” Gordon says. “People feed off each other’s energy, and you can’t see that if you’re inside in dark windows. People outside attract people. The more people outside, the more business.”
The trouble is, we’ll never become a really cool city unless we can become a cooler city.
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