Could off-white streets ease Phoenix’s heat?
City seeks solutions as climate change drives temperatures higher
Like Phoenix, Los Angeles is heating up.
On streets wedged between ocean breezes and towering skyscrapers, temperatures are increasing steadily, a rise fueled by climate change and the growing effects of the urban heat island.
So when the city looked for ideas to offset the heat, it went to one of the sources, the thousands of miles of paved streets and roads that absorb the sun’s radiation and keep temperatures high.
Drawing on existing research on “cool roofs,” the city devised a plan to coat residential streets with a light-colored sealant intended to reflect the heat away. Early experiments suggested the technique could lower surface temperatures by as much as 10 degrees.
It’s just one way urban areas are trying to mitigate hotter temperatures. Some cities, such as Dallas, are planting trees to shade neighborhoods and filter the air.
Phoenix is working to expand its own shade canopy and studying ideas like overhead cooling at light rail stops.
And beneath downtown Phoenix’s streets, miles of underground pipes carry cool air to the ever-growing cluster of high-rises in the Phoenix skyline, reducing the number of heat-radiating air-conditioning units on rooftops.
“This is very relatable across a variety of different locations,” said Greg Spotts, assistant director of the Los Angeles Bureau of Street Services. “This idea that we all need to start adapting to climate change — not just reducing our carbon emissions.”
L.A. city officials had a fairly unconventional idea — take 15 residential blocks in the city and make them shine off-white.
Spotts said the idea was hatched from a 2013 project when other city departments were working on cool-roof initiatives.
Spotts’ department partnered with the Lawrence Berkeley National Laboratory and began researching the possibility of implementing something like a cool roof, but on the street.
“Although the environmental community found this was a slam dunk and everyone should be doing it, we couldn’t find an example of it … on a public street in California,” he said.
They were the first, he said. Spotts said officials tested the product in a sports complex parking lot to see how it would perform before rolling it out on residential streets.
It showed about a 10-degree drop in temperature on the surface itself, he said.
Last May, after securing $190,000 for a pilot program, the city installed the first of its 15 off-white roads — one for each City Council district, each a block long.
Although it’s too soon for formal data collection, Spotts said city staff has seen about a 10-degree drop on the streets themselves, whatever part of town they’re in.
“Our city is large enough that we even have some microclimates,” he said. “Yet we have a pretty consistent 10-degree Fahrenheit difference.”
Spotts said they’re hoping to expand the project by several blocks in a couple of to-be-determined neighborhoods next fiscal year.
Ideally, they’d target the city’s hottest areas because the pavement’s effects on temperatures in adjacent buildings aren’t completely known, he said.
Expanding the project could be a breath of fresh air for L.A. commuters, especially those facing the “last mile” problem.
Getting to a bus stop or rail station may be easy enough, but sometimes making the last mile from the bus stop to work or home is more difficult.
The hotter it is, the more difficult it becomes.
The threat of rising temperatures is becoming more real in urban areas, where heat deaths are increasing each year. In a 2016 report, the Los Angeles
Times estimated that the sprawling metropolitan area would warm 5 degrees on average by 2050.
“There’s a public health aspect to it,” Spotts said. “The ‘last mile’ problem is going to become worse as the city gets hotter. How are people going to get to the rail if it’s going to be excruciatingly hot?”
Aside from the temperature drops, the attention the program has garnered surprised Spotts.
“We started getting national and international press coverage,” he said, laughing. “In the public works department, we’re not really used to that.”
Heat, especially the kind Phoenicians have grown accustomed to, doesn’t have a catch-all fix.
Arizona State University and its Urban Climate Research Center have research projects ranging from rubberized concrete to alternative public transit, all with the goal of dampening the urban heat island effect.
David Sailor, the center’s director, has long studied the urban heat island effect. While earning his doctorate at the University of California, Berkeley more than 20 years ago, he focused on how to cool L.A. through planting trees and installing reflective surfaces.
“I’ve come back to the same question multiple times as have many others,” he said. “Which is how much can you cool a city through these different strategies?”
Sailor said it’s important to be specific. The question isn’t always as broad as, How much can we cool a
city? It’s narrower: How can we cool this especially vulnerable neighborhood?
Where does extreme heat overlap with high populations of the elderly, the homeless?
In a city like Phoenix, which is already hot and only getting hotter, it’s easy to get lost in terms like “urban heat island,” he said.
“Just that phrase, ‘the urban heat island,’ is too vague,” he said. “When you’re thinking about urban heat in Phoenix, there’s both surface temper-
atures as well as air temperatures that are important.
“Ultimately, you’re interested in the outcomes of these temperatures for humans and our environments. We care not only about temperatures but also humidity, air quality and so forth.”
While reflective surfaces are the “first line of defense” against radiation and heat from the sun, Sailor said it’s important not to rely on those surfaces too heavily. The radiation could be reflected off and cast on nearby buildings and windows, he said.
On the other hand, it can quickly lower air temperatures.
“Of course, that’s one part of the urban heat puzzle,” he said. “The other part is that you’d like to see lower air temperatures, and highly reflective surfaces are going to do a much better job.”
In downtown Phoenix, what’s beneath the reflective pavement could also help.
About two dozen feet beneath the Phoenix Convention Center is a small office, staffed around the clock and outfitted with computer monitors, hard hats and safety goggles.
Across from the office is a tank, nearly 30 feet deep, of water chilled at 34 degrees. Shards of ice shimmer on the surface.
Connecting the two is a labyrinth of pipes, carrying the chilled water through downtown Phoenix, to inmates in the Fourth Avenue Jail, students at ASU’s downtown campus, and Arizona Diamondbacks fans at Chase Field.
The pipes stretch under downtown Phoenix and, through this one system, provide air-conditioning to more than 40 buildings downtown.
From the small underground room, technicians keep an eye on the miles of pipe that run under the streets and cool nearby structures.
Traditionally, each building downtown would have its own air-conditioning unit on its roof. While generating air-conditioning for those inside, the units would expel heat into the surrounding area.
In a clustered downtown, that can quickly compound the urban heat island effect.
But, with the NRG Energy system, dozens of buildings use this one underground system. By generating the air conditioning from an underground plant, the effect on the environment is scaled back.
Heat is still expelled with NRG’s system, but it’s comparatively small, said Jim Lodge, the firm’s vice president and general manager.
Lodge gave the example of Chase Field, which is used only part of the year, and then only for home games. Connecting it to a broader downtown system made more sense to allow its chillers to help cool the rest of downtown made sense, he said.
“Pretty much every other week, they’re here — so if you think about the large amount of cooling equipment that had to be put into that stadium to cool it, it was really an underutilized asset,” he said. “If you think about it, one week later it’s still 110 and you’ve got all these chillers sitting over there turned off and not being utilized.”
Temperatures aren’t going to suddenly stop increasing, so leaders in the public and private sectors have focused on ways to mollify the urban heat island effect.
From a chilled light rail stop powered by NRG — in downtown Phoenix near Third and Washington streets — that sends an overhead blast of cool air on commuters at the push of a button, to planting trees and curbing greenhouse gas emissions, programs are set up to address Phoenix’s deadly heat.
“Being a really hot city is part of our DNA,” said Mark Hartman, Phoenix chief sustainability officer. “Much of the research that’s happened over the last 20 years has all happened in Phoenix.”
Hartman said city staff are preparing a sort of urban heat island master plan this year that will include a comprehensive list of the city’s efforts.
The city has partnered with Harvard University to analyze public transit routes and find “cool corridors.”
“Just one block off that (busy routes), there’s shaded streets,” he said. “Why don’t we just have routes go along those shaded streets?”
The city already has a tree and shade master plan, which was passed in 2010 and extended to run through 2050.
In May, the Phoenix City Council approved funding for maintaining and replacing trees.
The city’s goal of reaching a 25-percent tree canopy could lower a typical neighborhood’s temperature by as much as 4.3 degrees and, in cases where the neighborhood is bare, could lower temperatures as much as 7.9 degrees, according to city documents.
Richard Adkins, Phoenix’s forestry supervisor, said it’s important not just to plant trees, but to ensure the city is performing routine maintenance and protecting the trees it has.
The city’s tree canopy is between 9 percent and 12 percent, he said.
The city maintains an urban forestry website that allows residents to see where trees are and how much they cost.
The city planted nearly 3,000 trees and had to remove just more than 1,000 in 2017, Adkins said.
At a January policy session, the council voted to reduce Phoenix’s greenhouse emissions 30 percent from 2012 levels in the next seven years. Levels are already down nearly 24 percent, according to a city staff presentation.
There’s no single answer to alleviating Phoenix’s heat, and that’s not lost on those studying the problem.
In the smorgasbord of potential solutions, the network
The city’s goal of reaching a 25-percent tree canopy could lower a typical neighborhood’s temperature by as much as 4.3 degrees and, in cases where the neighborhood is bare, could lower temperatures as much as 7.9 degrees, according to city documents.
of routes for mitigation, the answer to climate change’s question likely doesn’t lie in one single initiative or program, but in making them all work together.
“There’s more than one way,” Sailor, the ASU professor, said, “to cool the environment.”
The relentless heat that plagues metro Phoenix claimed at least 150 lives in 2016 and slogged on through 2017 — bringing with it the warmest single year since records started in 1895.
Climate data from the National Oceanic and Atmospheric Administration’s National Center for Environmental Information shows that every U.S. state averaged above normal temperatures in 2017.
Phoenix, the nation’s fifth-largest city, faces daunting changes in climate. A 2017 Republic investigation showed how heat discriminates, often rising in lowerincome areas with fewer trees than nearby, more affluent neighborhoods.
And heat doesn’t affect people uniformly.
The elderly or chronically ill are at greater risk and low-income families may lack the necessary resources to address their exposure to the heat. The World Health Organization estimates that, between the years 2030 and 2050, climate change will cause an additional 250,000 deaths globally each year, because of malnutrition, malaria, diarrhea and heat stress.
Environmental coverage on azcentral.com and in the Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmental reporting team at OurGrandAZ on Facebook, Twitter and Instagram.