The video monitor shows long dark shadows with a scattering of inky dots. Ariane Middel, an urban climate scientist at Arizona State University, is focused on the shadows. The dots represent shade in the city of Phoenix, and there aren’t nearly as many of them as Middel would like to see.
The images are generated by a thermal exposure model created by Issac Buo, a visiting scholar from Estonia, at ASU’s SHaDE Lab, which Middel leads. The lab is using the model to create a high-resolution shade map for the Phoenix metro area.
Earlier this year, Middel sat at a corner desk in her office in the midst of a chaotic jumble of files, plastic grass decorations, revolving chairs and anemometers. Just a few feet away stood two MaRTy – mobile biometeorological carts – that she developed to collect data about how heat impacts the human body.
utilizing the model to generate a shade map for the Phoenix metropolitan region. Middel has
been investigating the urban heat island (UHI) phenomenon in Phoenix and other extremely hot
cities worldwide, including Singapore, for several years. (Photo courtesy Deanna Dent)
For several years now, Middel has been studying the urban heat island (UHI) effect in Phoenix and other exceptionally hot cities across the globe, like Singapore.
The urban heat island effect is the phenomenon where urban areas are significantly warmer than their rural counterparts because of the heat-absorbing properties of human-made structures such as buildings, roads and concrete combined with human activity. This has negative impacts on energy demand, air quality and public health.
Middel said that the projects can help cities put money into heat-mitigation programs that work.
“(The city of Phoenix) is already doing a lot with little funding,” she said. “Other cities look up to Phoenix when it comes to heat mitigation, to see what’s working here, what’s not working, to learn from that experience.”
Two of the projects in Phoenix that have caught the eye of other cities are the cool pavement program, which aims to cover roads around the city with reflective coating, and the urban tree planting program, which will increase tree canopy in the city.
Researchers from Las Vegas knocked on Phoenix’s door
Last spring, a group of master’s students at the University of Nevada, Las Vegas, presented their study of the city of Phoenix’s heat initiatives. In the audience were Aaron Colleta and Cassidy Bowman, both Ph.D. students who have been working with the city of Las Vegas’s planning department to work out its own heat mitigation plan.
They were there to find clues that they hope lead them to one thing — the viability of expanding urban tree canopy in Las Vegas. Soon after the presentation, Bowman pulled out the organizational chart of Phoenix’s heat office and started sending cold emails.
Similar to Phoenix, Las Vegas is one of the fastest-growing metro areas in the U.S. In May, the city announced a plan to plant 60,000 trees by 2050 to cope with looming heat island effects.
The researchers are concerned about tree equity and inclusion, so as not to exclude low-income communities. When they eventually landed a Zoom call with the office, they were eager to learn everything they could about Phoenix’s tree canopy program.
Colleta said that Phoenix and Las Vegas have similar geography, infrastructure and temperature, so it was the perfect place to look to for guidance.
“You can expand the tree canopy and plant more trees to make it cooler, but you also need to tell people that we’re going to run out of water,” Colleta said. “It was really important to hear (Phoenix’s) narrative strategy about how you can accomplish both things, even though they feel at odds with one another.”
Aside from these takeaways, Bowman also realized the importance of other more mundane problems like how to communicate effectively with the community and where to source trees.
Bowman said, “We were almost hesitant to get too much momentum behind the tree canopy initiative until we had fully thought through our water messaging options,” referring to how the city of Phoenix has been able to justify taking up more of the limited water resource to grow more trees.
And then there was the question of where the trees would come from. Colleta noted that Phoenix has been able to put together quarterly meetings with a “really broad group of stakeholders, which I thought was pretty brilliant.”
“We do talk about this coalition to broaden that circle to include community members that we’ve overlooked. The idea of the supply chain or how we even get trees here, what they look like and so making sure that community nurseries and growers are part of this,” he said.
The meeting also prompted Bowman to learn something else about trees — what she calls mobility issues, which include reducing the temperature, eliminating energy costs and the economic development benefits for households.
“We found a whole new area we ignored. Like where to plant them [trees] in front of the house to generate shade, but how it could also reduce bills for certain people,” Bowman said.
The benefit of tree planting is most evident in the Garfield district of downtown Phoenix.. Community organizer Joanna Repucci, a handful of volunteers and dozens of homeowners and renters in the downtown neighborhood recently dug and planted 140 saplings as a part of an annual community tree-planting project. They have planted more than 400 trees since 2018 and Repucci wants to hit 500 this year.
“It makes a huge difference when you’re walking around,” she said.”It’s the ambient heat, the reflection of the road, the buildings; and the shade that I found is the only thing I feel confident will mitigate heat for our future generations.”
Middel said that community planting programs have grown in significance.
“The city does not own enough land to plant trees, so they need the communities to be on board,” she said.
The two Las Vegas researchers said they also are intrigued by Phoenix’s cool pavement program, but for now, they’re focused on increasing Las Vegas tree canopy. Thecool pavement program involves coating roads with a light-colored material that reflects more sunlight, reducing the urban heat island effect and lowering surface temperatures.
Why is Phoenix at the forefront and why do cities have to start to worry about heat?
Fear of extreme heat is nothing new in Phoenix and experts fear the city could become uninhabitable. Phoenix is the second-fastest warming city in the U.S., with up to 200,000 people at risk due to extreme heat. By 2050, it is predicted that there will be more than 80 dangerously hot days per year.
Earlier this year, David Hondula, the nation’s first heat officer, told The Guardian that Phoenix is already uninhabitable in the summer for many of its residents. In 2022, nearly 400 people died from heat waves, a 50 percent jump from 2020.
By 2050, many cities around the world will experience “dangerously hot days” for at least a month, according to a study by researchers at Harvard University and the University of Washington.
Scientists warned that extreme heat and humid environments make it harder for people to cool down because they cannot sweat effectively. This is worrisome, especially for the elderly and young children.
Phoenix has become a hotbed for tech companies seeking low taxes and a qualified workforce, Californians seeking affordable housing and retirees seeking the sun and world-class resort experiences.
As a result, the fifth-largest city in America changed drastically. Only one thing is constant, the 110-plus degrees Fahrenheit heat that sears the city most of the year with the death toll rising year after year.
Due to its unique geography and climate, Phoenix has become an early battleground for the fight against rising heat levels in urban cities around the world. Last year, it created the nation’s first-ever Heat Mitigation Office to fight the increasingly deadly heat waves sweeping through the valley.
So what works, and what doesn’t?
The heat office is a Phoenix city government department that aims to reduce the impact of urban heat island effect by promoting and implementing strategies to mitigate the negative effects of extreme heat on public health and infrastructure.
Middel and the heat office are working together to study their effectiveness by collecting heat data and studying satellite images of the city over time to see temperature changes after cool pavements and trees have been applied — and the results vary.
“We are like a living laboratory. We have the capability to test different strategies to see what works and what doesn’t work so that other cities can follow our lead,” Middel said.
Her lab has already produced useful findings. For example, while investigating the performance of shade, she has found that artificial shade like awnings or structures are as effective as trees in providing heat relief for people, especially since they can be installed faster and cheaper.
Phoenix’s 2010 Tree and Shade master plan to increase the city’s tree canopy to 25 percent by 2030 has been underperforming, stagnating at around 12 percent after more than a decade.
“It’s really challenging for cities to plant trees,” Middel said. “Trees have a really hard time surviving in Phoenix, especially when it’s hot. They die within 6 to 8 years,” Middel said.
The cool pavement program has shown more promising results. ASU researchers found out that the new reflective coating can bounce off sunlight and keep pavement at least 10 degrees cooler.
Heat mitigation can be an expensive proposition.
The programs have been running on patchy pockets of money allocated by the city council, but this year, the heat office secured approximately $6 million from the federal government to spend on neighborhood and school tree planting programs, according to Lora Martens, the city’s urban tree planting program manager.
It takes time to figure out what programs work because it takes time for trees to grow and new types of buildings to be built to observe the results of their effectiveness when it comes to heat mitigation. Computer modeling, though, can help.
“You can use models to design scenarios, and then run heat mitigation strategies to see what impact it has if I plant more trees over here or if I change a single-family home to an apartment building,” Middel said. “So you can do this in the computer very easily and there are micro-climate models that can simulate what the impact on heat distribution is in those neighborhoods.”
methods of reducing heat and determine their effectiveness. The goal is to enable other cities to
replicate Phoenix’s success by implementing successful heat mitigation strategies. (Photo courtesy
Ariane Middel)
Singapore is also facing rising urban heat problems. Middel works closely with the “Cooling Singapore” team — they share her MaRTy invention, which they renamed “Smarty” to run similar tests.
Part of the process is to use computer models similar to the one used in Singapore, where Middel can run microclimate simulations that show the distribution of heat around different neighborhoods. Then she inserts another layer of transportation patterns to pinpoint areas where shade is most needed, which helps with the city’s urban planning.
“There’s a lot going on in the background that is not necessarily in the press or advertised and the city of Phoenix is really very proactive,” Middel said. “I think it’s a really good investment.”
Contact the reporter at orithy@asu.edu.
