Dr. Melissa Guardaro: Cities coping with extreme heat
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Dangerous extreme heat events are becoming more frequent and widespread—and the urban heat island effect makes city dwellers particularly vulnerable.
On July 18, 2024, SciLine interviewed: Dr. Melissa Guardaro, an assistant research professor of sustainability at Arizona State University. See the footage and transcript from the interview below, or select ‘Contents’ on the left to skip to specific questions.
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Introduction
[0:00:19]
MELISSA GUARDARO: My name is Melissa Guardaro and I am an assistant research professor in the School of Sustainability at Arizona State University. And I’m also the Associate Director for Resilience Hubs at Knowledge Exchange for Resilience Center at Arizona State University. I am an extreme heat researcher. And I’m most concerned about governance—not just government, but governance issues around extreme heat—and also adaptive capacity of people at the individual and household level.
Interview with SciLine
Why are cities getting hotter?
[0:00:56]
MELISSA GUARDARO: I think that when people look to their past, they can say things like, “Oh, we never had air conditioning,” or “Oh, you know, it was never this hot,” and truly, the hottest has been getting hotter, the dryer has been getting drier, and the wet has been getting wetter. And a lot of that is due to climate change. But also, we have a situation happening in cities called the urban heat island effect. And it’s not just one urban heat island, it’s actually several urban heat islands. And you can experience this when you get in your car. You don’t need to be a scientist, but you just see the temperature change as you make your way through different parts in the city. And that has to do with the materials that we use to construct cities, how they’re designed, the wind flow, and really it impacts the thermal comfort for people.
When it comes to health and safety, why is the overnight low temperature more important than the daytime high?
[0:02:00]
MELISSA GUARDARO: There’s been a lot of coverage of the high temperatures, and some of them are quite high and shocking. But in actuality, it’s the overnight low temperatures—how much an area cools off at night—that’s most important for human health. And we have been seeing a shockingly high number of days that, overnight, it just doesn’t cool off to a point that’s safe for human health. So, human health is compromised at about 85 degrees or higher at night. And in Phoenix, we’ve experienced a number of days where the lows have been higher than 90 degrees, if you can believe that.
Can cities solve the problem of urban heat by planting trees?
[0:02:36]
MELISSA GUARDARO: Planting trees is not a one-size-fits-all solution—it really depends upon where you are in the United States. And you have to look at tree planting as just one point in a system of how you’re going to attack extreme heat. So, in Arizona, for instance, the areas that desperately need shade are also the most disadvantaged areas. And it costs money to maintain a tree. It costs money to plant a tree. And a lot of these communities don’t want that burden. And further, they’re renters too, they’re really don’t have control over trees or any other vegetation on their property. So, it’s really important to understand that planting the right tree in the right place at the right time—there’s a whole confluence of factors that come into play. You also need to balance planting trees with water usage. So, in a place like the desert, that’s not necessarily helpful to try to provide shade structures solely based upon trees in other areas that may be more so. But we saw in Louisville, Kentucky that they also then had a beetle that attacked some of their trees. So, while they had a robust tree canopy, the invasive species just then went and decimated some of their canopy. So, trees are not the only answer. They’re just one part of one answer.
What types of neighborhoods are particularly vulnerable to extreme heat?
[0:04:02]
MELISSA GUARDARO: Research has shown that cities that were historically redlined, those areas today tend to be the hottest areas of the city. And they have less park infrastructure, less shade infrastructure, and it’s just a historical disinvestment in the area that is just showing right now that it’s that much hotter.
What can cities do to improve residents’ comfort, health, and safety?
[0:04:30]
MELISSA GUARDARO: Cities can really make decisions with extreme heat in mind and understanding that, starting today, that’s as cool as it’s going to get. We’re only going to get hotter, and this is only going to get more intense. So, understanding the equity issues behind heat that there are neighborhoods that are substantially hotter than others, understanding the intersectional nature of extreme heat, where housing, drug abuse, pre-existing health conditions really come into play. And there have been really great examples of just governance issues around heat and getting a lot of different people together in the room to discuss best practices. The city of Phoenix has appointed a Chief Heat Officer that will stay on to really coalesce decision making so that extreme heat can be considered when you’re operating the city.
Why can’t FEMA provide assistance to places experiencing extreme heat?
[0:05:31]
MELISSA GUARDARO: It’s going to require legislation in order to do so, and there are bills pending right now. But by not having it in there, you do not have funds allocated both for the emergency management portion of that and also long-term mitigation adaptation. So, we’re seeing a lot of movement with people trying to make sure that that’s included in a FEMA declarable disaster.
What is being done in metropolitan Phoenix, and the state of Arizona, to mitigate the effects of extreme heat?
[0:06:01]
MELISSA GUARDARO: Last year, metropolitan Phoenix experienced 30 plus days of 110 degrees Fahrenheit in July and that was really a crisis. Even though it’s a dry heat, 110 is unbearable. And again, the overnight lows were extremely high. And Governor Hobbs declared a state of emergency for extreme heat—it was the first time that was ever done in the state. And in doing so that then set in motion state agencies having to become responded to extreme heat and make that part of their plans ongoing. That also allowed for the appointing of a state Chief Heat Officer, Eugene Livar—which we’re all very excited to have him on board—where you actually have a point person. Someone who is going to make sure that extreme heat is top of mind when we’re talking about policies and procedures. So, an outgrowth of that is the extreme heat preparedness plan. Knowledge Exchange for Resilience at ASU was an integral part of that. We developed the recommendations for that, and it ended up being both emergency preparedness for this summer, but then also long-term mitigation and adaptation strategies. And sometimes it’s not just having governments by themselves work. In Arizona, we have the Arizona Heat Resilience Working Group—which I co-lead—and this is a group of cities, nonprofits, health departments, the Arizona faith network, utilities, that all get together to share best practices and to try to troubleshoot together. So, this is kind of a tiger team that is really working across silos, across sectors to come up with some solutions for extreme heat.
What should other cities and states do to prepare for extreme heat?
[0:07:56]
MELISSA GUARDARO: Cities and states should be thinking about extreme heat, no matter where you are in the United States. And different regions have different impacts. So, in Arizona, we’re actually at the forefront. Our built infrastructure, by and large, all has air conditioning as part of it. And there are things that we do just as part of business as usual, that other places are going to have to start to consider. So, for instance, if you have a playground, generally speaking, there is some sort of shade structure around that to protect the children from extreme heat. Other states and cities really need to take heat seriously. This is an equity issue. It’s a public health issue, and it’s not going to go away. It’s just going to become more intense.
