As temperatures rise, his research could help cities stay cool

A growing number of cities are looking for strategies to offset the effects of higher temperatures on their communities. In the DC area, eight of the hottest summers on record have occurred since 2010, according to the Washington Post’s Capital Weather Gang.

Ladd Keith is an assistant professor of planning and sustainable built environments in the College of Architecture, Planning and Landscape Architecture at the University of Arizona. Keith and a team of researchers are exploring how communities can create ‘cool corridors’ that consider thermal comfort and safety. As part of a project, they are collaborating with the city of Tucson to examine whether innovations such as cooler pavement surfaces can make walking and cycling more tolerable and extend the life of streets and roads.

Keith said it’s important for leaders to understand the effect rising temperatures can have on communities and why cities should consider integrating heat-resilience strategies into infrastructure planning. He is also co-author of instruction manual on how communities can plan for urban thermal resilience. This interview has been lightly edited for length and clarity.

Q: What attracted you to this particular field of study?

A: Prior to returning to academia, I was co-chair of the Tucson City Planning Commission and got really interested in how cities plan for climate change. This was around 2005, 2006. I realized that most of the resources available to communities related to climate change at the time were all for coastal communities. But at the time, there was almost nothing available for the cities that took care of [extreme heat]. That has really changed, especially in the last three years.

Q: So heat is sometimes overlooked because you can’t see it, but you can definitely feel it.

A: It’s a bit ironic because the fingerprint of climate change is literally rising temperatures. Yet this is the last thing we planned. And so cities are really, really far behind in how they plan and govern. If you look at the number of floodplain managers and flood risk professionals in the United States, there are tens of thousands. And we currently only have three dedicated employees in the Miami, Phoenix and Los Angeles offices who specialize in heat. So even though it’s the #1 weather-related killer, we just don’t treat it very well.

Central and southwestern states suffocate as new heat dome builds

Q: Can you explain what the concept behind cool hallways is?

A: I would describe it as a multi-modal transportation route where thermal comfort for pedestrians, cyclists and transit users is prioritized as an essential design element. The goal is to increase thermal comfort along these central corridors through the use of heat mitigation strategies. Features such as trees or construction of new structures, increased green vegetation in urban settings – and especially for transit users, improved transit stops and bicycle parking. You can imagine other features – drinking fountains, things like that.

Q: Here in DC we’ve looked at travel corridors in terms of speed and safety, that’s where bus shelters come in, but it seems like there needs to be more thought given to not only those elements, but also about elements that can also control the temperature?

A: Absolutely. And I think regionally across the United States, cities are so different with so many different climates and different natural vegetation. So what counts as a cool hallway in a place like Tucson can be quite different from Washington, DC. And so I think there’s a local flavor to consider in cool hallways. But the idea is to elevate and integrate the notion of thermal comfort for pedestrians, cyclists and public transport users.

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Q: Can things that help heat also help cold places?

A: That’s a good question. Certain elements would certainly be the same – better sheltered bus or tram stops or a light rail would certainly help with both the cold and the heat. So you can look at thermal safety both ways, for sure.

Q: How can cool corridors make cities more livable? And can they make certain types of travel more comfortable for people?

A: The idea is to make walking and cycling more comfortable and safe for the whole community. But above all, it is a matter of equity because for members of the community who may not have any means of transportation other than walking, cycling or public transport, they are exposed to a extreme heat during their daily commute. For vulnerable or marginalized members of the community, cool corridors can really be a public health issue, a public safety issue. There are also many wider benefits. The transportation sector is one of the biggest drivers of greenhouse gas emissions in the United States, so if we’re going to reduce the greenhouse gas emissions that cause warming temperatures, we’ll have to help make the more feasible and attractive vehicle-free transportation options.

Q: Are we seeing cities start to incorporate thermal resilience into their planning?

A: This spring, the City of Phoenix began planting many trees along one of its first officially designated Cool Corridors. The City of Los Angeles has a program that aims to combine cool pavement with urban forestry in some of the hottest areas of the city. One of my favorite examples is Las Cruces in New Mexico, which is obviously a much smaller town. They had cool corridor pilot projects in 2018, so they were one of the pioneers in this area. I like to point this one out because cool hallways aren’t just for big cities that have a lot of resources.

Q: Within communities, do certain populations tend to be more vulnerable to the impact of oppressive heat and could cooling corridors be a strategy to improve the quality of life in these areas?

A: Thermal equity is a very important concept. The heat is not evenly distributed in the city. And unfortunately, vulnerable neighborhoods are often marginalized, low-income, minority populations. There have been several studies that have shown that formerly redlined neighborhoods are much warmer than their wealthier counterparts, even to this day, up to 12 degrees. Cold aisles can help correct some of these inequalities.

Q: Can you tell me about the work your team is doing in Tucson with the Cool Pavement Project?

A: This is an evaluation of the Tucson Cool Pavement pilot program and it’s funded by the National Institute for Transportation and Communities of the United States Department of Transportation. And so I, along with my research colleagues Kristina Currans and Nicole Iroz-Elardo, are partnering with the city [to evaluate] an asphalt rejuvenator that is believed to have heat reduction benefits when applied. The city applied this asphalt rejuvenator last December and we took action [of surface temperatures] and we’re doing the analysis right now.

Q: What is a cool pavement?

A: There are many types of cold pavement, so it’s not very well defined because they’re relatively new technologies. You may have seen pictures of people painting streets as literally white or lighter colors, like in Los Angeles or Phoenix. [Tucson’s project] is interesting because it is an asphalt rejuvenator that contains different chemicals to reflect the sun, so it is more like sunscreen than paint.

DC has one of the most intense urban heat islands in the United States

Q: What are you trying to find out?

A: The goal of the project is really to see if the asphalt rejuvenator works well as a fresh pavement treatment. We take surface temperature readings throughout the day and night to see if it reduces the heat gained throughout the day and if it reduces the heat emitted from the road. Nighttime heat is also incredibly dangerous. We are also taking steps to assess how pedestrians would feel if they walked on this road.

Q: Are cool hallway projects expensive?

A: Because cool hallways are such an open concept with so many applications, it depends on what you’re talking about. Is it just a few more trees? Is it an increase in bus shelters or shade along the road? Or is it a whole cool hallway with cool pavement? Certainly pavement and fresh treatments can be more expensive. But as more cities adopt them, prices may come down as they become more widely available.

Q: Is there anything else about the work you do in this area that you would like to mention?

A: One of the most important things is that our governance structures for heat are much further behind [how we manage] other climate risks. If you ask anyone what transportation resilience looks like, people are often interested in flood resilience or hurricane resilience. What I mean is that we should consider heat resistance with these other components.

About Dianne Stinson

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