Overview
- Keenan Gibbons of SmithGroup led a study that used unmanned aerial vehicles (drones) with high-resolution thermal cameras to map heat patterns in a public streetscape located along Huron Street in Ann Arbor. The system captured imagery at a resolution finer than 1.5 × 1.5 centimeters per pixel, allowing for the visualization of heat differences at a microscale that is impossible to detect with standard satellite thermal sensors, which typically have a resolution of 30 × 30 meters per pixel.
- The project’s goal was to establish a preconstruction thermal baseline for the site before the installation of planned cooling interventions — including shade trees, green space, and redesigned hardscapes. Measurements focused on documenting the thermal behavior of common urban materials, quantifying surface area by temperature at solar noon, and analyzing diurnal variation to understand how heat intensity changes throughout the day. (Source: Gibbons, K. (2025). Drone-based thermal visualization for mitigating urban heat islands. Journal of Urban Affairs. DOI: 10.1080/07352166.2025.2526493)
- By producing highly detailed maps, the research was able to pinpoint the materials and locations most responsible for localized heat retention, providing a benchmark against which the cooling effects of the post-revitalization design can later be measured.
- Drone visualization of heat islands could plug directly into Ann Arbor’s A2ZERO climate action plan, helping prioritize where to expand tree canopy, install shade structures, and replace heat-retaining materials. By providing a precise before-and-after measure of surface temperatures, it would give the city hard data to track whether its heat-mitigation strategies are actually working.”
Transcription
David Fair: This is 89.1 WEMU. And today, we're going to talk drones, urban heat, ozone creation and what that can tell us about how to better mitigate environmental impact. I'm David Fair, and welcome to this week's Issues of the Environment. Back in 2018, the landscape architecture firm SmithGroup launched an innovative study of heat patterns along an urban streetscape. In this case, the study was conducted along Huron Street in Ann Arbor with the idea of learning how to better mitigate urban heat islands. Keenan Gibbons is a lecturer at the University of Michigan, but, most importantly, serves as principal landscape architect at SmithGroup. Keenan led the study and is on the other end of the WEMU phone line. Thanks for the time today, Keenan! I appreciate it!
Keenan Gibbons: Hey! Thanks for having me, David!
David Fair: Anyone who's walked through a concrete and asphalt urban area on a hot summer day knows that the surface level temperatures well above the air temperature. What about that kind of observation led your team to want to study more about it?
Keenan Gibbons: Yeah. I think we all can relate to getting out in a parking lot on a hot summer day versus the forgiving shade of a nearby park. And it's a very qualitative understanding. And so, my goal is to make it more quantitative and put numbers to it and understand we know pavement's hot, but how hot actually is it, and better inform our decisions on projects and design going forward.
David Fair: The phenomenon is known as "heat islands". How do you define a heat island?
Keenan Gibbons: I think it's often been observed at the larger scale and regional scale, but what I've been able to do with the drone is really look at that local scale of where heat's occurring in a city and why it's occurring, which is usually due to human or man-made development versus green space that can be immediately adjacent to it and much cooler by comparison.
David Fair: You mentioned drones. How did you use drones to gather information for the study?
Keenan Gibbons: So, that was the real opportunity, David. The satellite flies about 400 miles overhead, and it has thermal infrared cameras and sensors on it. But the drone, I'm not allowed legally to fly more than 400 feet. So, I'm able to get in really close and take a much clearer picture of what's happening and where it's happening and why versus a satellite.
David Fair: Beyond the drones gathering information, what all went into studying that stretch of Huron Street in Ann Arbor?
Keenan Gibbons: That streetscape project was underway, and I was one of the core designers in 2018 at the time. And it queued up really well with SmithGroup's acquisition of a couple of drones to do this type of work. So, I saw an opportunity to get in there with the drone ahead of construction and then, a year later and then subsequently five years later, more recently, see the impact that the streetscape improvements made, in terms of combating the heat island effect.
David Fair: We're talking with Keenan Gibbons on WEMU's Issues of the Environment, Keenan is Principal Landscape Architect at SmithGroup. Now, as you first started to get the information returned to you from the drones, how big a differential was there between ground and surface level temperatures to air temperature on average?
Keenan Gibbons: Well, it depended on the material. Trees and plantings were definitely the closest to the air temperature, usually within just a couple of degrees. Likewise, shaded pavement, like shaded concrete, usually was within just few degrees of the air temperature. But then, when you move just a few feet away, it would jump 20 feet on concrete. In some cases on hot mixed asphalt pavement, it will jump upwards of 80 degrees. So, on an 84-degree day, we're looking at temperatures in the 160 to 170 degree Fahrenheit range on the surface.
David Fair: Unhealthy for the public, unhealthy for the environment. How do you assess what kind of impacts it's making environmentally and in terms of public health once you have these figures in hand?
Keenan Gibbons: I look at it in two different ways: one, at a more micro breakdown of the temperatures to see how the urban material or any material performance for our architectural designs and what we're doing in urban design, but then there's the impacts on human health. And we'd look at sort of the danger zones, and we've been benchmarking temperatures provided by the National Weather Service to sort of correlate these temperatures the drone provides and see what type of impact we are actually having on human health.
David Fair: Well, ultimately, the goal is to find mitigation efforts that can offset the adverse impacts in our concrete jungles. The City of Ann Arbor has a goal of being carbon neutral by 2030 and Washtenaw County by 2035. Now, based on your findings along this streetscape, are there additional steps that have to be taken to make a difference in such a short period of time?
Keenan Gibbons: Well, yeah. And even in the project that I was on and that we've used as a case study here, it's not necessarily saying that what went in was the design solution as much as an ability to see the difference certain materials and plantings make. Shade trees, building shade: that's the number one reducer of the heat island, and likely in terms of carbon as well because trees offset carbon and all the resources that are going into combating the heat island effect, like HVAC air conditioners and all of that, compound on these hot days when shade and more considerations of the material choices that we make could simply offset that and help reduce it. So, I hope they're on track, and it's encouraging that they're making goals aligned with that.
David Fair: It seems as though part of the solution is finding ways to create shade and cool things off, but what about the construction materials themselves? When we're looking at asphalt and concrete, are there choices that could make a difference in reducing the impact of these heat islands?
Keenan Gibbons: Yeah, there are. And I think the number one contributor that I encounter is asphalt or black rubber bituminous rooftops. Ann Arbor has a large portion of those, and they perform as a rooftop membrane, but there's alternatives now that are comparative in cost of light and color and don't impact the heat island the way these rooftops that we have now have. So that's one, and I think there's some regulation opportunity there, not to introduce new regulation, but the EPA protects humans from materials like asbestos or polyvinyl chloride, PVC, and I don't see how dark bituminous or asphalt rooftops are far removed from that, in light of all the findings that we've had.
David Fair: Our Issues of the Environment conversation with Keenan Gibbons continues on 89.1 WEMU. Keenan led a study in Ann Arbor on streetscape heat islands as part of his work for SmithGroup and has been explaining the study and its findings to us. And now, we're starting to move into some solution stages. I know you know the City of Ann Arbor is entering final stages of putting its new Comprehensive Land Use plan together. It does include more density. It will include bigger and taller buildings in some areas. Now, you just kind of touched on some regulatory measures that might be able to help as we move into the future. Based on what you've learned in this very micro study, what offsets could we include to accommodate these on a more macro level?
Keenan Gibbons: That's a great question! Well, I think more impetus or support needs to be on greening our streets and our public spaces. And that word "green" can be very polarizing, in terms of what it means and what it evokes in different people.
David Fair: So, what do you mean by it?
Keenan Gibbons: So, for me, it is putting trees no greater than 30-foot on center. I've been on a number of projects over the last 15 years in southeast Michigan and Detroit where we've sometimes had to go 60 to 90 feet with the trees and really just looking at the results five years after these trees have gone. And they shouldn't be more than 30-foot on center if not more like 2025 to try to almost make like a urban forest as we're thinking about our streets. Likewise with the rooftops and building temperatures, consideration for the solar impacts and the sun hitting them and not letting them have just a black roof, but a lighter color or even a green roof helps offset the resources that go into combating the heat island effect.
David Fair: With what you've learned along this short, five-block span of Huron Street in Ann Arbor, how is SmithGroup taking this information and applying it to the work it does in other communities around the state?
Keenan Gibbons: So, we've been looking at, even across the country now because there's lots of demand for this type of work in the past couple of years, because summer is hotter than the summer before, we've been look at comprehensive heat master plans and using the satellites to identify hot spots, but then zooming in with the drone to develop appropriate treatment options to understand what's happening and then, likewise, take the data we've already developed to forecast design before it happens, so we can take these numbers and these benchmarks that we've developed and apply them to our proposed designs in a community and forecast what the thermal performance and comfort level is going to be before we actually do it, which is a game-changer.
David Fair: Do you think this is a first step in redefining what it is to municipally design a community?
Keenan Gibbons: I think it should be part of a multi-pronged strategy, yeah, but it's a really helpful one. In a community or a development, we've seen a public, private, and institutional, in terms of the need and interest in it, just because you can save money on the resources that are going into fighting civil material and design choices up front before they become a problem, versus what we're seeing a lot, especially in my work in the Midwest, where there's been infrastructure in place for a half-century or more that maybe they got it wrong and were trying to retrofit and fix it after the fact.
David Fair: Well, thank you so much for taking the time to share the information today, Keenan! I appreciate it!
Keenan Gibbons: Thank you, David! I'm happy to be here!
David Fair: That is Keenan Gibbons, principal landscape architect at SmithGroup, and he led a study on heat islands along Huron Street in Ann Arbor. For more information on that, simply stop by our website at WEMU.org. Issues of the environment is produced in partnership with the Office of the Washtenaw County Water Resources Commissioner, and you hear it every Wednesday. I'm David Fair, and this is your community NPR station, 89.1 WEMU-FM Ypsilanti. Celebrating 60 years of broadcasting from the campus of Eastern Michigan University!
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