Is It Getting Hotter in Our Cities? It's the Urban Heat Island Effect!
Florida is known for being hot in the summer, but Florida cities are even hotter. Energy from the sun gets absorbed by buildings and paved areas (like roads) which makes the whole urban area significantly hotter than natural areas. This is a phenomenon known as an urban heat island. Today we are going to explore urban heat islands and their associated impacts on our natural world.
- Climate Kids - https://climatekids.nasa.gov/heat-islands/
- Learn About Heat Islands - https://www.epa.gov/heatislands/learn-about-heat-islands
- Planting Trees for Energy Savings - https://gardeningsolutions.ifas.ufl.edu/design/landscaping-for-specific-sites/planting-trees-for-energy-savings.html
- Public health benefits of urban trees: https://www.nature.org/content/dam/tnc/nature/en/documents/Public_Health_Benefits_Urban_Trees_FINAL.pdf
How You Can Help:
- Plant a tree – Planting trees that shade west and east-facing walls will help to keep your house cool during summer, but make sure to do your research so you plant the right tree in the right place. Find your local Extension office here: https://sfyl.ifas.ufl.edu/find-your-local-office/ OR read information on planting trees: https://edis.ifas.ufl.edu/pdf%5CEP%5CEP31400.pdf
- Support green infrastructure - Let your city or town know that you value a greener city. Talk to commissioners, speak at meetings, and let your thoughts be heard! You can learn more about green infrastructure and its potential impact on your local built environment, HERE: https://soils.ifas.ufl.edu/extension/videos/low-impact-development/ OR http://www.pinellascounty.org/publicworks/pdf/green-infrastructure.pdf
- Encourage neighbors, family, friends, and local governments to keep current trees intact - Large, mature trees provide significant pollution removal among many other ecosystem services including mental and physical health benefits.
Sources for this Episode:
- Air Pollution Removal and Temperature Reductions by Gainesville’s Urban Forest - https://edis.ifas.ufl.edu/pdf/FR/FR27800.pdf
- T. Chakraborty, X. Lee, "A simplified urban-extent algorithm to characterize surface urban heat islands on a global scale and examine vegetation control on their spatiotemporal variability", International Journal of Applied Earth Observation and Geoinformation. 74, 269-280, 2019.
- Volatile trees - https://earthdata.nasa.gov/learn/sensing-our-planet/volatile-trees
On today's episode, we will be talking about urban heat islands. And if you've ever thought that it got hotter when you drove into a city, you weren't imagining it. Learn more on today's episode.
Welcome to “Naturally Florida,” a podcast about Florida's natural areas and the wild things that live here. I'm Lara Milligan.
And I'm Shannon Carnevale.
This podcast is brought to you by UF/IFAS Extension in Polk and Pinellas Counties.
If you remember back to our urban forestry episode, we were driving down the road in my Jeep. No doors and windows. Just being out in the air and taking it all in. When we turned off of a highway into a park and that park was covered with trees and you could hear birds, and it felt five to ten degrees cooler immediately.
You felt calmer and you were just going through nature. On the other side of the park we came out in a city, out into a residential area, and all of a sudden it was warmer again. And that is what we're going to talk about today.
Yes, yes. That was a great segue. We're going to be talking about something called the “urban heat island,” or sometimes people call it the “urban heat island effect,” which is essentially what Shannon was just describing. But basically in urban areas, right, we have lots of buildings, parking lots, various structures, and these structures are really good at absorbing the sun's heat because they tend to be darker in color.
And what they're not so good at is just reflecting that heat away. So they're kind of holding in this heat and then basically slowly releasing that heat over time. And it creates like this little bubble or island of heat in that area.
This happens in our natural areas, too. Just like the buildings, our natural areas are hit by sun and they absorb that heat as well. But the plants and shrubs and the ground have ways to release that heat in a much faster way.
Yeah. Yeah. So this is something we probably don't really think about. Like, we've probably learned all about the water cycle with evaporation. Maybe you've heard of evapotranspiration or just transpiration. But that process of the plants sucking up the water through the roots goes through the plants and basically converts from a liquid to water vapor in the form of a gas.
And that process of transpiration requires energy. And so through that process, it actually cools the air around it because it takes, it's using solar energy to complete that process.
So it's almost like the trees are sweating, right?
Yes. Yes. That's exactly a great, great analogy. So, yeah, the point being that buildings do not have the capability to cool themselves off like our trees and plants in natural areas do. And the result of that is warmer temperatures in these cities and developed and urban areas. And when we talk about urban heat islands, sometimes there's kind of two aspects that we talk about.
One is the impact of new surface temperatures of the manmade materials that we have in our cities. And then also the resulting changes in the temperature in the air in those areas. So there's been all sorts of different studies looking at changes in temperature. But, right, we live in Florida—it gets really hot in the summertime.
There was one study that looked at just conventional roofing material. And when the temperature—the outside air temperature—was 91 degrees, the roofing material could reach as high as 60 degrees warmer than the air temperature. Yeah. So that's obviously we're talking about, again, the surface temperature. But that is hot. I mean, right, I'm never envious of the people on the roof doing the roof work in the summer. That's really hot.
So obviously, right, the surfaces are getting really hot and that heat eventually has to go somewhere. So it's gonna be released slowly over time. And that is what we refer to, kind of these “atmospheric heat islands.” Again, just referring to the air temperature in those areas. So as that heat is released, that's gonna impact the temperature in that area.
So like what Shannon was talking about at the start of this episode with that little microclimate scenario driving in her Jeep, that is what we're feeling basically is these buildings releasing the sun's energy that they have absorbed throughout the day.
Right. When we drive over into those more developed areas.
And that happens with all of our surfaces. So when you think about walking out of a shopping mall into a, you know, black asphalt parking lot looking for your car because you forgot where you parked it again. (LAUGHTER) That heat that you can see the little shimmery heat coming up from the surface, that is just a massive amount of heat that’s, like you were talking about, heats up the air around us. And this is even evident at nighttime—right, Lara?
Yeah. And that's actually one of the big areas of study with urban heat islands. And a concern is because often we're seeing these impacts of the heating of these materials. After the sun is set that heat is now slowly releasing from these materials, which is, again, you know, that's not a natural system or natural setting that this is occurring.
Right. And that's something that anyone who's listening to this podcast can go out and see for themselves. So on a cool winter's night—you know, relatively cool, it’s Florida…(LAUGHTER) On a cool winter's morning or right after sunset when the road is still releasing that heat, that's where you're likely to see things like snakes—if you're out in an area that has a lot of habitat for those snakes.
So it's a good way for wildlife biologists to do some of their sampling in areas that are easy to access because the snakes are trying to warm up in those winter nights and they'll go to the road and absorb that heat direct from our nice little manmade roads.
Yeah. And that's actually a good point too and kind of like a word of caution if you live anywhere that has a lot of natural areas because, like, I'm stationed at a preserve and we often do unfortunately see a lot more roadkill, especially with snakes in the wintertime because they are out there seeking the warmth from the roadways.
And, you know, people just aren't always paying attention. So that's my little, I guess, word of caution or just be beware for that and be on the lookout.
Yeah, we also see things, you know, that are bigger that cause bigger problems for cars, like alligators might be attracted to the roads as well, especially in some rural areas like—oh, you know, like where I live. So that is something to keep an eye out for. That's a great point, Lara. But these warmer nights that happen in our more built areas, these have implications for a lot of our ecosystems, right?
Yeah. Yeah. And really, I mean, there's a variety of aspects of impacts when it comes to urban heat islands. So I already talked about the impacts with surface temperatures. But in terms of air temperature, urban heat islands can increase the air temperature by one to seven degrees during the day and as much as two to five at night which, again, I guess, you know, it doesn't seem like that much.
But really over time, if that's, you know, kind of persistently what we're seeing there are impacts to that. One of the impacts we're seeing is an increased use in air conditioning in these areas, which of course for us means more money out of our pockets. But it also results in increased emissions, right, from whatever source we're getting to power our air conditioning.
Yeah. And a lot of people don't think about how much that added warmth might affect them and their, you know, their day-to-day lifestyle either. So when we're talking about, say, four degrees difference at night, I mean, that can be the difference between wanting to sit around with family outside or not.
And if we're not getting as much of the colder weather we used to see when there was less of that built surface environment, then we're talking about things like: “Are the mosquitoes, like, more because it's warmer?” “Are there other pest species we’re not thrilled about because it's warmer?”
We're not talking about those seasonal cold snaps. We're talking about just continuous, always gonna to be three to five—you know, what’d you say, two to five degrees warmer— every night.
Yeah. When I talk to my friends in the urban forestry world, they're saying that urban heat island is kind of a hot topic right now and how to combat that, which I think is actually a good segue to our call to action for this episode. We've got lots of good stuff for you guys this episode. The first one, though, is kind of an obvious one—at least to me—which would be plant a tree or…
Or more than one! Yeah. (LAUGHS) So in Florida, Florida Arbor Day is celebrated on the third Friday in January every year. And then there's National Arbor Day in April. So those are two good reminders to plant a tree if this episode doesn't remind you enough. But, there's lots of ecosystem services or benefits that trees provide aside from combating this urban heat island, which again, we talked about in our urban forestry episode.
If you're gonna to plant a tree, there's a lot of homework that we encourage you to do. But in terms of combating the heating element with cities in the urban heat island, it's best to plant a tree where it's gonna provide shade on any sides of your house that are facing the east or west. So you want to plant a tree that's going to cast shade on those sides of the building because those are going to be more exposed to the sun throughout the year.
And if you’re planting a deciduous tree, you can either do east, west or south side of your building because then it'll provide shade in the summertime. And then they'll lose their leaves—tada!—in the winter and let your house heat up a little bit from the sun and combat the heating costs associated with that.
Lara mentioned that there's a lot to think about when you're going to plant a tree, and that's true of planting a tree in a residential area or in a park or any city property like a right-of-way. If you're looking for somewhere to get that information, Lara and I both highly recommend reaching out to your local extension office.
Obviously, we're a little biased (LAUGHTER) because we work there, but our master gardener volunteers and our horticulture agents can recommend a fantastic tree for your yard, or a park near you if you're working with your local city or town. And so they will help you pick a species appropriate for your area and your climate—or rather your ‘“hardiness zone,” which gets back into that winter stuff.
Or they can also help you pick something that's just a good size recommendation for your yard. If you don't have space for a huge overstory tree like a sycamore, you probably do have space for something like a crepe myrtle or a small birch tree or something of that nature. So reach out to your extension office if you need any help
with where to plant your tree in your yard, how to plant a tree in your yard or which tree to plant in your yard.
Yeah, for sure. And it definitely depends on what your goals are. And again, they can help you sort through all of that. But we tend to stress native trees and native plants just in general for the lower maintenance. They're adapted to thrive and survive here better than some of our non-native. But again, we're trying to get at also reducing carbon emissions.
So any time there's less maintenance, that's better. Long-lived trees, too, provide a lot of benefits. So keep that in mind as another thing to consider. How long is this tree going to live? They'll help to filter out more pollutants, help to capture more stormwater. They're just all around beneficial. And if you're a pine tree fan like me (LAUGHS)…
—and Shannon—evergreens in general are really good for capturing particulate matter in the air. Just think air pollution, because, right, their leaves are always there. So they're able to provide that service as well.
Another call to action that we think would be helpful in this regard would be “green infrastructure.” And that's something that you might hear that term thrown around all the time, like, oh, this is green, that is green. But green infrastructure is specifically talking about infrastructure that in some way, shape or form mimics nature and brings those natural system benefits to the built environment like buildings, parking lots and roads.
And so some examples of that might be green roofs, cool roofs, cool pavements, or a smarter growth, which just means planning where growth will happen in your city so that it's not a shotgun approach. It's planned and can really maximize the benefits of the natural areas surrounding your city.
Yeah, there's a ton of research. I actually took a whole course on industrial ecology. Yes, it's a thing. But there's people out there doing tons of research on the various materials that we use in the built environment. And so they've figured out which ones are less likely to absorb the sun's heat—again, kind of combatting this urban heat island.
So there's definitely options out there. New things, new technology coming out all the time. So it's a great opportunity and a great thing for you to encourage your local city or town or county to participate in and implement.
And that brings up a great third call to action, which is for keeping current trees intact in your area, making sure that they are maintained properly and that your city or your town, that they know that you value those trees.
And so using your civic engagement, make sure your thoughts are heard—that you want a good, sustainable urban tree canopy, that you support the proper maintenance of trees in your area, and that these big healthy trees that have been cared for over the decades are going to have the best effect in our local environment because they are those long-lived trees that are larger and produce those benefits at a very good per tree amount of effect. A larger, older tree will provide more effect, more positive effect than a young one.
Yeah. And I think, you know, I've worked with a lot of cities as well as the county over the years, and they really do put in a lot of effort to give everyone an opportunity to have their voice be heard in a variety of ways. I know, like, I worked with a local city, we did community discussions. You could come and voice your opinion virtually or in-person.
And then if that didn't work, there was a survey sent out. So I know a lot of us we say, like, “I don't have time,” and that is a valid point. We are all very busy people. I know commission meetings are, like, at the non-ideal time. (LAUGHTER) But there are different ways and avenues that you can voice your opinion, even if it's just sending a quick email, you know, on your lunch break or something, just to say like, “Hey, I support this.”
It could be as simple as that. And if they, you know, a commissioner gets enough emails about something, then he might decide to take action. So we just empower you to use your voice and support our trees and help us combat this urban heat island. Because as we know, Florida is only developing more and more. And yeah, we need to do something about it.
Mm hmm. And not to belabor the point, but for those of us who live in a more rural area—or a less urban area than Lara over in Tampa (LAUGHTER)…If you live in a smaller town or city, calling up your local city hall and asking to talk to their parks person (or their biologist or whoever they might be) and just tell them, like “Hey, that tree in the park, I love it and it really makes my life better. And I really appreciate that you guys take care of it.” You will seriously make that person’s day.
And if you let your commissioners in your smaller cities know that you think that this is a valuable quality of life thing for you, they will take notice of that. Especially in the small cities, they are all fighting to get more engagement from the residents.
And this is important because—while you've heard Lara and I talk about urban heat islands and all the benefits of urban forestry and the microclimate and all these things that make you happy—there’s so much emerging research on mental and physical health that comes along with being near trees and being around their air filtering-and-happiness-bringing green little leaves.
There's so much cool research about how it can lower stress over your lifetime and thereby reduce your risk of heart disease. It is amazing, and I highly encourage all of you listening to go check into that because going out into nature is one thing, but if we can bring nature into our cities and reduce this urban heat island, it will also have untold benefit on our local mental and physical health as well.
Yeah, and I would just say again, a reminder that there are Arbor Day events coming up—whether it's Florida Arbor Day, National Arbor Day—and so just do a quick search and see if your local city, town, county is doing anything. Oftentimes they do have free tree giveaways.
So definitely worth seeking that out if you are interested in planting a tree. I hope you are, but if you're in an apartment like me and you don't have that option, there's tons of planting events as well that people are doing in honor of Arbor Day. So check them out and we will again provide tons of resources in the show notes. We hope that you guys learned something new today and we look forward to talking to you next time.
Thanks for listening to “Naturally Florida,” a podcast about Florida's natural areas and the wild things that live here. Stay updated on new episodes by subscribing on your favorite podcast platform. If you enjoyed today's episode, consider sharing it with a friend. “Naturally Florida” is produced by your hosts Shannon Carnevale
And Lara Milligan.
If you have questions or suggestions, submit them online at naturallyfloridapodcast.com. This podcast is brought to you by the University of Florida's Institute of Food and Agricultural Sciences Extension, an Equal Opportunity Institution. Thank you for listening.