What a bicycle can tell us about the urban heat island

Post by Jenny Seifert

Staying cool may no longer be a concern to Madisonians this year, as we reluctantly start to don our sweaters, but managing the higher temperatures caused by the urban heat island will be a challenge for summers to come. Hotter cities cause higher energy demands and costs, increase air pollution and present serious health risks, making solutions to reduce the urban heat island effect crucial for creating sustainable cities.

One solution could be none other than to plant more trees. Studies have shown urban trees and forests help to cool off cities, but whether that means we need more urban forests or just more tree-lined streets is still unknown.

Knowing such details could help city planners and city dwellers plan for a future under climate change, which could exacerbate heat island effects with increasing average temperatures and more heat waves.

Fortunately, WSC graduate student Carly Ziter is chasing down such details…by bike.

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Carly Ziter collects urban heat island data with the contraption attached to her bike.

This past summer, Ziter rode all around Madison collecting real-time temperature data with a custom-built contraption strapped to her bike. Her survey of the urban heat island landscape builds on data from a network of stationary sensors installed by her fellow WSC researchers for our previous heat island research.

Before diving into data analysis this fall and winter, she took a moment to explain her unique study.

Why is this research important?

CZ: Temperatures don’t differ just between a city and the surrounding area, but within the city as well. Our study looks at the role of urban forests – areas like forested parks and conservation areas in the city, as well as street trees – in cooling off the city.

We know trees are really important for reducing the urban heat island, but to best manage urban forests to beat the heat, it’s important to understand the details. For example, do only large forested areas provide relief from the heat or can street trees fill this role, too? How much added benefit do trees give compared to grass or other plants? In other words, how can we get the best bang for our buck?

This kind of information will be valuable as our urban forests continue to change in the future – for example, as a result of invasive insects such as the Emerald Ash Borer or in response to policies that govern street tree planting and maintenance.

What is unique about your data-collection method?

CZ: Because our equipment is highly portable, it allows us to study a greater area of the city in detail, and also to travel into human-scale spaces, like parks and forests that aren’t easily accessible with other methods.

This is a method that has been used a few times in others cities, but is still relatively new for urban forest research. So we really are exploring new frontiers in terms of the kind of data collection we do!

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Ziter is researching how trees can help cool off cities.

Do you have any interesting stories from your data collection?

CZ: The equipment on my bike really stands out. So I get a lot of questions from fellow cyclists or pedestrians about what that weird structure on my bike is. I really love these conversations, as it’s a chance for me to incorporate science communication and outreach into my work in real time! I try to keep track, and so far I’ve had conversations with over 30 different people on the road.

I’ve also learned a lot more than I ever thought I’d need to know about things like wiring, data logger assembly and programming, and quick mechanical fixes in the field. You really have to be creative in this kind of work.

What are you finding so far?

CZ: Something we’ve noticed from the preliminary data is that there’s tremendous variability in temperatures on a typical summer day, even within the city limits. So, just because the weather report says a certain thing, you can be experiencing temperatures several degrees warmer or colder just based on where you are within in the city, as well as on the environment surrounding you.

What could these findings mean for how we design cities into the future?

CZ: Our findings will help us understand how urban forest management can act as a lever to reduce harmful summer temperatures within our cities. For example, should cities focus on a few large green spaces or several smaller ones? Is there a certain number or density of trees that are best at reducing temperatures in an area?

In addition to thinking about future city design, these findings can help us understand the implications of our decisions in existing cities. For example, this research can shed light on how policies we put into place regarding street trees might affect city temperatures, or whether we should focus tree-planting efforts in certain areas of the city. Something that’s important to remember when you’re dealing with trees is that they take years to grow. So decisions we make about our cities now are going to have implications decades into the future.

What motivates you to do this research?

CZ: The urban heat island is not just interesting ecologically, but has huge implications for human comfort, health and safety. This issue will only become more pressing as more and more people move into cities, and as temperatures continue to warm. As a scientist, it’s important to me that my work is contributing to current environmental challenges and that I feel that my results will be meaningful to the community.

I’m also motivated by the incredible care and respect that local citizens have for urban trees here in Madison. Issues like the Emerald Ash borer, for example, are really bringing out how important – and how loved – city trees are to local citizens. Understanding how personally valuable these trees are to many people motivates me to learn more about their ecological value as well, so that we can continue to be good stewards of our urban forests and make good decisions about their future.

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