From Rooftop to Alleyway, Chicago Fights Extreme Urban Heat With Greener Ideas

One of Chicago’s most beautiful and hidden gardens is located on top of City Hall, part of an effort to ‘green’ roofs in order fight rising temperatures. Hari Sreenivasan reports on the actions the city of Chicago is taking to mitigate climate change in an urban landscape.

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    Next, our series on Coping With Climate Change looks at how the city of Chicago is dealing with ever warmer temperatures by trying to cool things down with changes to its landscape.

    We turn again to Hari Sreenivasan, who traveled there recently.

  • LUXORA COLEMAN, Chicago:

    This is your granddaddy. That's me.


    Fifteen-year-old Janell Coleman only knows her grandfather through the photographs that her grandma Luxora Coleman shares with her.


    What I can remember about 1995 is that my husband passed in his apartment. He was on the couch, and sitting up, and his — his room was extremely hot when I arrived there. And the only thing that was going was a ceiling fan.


    That July in Chicago, the heat index reached 120 degrees for four straight days. Thousands of residents lost power, roads buckled, and more than 700 people, mostly the elderly and ill, died due to heat-related causes.

    Since then, the city has been working to prevent such a tragedy from occurring again by improving heat emergency warnings and opening summer cooling centers.

    But how can a city control the heat?

    Cities are usually hotter than their surrounding rural areas, because all the buildings and pavement absorb the sun's heat during the day and keep giving off heat into the night. It's called the urban heat island effect.

    Here's a map of Chicago from the city's Department of Environment. These red built-up pockets are where the temperature is hotter throughout the city. Or look at this satellite view of Phoenix's night temperatures, where yellow areas are the hottest. The difference between Phoenix and a neighboring rural town is about 11 degrees.

    And making all that worse is the fact that scientists have seen a rise in surface temperature in the last century around the world. By looking at data from urban and rural areas, land and sea, they have been able to account for local impacts, including weather stations near heat-retaining structures.

    That is, they know that Chicago is warmer, and not just because of all those buildings.

    Thomas Peterson is a climatologist with the National Oceanic and Atmospheric Administration.

    THOMAS PETERSON, Climatologist, National Oceanic and Atmospheric Administration: We look at temperature at rural stations and we look at temperatures at urban stations.

    And we see if they are showing the same thing in the long-term trend variability and change. And they are showing the same thing in our record, both in the U.S. record and in the global record. What we find is when we account for the different factors that impact temperature at a location, we see that the temperature in urban sites is warming at about the same rate as temperature in rural sites.


    Joseph Fernando of the University of Notre Dame has been studying the urban climate in both Chicago and Phoenix.

    He has seen the impacts of the heat island effect and says it's gotten more intense because of the overall global temperature rise.

    JOSEPH FERNANDO, University of Notre Dame: So, that means cities usually have higher temperatures compared to rural, not only due to urban heat island, but also the climatic change. So climate change basically exacerbates the effects at night.


    Fernando says that as earth's temperature increases, a city's developed areas will retain even more nighttime heat than other areas.

    How significant is that difference between rural and urban in, say, a city like Chicago?


    Well, now, here it's about five degrees. In 1970, it's about two-and-a-half degrees. So it has doubled up over 40 years.


    This past summer, Chicago once again saw record-breaking high temperatures. According to a climate assessment commissioned by the city, Chicago's annual average temperature has warmed by more than two degrees Fahrenheit since 1945.

    Unless something changes this trend line, by the end of the century, a Chicago summer could feel like an Atlanta, Ga., summer, and there could be more frequent, longer, and more intense heat waves like that of 1995.

    There also could be more rain, since higher temperatures means less precipitation falls as snow.

  • KAREN WEIGERT, Chicago Chief Sustainability Officer:

    The data there really set the stage for us to think about what solutions could be in place. So, the data suggested things like we will see more high-heat days, more heat events, more rain, more storm events, in the context of an overall change and some warming.


    Karen Weigert is the chief sustainability officer for the city heading up Chicago's ambitious mission to cool the city down.


    We're in the midst of, right now, a $7 billion multiyear program on building a new Chicago. So we're redoing and renovating infrastructure throughout the city.


    They're changing everything from head to toe or, in a city's case, from roof to street.

    One of Chicago's most beautiful gardens is one very few people get to see, a 23,000-square-foot green roof that sits on top of City Hall.

    The difference a green roof makes is measurable. That side of City Hall's roof used to be traditional black, like most roofs.

    On a hot day, when it was 90 degrees out, they came out and measured the surface temperature. It was 169 degrees, vs. this side of City Hall, where they have a green roof, and the surface temperature was 90 degrees, almost an 80-degree difference.

    Michael Berkshire administers green roof projects for the city.

  • MICHAEL BERKSHIRE, Chicago Green Projects Administrator:

    The rooftops are one of the last kind of frontiers that you can really look at, and it's a significant amount of space.


    Berkshire says the plants on green roofs soak up heat, and keep both the buildings underneath and the air above them cooler. That, in turn, reduces the cost of air conditioning. This roof saves City Hall about $3,600 a year.

    Chicago has 359 green roofs covering almost five-and-a-half million square feet. That's more than any other city in North America. MillenniumPark is the largest green roof in the world at 25 acres, covering parking garages, a railway, and an opera house.


    What's interesting about a green roof is that it provides the benefits that can help mitigate in terms of, you know, keeping the temperatures lower.

    But then in terms of the adaptation, we're going to see more rainfall and heavier rainfall events.

    So the more rainfall you can absorb on site, the less we're going to overburden that combined storm sewer system.


    So, a green roof not only helps reduce the heat; it also cuts back on storm water runoff.

    To encourage more of them, Chicago has mandated that all new buildings that require any public funds must be LEED certified, or designed with energy efficiency in mind. And any project that includes a green roof in its application gets a faster permitting process.

    Faster permits mean faster move-ins and more revenue. That, combined with energy savings, is the kind of green that incentivizes developers like Jason Westrope.

  • JASON WESTROPE, Development Management Associates:

    If every rooftop in Chicago was covered with green roof, the city could save $100 million in energy every year, so there is a direct benefit between the amount of heat energy gained by a building that's not covered, or protected, by a green roof, and that does translate into cooling costs downstairs.


    Downstairs is 900 Michigan Avenue, a luxury retail, office, and condo building. The green roof was installed because of the city's incentives, but they expanded it when they realized it was attracting tenants.

    Chicago is also taking the fight to the streets.

    To see one of Chicago's most ambitious projects, we met Janet Attarian in a downtown alley. She is a project director for the city's Department of Transportation.

    JANET ATTARIAN, Chicago Department of Transportation: What's special about this alley is that it has permeable pavement. And what that means is that the pavement is designed to allow rainwater to pass through the pavement and be able to access the earth underneath, so that it can infiltrate into the soils, as it would naturally do if we were in a farm field.

    An alley that has water that's basically being stored underneath it, as that evaporates, it helps keep the air around it cool.


    Traditional alleys absorb heat, and cast away potentially cooling rainwater. When you realize there are 1,900 miles of alleyways in Chicago, more than any city in the country, you start to see the potential of green alleys.

    Attarian says that the goal is to make complete street systems, from bike lanes to widened sidewalks for increased pedestrian traffic to landscaping that provides shade.

    She also took us to an intersection in South Chicago, a main thoroughfare for trucks coming from around the Midwest and one of the prototype examples of Chicago's newly engineered streetscapes.


    The light bounces off, and also the heat bounces off, if you will, right?


    OK. Yes.


    It doesn't absorb the heat. It's like when you put on a black T-shirt on a hot day vs. a white T-shirt.


    Literally, between these two lanes, if you put thermometers down for an hour each, they would have a different temperature.


    They should have a different temperature. And we actually have a laser that's pointed at it so that we can measure temperature right at the surface.


    This streetscape is a test bed in many ways. The composition of some lanes is more porous to soak up rain. Other lanes are coated with a micro-thin concrete to reflect more light and keep the street from absorbing so much heat. And the curbs are catch basins, so excess runoff feeds sidewalk gardens, instead of ending up in the drain.

    Moving forward, the city is looking to further understand where the city's hot spots are. Thermal radar and mapping will allow them to pinpoint where heat is having the biggest impact.

    While all of these efforts may be expensive, Karen Weigert says it would be more costly not to act.


    But it really comes down to what do we do today to make sure we're pointed in that right direction. So there's an economic value case out there, and there's also just huge benefits to bring to Chicagoans right now.


    Chicago's efforts are being studied by cities around the country. They're still early experiments yet, and it will be years until all the roofs are green or the streets are paved with permeable and reflective materials.

    Until then…


    This is the fan I use in my bedroom.


    … residents do what they can to stay cool.


    You can see a slide show of some of Chicago's most impressive green roofs, plus find all of our Coping With Climate Change reports on our website.