Cities get hotter during heat waves. Here’s how they can adapt for climate change
The cities of today were built to withstand the temperatures in our record books — and climate change doesn’t care about our record books.
Weather patterns are changing, heat waves are becoming more intense and our buildings, roads, rails and homes simply aren’t designed to handle all of it.
“We are having these 100-year events happening every two to three years now,” said Luna Khirfan, an associate professor at the University of Waterloo’s School of Planning.
Khirfan is one of many urban design experts who say it’s time to throw out the record books and build our cities to withstand more extreme temperatures in the future. That means incorporating more nature into our designs, giving up pretty but inefficient glass buildings and weaning ourselves off air conditioning, which only hastens global warming while allowing us to ignore its effects.
“Air conditioning is actually a maladaptation, not a good adaptation, because you’re contributing to emissions when you put your AC on,” Khirfan told Global News.
Even if we can’t give up air conditioning, she says there are many ways we can reduce our need for it by building better structures and city infrastructure.
However, the solutions can be very different from one city to another, according to Mattheos Santamouris, a professor of high-performance architecture at the University of New South Wales in Australia. Santamouris has spent decades showing dozens of cities how to save energy, build renewable infrastructure and protect themselves against the intensity of climate change.
“Solutions in a coastal city may be completely different from the solutions for a city in the desert or a city with very high humidity,” he told Global News.
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Santamouris says cities that get proactive about mitigating climate change will reap the benefits in the future when more short-sighted cities will be looking for help.
“They will sell their technologies,” he said. “They will be the leaders.”
Here’s how today’s cities are failing us — and how our leaders can take steps to address the problem before it’s too late.
City heat traps
One of the biggest challenges to staying cool in a city is the fact that it’s a city — a vast collection of glassy skyscrapers, gas-guzzling cars, energy-sucking air conditioners, glaringly hot asphalt and dirty, sweaty people. All these factors contribute to what’s called the “urban heat island effect,” which can make a city one to three degrees Celsius hotter than the surrounding area during the day and warmer at night, according to decades worth of urban studies.
Glass-and-concrete cities absorb a lot of heat during the day, and they’re much slower to cool down at night as a result, according to the current scientific understanding.
“Heat islands can affect communities by increasing summertime peak energy demand, air-conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality and water pollution,” a page on the U.S. Environmental Protection Agency (EPA) website says.
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More than 600 people die of heat-related illness in the U.S. each year, according to the Centers for Disease Control and Prevention (CDC).
Khirfan points out that the heat island effect contributes to that number by nudging temperatures up in urban areas.
For example, a CDC study that examined a deadly 1995 heat wave in Chicago found that people were more likely to die of heat-related effects if they lived on the top floor of an apartment building. The study points out that top-floor rooms are usually slightly warmer than lower floors because of radiant heating coming from the rooftop, which absorbs the intense heat of the sun.
The study was conducted by public health researchers with the CDC and published in the New England Journal of Medicine in 1996. It’s often cited in municipal and federal documents addressing climate change in cities, and Khirfan says it still holds up today.
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The study shows that cities are more dangerous for vulnerable people during a heat wave. That’s why it’s so important for urban planners to make sure every building, park and transportation route is built to endure the heat and reduce the urban heat island effect.
Santamouris says it’s possible to reduce the heat in a city by 2.5 to 4.5 C once city leaders decide to take the urban heat island effect seriously.
“It’s very important… to stop living with myths and rely more on science,” he said.
The best way to reduce the urban heat island effect is through more vegetation, according to long-standing guidance from Health Canada and the EPA. Plants absorb greenhouse gases and sunlight while cooling the air around them, making them an extremely useful tool for fighting the urban heat island effect.
However, real estate is at a premium in many cities so it’s often a challenge to carve out space for a leafy, tree-filled park. That’s why many cities have launched green rooftop projects to turn unused rooftop space into eco-friendly, temperature-reducing vegetation.
Singapore has become a model for incorporating green roofs into its architecture through its Landscaping for Urban Spaces and High-Rises (LUSH) policy. The incentive policy rewards builders for creating green space equal to the footprint of the building they put up. That can mean a completely flat, green roof, a series of green balconies or even walls of greenery on the exterior.
“It’s a very green city… perhaps the most green city in the world,” said Santamouris, who lived in Singapore for several years. “They have really used the highest potential of greenery for mitigation.”
The LUSH policy has sparked many elaborate architectural designs, including this tiered garden at the Parkroyal hotel.
Chicago has also taken the lessons of its deadly 1995 heat wave to heart. The city now boasts more than 500 green roofs covering nearly 517,000 square metres of rooftop, according to city data.
Dozens of cities around the world have launched similar projects, either through mandatory green-roof initiatives or incentive programs designed to encourage voluntary construction.
Green growing pains
Critics of green rooftops argue they’re expensive to build and maintain and that legislating them into use can result in those costs being passed on to condo owners.
In Vancouver, for instance, real estate developers have pushed back against a city plan to make green roofs mandatory. The Urban Development Institute, which represents more than 850 industry stakeholders, sent the city a letter last year demanding that it hold off on a mandatory green rooftop motion so more factors could be taken into account. The UDI raised concerns that such a policy might conflict with existing designs, add costs to construction and set goalposts that would be difficult to meet. The group also called for more consultation on the proposal.
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Green roofs are one solution to what is a very complex problem,” UDI president and CEO Anne McMullin told Global News in a statement. “This may work for one type of building in a particular region or climate but not another.”
McMullin says her organization supports a more performance-based building standard that lets builders use whatever technology is most cost-effective and practical to meet the environmental goals of a given project.
Many city programs acknowledge that it’s expensive to switch an existing rooftop over to a green roof. Instead, they target large new builds or re-roofing projects with a combination of bylaws and incentive programs.
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For example, Toronto became the first North American city with a green roof bylaw in 2009, when it introduced a graduated system requiring large new builds to feature between 20 and 60 per cent green-roof coverage.
Toronto real estate developers complained about the bylaw when it was introduced, saying it could add $200,000 to the cost of a building, Reuters reports.
The city eventually relaxed its guidelines for certain industries, but the bylaw remains in place today.
Many other cities offer incentives to encourage green rooftop construction without making them mandatory.
Some cities have tried to pass mandatory green-roof initiatives with mixed results. In Denver, for instance, citizens passed a ballot initiative in 2017 to make green roofs mandatory for all new and re-roofed large buildings.
However, city councillors repealed that measure after only a year, citing the high cost (an estimated US$193,000 for a five-storey building) that it forced on building owners. Denver lawmakers replaced the original green roof law with a “cool roof” initiative, which it said would be easier and between 20 and 90 per cent cheaper.
The concept behind a cool roof is simple: if you paint a rooftop with a light-coloured silicone sealant, it will reflect more solar radiation than if it were grey or black. That keeps the rooftop a little bit cooler and protects occupants from radiant heat on the top floor.
“Cool roofs are best suited for projects with limited budgets and a primary focus on energy savings, while green roofs are preferred when life-cycle costs, public benefits and broader environmental impacts of interest,” the EPA website says. “Both options are important strategies for mitigating heat island effects.”
Toronto modified its green-roof bylaw in 2011 to allow cool roofs as an alternative in some circumstances, such as with new industrial buildings. Several other cities, including New York City, Los Angeles and Portland, Ore., have also introduced cool roof initiatives.
Some roofing companies have also started offering cool roof services to homeowners, using either painted ceramic shingles or light-coloured metal roofing.
Better shapes and materials
Khirfan says massive, glassy skyscrapers only create more heat in a city because the windows reflect sunlight onto the ground and fail to insulate the inside environment, forcing occupants to crank up the air conditioning. That, in turn, pumps harmful emissions into the air, adding to the heat island effect.
She says the best way to avoid this problem is to build structures with smaller windows and more heat-absorbent cladding, such as light-coloured wood.
Designers are also starting to look at the benefit of using irregular shapes in their buildings. This could create more shade on a building’s facade and thereby reduce the temperature inside, Khirfan says.
Rails and roads aren’t ready
One of the sticking points in preparing for a hotter future is our transportation infrastructure. Asphalt softens under intense outdoor temperatures — usually higher than 40 C — and it can break apart when used in such a state. Metal railway lines also expand on very hot days, causing tracks to bend and warp.
Some cities try to prepare for these problems by imposing traffic restrictions during a heat wave. In Paris, for example, the city banned older, higher-polluting vehicles from the roads and reduced speed limits amid this week’s heat wave.
Santamouris says these measures are extremely helpful because the smog generated from carbon-burning vehicles on a hot day can significantly increase outdoor temperatures. He says the problem is particularly dangerous in highly polluted cities like Tokyo, where smog during a heat wave can make it feel “like you have two suns.”
Khirfan says scientists are trying to come up with more temperature-resistant materials to deal with this problem, but there is no easy (or cheap) solution. Instead, we may have to get used to slowing down on the highway or on a train when it’s hot out because those routes simply can’t safely accommodate high-speed traffic.
“It seems that things are accelerating much more,” she said. “To construct infrastructure projects takes years and sometimes decades to finish.
“I don’t know if we can keep up.”
However, Santamouris is more hopeful. He’s seen experimental materials that can remain 15 C colder than the ambient air temperature. He’s currently helping to develop a roof sealant that remains 6 C cooler without using electricity.
“These issues of mitigation and improving comfort in cities should not be seen just as a problem and a challenge,” he said. “They should be seen as an opportunity.”
—With a file from Reuters
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