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Is Your City Ready for Global Warming’s Coming Heat Waves?

Cities will bear the brunt of future heat waves, but good urban planning—and ancient Japanese cooling techniques—could help reduce the threat.
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Climate planners in Vienna and other cities are trying to redesign urban landscapes to prepare for coming heat waves. (Photo: Bob Berwyn)

Climate planners in Vienna and other cities are trying to redesign urban landscapes to prepare for coming heat waves. (Photo: Bob Berwyn)

This week, about 14,000 scientists from around the world are in Vienna for the European Geosciences Union general assembly. For science and environmental journalists, it’s like being a kid in a candy store with just a quarter in your pocket — so many sessions that it’s hard to choose.

On Monday morning, scientists from Belgium, Holland, and the United Kingdom appeared to present some of their latest work on heat waves. The build-up of heat-trapping greenhouses in the Earth’s atmosphere vastly increases the chances of heat waves, and they are becoming more frequent, more intense, longer, and deadlier.

Cities will feel the effects most of all because they already warm up faster than the surrounding countryside as pavement and concrete absorb incoming solar radiation. By 2050, the heat-stress index for cities will increase twice as much as for adjacent rural areas, says Hendrik Wouters, a postdoctoral researcher at the University of Leuven in Belgium, whose research involves a fairly simple metric to help cities prepare for the consequences of global warming.

Cities need to anticipate these heat waves if they want to cut the number of resulting deaths.

“Heat waves arealready affecting our cities today. We see power surges, other failure of infrastructure, and we know hospital admissions spike,” Wouters says. “We also know the urban heat-island effect becomes more intense and we wanted to quantify that, so we looked at how often temperature alarm levels are exceeded. When you count that, it gives you a measure of how much heat stress impact will evolve in the future.”

While it may be a simple metric, projecting effects in the future is still a complex equation: A 35-year climate simulation takes three months of calculation time on a very fast supercomputer, Wouters says.

And the future is not pretty, unless greenhouse gas emissions are cut soon and drastically. Under the business-as-usual emissions scenario commonly used in global climate models, Wouters says the Belgian cities he studied will experience at least 25 days when the heat alarm level is exceeded by 10 degrees Celsius. With immediate greenhouse gas cuts, the heat stress level will remain similar to today.

The fact that cities will feel the heat much more than rural areas means cities also have a disproportionate responsibility to mitigate by transforming themselves into compact, green areas with a small carbon footprint.

The public-health effects of heat waves in cities can be extreme, leading to thousands of deaths, as documented in Paris, France, during the summer of 2003 and in other cities around the world, as recently as 2015 in India. To help emergency workers prepare, Francis Pope of the University of Birmingham in England studied how the speed of ambulance response will suffer when temperatures spike.

It’s easy to see how the results of the Belgian and U.K. studies could be used together to help improve public health and cut the number of deaths from heat waves in urban areas. And it’s time for for cities everywhere to start taking these challenges seriously, says Hanns Moshammer, with the Institute of Environmental Health at the University of Vienna.

Shaded squares with cool, wet fountains have been a way that cities have adapted to hot summer days for centuries, as in the Place Caramy in Brignoles, France. Climate researchers are studying whether there’s a way to use water on a larger scale to protect vulnerable city populations from the deadly consequences of heat waves. (Photo: Bob Berwyn)

“We need to reconsider our organization and infrastructure. What we are really concerned about are acute events like heat waves that require preparedness and communication, telling people what to do in advance.” For the long-term, doctors also need to consider indirect effects, like the spread of new diseases linked with increasing temperatures, Moshammer adds.

In Vienna, city planners are trying to include climate change projections into their decision-making process, according to Maja Zuvela-Aloise, a climate scientist who specializes in developing detailed climate models for urban areas. Such models can project the effects of mitigation down to about 100 square meters — enough to show much of an area needs to be covered in vegetation to lower the temperature by a couple of degrees.

“We are investigating green roofs,” Zuvela-Aloise says. “According to the city’s building registry, 45 percent of roofs could be covered with climate-cooling vegetation. Right now, only 2 to 3 percent of Vienna’s roofs are green, and the models show greening all available roofs would have a significant moderating effect, perhaps cooling sidewalk temperatures by a degree or two,” she says.

Another way of cooling cities is very old: Since the Middle Ages, and perhaps longer, central squares with fountains and trees have served as urban cooling shelters on hot summer days, and, at the Delft University of Technology, Anna Solcerova is quantifying that cooling effect and studying how modern cities can use water to reduce the effects of extreme heat.

In her latest research, Solcerova experimented with Uchimizu, the ancient practice of sprinkling water in temples, gardens, and streets to suppress dust and temperatures. She says Japanese officials are already trying to revive Uchimizu as a way of mitigating the growing number of heat waves in cities.

“We use very sophisticated ways of measuring this, including buckets of water and duct tape,” she jokes, describing her research, which was actually a three-dimensional visualization to measure exactly how much water is needed to cool the air in a given area. On hot days, just one liter of water applied over three square meters can cool the air by about two degrees Celsius at head height, and by three degrees Celsius at ground level. But because drinking water is a precious resource, she suggests using rainwater or gray water.

It’s also a way for city residents to get directly involved in climate change mitigation. Individual home or building owners could develop water-based cooling systems, using rooftop cisterns and systems to re-collect the water to help dissipate heat.