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Series: City of the Future 

Global
CORPUS Magazine

Summer in the City – How Our Urban Eco-Systems Stay Cool Even in Extreme Heat

Not only does the heat seem to build up in cities in summer, but the so-called urban heat island effect is also measurable. On an annual average it can amount to as much as 3°C more than in the surrounding area, and sometimes 5°C on hot days and even more in the following nights. As a result of global warming, temperatures in our cities will continue to rise – with serious consequences for health and the environment. Individual buildings can be cooled, but what about entire cities? We have been scouring the globe for strategies and solutions. A new part of the City of the Future series.

Portland as warm as San Antonio? Berlin as warm as Canberra? According to research by the Crowther Lab of the Swiss Federal Institute of Technology (ETH), this could be reality in 2050. The experts in Zurich looked at 520 cities with populations of over 1 million and the changing climate forecast for them. According to the study, 77 percent of the world’s cities will experience significant climate change. This will be starkest in the northern hemisphere. In Europe, for example, cities could then be 3.5°C warmer in summer than they are today. Translated, this means that London would have the climate of today’s Barcelona, and Stockholm that of Vienna. In tropical regions, temperatures will change less, but precipitation will shift significantly. In short, the rainy season will be wetter, but, more importantly, the dry season will be significantly drier.

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Even today, our cities are measurably warmer than their hinterlands, and climate change will reinforce this effect. The consequences are serious, as high temperatures and heat waves will endanger our health and claim human lives, energy consumption due to air conditioning will increase, and productivity can be expected to fall. But how can entire cities be cooled? All around the world, there are many different approaches to doing this, and these can make a significant contribution to quality of urban life.

But, first of all, why do cities heat up so much? Several factors come together here. Concrete and asphalt surfaces literally absorb the heat and trap it in the urban environment; unfavorable building arrangements can inhibit air circulation, while emissions from traffic, industry and – ironically – air conditioning do the rest. But, as so often, these problems also point to possible strategies for really cooling cities down.

GOING GREEN

Trees not only provide welcome shade, but also release water vapor via their leaves, which cools their immediate surroundings. The more parks and gardens a city has, the more agreeable the microclimate. Now the horizontal space available for new green spaces is often limited – so it’s worth turning to the vertical. Singapore, for example, has greened 100 hectares of building facades – by 2030 the surface area is set to double, which will be achieved through regulation, among other things. The Landscaping for Urban Spaces and High-Rises Ordinance calls for the integration of green spaces on the same scale as the plot of land for each new building. The German city of Karlsruhe is following a similar approach and has greened the roofs of 5,000 buildings. It is also increasingly planting so-called “trees of the future”, i.e. species that are not necessarily native but are likely to cope better with the anticipated higher temperatures. 

MOBILIZING WATER

Evaporative cooling is also what gives ponds, lakes and wells their cooling effect on the environment. In addition to these so-called passive systems, there are also active cooling solutions based on water. In Japan, sidewalks and gardens have been sprinkled with water since the Edo period to keep the environment cool. Meanwhile, devices are now in use that distribute a fine spray – in the Chinese city of Chongqing, for example. At bus stops, water cooled to 5 to 7°C is sprayed to cool the surroundings as well as those waiting. With these solutions it is of course important to bear in mind that water is sometimes in short supply, especially during heat waves.

LET THE WIND BLOW

We all know that the wind has a cooling effect. However, in many cities it is virtually stopped in its tracks by the building layout. Stuttgart in southern Germany suffers particularly from summer heat and smog due to its location in a basin. In order to channel the cooler air from the surrounding hills into the city, the city has so-called ventilation corridors – wide, tree-lined streets that extend through the city and act as “wind channels”. In addition, no new buildings may be built on certain hills, so that the air can continue to circulate as freely as possible. The principle works well, and Beijing, for example, is considering an adaptation, taking account of local wind patterns, of course. A fresh breeze is also very welcome in Abu Dhabi, given the prevailing temperatures. In the model desert city of Masdar City, an almost 50-meter-high wind tower, among other things, provides cooling. It “captures” the cooler wind at height and feeds it through the streets like a kind of large air conditioner. Thanks to this and other measures, it is possible that, despite temperatures in the surrounding desert of 35°C, the prevailing temperature in the city itself is only 20°C.

And in the next part of our series City of the Future: Why short distances are important for quality of life and how this idea is shaping urban planning in Melbourne. 

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