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City Heat: preparing for urban heat waves

Urbanisation is said to be one of the reasons why built-up areas throughout Europe are feeling the burn, with asphalt surfaces retaining heat far longer than natural terrain Urbanisation is said to be one of the reasons why built-up areas throughout Europe are feeling the burn, with asphalt surfaces retaining heat far longer than natural terrain Christian Vinces
31 Oct
Deadly heat waves could become more frequent in cities thanks to a combination of urbanisation and climate change

Research by climatologists at the University of Ghent finds that heat stress from heat waves will hit cities harder than the countryside.

‘A heat wave is a period of at least three consecutive days with a maximum temperature of more than 30ºC and a minimum temperature of more than 18ºC,’ explains Hendrik Wouters, climatologist at the University of Ghent. Belgian cities, which provided the case studies for Wouters’ research, were predicted to experience an increase in the annual number of heat wave days from 6 to 17 by the middle of the century.

As well as the frequency, the intensity of these heat wave days were predicted to increase. ‘The combination makes heat stress twice as likely for urbanites as for rural residents,’ says Wouters, adding that if these trends continue, heat waves could become ‘the most deadly kind of natural disaster in the future’.

The so-called urban heat island effect is responsible for the extra heat being felt by cities. By comparison, only seven heat wave days were predicted for areas in the Belgian countryside. ‘Stone and concrete convert more solar energy into heat, retaining it for longer,’ explains Wouters. This is felt mainly at night as surfaces continue to radiate heat even after the sun goes down, preventing the air from cooling for the next day.

‘The substantial presence of human and industrial activities also generate heat and there are fewer plants or water surfaces to provide cooling,’ Wouters adds. He warns that urban spaces with limited access to green areas will experience higher mortality rates, reduced work performance, and result in higher energy consumption.

‘On the other hand, our study tells us that it’s not only climate change that influences the temperature,’ says Wouters, ‘it’s also urbanisation itself, which local governments can do something about.’ He recommends that more vegetation, water, shade and less paving would reduce the heat load of cities to partially compensate for the heat effect caused by global warming. Building upwards would also be a cooler solution than building outwards, as it would avoid increasing the surface area of asphalt and concrete further into the countryside.

This was published in the November 2017 edition of Geographical magazine.

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