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Removing reflective surfaces, increasing natural shade and harnessing the power of sewage are all options to limit the heat island effect – but progress will stall without collaboration and political boldness

Below a cloudless, blueberry-blue sky, where the sun blazes fiercely and gleams from London landmarks, a multi-person mass of liquifying limbs smoulders. The caption for Zoom Rockman’s Private Eye cartoon reads: “I love London; it’s such a melting pot.”

But few people were laughing when, on 19 July, the UK temperature exceeded 40C for the first time, according to the Met Office, and the city’s infrastructure melted – literally. Half of the six areas to surpass that level were in and around the capital: St James’s Park, Kew Gardens and Northolt. 

With global warming an increasingly hot topic and residents figuratively melting, the heat is being turned up on politicians, planners and other key stakeholders to keep cities cool.

The way our cities have been designed is no longer appropriate for modern times

Just days after the record high temperature, the mayor of London, Sadiq Khan, loosened purse strings. He awarded £2.85m from the Green and Healthy Streets fund to 19 projects, including rain gardens, tree pits and sustainable drainage areas. Further, a £1m grant will support “innovative and exemplary projects” on the Transport for London Road Network, and £150,000 was released to improve walking routes connecting green spaces.

“We cannot shy away from it: the climate crisis is on our doorstep,” wrote Khan on LinkedIn in early August, announcing the funding decisions. “We’re taking action before time runs out and investing £4m … to make London more resilient to heatwaves.” 

He added: “Working with London boroughs and TfL, these projects will make London more resilient against extreme weather, plus make our streets more green and pleasant for Londoners. It’s a win-win.”

Collaboration and long-term planning are paramount to reducing the impact of extreme heat in cities. And investing in innovative technology solutions can accelerate the virtuous circle to which Khan alluded.

Beware the heat island effect

Indeed, embracing an approach to building that keeps nature in mind, rather than seeking to dominate it, will lead to better urban spaces for both people and the planet. So says Chris Bennett, co-founder and managing director of sustainability services at Evora Global, a London-headquartered real asset consultancy. 

“Our urban environments are dominated by densely grouped buildings made of reflective materials creating a ‘heat island effect’,” he explains. “This is why it’s often hotter in cities than rural areas.”

Bennett believes simple tech and nature-based solutions will make a big difference. “Reducing hard reflective surfaces such as road pavements would help to lower temperatures,” he says. “Re-engineering pavements to be permeable blocks, instead of concrete or Tarmac, would allow water to flow through the pavers in wet conditions and evaporate when the heat rises, creating a cooling effect.

“Also, incorporating trees and plants reduces the reflective nature of the streetscape, provides habitats for wildlife and offers shelter from harsh ultraviolet radiation and solar heat during summer.” 

Ironically, it is partly due to technology that we find ourselves in this sticky situation. Since the 1960s, planes, trains and automobiles have heavily contributed to global warming, and cities have evolved to accommodate gas-guzzling vehicles. So it’s time for a swift U-turn, says Bennett.

“In London, we are blessed with many urban parks and squares created by the Georgians and Victorians. But many of the city’s trees have been lost to provide car parking spaces,” he says. “Planting street trees will increase protection from the climate by reducing heat stress and limiting the degradation of the urban construction materials, making buildings last longer.”

Appropriate early-stage design 

Another expert urging cross-industry action is Håvard Haukeland, co-founder of Spacemaker AI. His company provides early-stage analysis for architects and urban planners and enables buildings to be designed with the local microclimate in mind to minimise urban heat islands. 

“The way our cities have been designed is no longer appropriate for modern times,” he says. “As temperatures rise due to climate change, the design choices previously made either due to tradition or practical considerations around energy efficiency are making our cities even hotter.”

Haukeland contends that architects and urban planners need to step up. “While solutions such as additional greenery or reflective roofs can help keep things a little cooler, the reality is the most impactful solutions are done at the early stage when new developments are being built,” he continues. 

Design adaptations – including rotating structures to “open up” for wind or even altering the shape of a building – can make “the biggest difference to microclimates”, Haukeland says. Although these solutions are “much harder to implement”, he asserts that designers “must consider microclimates at the outset”.

That may be so, but how should cities upgrade older infrastructure to make it better able to withstand extreme heat? “This is the critical question when you think about the number of heritage and older buildings we have in the UK,” says Ian Ellis, smart buildings expert at Siemens Smart Infrastructure. Sensors that capture data and allow deep analysis of how people use buildings – especially as hybrid-working strategies are firmed up – could be the answer.

“This technology is already being used in buildings across the UK, where it can provide usage data on the flow of people through a building, where they congregate and how they use it,” says Ellis. “Data like this provides invaluable insights in optimising other technologies like heating and ventilation systems.”

Sensors, shade and sewage

Sebastian Peck, a partner at Kompas – an early-stage venture capital firm focused on transforming the built environment – lists some pioneering solutions to cool cities. “Vertical Field is installing sensor-controlled smart planters to purify the air from carbon dioxide and, when mounted to buildings, they help insulate them from the sun,” he says. 

Meanwhile, Lumiweave has developed an innovative fabric that provides shade during the day and harvests the sun’s energy to illuminate itself and its surroundings at night. “And,” Peck continues, “TreeTube has a patented modular system of tubes that lets tree roots grow safely in a tunnel without disrupting their surroundings.”

Peter Hogg, UK cities director at global design, engineering and management consulting company Arcadis, offers a more practical but pongy example. “We are looking at using effluent as a heat exchanger that allows you to extract energy used for cooling with minimal carbon impact. Imagine the potential in a city the size of London, which houses 8.5 million people.”

At this stage, no idea should be flushed away. And while there is much work to do, the willingness to force change – and think up unusual solutions – is finally evident, suggests Hogg. “The pandemic was a watershed,” he says. “There is a collective understanding that this situation must be addressed. Today, building plans that fail to consider the climate challenge won’t attract investors. 

“Before the coronavirus crisis, you would have to go to the Netherlands or the Nordics to find people taking this seriously. We now acknowledge that significant behavioural and structural changes are required, and quickly.”

Peck concludes that enough technologies are available to cool cities but to harness their power, leaders must be bold. 

“The difficulty is that urban planners need to rethink our cities, make them greener and ensure water is put to good use,” he says. “But changing and building back existing urban infrastructure is expensive. Cities are under pressure to demonstrate to the public that their scarce resources are well invested.

“In other words, cooling our cities is not a technological challenge, but a political one.”

This article was first published in Raconteur’s Smart Cities report in August 2022