Not a paradise in the sun: the growing danger of urban heat islands

It might be a bit premature to start worrying about #heatwaves in western #cities just after the spring equinox but, based on recent history, the role that so-called urban heat islands (#UHI) play in making cities #unsustainably hot will be news before long.

Given the seemingly ceaseless rain that Europe — and the UK in particular — endured in February, it’s hard to remember just how hot conditions were in cities just two years ago. According to Copernicus, the EU’s earth observation unit, 2022 was the second hottest year on record in Europe with summer temperatures in Europe at 1.4 deg C above average.

According to one academic calculation, soaring temperatures in that year may have been responsible for 70,000 excess deaths in Europe. In Italy, the authorities issued red extreme heat warnings for 16 cities across the country. In the UK, a wildfire in Wennington, east London destroyed almost 20 houses.

A study into more than 850 European cities with populations of more than 50,000 — and which found London and Paris as recording the most heat-related deaths over the 20 years to end of 2019 — identified urban heat islands as a contributory cause.

This phenomenon is created by the dark-coloured, human-made materials such as bitumen used on roads and in buildings absorbing and storing heat during the day which is then released at night, helping to keep temperatures uncomfortably hot during the night time hours. Residents experience higher temperatures than surrounding rural areas, thus the phenomenon’s name. Meanwhile urbanisation often leads to the loss of green spaces that would offset that impact by cooling the city.

Climate injustice

This climate impact is also one of environmental injustice. According to the World Bank, low-income communities, neighbourhoods bereft of green spaces and other marginalised populations bear a “disproportionate burden” of the economic costs associated with urban heat. It also creates a climate doom loop as the extra energy needed to power air conditioning needed to make homes and workplaces inhabitable adds to greenhouse gas emissions that cause climate change.

Many cities are not prepared to cope with a much warmer climate and will need help to harness both financial and knowledge resources to enact solutions to help cool their urban environments.

One city that has been leading the challenge is Singapore, whose Green Plan 2030 has set “concrete targets” (no pun intended, presumably) to plant 1 million extra trees, develop over 130 hectares of new parks, and ensure every household is within a 10-minute walk of a park.

Last year it hosted a “deep-dive on urban heat” as part of the World Bank’s Global Platform for Sustainable Cities. It focused on incorporating climate adaptation and cooling solutions into planning, as well as policy and regulatory frameworks for implementation and approaches to financing.

The good news is that the debate is at least underway. Earlier this year, parliamentarians in London, who found that urban temperatures can be up to 8 deg C warmer than surrounding rural areas, recommended nature-based solutions such as parks, trees, water bodies and green infrastructure — including green roofs —as ways to deliver significant cooling effects.

As city families start to plan their holidays to an island in the sun, they should bear in mind that home could soon be a less pleasant island of its own.