Hot Town, Summer in the City

It’s been a hot summer across Europe and much of North America, and this has generated lots of discussion about the impact of heat on our health. Cities in particular have been under the spotlight as heat is intensified through the urban heat island (UHI) effect which causes cities to be significantly hotter than surrounding rural areas.

Heatwaves are  happening more and lasting longer, with measurable impacts on our health and wellbeing. Exposure to excessive heat has been linked to increased mortality, accelerated ageing, and reduced economic productivity.

Martin Prince-Parrott, author of Urban Healthonomics, examines urban heating as he reframes essentials of the urban experience like housing, infrastructure and public spaces. His research shows that

·      Over the next three decades, 75% of the world’s majorcities – 520 in total – will undergo a profound transition into unfamiliar climates. By 2050, over 970 cities will experience average summertime highs of 35 ̊C (95°F) – nearly treble the current count of 354 cities experiencing these temperatures. This surge in scorching temperatures will expose urban populations to unprecedented levels of heat, skyrocketing by 800% to reach 1.6 billion people by the middle of the century.

·      In 2021 the equivalent of each person on Earth lost 139 hours (3.5 weeks) of productive work hours due to extreme heat.

·      Heatwaves are linked to a 20% heightened risk of hospital admissions for pneumonia, particularly during prolonged or intense heatwaves, among people aged 75 and older.

·      Heatwaves propelled by climate change have cost the global economy at least $16 trillion since the early 1990s (equating to approximately $484,000,000,000 per annum).

We all experience urban heat differently, and this summer I’ve experienced it in four different cities. It’s given me some perspective on what cities do well and what they could do better to make them more habitable during periods of prolonged and intense heat.

In addition to London where I live, I spent time in three other cities experiencing extreme heat.

1.   Paris

Paris in early July was punishingly hot. Two things offered great relief: the Plane tree and the Paris plages.

Plane trees are a hybrid species known for their resistance to pollution, distinctive mottled bark, and large, shade-providing canopies. They are everywhere – and have been a  mainstay of Paris since Napolean ordered their planting to protect his troops from heat while marching - and nowhere in such scale and scope as the Bois de Bologne  where I camped on the banks of the Seine. I think I was in the coolest place in Paris. 

The Paris Plages are an outcome of the city’s impressive efforts to clean up the Seine for swimming , Accelerated for last summer’s Olympics by Paris Mayor Anne Hidalgo, the city opened three Paris swimming sites and several more outside the city in July. I swam in two places – Notre Dame and Val-de-Marne, and both were lovely.

the magnificent Paris Plane tree

a swim in the Marne

2.   Lisbon

Lisbon in late July was also punishingly hot, but it benefits from breezes from the Atlantic that are felt on the banks of the Tagus river, where boat excursions are available in many forms and durations throughout the day, accessed at several points along the river. There is also easy access to beaches – Cascais and Estoril are within half an hour by public transport and with a range of publicly accessible beaches which are also sheltered and safe. I was impressed with the mix of people on the beaches, both generationally and ethnically. Very different to the Algarve in the south of Portugal where beaches are more segregated.

Culturally the city is outdoor-based with open-air cafes and bars, particularly vibrant in the late evenings when it’s cooler. Buildings, like most on the Iberian peninsula are designed for heat with shutters, shade and balconies.

a beach at Cascais, 20 minutes from Lisbon centre

3. Boston  

Boston in August is hot and very humid, but its location

on the Atlantic coast with its own harbour and harbour islands offers an easy escape from the heat. Ferries bring you out to the islands – which collectively are a state park.

As most visitors to the US know, AC rules in homes, cars, offices, shopping malls and restaurants. Any building without AC is considered primitive and while there is no specific law in Massachusetts that mandates the installation or use of air conditioning in residential or commercial buildings, it’s hard to find a building without it.

Boston excels at outdoor events in the summer, and I attended several – Shakespeare on Boston Common, two concerts at the Hatch Shell on the Charles River Esplanade, and a jazz festival in Medford Square.

Swimming is accessible in the city at Pleasure Bay in South Boston (I highly recommend), a sheltered part of Boston Harbor designed by Frederick Law Olmstead. Fresh water swimming is available in the Mystic River Watershed, Crystal Lake in Newton and the Blue Hills Reservation, accessible by public transport.

view of Boston from Pleasure Bay

4.    London

Unlike Paris, Lisbon and Boston London is only now getting used to prolonged periods of heat, and its infrastructure reflects this. London’s offices, buildings and transport networks are seemingly more equipped to keep us warm in the winter than cool in the summer. And according to the CPRE,

London tends to get hotter than surrounding regions because the sun's rays are absorbed by building services instead of greenery and vegetation, and this radiation is then released into the air as heat, adding to soaring temperatures.

Not only is prolonged heat a new thing for Londoners it is also vastly unequal in its effects. A recent study published in the BMJ showed that elderly, females, ethnic minorities and those living in the most deprived areas all had increased risk of death during periods of heat.

On the positive side, London is slowly becoming a swimmable city. Its collection of outdoor lidos (including a proposed lido on the Thames) and swimming ponds are valuable assets. Some of us even swim in the Thames.

swimming in the Thames at Ham

Even with the heat-mitigating features I’ve mentioned, residents of each of these cities suffer in the heat.

Paris and London rank toward the top of European cities for heat-related deaths, while Lisbon performs better.  Boston performs comparatively well in North America, but is still impacted by extreme heat. Some of these outcomes reflect an ageing population and are also correlated with income. As

Ben Clarke, a climate scientist at Imperial College London and co-author of the European study commented,

“Heatwaves don’t leave a trail of destruction like wildfires or storms -- their impacts are mostly invisible but quietly devastating. A change of just 2 or 3C can mean the difference between life and death for thousands of people.”

So what can be done?

Urban Healthonomics author Martin Prince-Parrott puts forward several approaches to cooling cities during periods of extreme heat

·      Maximise shade – by introducing methods of self-shading and synthetic canopies

·      Improve urban breathability and airflow – through windcatchers and urban greening

·      District heating and cooling systems

·      Vapourwave – misting systems in public spaces

·      Communal cooling spaces

Making cities more swimmable is the mission of the Swimmable Cities Alliance, which presents another approach to living in increasingly hot cities. Then alliance is made up of 125 organisations across, 72 cities and towns, across 27 countries and is growing through the collective efforts of experts in urban swimming environment design, public mediation, community building, policy, safety, public health, waterway restoration and water quality.

A key tenet of the alliance is that swimming in urban waterways should be a right, ratified at the first Swimmable Cities summit held last month in Rotterdam. It was noted that in many cities public perception often lags behind reality, with lingering fears of dirty water and chemicals left by industry, and that swimming spots cluster in wealthier areas, or come with hidden costs.

The alliance is committed to ensuring that

“Every citizen should feel that urban waterways are theirs to experience and protect. Clean and safe urban waterways are not just environmental assets, they are vital spaces for connection, health and wellbeing.”

As autumn approaches and the days are getting cooler, Londoners will understandably be less concerned about heat mitigation measures. But I urge you to consider joining the Swimmable Cities Alliance, to read Martin’s book about Urban Healthonomics and to do everything you can to protect and augment the vital green spaces around you – they may one day save your life.

Clare Delmar

Listen to Locals

29 August 2025