Heatwaves have an amplified impact in cities, causing disproportionate discomfort, health risks and mortality rates – an effect that’s expected to worsen as temperatures rise, according to new research. But the scientists also find taking measures to adapt cities to higher temperatures can reduce heat-related deaths by between 32 and 69 per cent.

The Intergovernmental Panel on Climate Change (IPCC)’s projections of future climate change suggest it’s likely heatwaves may become longer and/or more frequent by the end of the century. That’s expected to make baking city summers even more unbearable.

Relatively little research has been done to find out how effective attempts to adapt to hotter temperatures will be.

In the new study, researchers from a group of UK universities set out to give a risk assessment of how higher temperatures will affect city-dwellers – examining projections of urban temperatures into the future, as well as predictions of how populations will change.

Focusing on the Greater London region and its surrounds, the new paper, out today in the journal Climatic Change, then sets out how adaptation options could ease the damage and avoid some heat-related deaths.

Rising temperatures, health and cities

In the UK, temperatures are expected to rise more in the south east than the rest of the country. The UK government’s CP09 climate projections predict the average daily maximum temperature in summer will rise by between 1.2 and 7.3 degrees Celsius, by the 2050s.

That’s likely to have a significant effect on society, the paper says. There’s a limit to how much heat even healthy adults can tolerate. And beyond that threshold, people are more likely to suffer from heat exhaustion and heat stroke, which can lead to death. Babies, children and the elderly are particularly vulnerable, it adds.

Other heat-related health problems include sunburn and breathing problems from poor-quality air. The buildings we live and work in can make this effect worse. Certain kinds of buildings can amplify outside temperatures.

Studies suggest the way insulation is installed, for example, has a significant effect on heat inside buildings. Meanwhile, blocks of flats tend to be hotter in general than detached buildings.

Cities tend to be hotter than the countryside because moist, permeable vegetation is replaced by a dry, impermeable concrete jungle. The so-called urban heat island effect (UHI) means extreme temperatures in cities are likely to be higher.

And it’s a problem, given how many activities, people and assets are concentrated in places like London. After a hot day, night temperatures in the city can be up to 12 degrees higher than in the country.

Mapping the changes

There are many factors at play here. The researchers say it was important for their modelling to take into account the frequency and severity of heat effects, the UHI effect and the vulnerability of different sections of the population, as well as socio-economic changes and the potential effectiveness of adaptation efforts. They created a modelling framework designed to take these aspects into account across the Greater London area.

According to epidemiological studies, temperatures above a mean daily threshold of 20 degrees Celsius, there is an almost immediate average increase in mortality rates of 3.1 per cent per one degree rise.

To examine the effect of adaptation measures, the researchers adjusted that threshold upwards by one and two degrees Celsius. That was intended to simulate decreasing indoor or outdoor temperatures – through using air conditioning, for example – or people becoming better prepared for the heat by changing their habits.

By the 2050s, under a high emissions scenario, climate change and changes to urban land use could see 842 additional heat-related deaths in Greater London, the paper says.

And by the 2030s, the researchers found between 59 and 76 per cent of people living in flats and 24 to 29 per cent of residents in detached houses could be affected by discomfort from the heat.

That’s expected to increase if green spaces continue to shrink and heat emissions from towns carry on rising.

But by adapting to higher temperatures, it’s possible to reduce the number of heat-related deaths, as the chart below from the paper shows.

If the threshold at which deaths start to rise is delayed by one degree, the researchers predict heat-related deaths could fall by between 32 and 42 per cent. Raise that threshold to two degrees and the cut in deaths increases by between 57 and 69 per cent.

Adapting buildings and changing habits can also make life generally pleasanter in our homes and offices, reducing the level at which we start to feel uncomfortable from the heat.

Adapting to the future

Summer in the city looks set to become hotter – and unless urban policymakers counteract the effects of extreme temperatures, that could mean a higher death toll.

As the IPCC’s forthcoming report on the impacts of climate change will explore, heat-related health problems are only one of many public health considerations to take into account as climate change morphs the environment we live in.

What’s more, it’s important to realise adaptation is only about ways to cope with the warming we’ve already locked ourselves into through past emissions. Emissions need to come down to limit temperature rise beyond that which we can no longer avoid.

But the study is an important first step in quantifying the kind of savings a joined-up adaptation plan spanning areas such as urban planning and healthcare could afford Londoners.

Main image: Creative Commons 2010.