Hot Time, Summer in the City: Who is at risk?

19 – 25 October marks the inaugural Global Climate Change Week (#GCCW). GCCW is a new initiative designed to encourage academics in all disciplines and countries to engage with their students and communities on climate change action and solutions. UCL IEDE, UCL-Energy, UCL ISR and UCL ISH academics and students will be holding events and blogging through the week to share thoughts and ideas for the future.

When asked what the recent focus of my research has been at conferences, networking events and other social occasions, I often get the same answer: “But is indoor overheating really a problem in the UK?” or, if the conversation is taking place on one of those drizzly autumn London days: “I wouldn’t mind it being a little warmer to be honest!”

Cold temperatures and winter fuel poverty are currently the main concern in heating-dominated countries, such as the UK, and are projected to remain a major issue by at least the middle of the century. Cold-related mortality rates in the UK currently exceed the corresponding figures of heat-related mortality by an order of magnitude. However, as our climate is changing due to anthropogenic global warming, we will experience wetter, windier winters and hotter, drier summers in the coming decades, and we will need to prepare for changing weather patterns.

An anonymous writer in 1928 noted that “London’s annual heat wave is always forgotten by the next year. According to Londoners it rains every day of the year – except when there is a fog. But there are some hot days…” Coming back to this century, whilst the media reaction to summer hot spells warning us for ‘barbeque summers’ may be sometimes exaggerated, the frequency and severity of extreme heat events have appreciably increased in mid-latitude countries in recent decades. Heat waves like the ones experienced in France and parts of the UK in 2003 and 2006 have caused both deaths and economic losses. According to current climate change projections, temperatures like the ones recorded during the 2003 heat wave will become common by the middle of the century and this will lead to a greater risk of overheating in buildings, as highlighted by the recent Zero Carbon Hub Tackling Overheating in Buildings project and the Committee for Climate Change 2015 Progress Report to Parliament.

Part of the problem is the fact that the UK building stock and infrastructure are unprepared to cope with extreme heat. British homes were designed to capture solar heat gains in the daytime and limit heat losses whereas buildings in warmer countries (e.g. examples of traditional Mediterranean architecture) aim to do the exact opposite.

Who is more vulnerable to heat? Over prolonged periods, heat-related thermal discomfort may lead to serious health impacts for individuals. It can also cause sleep loss which may contribute to health risks for the person concerned and for others, as well as loss of work productivity. With regard to heat-related mortality, epidemiological evidence suggests that the elderly, the chronically ill and the socially isolated are more severely affected. But income might also be a modifying factor as the fuel poor might not have access to cooler spaces, or the means to adjust their immediate environment by purchasing a cooling device.

And where are people more vulnerable? Although this varies across geographic regions, studies from the 2003 and 2006 heat waves have indicated that people living in urban areas are likely to be more at risk. Overheating is likely to be exacerbated in cities due to the heat island effect, a term used to describe the phenomenon of temperatures in urban areas being systematically higher than temperatures in their rural surroundings. Importantly, heat islands are more pronounced at night. As a result, the potential to cool down urban buildings through night time ventilation might be limited during a heat wave. In addition, people living in cities might not be able to open windows due to concerns over privacy, security, safety of small children and pets, outdoor air pollution and noise. Highly exposed types like the top floors of purpose-built flats and bungalows are more prone to overheating.

Identifying areas where heat risk mitigation interventions should be prioritised is, therefore, an essential part of public seasonal health policy. Our team recently developed a method to identify ‘hot spots’ of heat risk in London by overlaying a set of heat vulnerability risk factors across the city map (location within the heat island, building characteristics and resident age).