London School of Hygiene & Tropical Medicine

According to a joint heat-health warning issued by the UK Health Security Agency (UKHSA) and Met Office, parts of the UK are forecast to experience heatwave conditions as temperatures rise over the next few days in July. 

A heatwave is defined by the UK Met Office as periods of at least three consecutive days in which the regional health-related temperature threshold is met or exceeded.

Prolonged high temperatures can have a profound effect on the body. In summer 2022, temperatures exceeded 40°C for the first time in England and an estimated 2,985 deaths were associated with five distinct periods of heat, peaking between 17-19 July.

Periods of extreme weather can also significantly impact healthcare systems, with an increase in calls to services, cancellations of surgeries and in some cases, power blackouts or complete failures of energy infrastructure.

As the global climate continues to change, it is expected that heatwaves will increase in frequency, duration and intensity around the world, although such shifts will vary across regions.

Researchers at the London School of Hygiene & Tropical Medicine (LSHTM) are working with partners, including the UKHSA, to better identify those most at risk and understand what measures, messaging and precautions could be introduced to protect communities.

Explaining the health risks associated with extreme heat, Associate Professor Sari Kovats, based at LSHTM’s NIHR Health Protection Unit in Environmental Change and Health, said:

“Extreme temperatures override our bodies’ ability to thermoregulate. Heat can put a strain on our cardiovascular and other systems, and the stress caused can lead to premature mortality. Heat illness can also occur through damage to organs because of increased body temperature, dehydration, heat cramps and exhaustion. 

“Both environmental and social factors influence the risk of dying in a heatwave. People of older ages and those living with pre-existing health conditions, such as diabetes, are at significant risk, as well as people with limited mobility or with mental illness who may be less able to take action to protect themselves.

“Heat is also associated with increased risk of pre-term birth and still-birth. Researchers at LSHTM in the CHAMNHA project, which looks at data from sub-Saharan Africa, have found that high seasonal temperatures can increase the risk of maternal complications and also interfere with infant care.

“It’s important to follow public health guidance, such as keeping hydrated and avoiding unnecessary travel, outdoor exercise or strenuous activities, to reduce health risks during a heatwave. People at highest risk must also have access to help where needed and those that care for them should be well informed.”

Explaining how heatwaves and extreme weather events are measured, Assistant Professor Malcolm Mistry, based at LSHTM’s Environment and Health Modelling Lab, said:

“Our climate system is inherently chaotic and forecasting the weather beyond two weeks is still very challenging, even for state-of-the-art forecast models. Air temperature is the most widely used surface measurement taken by observatories and weather stations. Observations taken by satellites over the past five decades have also enabled monitoring of weather even in parts of the world where ground stations are sparse or non-existent. 

“It’s important to emphasise that heatwaves themselves, like many other extreme weather events, are not unusual in any given year. This is because our planet’s climate system has a ‘natural variability’. In order to determine whether the weather we’re experiencing is unusual, we use historical records for a specific region over a long period of time and see if the current events are more frequent or stronger in magnitude than the ‘normal’.

“The consensus within the climate modelling community is that the frequency, magnitude and duration of most extreme weather events are expected to increase globally in a warming climate. However, there remains uncertainties in some estimates, such as for heavy rainfall, with some regions of the world projected to experience drier conditions than others.

“From a long-term perspective, society and policy makers need to take measures to increase our resilience to extreme temperature and other weather events, and we need to have plans in place to support our most vulnerable when we see precautionary warnings being issued. Moreover, the ‘Early Warning for All’ initiative of the UN is a stark reminder to us that not every region in the world is equipped to forecast or disseminate such warnings.

“Green spaces, better quality housing, temporary cooling centres in heat-prone areas and portable relief centres are all examples of measures that could be adopted to help protect communities. Large-scale sporting events, such as the summer Olympics, as well as outdoor public events such as the Glastonbury music festival, may also need rescheduling outside peak summer months to protect attendees from the potential effects of extreme heat.”

Further information on heat-health warnings in the UK can be found on the Met Office website.