Wildfires and heatwaves: Expert analysis on public health impact

How wildfires and heatwaves can affect physical and mental health

Wildfires and heatwaves, Dr van Daalen explains, “strain the cardiovascular system. This can lead to dehydration, heat exhaustion, heatstroke, kidney problems, and the worsening of existing heart and respiratory conditions.” They can also affect mental health, she adds: “Heat disrupts sleep, impairs concentration, and tends to worsen anxiety, depression, and existing mental health conditions.”

“Wildfires bring a different set of risks,” she explains. In addition to the immediate physical dangers such as burns, injury, and fast-moving, unpredictable fires that can make evacuation difficult, wildfire smoke “can travel much further than the fire itself, sometimes thousands of kilometres. It contains fine particulate matter, which we call ‘PM2.5’. These particles are roughly a fraction of the width of a human hair and bypass the body's usual defences, getting deep into the lungs and even into the bloodstream. They can cause breathing difficulties, asthma attacks, and increased cardiovascular risk, often in people who don't realise they’re being exposed at all.”

Dr van Daalen stresses that wildfires can also lead to mental health issues. Large-scale evacuations, such as those we are currently seeing in France and Spain, can combine fear, loss, and displacement, “which are well known drivers of anxiety, depression, and post-traumatic stress. They are interconnected public health challenges whose effects can continue long after temperatures fall or the flames are extinguished.”

Who is most vulnerable?

Ageing reduces the body’s ability to regulate temperature, Dr van Daalen says, adding: “Chronic conditions make both heat and smoke more dangerous, and some medications can also affect hydration, sweating, or cardiovascular function. Reduced mobility or social isolation can make it harder to evacuate or respond to warnings, too.” 

Pregnancy places extra demands on the cardiovascular system, she explains. “Extreme heat exposure has been linked to higher risk of preterm birth and low birth weight.” Infants and young children face different risks. “Their bodies regulate temperature less effectively, they can’t always communicate that they’re too hot, and because they breathe more air relative to their body size, they take in proportionally more smoke and pollutants than an adult would in the same environment.”

Outdoor workers and firefighters, people experiencing homelessness, people living in fire-prone areas, those in low-income households who may not be able to afford cooling mechanisms, and people with disabilities or those who are socially isolated are other people Dr van Daalen lists as some of the vulnerable groups. “Vulnerability is rarely down to one factor. Risks accumulate. It is this stacking of vulnerabilities that often determines who experiences the most serious health impacts.”

Scale of illness, hospitalisation and mortality

Heat is estimated to cause roughly “half a million deaths a year globally”, Dr van Daalen states, adding that in the last few years in Europe, “we've seen tens of thousands of heat deaths every summer.”

Dr van Daalen points to a recent meta-analysis covering over 124 million patients, which found consistent links between wildfire smoke and increased hospital admissions, ED visits, and all-cause mortality. “Importantly, that burden isn’t confined to the fire zone,” she says. “For example, smoke from the 2023 Canadian wildfires caused a measurable spike in asthma ED visits across the eastern US, hundreds of miles away.”

How public health systems can prepare for the future, including climate risk

When it comes to preparing for the current high temperatures, which Dr van Daalen acknowledges are being “driven by climate change”, she believes we need to integrate heat and wildfire risks into routine health planning, strengthening early warning and surveillance systems. “Health services also need clear surge plans for increases in respiratory, cardiovascular, kidney and mental health problems,” she says, alongside targeted support for vulnerable populations. Climate risk can also be built into everyday care. “For example, by reviewing medications and care plans for high-risk patients before summer or wildfire season begins, rather than waiting until they arrive in an emergency department.”

Dr van Daalen points to the need for dedicated wildfire warning systems. Wildfires can move much faster than people expect, especially in high winds. “Early evacuation warnings, and pre-planned routes for people who may need extra help evacuating, save lives.”Alongside, real-time air quality monitoring “can warn people when wildfire smoke exposure becomes dangerous, advising them to stay indoors or, if they must go outside, to use N95, P100 or FFP2 respirators.” 

Communities can reduce exposure through cooler and better-insulated housing, increased urban tree cover, accessible clean-air and cooling centres, resilient energy systems, reflective roofing and stronger protections for outdoor workers, Dr van Daalen suggests, pointing to how cities can play a role by providing accessible public cooling infrastructure. “Barcelona is a good example. After a severe heatwave in 2019, the city built a network of climate shelters, which were in the main libraries, community centres, museums, and shaded green spaces.” 

The message is loud and clear, Dr van Daalen says. “These are no longer once-in-a-generation disasters. The health systems that cope best will be those that treat climate adaptation as a core public health function - planned and funded with the same seriousness as vaccination programmes, disease surveillance and clean water.”