Heatwaves: Heat and hot weather lasting days with significant societal impact
Heatwaves: Dangerous natural hazards killing 489,000 people annually worldwide
Dr. Sophie Mercier (Paris Emergency Medicine Director) will never forget the summer of 2003. The morgue overflowed. Hospitals ran out of beds. Bodies piled up in refrigerated trucks. Elderly residents died alone in sweltering apartments. Within two weeks, France lost 15,000 citizens to extreme heat.
“We were completely unprepared,” Dr. Mercier recalled, voice still heavy with grief two decades later. “Temperatures reached 40°C for days. Air conditioning was rare. People didn’t understand the danger. They thought, ‘It’s just hot weather.’ But heat kills—silently, quickly, mercilessly.”
The most devastating part haunted her: “Most deaths were preventable. Simple interventions—cooling centers, hydration stations, welfare checks on vulnerable people, public awareness campaigns—could have saved thousands of lives. We learned the hardest way possible that heatwaves are deadly natural disasters requiring emergency response systems just like earthquakes or floods.”
That summer, Europe lost more than 70,000 people to heat. According to WHO, heatwaves, or heat and hot weather that can last for several days, can have a significant impact on society, including a rise in heat-related deaths. Heatwaves are among the most dangerous of natural hazards, but rarely receive adequate attention because their death tolls and destruction are not always immediately obvious.
A study found that from 2000–2019 approximately 489,000 heat-related deaths occurred each year, including more than 70,000 who died during the 2003 heatwave in Europe. For more on climate-related health impacts, see our articles on climate change and extreme weather at ObserverVoice.com.
Growing Threat from Climate Change
Population exposure to heat is increasing due to climate change. Globally, extreme temperature events are observed to be increasing in their frequency, duration, and magnitude. Between 2000 and 2016, the number of people exposed to heatwaves increased by around 125 million.
While the effects of heat may be exacerbated in cities, due to the urban heat island (UHI) effect, the livelihoods and well-being of non-urban communities can also be severely disrupted during and after periods of unusually hot weather. Heatwaves can burden health and emergency services and also increase strain on water, energy and transportation resulting in power shortages or even blackouts. Food and livelihood security may also be strained if people lose their crops or livestock due to extreme heat.
WHO provides fact sheets on climate change and health and heat and health. Related topics include air pollution, occupational health, ultraviolet radiation, and water, sanitation and hygiene (WASH). For more on environmental health threats, see our article on climate adaptation at ObserverVoice.com.
Severe Health Impacts
The health impact of a heatwave depends on the intensity and duration of the temperature, the acclimatization and adaptation of the population, and the infrastructure and preparedness. Exposure to heat causes severe symptoms, such as heat exhaustion and heat stroke – a condition which causes faintness, as well as dry, warm skin, due to the inability of the body to control high temperatures.
Other symptoms include swelling in the lower limbs, heat rash on the neck, cramps, headache, irritability, lethargy and weakness. Heat can cause severe dehydration, acute cerebrovascular accidents and contribute to thrombogenesis (blood clots). People with chronic diseases that take daily medications have a greater risk of complications and death during a heatwave, as do older people and children.
Reactions to heat depends on each person’s ability to adapt and serious effects can appear suddenly. This is why it is important to pay attention to the alerts and recommendations of local authorities. WHO provides Q&A on How do I protect myself in heatwave?, WHO’s role in Humanitarian Health Action, and What is WHO’s role in emergencies?.
WHO’s Comprehensive Response
The magnitude of human costs from heatwaves can be reduced if adequate emergency prevention, preparedness, response and recovery measures are implemented in a sustainable and timely manner. WHO works with the health sector to strengthen governance, preparedness and response to heatwaves, by developing contingency plans that map the risks, vulnerable populations, available capacities and resources.
These plans also include early warning systems and ensure vulnerable populations, such as those in health facilities, nursing homes and schools have adequate provision of cooling equipment. As the health cluster lead for global emergencies, WHO works with partners to respond to: ensure appropriate food supplementation; restore primary care services, like immunization, child and maternal health, and mental health; assemble mobile health teams and outreach; conduct epidemic surveillance, early warning and response; call for emergency funding to support health action.
WHO’s Health Emergencies Programme coordinates comprehensive emergency response. WHO provides Disaster statistics through UNDRR and Latest Disease Outbreak News (DONs). WHO’s technical work includes Climate Change initiatives and Managing health risks during mass gatherings.
Essential Publications and Resources
January 2011 WHO published Public health advice on preventing health effects of heat explaining that the most important actions to take during a heat-wave are: to avoid or reduce exposure, to communicate risks effectively, to take particular care of vulnerable populations. December 2004 WHO published Heat-waves: risks and responses documenting that high air temperatures can affect human health and lead to additional deaths even under current climatic conditions.
WHO created comprehensive infographics including Keep your home cool during a heatwave, During a heatwave, help others who suffer from the heat, Throughout a heatwave, keep yourself cool and hydrated, and If you feel unwell during a heatwave providing practical guidance for public protection.
International Commitment to Heat Preparedness
World Health Assembly passed WHA 64.10 on Strengthening national health emergency and disaster management capacities and resilience of health systems recognizing that heatwaves require coordinated emergency response systems. This resolution establishes framework for countries to develop comprehensive heat emergency preparedness plans.
Dr. Mercier now leads France’s national heat-health warning system. “After 2003, France transformed its approach completely. We established color-coded heat alerts—green, yellow, orange, red. We created heat emergency plans for every municipality. We trained health workers to recognize heat illness early. We opened thousands of air-conditioned cooling centers. We conducted daily welfare checks on isolated elderly people during heat alerts.”
The results speak for themselves. “In 2019, we experienced temperatures even higher than 2003—over 45°C in some regions. But deaths dropped 90% compared to 2003. Our heat-health warning system saved thousands of lives. Early warning, community preparedness, targeted interventions—these simple measures work.”
“Heatwaves will only get worse with climate change,” Dr. Mercier warned. “Every country needs heat emergency systems now. Not after a catastrophic death toll like we experienced. The science is clear. The solutions exist. The question is: how many people must die before governments act? We learned from tragedy. Other countries can learn from our experience without paying the same terrible price.”
For more information, visit WHO’s heatwaves topic page or explore related content at ObserverVoice.com.
Frequently Asked Questions (FAQs)
Heatwaves, or heat and hot weather that can last for several days, can have significant impact on society, including rise in heat-related deaths. Heatwaves are among most dangerous of natural hazards, but rarely receive adequate attention because their death tolls and destruction are not always immediately obvious. A study found that from 2000–2019 approximately 489,000 heat-related deaths occurred each year, including more than 70,000 who died during 2003 heatwave in Europe. Population exposure to heat is increasing due to climate change. Globally, extreme temperature events are observed to be increasing in their frequency, duration, and magnitude. Between 2000 and 2016, number of people exposed to heatwaves increased by around 125 million. Heatwaves can burden health and emergency services and also increase strain on water, energy and transportation resulting in power shortages or even blackouts. Food and livelihood security may also be strained. Related: climate change, air pollution. WHO provides fact sheets on heat and health.
Health impact of heatwave depends on intensity and duration of temperature, acclimatization and adaptation of population, and infrastructure and preparedness. Exposure to heat causes severe symptoms, such as heat exhaustion and heat stroke – condition which causes faintness, as well as dry, warm skin, due to inability of body to control high temperatures. Other symptoms include swelling in lower limbs, heat rash on neck, cramps, headache, irritability, lethargy and weakness. Heat can cause severe dehydration, acute cerebrovascular accidents and contribute to thrombogenesis (blood clots). People with chronic diseases that take daily medications have greater risk of complications and death during heatwave, as do older people and children. Reactions to heat depends on each person’s ability to adapt and serious effects can appear suddenly. WHO provides Q&A on How do I protect myself in heatwave?. Related: occupational health, ultraviolet radiation.
Magnitude of human costs from heatwaves can be reduced if adequate emergency prevention, preparedness, response and recovery measures are implemented in sustainable and timely manner. WHO works with health sector to strengthen governance, preparedness and response to heatwaves, by developing contingency plans that map risks, vulnerable populations, available capacities and resources. These plans also include early warning systems and ensure vulnerable populations, such as those in health facilities, nursing homes and schools have adequate provision of cooling equipment. As health cluster lead for global emergencies, WHO works with partners to: ensure appropriate food supplementation; restore primary care services, like immunization, child and maternal health, and mental health; assemble mobile health teams and outreach; conduct epidemic surveillance, early warning and response; call for emergency funding to support health action. WHO’s Health Emergencies Programme coordinates response. WHO provides Latest Disease Outbreak News.
January 2011 WHO published Public health advice on preventing health effects of heat explaining most important actions to take during heat-wave are: to avoid or reduce exposure, to communicate risks effectively, to take particular care of vulnerable populations. December 2004 WHO published Heat-waves: risks and responses documenting that high air temperatures can affect human health and lead to additional deaths even under current climatic conditions. WHO created infographics: Keep your home cool during heatwave, During heatwave, help others who suffer from heat, Throughout heatwave, keep yourself cool and hydrated, If you feel unwell during heatwave. WHO provides fact sheets on climate change and health. WHO coordinates Managing health risks during mass gatherings.
World Health Assembly passed WHA 64.10 on Strengthening national health emergency and disaster management capacities and resilience of health systems recognizing that heatwaves require coordinated emergency response systems. While effects of heat may be exacerbated in cities, due to urban heat island (UHI) effect, livelihoods and well-being of non-urban communities can also be severely disrupted during and after periods of unusually hot weather. Population exposure to heat is increasing due to climate change. Globally, extreme temperature events are observed to be increasing in their frequency, duration, and magnitude. WHO’s Climate Change initiatives coordinate technical work. WHO provides Q&A on WHO’s role in Humanitarian Health Action and What is WHO’s role in emergencies?. Related: water, sanitation and hygiene (WASH).
- WHO Heatwaves Topic Page
- WHO Fact Sheet: Heat and Health
- Public Health Advice on Preventing Health Effects of Heat
- Q&A: How Do I Protect Myself in Heatwave?
- WHA Resolution 64.10: Strengthening Health Emergency Management
Disclaimer: This article is an adaptation of publicly available information from WHO’s Heatwaves
health topic page (WHO, Geneva. Licence: CC BYNC-SA 3.0 IGO). WHO is not responsible for the
content or accuracy of this adaptation. This content is for informational and educational purposes
only and does not constitute medical advice. ObserverVoice.com is a news and information platform
— not a healthcare provider.
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