Heatwaves

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.

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.

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.

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.