Heatwaves, periods of abnormally and uncomfortably hot and usually humid weather, are among the most dangerous natural hazards. Because of climate change, heatwaves are becoming increasingly frequent and intense, with 14 of the 15 warmest years on record all occurring in the 21st century. In 2003, the European heatwave resulted in deaths of more than 70 000 people.
This year, the trend is even more worrying. During May and June, heatwaves have already killed more than 2500 people in India and 1400 in Pakistan. Since June 27, many parts of Europe have been affected by a severe and unusually early heatwave. There have been record-breaking temperatures in North America, with wildfires in both Canada and the USA. Until now, guidance about how to respond to heatwaves and address heat-related health risks has been largely scarce. But two guides—Plan for Diabetes Care in Heat & Emergencies and Keep cool and carry on in the hot weather—were issued by the US Centers for Disease Control and Prevention and Public Health England, respectively, on June 29 and 30. On July 1, WHO and the World Meteorological Organization (WMO) jointly launched their guideline—Heatwaves and Health: Guidance on Warning-System Development. The recommendations are timely and have major implications for policy makers; emergency-response and hazards communities; meteorologists; and health professionals, who have a key role in preventing and managing heat-related illness.
The issues surrounding heat-health problems and the development of a heat-health warning system have been outlined for health practitioners in the guide by WHO and WMO. Direct heat-related medical conditions include heat rash, heat oedema, heat syncope, heat cramps, heat exhaustion, and life-threatening heatstroke. However, only a few deaths and illnesses are caused directly by heat. Most such cases during heatwaves are related to the worsening of existing medical conditions, such as chronic pulmonary diseases, cardiac conditions, kidney disorders, and psychiatric illness. Heat can also cause severe dehydration and acute cerebrovascular accidents, and contribute to thrombogenesis. Additionally, contributing factors that can increase the risks of heat-related illness and death include: age (with elderly or very young people at highest risk); socioeconomic factors such as living in social isolation or with little social support; medical conditions such as heart diseases, diabetes, respiratory or renal insufficiency, Parkinson’s disease or severe mental illness; and behavioural patterns such as overexertion during work or leisure, inadequate fluid intake, and neglect of protective measures against heat.
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