Heatwaves are periods of unusually hot weather, lasting two days or more, when the temperature surpasses the region’s average temperature.
Global warming is affecting the intensity, frequency, and duration of heatwaves. Record-breaking hot months are five times more frequent than expected. According to the WHO, between 2000 and 2016, the number of people exposed to heatwaves increased by around 125 million due to climate change.
Heatwaves are often more extreme in crowded cities due to the so-called ‘urban heat island effect, where concrete constructions absorb and retain heat.
Exposure to severe heat causes exhaustion and heat stroke — a condition where the body cannot bring its temperature down, which could lead to dehydration, cerebrovascular accidents and blood clots. People who work outdoors, those with chronic diseases, older citizens and children are extra-vulnerable to heat-related stress.
The WHO is working with governments to strengthen the preparedness and response to heatwaves by mapping the risks, vulnerable populations, available capacities and required resources.