A heatwave is a prolonged period of hot weather. The Bureau of Meteorology defines a heatwave as ‘three or more days of maximum and minimum temperatures that are unusual for the location’ (www.bom.gov.au). Heatwaves are dangerous to people and animals as it becomes more difficult to keep cool and stay hydrated under heatwave conditions.
Heatwaves result from certain combinations of temperature, humidity and air movement that result in unusually high temperatures. They can cause death and widespread health problems..
There have been many heatwaves in Australia, including the 1939 heatwave which killed 438 people in South Australia.
Heatwaves also have other effects. They can cause crop losses and the death of livestock, and severely damage roads and highways, bridges, railway lines and electrical equipment.
Heatwaves are different from many other disasters (such as bushfires or severe storms) as they can affect large areas over a long period of time.
Why are heatwaves dangerous?
During heatwaves, a lack of wind causes heat to become trapped close to the ground. As the temperature rises, people, animals and plants can experience heat stress.
Heat stress – people
Heat stress results when pressure is put on the body’s normal cooling process: too much heat is absorbed and not enough is lost. When someone is not able to cool down, their body temperature rises, their breathing quickens and their pulse increases. As their body gets hotter, water is lost from their blood causing it to thicken. This may lead to heat stroke which can result in serious, or even fatal, consequences.
Heat stress - animals
Animals can also suffer the effects of heat stress. Lack of shade or water can change an animal’s behaviour causing them to seek shelter under trees or near bushes, start sweating and panting, drool, drink more water and have a reduced appetite.
Heat stress - plants
Plants and crops are also affected by severe heat. When the temperature is high for a long time, plants lose moisture and can die. Even tough, native Australian plants can suffer from heat stress. As plants start to die from the effects of heatwaves, the threat of bushfire increases.