Australia’s southern states are scorching in extreme heat that was expected to break temperature records in Victoria, South Australia and New South Wales.
January and all-time records were forecast to be set, with temperatures approaching 50C across inland areas, according to the Bureau of Meteorology.
On Tuesday, preliminary readings of 48.9C at two locations will stand as a new high for all Victoria if confirmed, and four towns saw the mercury rise over 48C. All-time local heat records were set in three towns in far-western NSW including Broken Hill, which hit 47.8C and Flowers Gap which recorded 49.1C.
Extreme heat is the most common cause of weather-related hospitalisations in Australia, and kills more people than all other natural hazards combined. What does exposure to extreme heat – such as a temperature of 49C – do to the body?
1. What effect does extreme heat have on the body?
In warm environments, the body dissipates heat through the skin, which is responsible for about 90% of heat loss. It does so by sweating and by increasing blood flow to the extremities.
Prof Ollie Jay, academic director of the heat and health research centre at the University of Sydney, says: “Your heart has to work a lot harder because you’re basically redistributing this blood in an effort to keep cool towards the skin, but what this means is that your blood pressure would drop unless your heart beats more times per minute.”
“If you’ve got an underlying heart disease, now you’re a much greater risk of, say, a heart attack. It’s not heat stroke, it’s a different mechanism,” Jay says.
Dr Arnagretta Hunter, a cardiologist and senior lecturer at the Australian National University says extreme heat – especially warm temperatures in the evening and “the loss of overnight cooling” – has wide-ranging impacts on both physical and mental health. “You will see an increase in [hospital] presentations that have a cardiac problem … a kidney problem, geriatric admissions … people falling over [from dizziness].”
The degree of heat people experience could far exceed forecast figures, because the Bureau of Meteorology’s weather stations record ambient temperature in the shade. “If you’re out in the middle of the day in direct sunlight, the temperature can be as much as 15C hotter,” Jay says.
2. What happens during exposure to temperatures close to 50C?
“There are biological limits to temperatures that we can survive,” Hunter says. “How long is it safe to be outside at 49C? I think the answer is: it’s not safe to be outside at 49C for any protracted period of time.”
Extreme heat in parts of India and Pakistan, where temperatures have exceeded 50C, has led to hundreds of deaths. “Even short periods of time in that 50C-plus environment can lead to dehydration; the heart’s working hard,” Hunter says. “This sort of heat stress can provoke a heart attack, it can provoke an arrhythmia – rhythm abnormalities, it can provoke circulatory collapse.”
In Victoria, the 2009 Black Saturday bushfires killed 173 people. “That was catastrophically bad,” Hunter says. But, she points out, the heatwave that preceded it – during which a new state temperature maximum was set – killed more than twice as many, resulting in an estimated 374 excess deaths.
“We have to be careful when a risk [is] associated with a given temperature,” Jay says, because it depends on several other factors – including the amount of wind and humidity. “If there’s more moisture in the air, it makes it more difficult for the sweat that we’re producing to evaporate, which is the only way in which we can keep cool when it’s hot.”
“Clothing can prevent sweat from evaporating through it,” he adds – a problem for those in certain work environments. Age is also a factor: “Particularly above 75, our ability to sweat is quite diminished, which means that you’re a much greater risk of overheating.”
3. How to prevent heat stress
Public health authorities suggest staying well hydrated – drinking six to eight glasses of water a day, and avoiding alcoholic, hot or sugary drinks. People with heart failure and other medical conditions that may require limiting fluid intake should consult their medical practitioner.
Older people, babies, people with chronic illness or who are pregnant or breastfeeding are more susceptible to the effects of extreme heat.
Jay’s team has developed a free HeatWatch tool that provides individualised heat risk scores that take in weather conditions, giving figures based on “how hot we think you’re going to get, how dehydrated you’re going to become, how much work your heart has to do”.
Hunter suggests keeping houses and work environments as cool as possible – whether through air conditioning or fans, which can safely be used in combination with other measures in indoor temperatures up to 38C.
If it’s not humid, wetting the skin can also help, because most of the heat the body loses in warm environments is due to sweat evaporating.
Because of the impacts on both physical and mental health, Hunter suggests “taking it quietly through the day”. She says: “It’s not a day for exercise, it’s not a day for spending time outside. It’s not a day for complex decision-making.”