The Bureau of Meteorology has brought forward the annual launch of its online heatwave service after months of record-breaking temperatures.

The service normally runs from November 1 to the end of March.

Key points: The Bureau of Meteorology has launched its heatwave service early after high temperatures

The Bureau of Meteorology has launched its heatwave service early after high temperatures The service compares the forecast for the next three days to long-term 'normal' temperatures

The service compares the forecast for the next three days to long-term 'normal' temperatures Extreme heat has killed more people in Australia than all other natural disasters combined

National heatwave project director John Nairn said the bureau had noticed increasing heat episodes in northern Australia and parts of the east coast, prompting it to bring the service forward by three weeks.

He said starting the service early was unusual.

"It won't happen every year. On occasion, particularly if you have sections of the country being affected by drought, it is likely that we will see some earlier heat events," he said.

Why does it matter?

Extreme heat has killed more people in Australia than all of the other natural disasters combined.

In February 2009, now infamous for the Black Saturday fires, 173 people died directly as a result of the fire.

It is less well known that 374 people died because of the heatwave leading up to the fires.

Fatalities in extreme weather: Hazard Period Fatalities High-risk states Extreme heat 1900-2011 4,555 Vic, NSW, SA Flood 1900-2015 1,859 Qld, NSW Tropical cyclone 1900-2015 1,216 WA, NT, Qld Bushfire 1900-2011 825 Vic, NSW, Qld Wind storm 1900-2015 525 NSW, Vic, Qld Source: Andrew Gissing, Risk Frontiers

While the elderly and young are most at risk from high temperatures, for most a moderate level heatwave is just part of an Australian summer.

But Mr Nairn said it was something everyone should be aware of.

"If normally fit people don't adapt and change their behaviour under extreme conditions, they too can be affected by the heat," he said.

"They are fairly rare events so it is hard to get the message through sometimes, but as they build into extreme events it becomes important for everyone to pay attention.

"Unfortunately under the warming environment that we're seeing, we are seeing more extreme events turning up more frequently."

How does the heatwave service work?

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The service works by comparing the forecast for the next three days to the long-term 'normal' temperatures and how hot it has been leading up to the event.

It takes into account how unusually hot it is and how adapted people will be when the heatwave hits.

The bureau's definition of a heatwave is three or more days of high maximum and minimum temperatures that are unusual for a location.

Mr Nairn said overnight temperatures were the most important.

"The minimum temperature is probably the more dangerous temperature when you're looking at a heatwave," he said.

This is because hot overnight temperatures mean the maximum temperature is reached earlier the following day, so people are exposed to extreme temperatures for a longer period.

An example of a heatwave forecast map from the bureau's heatwave service. ( Supplied: Bureau of Meteorology )

Comparing extreme heat events

The methods behind the service also allow for comparison between events, providing context between heatwaves in different locations.

It is a difficult task because the effects of a heatwave are highly dependent on how different events are from normal conditions — what is considered a heatwave in London would be very different from what is considered a heatwave in Alice Springs.

Mr Nairn said without that context, in south-east Australia we would have to go back to 1939 for the previous event that was at the same level of intensity as 2009.

"There is not much living memory of that event [1939]," he said.

"The trouble with rare events coming up infrequently is that if we haven't learnt … we're not likely to be doing the right thing."

Temperatures soared during the 2009 Victorian heatwave. ( ABC TV, file )

But there are other more recent events globally that we can learn from.

Mr Nairn said the 2009 heatwave event was equivalent to the 2003 heatwave in western Europe, where there were about 30,000 deaths.

He said even considering population differences, Victoria had fared better than Europe.

"It's because we have relatively reliable power that feeds our air conditioning," Mr Nairn said.

"The French only have between a 5 and 15 per cent penetration for their air conditioning for cooling.

"But it does mean we have a very strong reliance upon power in order to keep that cooling operating."

This reliance could be a problem in the future.

"The longer a heatwave goes on, particularly if it is an extreme heatwave, it can begin to challenge our ability to maintain these utilities, such as power," Mr Nairn said.

"What we need now is for the public to understand their role in protecting themselves when they see these much larger events come through."