Heatwaves send temperatures soaring in many parts of Australia, but what are they?

Heatwaves are Australia's deadliest natural disaster. They have killed more people than bushfires, cyclones and floods put together.

Because Earth is a sphere, there is proportionally more energy near the equator.

The Bureau of Meteorology defines them as "three days or more of high maximum and minimum temperatures that is unusual for that location”.

During the extreme heatwave that hit south east Australia in 2009, 374 people died in Victoria and evidence exists for up to 500 heatwave-related deaths all together.

Events like 2009 are rare — the last comparable event in south east Australia occurred in 1939.

But it doesn't have to be a once in a generation event to put people at risk.

So what are heatwaves exactly, and why do they happen?

Read the ABC News story - “Heatwaves send temperatures soaring in many parts of Australia, but what are they?”