Severe heatwaves impact all natural and human engineered systems in a similar manner.

Systems susceptible to failure under thermal duress have natural or engineered design limitations. These limits are an adaptive response to commonly expected rates of heat accumulation found over both the long (climate scale) and short (acclimatisation) term. When these limits are exceeded, systems begin to fail. The larger the thermal load, the deeper is the impact and scale of failure. Definitions are set out as a means of deriving a metric for the measure of excess heat impact. Australia can use this objective measure for heatwave climate history, forecasts, warnings and assessment of risk arising from climate change.

A statistically stable system has been developed to provide guidance on heatwave severity in chart form providing a direct link with the level of impact anticipated due to the intensity of the heatwave (Nairn and Fawcett, 2013)