Single extreme events such as heat waves, bushfires, rainfall extremes, and tropical/extratropical cyclones have a large socio-economic impact on Australia. However, multiple natural hazards may occur in the same region, or at the same time, or both, forming compound events.

An example of such a compound event occurred during late January to early February 2009. One of the most severe heat waves in SE Australia saw Melbourne record temperatures of between 43^o and 45^oC. The Black Saturday bushfires resulted in multiple fatalities, property losses, and significant insurance claims. TC Dominic made landfall in northern Western Australia, causing heavy rainfall and flooding. In Queensland, a series of tropical lows on the monsoon trough and TC Ellie resulted in flood-producing rainfall over much of the northern part of the state. How could these events be dynamically linked?

Heat waves in Victoria are associated with Rossby wave breaking (RWB), and are more common when convection is enhanced in the tropics. There is a connection between the formation of the upper anticyclone which is a feature of these heat waves, and the influence of tropical cyclones on the propagation of Rossby waves. Furthermore, the upper-level PV trough which forms as a result of RWB may enhance rainfall over NE Australia. In addition, coherent PV maxima in the monsoon region have been shown to form from the debris of RWB along the eastern coast and are subsequently transported into the tropics by the large-scale flow. In some parts of northwestern Australia 40%–50% of the summertime rainfall occurs with a tracked monsoon disturbance in the vicinity.