Understanding the spatio-temporal influence of climate variability on Australian heatwaves

Some of the major drivers of extreme temperatures in Australia are related to large-scale variations in the climate. While many of the relationships between climate variability and heatwaves have been described, the preceding climate conditions and the circulation patterns responsible for interannual heatwave variations are still poorly understood. We have used rotated principal component analysis (PCA) to describe the variance of frequency, duration, magnitude and timing of Australian summer heatwaves. This provides a simple means of investigating both the spatial patterns of circulation and the preceding climate mode conditions of summer heatwaves. We find that spatial patterns of heatwave variability associated with El Nino-Southern Oscillation (ENSO) were focused in the north and northeast of Australia for heatwave occurrence. Patterns of heatwave amplitude in southeastern Australia were also weakly related to ENSO. The PCA did not find any direct, concurrent Indian Ocean Dipole (IOD) or Southern Annular Mode (SAM) signal. However, lead correlations indicate that winter IOD conditions can have a weak indirect effect on heatwave occurrence in northeast Australia and similarly, winter SAM conditions can affect heatwave timing in central eastern Australia. Regressions reveal that ENSO related heatwave duration and frequency in the northeast are related to the movement of the Walker circulation, while southeastern heatwave amplitude is associated with a north-south movement of the Tasman high pressure system. These results may lead to improvements in understanding the predictability and general preparedness for heatwaves in the summer season.