Combined Role of Enso and Iod on Compound Drought and Heatwaves in Australia

Compound drought and heatwaves (CDHWs) can cause significant socio-economic and ecological impacts. A better understanding of historical spatiotemporal changes of Australian CDHWs and their underlying physical mechanisms can help improve their predictability. We analyse changes in the extended summer season (Nov to Mar) of Australian CDHW metrics during the period 1958 – 2020. Our results suggest that CDHWs increased significantly in terms of their frequency, duration, amplitude, and severity in the recent period (1989/90-2019/20) relative to a historical period (1958/59-1988/89), particularly in the eastern parts of Australia. We further analysed the influence of co-occurring modes of El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on the frequency and severity of Australian CDHWs using multi-member ensemble data of the sixth round of the Coupled Model Intercomparison Project (CMIP6) models. We found that frequency, duration, and severity of CDHWs are significantly increased during strong El Niño phases across northeast parts of Australia compared to neutral conditions (neutral ENSO and IOD), which is widespread over northeastern and southeastern parts of Australia during the concurrence of strong El Niños and positive IOD events. Further, our results show that an extreme CDHW season in terms of their frequency, duration, and severity is likely to occur in every two seasons of strong El Niño (co-occurring strong El Niño and positive IOD) over the northeastern (northeastern and southeastern) parts of Australia. Our results highlight the importance of ENSO and IOD interactions for Australian CDHW events. Our findings provide insights into the importance of climate variability in driving Australian CDHWs, thus enhancing predictability and thereby improving our ability to mitigate their adverse impacts on society