High impact compound events in Australia

Many natural disasters in Australia occur as a result of meteorological drivers occurring in combination. These Compound Events (CEs) amplify risk to socio-economic and ecological systems relative to single meteorological events. We undertake a bivariate assessment for two hazard combinations important in Australia: heatwaves and drought, and strong winds and heavy precipitation. We use observations and reanalysis data to build a highresolution climatology spanning the period from 1980 to 2014 and identify the north-western Australian coast as a region particularly prone to the joint occurrence of wind and precipitation extremes. Heatwaves and drought frequently co-occur multiple times per year over most of Australia with shorter return periods in the tropical north. We show that CMIP6 models capture the return periods of both CEs well. We then examine projected changes in both CEs under future conditions (2066-2 100) under a moderate and high emission scenario. All CMIP6 models project decreases in the return periods (i.e. more frequent events) of co-occurring heatwaves and droughts with the south of Australia particularly affected. Northern Australia is projected to become more at risk from wind and precipitation extremes while southern Australia experiences lower risk. The high level of skill in simulating the two CEs examined, combined with the coherent spatial patterns projected by the CMIP6 models suggest there is merit in using these models to examine the large-scale risk of CEs in the future, and that these can be used to support national scale planning for the changing risk of CEs.

Automated summary

Many natural disasters in Australia are compound events, caused by multiple meteorological factors occurring together. These compound events pose greater risks to socio-economic and ecological systems compared to single meteorological events. Heatwaves and drought, as well as strong winds and heavy precipitation, are two important hazard combinations in Australia. The north-western Australian coast is particularly prone to the joint occurrence of wind and precipitation extremes. Heatwaves and drought frequently co-occur multiple times per year over most of Australia, with shorter return periods in the tropical north. CMIP6 models accurately capture the return periods of both compound events. Future projections show that co-occurring heatwaves and droughts are expected to become more frequent in southern Australia, while northern Australia is projected to face increased risk from wind and precipitation extremes. The high skill of CMIP6 models in simulating these compound events and the consistent spatial patterns projected suggest that these models can be used to assess the large-scale risk of compound events and support national scale planning for future risks.