Spatio-temporal variability of compound drought heatwave events (CDHEs) in Australian agricultural regions and their impacts on cereal crops

The impact of climate-related hazards is on cereal crop production is a growing concern, with food security a major global issue. Among these hazards, compound drought and heatwave events (CDHEs) are particularly damaging, yet their impacts on Australian cereal crops at the growing region scale remain understudied. This study quantifies the spatio-temporal variability of CDHEs across Australian cereal-growing regions, using yield impact-based definitions of heatwaves and droughts. Heatwaves were detected using the Excess Heat Factor (EHF), while droughts were identified using the self-calibrating Palmer Drought Severity Index (scPDSI). CDHE days were defined as the co-occurrence of heatwave and drought conditions. Results reveal that the frequency, severity, and spatial extent of CDHEs have increased sharply since the 2000s, particularly across western and eastern Australia, with hotspots of activity concentrated in the warmer months (August to February) in western and eastern Australian cereal-growing regions. Importantly, several historical yield anomalies (i.e. decreases in typical yield) since 2003 aligned with periods of high CDHE frequency and severity. Pearson's correlations between CDHE metrics and detrended cereal crop yields highlight statistically significant relationships in Southern and Eastern Victorian wheat and barley (r = -0.49, -0.45), Tasmanian wheat (r = -0.37), New South Wales Tablelands barley (r = -0.39), and Central North Victorian barley (r = -0.41). Collectively, these findings highlight the potential of Australian CDHEs to drive climate-related yield loss. This work improves understanding of past climate variability and extremes of CDHEs and their links to crop yield, supporting Australia's efforts to better prepare for, adapt to, and mitigate climate-related agricultural losses.