Heatwaves and human vulnerability: climate change challenges in Eastern Australia

As climate change intensifies heatwave frequency, duration, and severity, robust risk assessments are urgently needed to inform adaptation and emergency response planning. Such efforts are vital to safeguard future generations by preventing avoidable fatalities and reducing health burdens. This study investigates the evolving heatwave risk to Southeast Australia under a warming climate, a region experiencing a growing heatwave threat. To explore this phenomenon, we developed the Combined Heatwave Risk Index (CHRI), which integrates exposure, vulnerability, and hazard components. The CHRI addresses challenges in composite indicators, particularly the tendency to disproportionately emphasise high-population areas due to Australia’s skewed population distribution (exposure). Instead, the CHRI uses a weighted approach to balance factors, improving applicability across regions. Heatwave vulnerability incorporated demographic, socioeconomic, and health data from the 2021 Australian Census, and the Normalised Difference Vegetation Index (NDVI) as a proxy for environmental vulnerability. Heatwave hazard, defined as a function of frequency and intensity, was assessed using the Excess Heat Factor (EHF). Current and future heatwave risk was calculated using CMIP6 downscaled projections from the New South Wales regional climate modelling project (NARCLiM2.0) under SSP2-4.5 and SSP3-7.0 scenarios. Results show exposure is highest in coastal metropolitan areas, while vulnerability is more concentrated inland due to ageing populations, poorer health, and reduced vegetation. Hazard intensity is projected to increase substantially in inland New South Wales and Queensland. The CHRI therefore offers a flexible, stakeholder-relevant tool for governments, emergency services, and planners to support more equitable and targeted heatwave preparedness as climate extremes intensify, aligning with Sustainable Development Goal 13: Climate Action.