Assessing heat vulnerability and multidimensional inequity: Lessons from indexing the performance of Australian capital cities

• Forms a heat vulnerability index using socio-demographic, health, and environmental data. • Validated the heat vulnerability index against heat-related mortality data. • Finds higher heat urban exposure with varying sensitivity and capacity shaping vulnerability. • Identifies vulnerable groups: Indigenous, low English proficiency, and transit commuters. • Offers targeted strategies to boost climate resilience and thermal equity in Australian cities. Increased extreme heat, driven by rapid urbanisation and climate change, has caused increasing heat-related deaths, and posed significant threats to vulnerable populations. Studies have proposed many heat vulnerability indices, but most lack comprehensiveness in study design and validation. Furthermore, a significant gap remains for an analysis of inequity in heat vulnerability assessment research, a crucial component for promoting thermal equity. This paper introduces a Comprehensive Heat Vulnerability Index (CHVI) for Australia's capital cities, using socio-demographic, health, and environmental indicators at the finest statistical level, the Statistical Area 1 (SA1) scale, and employs the Gini coefficient to analyse inequity in heat vulnerability. Key findings include: (a) Heat vulnerability exposure decreases from urban to rural areas, with sensitivity exhibiting similar trends but more pronounced regional variations; (b) Adaptive capacity increases as exposure decreases, though this pattern is not consistent in city centres and certain regions; (c) The CHVI effectively measures heat vulnerability, demonstrating strong correlations with Pearson Correlation Coefficients of 0.68 and 0.92; (d) The distribution of heat vulnerability aligns with exposure trends but shows greater regional diversity, and city centres tend to have lower vulnerability levels; (e) Thermal inequity among SA1s is influenced by factors such as the Indigenous population, unemployment rates, English proficiency, and public transportation usage; (f) There is a slight variation in these factors of thermal inequity across each capital city. The findings provide a comprehensive understanding of heat vulnerability and thermal inequity in the Australian capital cities that could aid in informing climate resilience and adaptation strategies and policies for sustainable development.