Understanding regional differences in extreme heat vulnerability in Aotearoa New Zealand: Demographic sensitivity, social vulnerability, and climate justice

Abstract

Extreme heat is an emerging climatic and population health risk in Aotearoa New Zealand, yet its demographic and spatial dimensions remain poorly understood. While international evidence demonstrates clear associations between heatwaves and excess mortality, hospitalisations, and social disruption, limited research has examined how extreme heat intersects with demographic sensitivity and social vulnerability in New Zealand’s temperate climate. This thesis addresses that gap by providing the first national, spatially explicit assessment of extreme heat vulnerability in New Zealand, framed through the lenses of climate justice and intergenerational equity.

The study adopts a quantitative, cross-sectional design integrating daily maximum temperature observations from thirty representative climate stations (2009/10–2018/19 summers) with 2023 Census demographic data and the New Zealand Deprivation Index (NZDep2023) at Statistical Area 2 (SA2) level. Extreme heat is defined using station-specific 95th percentile thresholds, reflecting relative local acclimatisation. For each station, the mean number of summer days exceeding this threshold was calculated and spatially assigned to SA2s using a nearest-station approach in QGIS. Demographic sensitivity was operationalised through age structure, focusing on children (0–14 years) and older adults (65+ years), while social vulnerability was captured using ethnic composition and area-level, socioeconomic deprivation.

Results demonstrate substantial regional and interannual variability in extreme heat exposure. Warmer eastern and inland regions record higher temperature thresholds, yet relative exceedance days are not confined to traditionally hot areas, underscoring the importance of percentile-based measures in temperate climates. Exposure increased markedly in later summers, particularly in the summer of 2018/19, indicating a national upward shift in extreme heat frequency. Demographically, vulnerability is unevenly distributed. Older populations are concentrated in several South Island and coastal regions, while Māori and Pacific communities, characterised by younger age structures, are concentrated in specific North Island regions and urban areas. Overlay analysis reveals distinct spatial clusters where elevated heat exposure coincides with high proportions of either older adults or children, often alongside higher socioeconomic deprivation.

By embedding these findings within climate justice and intergenerational equity frameworks, the thesis demonstrates that extreme heat is not only a climatic hazard but also an issue of equity. Communities least responsible for climate change may face disproportionate exposure due to structural inequities. Simultaneously, children represent a cohort with both heightened physiological sensitivity and greater lifetime exposure under continued warming.

This research contributes to knowledge by integrating climatological, demographic, and socioeconomic deprivation data into a unified national vulnerability assessment for New Zealand. It provides a policy-relevant evidence base to inform heat-health planning, housing standards, urban design, and equitable adaptation strategies. More broadly, it demonstrates the importance of embedding justice-oriented frameworks into climate and population health research to ensure adaptation responses reduce, rather than reproduce, existing inequities.