Old housing, ageing residents, hotter nights: a sub-municipal map of structural climatic vulnerability in the Canary Islands

The dwelling stock mediates between outdoor climate and the indoor thermal exposure of residents, particularly at night, when older adults are most susceptible to elevated minimum temperatures. Sub-national assessments of climate-related health risk typically overlay a high-resolution climate projection with a demographic exposure layer but leave the residential infrastructure that mediates outdoor heat into indoor exposure outside the spatial analysis; dwelling-stock age and typology condition passive thermal performance and retrofit feasibility, making them natural candidates for that missing layer. We quantify, at the census-tract scale for the Canary Islands, the spatial alignment between dwelling-stock age, projected nocturnal heat exposure and elderly residential density, combining the 2023 INE socioeconomic atlas mean year of construction (CAT_TIME) with WRF-ARW 3 km CMIP6 projections of tropical nights under SSP5–8.5 for 2070–2099. The oldest quintile of dwelling stock (mean construction year 1962, 277 tracts) concentrates a density of residents aged 65 and older 5.8 times higher than the newest quintile (3805 versus 652 per square kilometre) and sits where the projected end-of-century increment of tropical nights is 14 nights/year higher (92.0 vs 80.9 nights/year). Because the projected climate signal is an outdoor exposure that the building envelope mediates rather than causes, the association is read as spatial co-location, not as a building-performance effect. Ordinary least-squares models controlling for population density, island and municipal functional-type fixed effects confirm that older stock co-locates with both higher projected nocturnal heat (0.25 ± 0.09 fewer tropical nights per construction year, p = 0.008) and higher elderly density (40.6 ± 4.1 fewer residents aged 65 and older per square kilometre per construction year, p < 0.001, R 2 = 0.52); the oldest quintile concentrates in Gran Canaria and Tenerife (89%). A battery of eight robustness exercises confirms the alignment, while its attenuation under the SSP1–2.6 low-emission scenario evidences a partial substitutability between climate mitigation and building-stock retrofit. These findings identify a structural climatic vulnerability of the Canarian dwelling stock — aligning the oldest housing, built before modern thermal-envelope regulation, with the densest elderly population and the most pronounced projected nocturnal heat — that warrants its explicit incorporation into sub-municipal climate adaptation and building-retrofit prioritisation.