Socio-demographic and environmental factors amplify typhoon-related excess mortality in Japan

Mechanisms shaping population vulnerability to typhoon-related mortality remain poorly understood. Constructing a Bayesian spatio-temporal model, we linked 12.9 million deaths across Japan from 2010 to 2019 to population-weighted typhoon wind exposure and assessed effect modification by income, natural hazard vulnerability and healthcare access. Typhoon exposure was associated with 2,426 cumulative excess deaths [95% credible interval (CrI): 139, 4,632] among adults ≥70 years, with mortality increasing within 0-1 weeks of exposure and more strongly in areas with limited healthcare access and greater hazard vulnerability. Among individuals <70 years, cumulative excess mortality was uncertain [781 deaths; -309 to 1,900], but delayed mortality increases were concentrated in lower-income and landslide-prone areas. These distinct patterns suggest that typhoon mortality reflects an interaction between acute exposure, demographic ageing and geographically uneven adaptive capacity, highlighting the need to incorporate local vulnerability into climate-resilient health systems.