Abstract
Anthropogenic climate change has accelerated the frequency, intensity, and duration of extreme heat events globally, posing profound challenges to public health systems. While the physical health sequelae of heatwaves are well-documented, the acute psychiatric impacts remain under-evaluated, particularly among marginalized and socioeconomically disadvantaged cohorts. This study investigates the association between extreme heatwaves and mental health service utilization across Greater Sydney, Australia, from 2012 to 2022. Utilizing a retrospective time-stratified case-crossover design linked with high-resolution meteorological data, we analyzed 148,632 emergency department (ED) presentations and acute inpatient admissions for psychiatric disorders categorized by ICD-10 codes (F00–F99). Heatwave severity was quantified using the Excess Heat Factor (EHF). Extreme heat conditions were significantly associated with an elevated overall relative risk (RR) of mental health presentations (RR = 1.16, 95% CI: 1.12–1.21), with the strongest associations observed on the day of exposure (lag 0) and persisting up to 72 hours. Subgroup analyses revealed heightened vulnerability among individuals diagnosed with substance use disorders (RR = 1.27, 95% CI: 1.19–1.35) and schizophrenia-spectrum disorders (RR = 1.21, 95% CI: 1.14–1.29), as well as residents of Western Sydney experiencing pronounced urban heat island effects and socio-spatial disadvantage (RR = 1.24, 95% CI: 1.17–1.31). These findings underscore the imperative of integrating psychiatric emergency protocols and targeted social support infrastructure into municipal climate adaptation frameworks to safeguard vulnerable urban populations.
