The link between elevated ambient temperature and mental health conditions has been increasingly well documented. However, the temporal dynamics of this relationship, including diurnal variation and lag periods, remain poorly understood. This is in part due to a historic lack of highly spatially and temporally refined data. In this time stratified case-crossover study, we investigated the association between hourly temperature exposure and psychiatric emergency department (ED) visits in Massachusetts using data from the Boston Emergency Services Team (2005-2019). Using a new exposure model, ambient temperature was estimated at 1x1km spatial resolution for each individual’s residential location for each of the 24 hours preceding their ED visit. Preliminary results showed non-linear associations between ambient temperature and psychiatric emergencies that increased with longer exposure periods, with 0-24 hours cumulative exposure showing the strongest association compared to 1-hour immediate exposure. Significant diurnal variation was also observed, with the strongest temperature-PES associations for ED visits occurring during morning hours and evening hours, while risk was lower for afternoon and night ED visits. These preliminary results indicate that heat impacts accumulate over the course of a day, which may help elucidate potential causal mechanisms. Findings also suggest the importance of considering temporal patterns when implementing heat-health interventions and provide insights for clinical resource allocation during periods of extreme heat.
