Objective: To examine temporal and seasonal variation in presentations of suicidality and self-harm to a large tertiary emergency department (ED) and to investigate the association of environmental variables, including temperature, sunshine hours, precipitation, and photoperiod with daily presentation rates.

Methods: Daily presentations for suicidality or self-harm to a tertiary hospital ED from July 2016 to December 2024 were analysed using Poisson regression. Analyses for meteorological variables were controlled by day of week and month of year.

Results: Mean daily presentations increased over time, with greater rates in the early week (Monday–Wednesday) and lowest on weekends. The rate of change of photoperiod lagged by 7 or 14 days was associated with a 5% increase in presentations per additional 1-minute/day day length (p = 0.048; p = 0.032), translating to a 20–21.3% increase in daily presentations in the weeks after the Spring Equinox. Sunshine hours were not associated with change in rate of presentations. Cumulative rainfall became significant at 14- (p = 0.008) and 30-day cumulative ranges (p < .001). Higher temperatures were associated with greater presentations, with 2.2% higher presentations per 1°C increase of mean (p < .001) or minimum temperature (p < .001).

Conclusions: These data support international literature of associations between suicidal behaviour and increased temperature, precipitation and rate of change of photoperiod, with greater presentations occurring in the weeks after the Spring Equinox. Along with findings of excess presentations during the early weekdays, resource planning should consider these seasonal variations in service demand.