ObjectivesTo evaluate the association between asthma-related emergency department (ED) visits and weather, air quality, monsoons, haze and cultural festivals in Singapore.DesignRetrospective cohort study.SettingA public healthcare cluster that covers 20% of the nation's adult asthma population.Participants2617 adult patients accounting for 5337 asthma ED visits between 2016 and 2024.Primary and secondary outcome measuresTemperature, rainfall, wet bulb temperature (WBT), wind speed and Pollution Standards Index (PSI) were correlated with asthma ED counts at 0-7 day lags. Associations between ED visits and monsoons, transboundary haze and cultural festivals were evaluated using one-way analysis of variance. Weekly seasonal ARIMA models with exogenous regressors were fitted, incorporating PSI as a covariate and adjusting for demographic, clinical and socioeconomic factors.ResultsAsthma ED visits were positively correlated with PSI (lag 0: r=0.142; 95% CI 0.107 to 0.178) and inversely correlated with rainfall (lag 3: r=-0.062; 95% CI -0.099 to -0.026) and WBT (lag 1: r=-0.067; 95% CI -0.104 to -0.031). Wind speed (lag 2: r=-0.049; 95% CI -0.086 to -0.013) and ambient temperature (lag 6: r=-0.045; 95% CI -0.081 to -0.008) showed weaker inverse associations. Mean PSI was higher during haze (82.67 vs 51.46, p<0.001) and festival periods (53.42 vs 51.57, p=0.001). Mean ED visits fell across successive haze events (2.60 in 2016, 2.36 in 2019, 1.46 in 2023) but peaked during the Northeast monsoons despite lower PSI, indicating weather influences beyond ambient pollution.ConclusionsPSI-ED association peaked on the same day of exposure but was no longer significant after adjusting for demographic and clinical factors. Pollution-linked festivals, transboundary haze and the Northeast monsoon were associated with increased asthma ED visits.