Time-series study on association between heatwaves and emergency ambulance calls: taking Dezhou city, Shandong province as an example

Objective To quantify the association between heatwaves and emergency ambulance calls in Dezhou city and to provide a more comprehensive insight into the health risk evaluation of extreme weather. Methods The data on daily records of emergency ambulance calls, meteorological factors, and air pollution from 2020 to 2022 in Dezhou city, Shandong province were collected. Heatwaves were defined by combining thresholds at the 90th, 92.5th, 95th, or 97.5th percentiles of the year-round daily mean temperature during 2020–2022 and durations of ≥2, 3, or 4 consecutive days, respectively. A generalized additive model with a distributed lag nonlinear model was used to estimate the relative risk of emergency ambulance calls during heatwave days compared with nonheatwave days. Results The impact of heatwaves on emergency ambulance calls lasted up to 7 days, with a cumulative relative risk of 1.12 (95%CI: 1.07, 1.17) for P90_2d. The effect of heatwaves increased significantly with increasing temperature thresholds and durations. There was no difference in the cumulative effect of heatwaves between sexes, while the older population aged 65 and above was more susceptible across age groups, with a relative risk of 1.60 (95%CI: 1.42, 1.81) for the most severe heatwaves. Respiratory diseases were most strongly associated with heatwaves among different disease causes of emergency calls, and the association increased with more severe heatwave types. Conclusion Heatwaves could significantly increase the risk of emergency ambulance calls. The elderly population aged 65 and above is particularly vulnerable to the harmful effects of heatwaves, and those with respiratory illnesses need to be particularly aware of the health risks of heatwaves.