Objective  To explore the added effect of heat wave on mortality in residents of Beijing and to provide evidences for developing public health strategies related to extreme weather events.

  Methods  The data on daily mortality, meteorological factors and air pollution during 2007 – 2013 in Beijing were collected. A distributed lag nonlinear model was applied to establish exposure-response relationships among air temperature, heat wave and mortality. The added effects of heat waves with nine different definitions were evaluated by comparing the mortality risk during heatwave days to that during non-heatwave days. Step function and quadratic spline function were used to evaluate the added effects associated with different heat wave durations, respectively.

  Results  With the increase of threshold and duration of heat waves with specific definitions, the total number of heat wave days in Beijing decreased gradually. The added effects of heat waves varied under different definitions. When the threshold was in the 95th quantile (27.62 ℃) and the duration was ≥ 4 days, the added effect of heat wave on non-accidental death was the greatest, with an increased mortality risk of 11% (95% confidence interval 95% CI: 4% – 18%). The added effect appeared when a heat wave lasting for more than two days and the added effect intensified sharply when a heat wave lasting for more than six days. The added effects of heat waves were associated with the increased mortality risk of respiratory diseases (34%, 95% CI: 12% – 60%) and circulatory diseases (14%, 95% CI: 4% – 24%). The populations vulnerable to the added effect of heatwave include the females, middle-aged people and the elderly; the most vulnerable people is those with less education.

  Conclusion  Heat wave could significantly increase the mortality risk of residents in Beijing and there existed an added effect due to continuous days with high temperature. The persons with respiratory or circulatory diseases, the female, the middle-aged people and the elderly, especially those with less education, are particularly vulnerable to adverse effect of heat waves.