Heat Waves in the United States: Mortality Risk during Heat Waves and Effect Modification by Heat Wave Characteristics in 43 U.S. Communities By: G. Brooke Anderson and Michelle L. Bell

 What is a heat wave?  In this study, a heat wave was defined as:  In this study, a heat wave was defined as: ≥ 2 days with temperature ≥ 95th percentile for the community for 1 May through 30 September.   Effect Modification?   Intensity   Duration   Time in Season   What day in the season did the heat wave occur?   Was that heat wave the first of the season?

 Method :  Bayesian Hierarchical Models were constructed to estimate effects of heat wave characteristics on mortality rates for:  Individual Heat Waves  Communities  Regions: Northeast, Midwest and Southern U.S.  The Nation  Daily apparent temperatures also incorporated  “Catastrophic Heat Wave” Model

Association between heat wave effects (percent mortality increase during the heat wave vs. non-heat wave days) and average daily temperature during each heat wave

 What they found:  Mortality risk increased:  3.74% during heat wave  2.49% for every  2.49% for every 1°F increase in heat wave intensity   0.38% for every 1-day increase in heat wave duration   5.04% during first heat wave of the season   2.65% during later heat waves

 Regional Trends in Effect Modification:  Effect modification was most pronounced in Northeast  2.50% increase in mortality rate per extra day of heat wave  Midwest region less affected by 1 st in season heat wave  Larger, more intense heat waves in the South  Mortality effects were smaller  Threshold temperatures higher in the South  Some southern cities showed no mortality increase  Charlotte, NC., Oklahoma City, OK., Dallas/Fort Worth, TX.

 Catastrophic Heat Wave observed:  Chicago: July 12 – 16, 1995  Mortality risk increased 133.9%  Model predicted increase of 18.9%  Milwaukee: July 13-15, 1995  Mortality risk increased 93.0%  Model predicted increase of 10.3%  Heat wave characteristic modification could NOT explain severe mortality risk increase

 Why do mortality rates increase during a heat wave?  Intensity & Duration  Increase strain on cardiovascular system  Timing in Season  Mortality Displacement  Acclimatization  Better practices later in the summer

 Why did mortality rates differ between communities?  Acclimatization of people in warmer communities  Different levels of exposure (A/C use, house type, clothing)  Different community-level responses  Different demographics (more elderly, sick or less-healthy)  Geographical, meteorological, pollution factors  Generally:  The cooler the region, the greater the heat wave effect

TTTTo Conclude: HHHHeat wave intensity, duration and frequency are expected to increase due to climate change. TTTThis study investigates heat wave characteristics that might contribute to an increase in mortality rates, and that should be noted for public health purposes.