Science Source

Mortality Displacement as a Function of Heat Event Strength in 7 US Cities

States that mortality rates increase immediately after periods of high air temperature
States that in the days and weeks after heat events, time series may exhibit mortality displacement—periods of lower than expected mortality
Examines all-cause mortality and meteorological data from 1980 to 2009 in the cities of Atlanta, Georgia; Boston, Massachusetts; Minneapolis–St. Paul, Minnesota; Philadelphia, Pennsylvania; Phoenix, Arizona; Seattle, Washington; and St. Louis, Missouri
Models baseline mortality using a generalized additive model
Defines heat waves as periods of 3 or more consecutive days in which the apparent temperature exceeded a variable percentile
Calculates the sum of excess and deficit mortality for each heat wave
Mortality displacement, which is the ratio of grand sum deficit to grand sum excess mortality, decreased as a function of event strength in all cities
Finds that displacement was close to 1.00 for the weakest events, and at the highest temperatures, displacement varied from 0.35 (95% confidence interval: 0.21, 0.55) to 0.75 (95% confidence interval: 0.54, 0.97)
Finds strong evidence of acclimatization across cities
States that without consideration of displacement effects, the net impacts of heat-wave mortality are likely to be significant overestimations