J46.1 Record-Setting Heat and Heat-Related Deaths in Maricopa County, AZ, in 2016: Cause and Effect?

Wednesday, 10 January 2018: 1:30 PM
Room 17B (ACC) (Austin, Texas)
David M. Hondula, Arizona State Univ., Tempe, AZ; and H. Putnam, A. Urban, P. Iniguez, and V. Berisha

Summer 2016 was a record-setting year in terms of summer heat and its impacts on health in Maricopa County, Arizona, USA. The month of June was the warmest on record in the NOAA Climate Division within which Maricopa County is located and the six-month warm season spanning May through October was the fourth warmest. This record-setting heat occurred coincidentally with a record number of heat-related deaths in the county according to the unique surveillance program run by the Maricopa County Department of Public Health. The 141 confirmed heat-related deaths in 2016 exceeded the previous record by 31 cases and was more than 50% above the prior ten-year average. We conducted a retrodictive analysis of the time series of heat-related death records to understand the extent to which the abnormally high heat-related death count in 2016 was driven by meteorology. We first estimated the historical association between observed weather and heat-related deaths for the time period 2006-2015 using a time series regression model. Subsequently, we used the model to generate “predictions” of daily heat-related deaths in 2016 based on the observed meteorology.

Simple temperature-mortality models all showed a clear and strong relationship with historical daily heat-related deaths. Mean temperature was more strongly associated with heat-related deaths over the period 2006-2015 than minimum or maximum temperature, although differences between the models were very small. However, there was a much weaker association of the relationship between modeled and observed heat-related deaths when the model predictions and observations were aggregated by year. Using a simple mean temperature-mortality model, we would have anticipated 80 heat-related deaths in 2016 based on the observed meteorology. Regardless of the exposure variable or model parameterization chosen, the prediction for 2016 using a simple temperature-mortality model fell well below the historical average number of heat-related deaths.

In summary, we were unable to find strong evidence that the unusually high number of heat-related deaths observed in Maricopa County, Arizona in 2016 was related to observed meteorological conditions. Most models, in fact, suggested that 2016 should have been a year with normal or below-normal number of heat-related deaths. If the conventional methods for estimating the temperature-mortality association are reasonably approximating a causal relationship, our results indicate that factors other than the weather were entirely responsible for the surge in heat related deaths in 2016. These findings highlight the importance of non-meteorological factors as drivers of the health burden associated with extreme temperatures, which have generally not been included in quantitative retrospective or prospective studies. Further, they highlight a shortcoming in preparedness and response efforts for heat in the community that should be diagnosed more specifically and addressed as soon as possible. We are challenged to look more broadly and deeply to identify and address root causes of heat-related deaths.

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