The Effects of Maximum and Minimum Temperatures on Deaths Attributed to Environmental Heat in Maricopa County, 2006-2013

BACKGROUND:   Environmental heat-associated deaths in Maricopa County (MC) are highest during the months of June, July, and August. During this period, the temperatures range from 92-118 °F for maximum daytime temperature, and 71-96 °F for nighttime temperature. Prolonged exposure to the combination of high maximum and high minimum temperatures has been thought to inhibit adequate body cooling, therefore, the number of heat-associated deaths tend to increase during these months. Study Objective: The purpose of this study is to investigate the relationship between environmental heat and mortality in Maricopa County, Arizona in order to determine the association between daily maximum and minimum temperatures and attributed deaths.

METHODS:   Maricopa County Department of Public Health (MCDPH) tabulated the number of confirmed heat-associated deaths during the summer months (June, July and August) between the years 2006 – 2013. In order to examine the relationship between minimum temperatures and deaths more precisely, the minimum temperatures were further grouped into following increments: 71-79 °F, 80-89 °F, and 90-96 °F. Correlation coefficients were calculated between the number of deaths and the minimum and maximum temperature.

RESULTS:   MCDPH identified 552 heat-associated deaths during the months June through August in the years 2006-2013. During this time span, the number of deaths in the given temperature ranges were:  72 (13%) between 71-79°F; 308 (56%) between 80-89°F; and 172 (31%) between 90-96°F. Seventy two percent of deaths occurred when minimum temperatures reached 84°F and above. A plot of basic mortality-temperature relation suggests a correlation between the average low and average high temperatures for the given years. Spearman’s shows significant correlation minimum and maximum temperatures and mortality, 0.631 p-values 0.000712 and 0.537, p-value 0.000388 respectively.  Analysis for indoor and outdoor heat associated deaths was performed as well.

CONCLUSIONS: Maximum temperatures in Arizona were once thought to be critical for community health.  These results suggest that during Maricopa County’s June, July, and August temperatures, both maximum and minimum temperatures leave people vulnerable to Arizona’s environmental heat. Per this study we see that minimum temperatures pose a threat in heat mortality.  Alerting people that they are at risk by being exposed to these minimum daily temperatures can keep our community safe and healthy.