Environmental and health impacts of extreme heat events
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In the United States (U.S.), extreme temperature-related deaths account for far more deaths than hurricanes, lightning, tornadoes, floods, and earthquakes combined. An extreme heat event (EHE) or a heat wave is a sustained period of substantially hotter and/or more humid weather. EHEs cause a wide range of health problems such as rashes, cramps, heat exhaustion, heat stroke, and, in some instances, death. Further, meteorology plays a dominant role in the formation of air pollutants. In particular, extremely high temperatures are conducive to the formation of certain air pollutants. In order to understand the adverse health impacts of extreme heat and air pollution levels prevailing during EHEs, it is necessary to define what constitutes a heat episode; however, there is a lack of scientific consensus on definitions and procedures to accurately identify EHEs. This work employs a hierarchical clustering technique to group 92 different EHE definitions into homogeneous sets and uses negative binomial rate regression approach to identify those definitions that are most strongly associated with mortality. Our findings suggest that definitions with thresholds that are either too extreme or too moderate are poorly associated with heat-related mortality for most climate regions. Additionally, the association between air pollution and health, especially mortality, is well understood. However, the role of air pollutants in modifying the relationship between EHEs and mortality is not well characterized in the U.S., yet is critical to generating accurate estimates of health burden. Our results indicate that air pollution confounds the relationship between EHE and mortality, and the extent of confounding varies with climate regions. Further, through this work, the sensitivities associated with selecting an EHE definition is taken into consideration when providing region-specific health and economic burden associated with EHEs. Ideally, the excess deaths and costs presented in this work could be useful to study and quantify the public health risk associated with EHEs, either in a prospective or a retrospective setting.