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Introduction
Heat waves are extreme weather events that can exert notable impacts on the economy and public health (Field et al. 2014). Although the definition of a heat wave varies by country and region, it is commonly characterized by a period of sustained abnormally hot weather compared to historical observations (Meehl and Tebaldi 2004). In the United States, a heat wave is often identified as a period of two or more exceedingly hot days, but the temperature metric used and the definition of extreme temperature can vary (Anderson et al. 2013; Chen et al. 2015). While the occurrence of heat waves is mostly a natural phenomenon, human activities that contribute to climate change are thought to increase the severity of heat waves (Meehl et al. 2007). Additionally, projections from global climate models indicate that the number of severe heat waves is likely to increase in the future due to increased emissions of greenhouse gases and greater urban heat island effects (Duffy and Tebaldi 2012; Coumou et al. 2013).
Heat waves have been consistently associated with increased risk of mortality based on evidence from historical extreme events (Semenza et al. 1996) and recent epidemiological studies (Anderson and Bell 2011; D’Ippoliti et al. 2010; Hajat et al. 2006; Wang et al. 2015). High ambient temperature can cause heat-related illnesses such as heat exhaustion and heat stroke, or aggravate several common cardiovascular and pulmonary conditions (Borden and Cutter 2008; Bouchama et al. 2007; Wilker et al. 2012). In the United States, extreme heat accounted for about 31% of all the weather-related deaths during 2006 to 2010 (Berko et al. 2014). A large study of 43 cities in the United States estimated that the daily mortality rate during heat wave days was 3.7% higher on average than non–heat wave days during 1987–2005 (Anderson and Bell, 2011). Epidemiologic studies have shown that the association between high temperature and mortality has decreased over the past few decades; however, contemporary health risks are still substantial (Bobb et al. 2014; Davis et al. 2003; Gasparrini et al. 2015). The decrease may be attributed to successful adaptation and mitigation strategies, such as heat warning systems, communication campaigns that lead to behavior changes, and increases in air-conditioning prevalence (Boeckmann and Rohn 2014; Hondula et al....