Heat waves kill more Americans, on average, each year than any other extreme weather event, and ambient heat causes more deaths than any other natural hazard, with the exception of cold weather.1^,2 Impacts are generally more concentrated in urban areas like New York City (NYC) due to the density of populations at risk, and may be exacerbated by characteristics of the landscape that intensify heat.3 In the summer of 2006, there were 46 heat stroke deaths in NYC associated with two July heat waves. Among cases where air conditioning (AC) status was ascertained, the vast majority did not have a working AC.4 In recent years, more than 80 % of decedents have been exposed at home.5

Furthermore, the NYC Panel on Climate Change projects that summers will be hotter and the number and intensity of heat waves will continue to increase.6 Heat illness prevention efforts in NYC have focused on improving access to and promotion of the use of AC, the most effective intervention supported by the literature.4,7^–11

Public messaging and the activation of emergency response plans are triggered by heat advisories, watches, and warnings released by the National Weather Service when the maximum heat index is forecast to reach 100 °F for any period of time, or 95 °F for at least two consecutive days.

During heat emergencies, NYC’s Office of Emergency Management coordinates a multi-agency response that incorporates widely recommended best practices for protecting health during extreme heat events.12 The response includes extensive risk communication and opening hundreds of “cooling centers,” which are air-conditioned public spaces, such as senior centers, public housing community rooms, and libraries that are open for extended hours and promoted as places where the public can seek relief from the heat. Public messaging is disseminated through press releases, heat safety brochures, email alerts to health care and social service providers, and emails and text alerts for members of the general public who sign up for emergency notifications. At-risk individuals are advised to visit a cooling center or use AC set at 78 °F or “low cool” to lessen strain on the energy grid while providing an environment that is protective of health. Information is provided to organizations serving populations with special health needs so they can help vulnerable clients stay cool. Heat safety brochures and other materials are distributed year-round.

Despite these extensive heat-illness prevention efforts, little is known about whether at-risk populations and their social contacts are aware of heat warnings or take effective steps to protect their health during periods of extreme heat. Some evidence from other localities indicates that vulnerable groups may not be receiving necessary heat information, and that awareness of extreme heat warnings is not always coupled with an understanding of heat-health risk factors and behavior change.13

To inform improvements in heat risk communications and other public health measures, we conducted quantitative and qualitative studies about heat-health awareness and behaviors. First, a telephone survey of a probability sample of NYC adults was administered to examine AC access, heat-illness prevention behaviors, and awareness of heat-health warnings. Next, we convened focus groups to elicit qualitative information about heat-health knowledge and behaviors among seniors, who are among the most vulnerable to heat illness and death, and potential senior caregivers.

Penetration of heat warnings was generally high among New Yorkers, however, awareness among the “most vulnerable” group was lower. Furthermore, nearly half of the most vulnerable group reported staying home during hot weather, where indoor temperature can be higher than outdoors during hot weather in the absence of AC.19 Stay-at-home behavior among this group was not associated with warning awareness, suggesting that messages in the warnings are not resonating with this group and/or that there are other important barriers to protective action. Reasons for not owning or using AC during very hot weather included cost, as well as a dislike of AC or a feeling that it was not needed, indicating that gaps in personal risk perception may also be an obstacle to heat-health protection. The focus groups also suggested a gap between risk awareness and personal risk perception.

Misconceptions about the benefits of electric fans may also impact risk perception. Retrospective observational studies in the USA have found no protective effect of electric fans during extreme heat.7^,8^,20^,21 Researchers have theorized that circulation of ambient air that is cooler than normal body temperature is necessary for fans to provide effective cooling through convection.22 However, nearly 20 % of survey respondents with a health risk factor who do not have AC or never/rarely used AC during very hot weather reported that the main reason was a preference for using a fan instead. Senior focus group participants expressed a similar preference for fan use during hot weather; many reported using fans incorrectly during hot weather.

Vulnerable people may have other reasons for staying home besides risk perception. While only a minority of NYC respondents cited health and safety concerns as reasons for staying home during hot weather, fears of crime or feeling that a neighborhood was unsafe were also reasons why residents stayed in unsafe home environments during the deadly 1995 Chicago heat wave.23 Seniors may also avoid leaving home for other safety reasons, including fear of injury.24 A 2011 survey of Toronto residents also found that the majority of people without AC stay home during hot weather; distance to cooling shelters and lack of transport were frequently cited as barriers to leaving home.25 In our survey, however, transportation was not singled out as a main barrier to leaving home (Table 3).

Studies in other areas have reported mixed findings about the relationship between warning awareness and behavior change.13 A multicity phone survey found that 90 % of respondents were aware of heat warnings but many did not consider themselves to be vulnerable to heat and few reported changes in their behavior as a result of the warnings.26 In France, however, increased awareness of heat warnings was positively linked with changes in prevention practices from 2005 to 2006.13 Of note, this study took place after the 2003 European heat wave, which killed more than 14,000 people in France, one of the deadliest heat waves ever recorded.27 The French public may have been more attuned to the dangers of heat after this devastating event.

The proportion of New Yorkers without AC (11 %) was consistent with estimates from the 2007 NYC Community Health Survey (13 %) and with findings of a multicity phone survey of residents aged ≥65 in Philadelphia, Phoenix, Toronto, and Dayton, Ohio.26^,28 The finding that many NYC residents own but rarely or never use an AC during hot weather because of costs is also consistent with the multicity survey.26 In addition, another multicity study found that densely populated cities—such as New York City—with lower and more variable temperatures during the warm season had more heat-related morbidity/mortality. The prevalence of AC in these cities also tended to be lower than more consistently warmer cities, suggesting that the higher burden of heat mortality in areas with more variable temperatures may be related to home AC prevalence.29

Findings from the survey and focus groups suggest that helping the public to understand and evaluate their own risk needs to be a component of heat-health programs, in addition to increasing access to home AC for the most vulnerable and making cooling centers accessible. Promoting “checking in” on vulnerable friends, family members, and neighbors during heat waves could encourage at-risk individuals to use AC and take other protective measures. NYC officials regularly urge the public to check on others during heat emergencies, but the frequency of this behavior had never been assessed. The survey indicated that 54 % of people check on others, a figure that can be used as a baseline to inform efforts to encourage “buddy systems.” While encouraging, more work is needed to target and evaluate the efficacy of this strategy for heat illness prevention.

There are several potential limits to our analyses. Closed-ended survey questions may miss information not included as a response option or obscure nuanced and multiple reasons for responses. Respondents may also interpret questions differently. For instance, rather than specifying a temperature to define “very hot weather,” respondents were allowed to answer based on their own perceptions of uncomfortable heat, since there is no single “safe” threshold. In addition, response categories for frequency of AC use at home during very hot weather were along a scale of “always,” “most of the time,” “half the time,” “less than half the time” and “never.” The “less than half the time” response likely includes levels of AC use that is inadequate to protect health and some levels of use that may be protective. The survey sample size was sufficiently large to estimate prevalences, but was too small to test for statistical differences in prevalence between subgroups in some cases.

No questions were asked about specific health conditions that are known to increase heat susceptibility, such as diabetes or cardiovascular disease. Poor self-rated health has been associated with an increased risk of mortality in many studies, even controlling for covariates such as age and comorbidities,30 and the measure has been recognized as a useful indicator for risk assessment.14 In NYC, poor–fair self-rated health status has been associated with self-reported chronic health conditions that increase heat susceptibility in the annual NYC Community Health Survey.15 However, the relationship between self-rated health and “objective” health status has not been fully described and explained.31 A number of factors can affect perceptions, and thus reporting, of one’s own health status, such as undiagnosed conditions or cultural norms. Misclassification remains a major limitation to this study, as health status is limited to self-reported data. Some heat-vulnerable people likely were not included in the group that we defined as “vulnerable” (using self-rated health status, age, and AC access), while others who are not heat-vulnerable may have been included.

Focus groups provided qualitative information about the knowledge, attitudes, and behaviors of a small group of people, and responses are not meant to be representative samples of seniors and potential caregivers in NYC. Senior participants were relatively mobile and able to attend early evening focus groups. However, seniors in relatively good health today may experience declining health in the future, and can still provide a source of insight into heat-health attitudes and behaviors useful in shaping programs. Finally, a systematic analysis of all heat-related media from the summer of 2011 was not performed.

On average, heat waves are the most lethal extreme weather event in the USA.2 Despite substantial efforts to prevent heat-related morbidity and mortality, 30 % of the most vulnerable New Yorkers in this study population were unaware of warnings about dangerously hot weather in 2011. Even those who are aware of warnings may not consider themselves to be at risk, or consider AC to be a primary protective strategy during hot weather. Many vulnerable people stay home during hot weather, even if they cannot stay cool there. Other urban areas may face similar challenges.

More effective communication and educational efforts are needed to reach heat-vulnerable populations and help motivate effective protective behaviors. More research is needed to understand which risk communications methods and programs are most effective in motivating people to engage in protective behaviors, including use of AC and utilization of cooling centers. In the meantime, heat-health risk communication should emphasize that extreme heat can be deadly, hot indoor environments are dangerous during extreme heat, and that AC is a life-saving intervention for people who are vulnerable to heat illness. Closer collaboration between public health agencies and meteorologists and others in broadcast media should be explored to help ensure clear and accurate risk communication and amplify the reach and effect of public health messages.

Access to AC was also lower among those with low household income. Increasing access to AC in the home—for example, assistance with purchasing and operating costs—and enlisting members of the general public to check on heat-vulnerable social contacts, including informing them of effective ways to protect themselves and actively assisting them in staying cool, will also likely be important strategies to avert illness and death during heat waves, now, and in the future.