An increase in the number of unusually warm days has been observed at the global scale since 1950 [1,2]. In that context, the relationship between extreme heat and mortality has been widely documented [3,4,5,6,7]. There is also evidence for a relationship between extreme heat and morbidity [8,9,10].

The impact of extreme heat on mortality is influenced by the existence and quality of health services, living conditions such as housing, individual coping strategies and the existence of heat plans [11,12]. Consequently, national action plans have been implemented to prevent and minimize the impact of extreme heat on health in affected countries such as Portugal and Spain [13,14].

Heat-related risk perceptions can change according to personal experience and level of trust in authorities [15]. Perceptions of extreme heat-related risks may influence community behavior [16,17].

It is therefore important to understand the general population’s knowledge about national heat plans, extreme heat-related risk groups, symptoms and protective measures. We conducted a survey with residents in Lisbon and Madrid in order to assess that knowledge.

We carried out a cross-sectional observational study, using a questionnaire previously utilized in Brussels and Amsterdam (see Appendix A) [18]. We conducted the survey in Lisbon on 20–22 June 2016 and in Madrid on 29 June–1 July 2016. This summer period was chosen to be able to ask about heat awareness during a warm time. A team of two surveyors and a field coordinator carried out the survey in each city. We used a convenience sample of passers-by located in six survey locations in each city presenting different socio-economic backgrounds [19]. At least 20 interviews were carried out per each of the 12 survey locations. Passers-by were asked to participate and provided verbal consent. Interviews were conducted in Portuguese, Spanish or English. Individuals older than 12 years, living in Lisbon or Madrid and speaking one of the survey languages were eligible for inclusion. We excluded respondents who were not living in Lisbon or Madrid and without information on age, education or nationality.

The questionnaire included questions on the demographics age, sex, nationality and mother tongue. Locals or foreigners were categorized using nationality; locals were identified if respondents’ nationality was Portuguese in Lisbon or Spanish in Madrid, and foreigners if not. Mother tongue was established according to the nationality of the respondent. We used open questions to ask whether respondents could name any heat-related risk groups, symptoms for extreme heat, protective measures against adverse heat-related health effects and responsibility to take actions about increases in temperature, without providing the respondents with any answers. Multiple answers were possible and we recorded each of the reported answers of the open questions in a check-box format. We calculated the proportion of respondents who reported responses to these open questions. In addition, respondents were asked whether they were familiar with the national heat plan, whether they believed there has been an increase in temperature in the recent past, whether they considered themselves sensitive to extreme heat and whether the government was doing enough to raise awareness on this issue.

We compared the 12 survey locations that we had selected according to socio-economic background. We compared the results between Lisbon and Madrid, using Pearson Chi-square Tests and Fisher’s exact test when appropriate. A p-value (p) of <0.05 was considered to be statistically significant based on two-sided tests. Data were analyzed using Stata 14 (StataCorp, College Station, TX, USA).

Following the Portuguese and Spanish pertinent laws [20,21], the study was exempted from ethical committee approval, since data related to individual health was not collected, nor were individual names.

Our study showed that less than a third of the respondents had knowledge about the existence of a national heat plan, whereas practical concepts to face extreme heat, such as knowledge of risk groups and protective measures, were widely recognized.

Regular exposure to extreme heat in Lisbon and Madrid can explain the knowledge of some of the practical measures to be protected against the heat. Also, the low perception of being sensitive to heat can be explained by the regular exposure to heat. Previous experience from a natural hazard without direct damage can decrease the risk perception [15,22]. A very remote perception of risk may mean less perceived need for information and it has been reported as a reason for low knowledge of the heat plan [23]. This perception could mean avoidant behavior towards preventive measures [17].

Locals also had a better knowledge about certain risk groups, symptoms and protective measures and knew better about the heat plan when compared with foreigners, despite having a lower education. This could be explained by locals being more exposed to local media and better targeted by local campaign messages [24]. This is also supported by our finding of greater heat plan knowledge in foreigners whose mother tongue was Portuguese or Spanish (in Lisbon or Madrid) compared to foreigners from countries speaking other languages. This can be explained by communication materials mostly being disseminated in Portuguese for Lisbon and in Spanish for Madrid [14], which may be less effective for residents of other nationalities. Evidence suggests that immigrants who are comfortable with the local language are more exposed to health information and have a higher trust in it than those who do not master the language [25]. The use of other languages for communication materials on heat should be piloted in neighborhoods with high proportions of foreigners. Individuals from other nationalities belonging to risk groups should be specifically addressed by their general practitioners in Lisbon and Madrid in order to enhance the recommendations to face extreme heat.

Similar surveys in Brussels and Amsterdam [18] identified a difference in knowledge among respondents with different educational levels where respondents with a lower educational level reported a lower knowledge. Consequently, it was recommended to target awareness-raising campaigns at citizens with a lower educational level in Brussels and Amsterdam. Our findings in Lisbon and Madrid show that educational level is not significantly associated with a lower knowledge about the plan. This difference between the study in Brussels and Amsterdam and our study may be due to education not being such an influencing factor on where citizens are more regularly exposed to extreme heat, such as in Lisbon and Madrid. We showed that citizens from other nationalities were less knowledgeable, independent of educational level, and should be specifically targeted. Both studies identified specific groups; therefore, they highlight the importance of addressing specific groups when communicating public health messages on heat.

The familiarity with the existing national heat plans was lower in Madrid (25.2%) than in Lisbon (37.2%), Amsterdam (33.1%) and Brussels (39.3%) [18]. When compared with other northern European cities such as London, Norwich, Brussels and Amsterdam [18,26], respondents in Lisbon and Madrid more often stated that their government provided too little awareness about extreme heat. This may be related to citizens in these two cities being less knowledgeable about the government’s actions, such as the heat plan, therefore feeling that their governments do not inform them enough. National and region-specific adapted campaigns about heat plans, specific groups and measures are therefore recommended [3]. Further qualitative methods could be used for in-depth understanding of the reasons for this knowledge.

The main limitation of our study is the small sample which doesn´t allow generalizability to the cities of Lisbon and Madrid. Nonetheless, these results provide insight on the knowledge and attitudes of citizens to health risks and heat plans. Another important limitation is that nationality was used as a proxy for the respondents’ mother tongue while that may not have been the case.

In Madrid and Lisbon, citizens’ knowledge of the impact of extreme heat was higher for practical concepts such as certain risk groups and protective measures than for the existence of a national heat plan. This practical knowledge can have public health implications, where the general population can be mindful of identifying those people at risk. Foreigners were less aware than locals, despite having a higher educational level. Knowledge of heat-related risk groups and how citizens can protect themselves from extreme heat should be improved. Tailored and targeted approaches should be considered during health campaigns to reach residents from other nationalities.