Heat warnings at your fingertips: public preferences for timing and temperature in Germany

The impacts of natural hazards on society are increasing. In response, many countries have developed multi-hazard digital early warning systems (EWS) to avoid harm when hazards are immanent. Some of these systems are automated, particularly for sudden-onset natural hazards. However, the deadliest natural hazard is excessive heat and heat is often not included in the standard portfolio of warnings. Additionally, warning protocols for sudden-onset hazards are not necessarily appropriate for excessive heat because of differences in timing and duration. Of course, EWS are only effective if used. We assess whether and how German residents (n=2,007) would like to be warned about extreme heat and which features of a digital heat EWS they consider most useful. On average, respondents would like to be warned two days before temperatures are predicted to reach 32° Celsius or higher. They also prefer to be warned by a push notification from a warning app which also provides personalised information about what to do and how to cope with the heat. Older respondents preferred to be warned at a lower trigger temperature. Disseminating heat warnings through the relatively newly established cell broadcast system was not preferred, possibly because warning messages on what to do in hot weather cannot be personalised. Our results can help to mainstream the inclusion of heat into the warning landscape. Except under extreme conditions, warnings, with the help of AI, should move away from meteorological index-based warnings towards people-centred impact warnings.