Seeing the hazard: Effects of visual communication in flood warning messages

This study aimed to provide deeper insight into ways of communicating flood magnitude in early warning messages (EWMs) through the use of visual cues. A total of 1,280 participants evaluated EWMs that varied in their visualization formats (warning symbols or a map) as well as in the magnitude of the communicated flood scenario. The anticipated flood magnitude served as a proxy for the understandability of the EWMs.

Survey results show that participants estimated the magnitude generally well, specifically for extreme events, while for medium events the magnitude could not be determined as clearly. There was only a small significant difference between the usage of a generic warning symbol and that of a hazard-specific symbol. Maps had a significant effect and worked best in comparison to the magnitude we assigned to the described flood scenarios. Along with the name of the area at risk, the time of inundation, recommendations on safe behavior, and an evaluation of the severity of the situation, maps are the most favored item to be included in EWMs. Visual cues in general offer the opportunity to communicate across language barriers, but in the future there needs to be international standardization of color schemes and symbology.