Seeing the Hazard: Effects of Visual Communication in Flood Warning Messages

Abstract

Early warning messages (EWMs) are a crisis communication tool to prepare citizens to take action, save lives, and prevent damage in case of an approaching flood. They should be simple, but at the same time sufficient, inform recipients about the magnitude, timing, and possible impacts, and offer recommendations on actions to take. Past flood events in Germany have revealed communication problems with the distributed EWMs, as although citizens did receive one, the magnitude was not well communicated, leading to confusion and either no or maladaptive behavior. To better communicate such information, visual cues can be added to EWMs. In an experimental online survey, 1280 participants were confronted with flood EWMs including different warning symbols or a map displaying a fluvial flood scenario (riverine flooding with several hours of lead time). The influence of the warning symbology on the perceived event magnitude served as a proxy to gain deeper insights into the effectiveness of including visual cues. 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.