The risk of storm floods is increasing and is enhanced by climate change, as the water level is rising and the temperature shift is warming up oceans and the atmosphere, increasing storms and heavy rain. Therefore, governments, cities, and urban areas, often settled close to water due to economic benefits, should react and prepare for this by further developing emergency management. In doing so, we examine how mobile applications should be designed to support citizens during storm floods to support and self-secure them. Therefore, we initiated a design science research project, conducted interviews with citizens and emergency-relevant stakeholders, identified twelve issues, formulated twelve meta-requirements, and derived four initial design principles. We instantiated these with a prototype that we evaluated with ten more citizens and emergency-relevant stakeholders to approve and further develop these. The derived design principles were approved, and three new ones were derived, highlighting the possibilities of local-based evacuation routes, bidirectional communication, and data collection by citizens. Overall, this study contributes to the emergency management domain, focusing on floods with meta-requirements, design principles, and an IT artifact to support practitioners with guidance and lay a theoretical foundation for further research in developing extensive mobile applications for evacuating citizens in large cities before and during floods.