Urban centres worldwide are adversely affected by flooding and air pollution. Better prepared citizens are crucial to limiting the impacts of these hazards, and both lay knowledge and personal experiences are important in complementing and challenging expert opinion. For the first time, this study offers a critical comparison of how different two-way communication 10formats have been used worldwide between experts and the public in relation to flooding and air pollution risk. Through a systematic review, we analyse social media, educational programmes, serious games, citizen science, and forums in terms of their effectiveness in respect of communicating short-term incidents, long-term awareness, and long-term knowledge in the context of flooding and air pollution risk. We find that there is neither a one-size-fits-all, nor superior, format of communication. No single format is effective in fulfilling all three communication pruposes. All five formats analysed appear 15 to be successful under different circumstances and are never representative of all segments of the population. Communication between experts and the public is difficult and full of tensions, information alone is not enough. Our study shows different ways of incorporating strategies to build trust between experts and the public and make communication more fun and accessible, breaking down hierarchies and creating safe spaces for co-creation where everyone feels empowered to participate and benefits. 20