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 formats 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 dealing with incidents, raising awareness, and promoting knowledge exchange 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 purposes. All five formats analysed appear to be successful under different circumstances and are never suitable for 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 everyone benefits.