Case studies from Brazil explore the evolution of engagement of citizens and society in flood risk assessment through three frameworks that include social aspects of risk. Such assessment requires in-depth multifaceted understanding of the complexity associated with physical factors such as depth, intensity and frequency coupled with societal interaction with reference to social memory, perception, management and adaptation. It is proposed that despite increased complexity, these assessments may be more accurate and promote risk reduction. The case studies (for events in 2015, 2018 and 2022) used different methods of interpretation. They highlight the importance of experience, of social memory and of full participation on risk response, including research around citizen science using social media data to fill gaps in hydrological datasets. The case studies exemplify some of the innovative and non-traditional complementary ways of data collection, analysis and interpretation for including human dimension of flood risk assessment.