Developing more useful equity measurements for flood-risk management

Decision-makers increasingly invoke equity to motivate, design, implement and evaluate strategies for managing flood risks. Unfortunately, there is little guidance on how analysts can develop measurements that support these tasks. Here we analyse how equity can be defined and measured by surveying 167 peer-reviewed publications that explicitly state an interest in equity in the context of flood-risk management. Our main result is a taxonomy that systematizes how equity has been, and can be, defined and measured in flood-risk research. The taxonomy embodies how equity is a pluralistic and unavoidably ethical concept. Despite this, we find that most quantitative studies fail to motivate or defend critical value judgements on which their findings depend. We also find that studies often include only a single equity measurement. This practice can overlook important trade-offs between competing perspectives on equity. For example, the few studies that employ distinct principles show that conclusions about equity depend on which principle underlies a specific measurement and how that principle is operationalized. We draw on our analysis to suggest practices for developing more useful equity indicators and performing more comprehensive quantitative equity assessments in the broader context of environmental risks.