What defines a flood

While the term 'flood' may elicit clear images of rushing water or overflowing river banks, genuine concerns around formally demarcating this phenomenon remain. In this paper, we investigate the phenomenon's conceptual space, discussing its physical and social components. We highlight key features of the term, as it is commonly used, while illustrating existing conceptual challenges, including the lack of direct reference to the assumptions about how things ought to be, what the philosophical literature calls normativity, involved in setting relevance parameters and the rarity threshold. We propose defining the flood phenomenon by referencing both its physical and normative properties. Within this demarcation framework, physical floods constitute pools or fluxes of water beyond a normatively-specified rarity threshold. A second demarcation occurs when a notion of desirability is used to identify if the presence of water is bad or good. Anthropocentric floods are then physical floods deemed undesirable or desirable. Recognizing the uncertainty present in identifying and adopting notions of desirability can then help explain instances of lack of consensus in communities, what we call interventional ambiguity, on whether to seek engineered solutions to specific flood-related problems. Our demarcation framework can facilitate cross-disciplinary communication and motivate further refinement of flood-related concepts.