Multiform flood risk in a rapidly changing world: what we do not do, what we should and why it matters

Multiform flood events are among the many climate hazards that must be appropriately defined to avoid misrepresentation of risk in a variety of modeling and assessment efforts, especially as social and economic transformational demands to avoid the worst impacts of climate change are highlighted in global reports such as the IPCC AR6, The May 2022 G7 Foreign Ministers' Statement on Strengthening Anticipatory Action in Humanitarian Assistance and The United States Bipartisan Infrastructure Bill. For example, anticipatory action program development must acknowledge that even within the context of a single event, such as a tropical cyclone, different types of floods can occur, at various time and geographic scales (with some overlapping and some not). Further, risk communication must be enhanced with multiform flood risk in mind, so that early warning messaging capturing the spatiotemporal evolution of various flood subtypes can be clearly disseminated, at appropriate lead times, to the right populations. Lastly, as other compound event types evolve, the process of moving towards flood-type specific risk assessment can inform progress towards disaggregate risk of other disaster types. Doing so is of increased importance as more sophisticated global economic models and strategies for mitigating compound risks emerge, and as climate change leads to a future with growing risk from currently known and unknown disaster types and subtypes.