Assessing population exposure to coastal flooding due to sea level rise

Exposure of populations to sea-level rise (SLR) is a key indicator of climate impacts on coasts, yet assessments often rely on narrow spatial zones that imply different time horizons of impact. We show how choosing among common spatial zones—the future high-tide line (specified SLR levels), coastal floodplains (e.g., 100-year floodplain), and the low-elevation coastal zone (LECZ)—produces differing exposure estimates across space and time. We implement a spatio-temporal flood-modeling approach that integrates across these zones to estimate the expected annual exposure (EAE) of population to flooding in any given year. Applying the model to the coastal United States, we find that clearer, more explicit choices of spatial zone and associated temporal implications improve adaptation planning by indicating the relative likelihood and magnitude of populations affected by future SLR.