  Coastal planners and decision makers design risk management strategies based
on hazard projections. However, projections can differ drastically. What causes
this divergence and which projection(s) should a decision maker adopt to create
plans and adaptation efforts for improving coastal resiliency? Using Norfolk,
Virginia, as a case study, we start to address these questions by
characterizing and quantifying the drivers of differences between published
sea-level rise and storm surge projections, and how these differences can
impact efforts to improve coastal resilience. We find that assumptions about
the complex behavior of ice sheets are the primary drivers of flood hazard
diversity. Adopting a single hazard projection neglects key uncertainties and
can lead to overconfident projections and downwards biased hazard estimates.
These results highlight key avenues to improve the usefulness of hazard
projections to inform decision-making such as (i) representing complex ice
sheet behavior, (ii) covering decision-relevant timescales beyond this century,
(iii) resolving storm surges with a low chance of occurring (e.g., a 0.2%
chance per year), (iv) considering that storm surge projections may deviate
from the historical record, and (v) communicating the considerable deep
uncertainty.
