  Low-lying coastal cities across the world are vulnerable to the combined
impact of rainfall and storm tide. However, existing approaches lack the
ability to model the combined effect of these flood mechanisms. Thus, to
increase flood resilience, modeling techniques to improve understanding and
prediction of the combined effect of these flood hazards are critical. To
address this need, this study presents a modeling system for assessing the
combined flood risk to coastal cities under changing climate conditions that
leverages ocean modeling with land surface modeling capable of resolving urban
drainage infrastructure within the city. The modeling approach is demonstrated
in quantifying the future impact on transportation infrastructure within
Norfolk, Virginia USA. A series of combined storms events are modeled for
current (2020) and projected future (2070) climate conditions. Results show
that pluvial flooding causes a larger interruption to the transportation
network compared to tidal flooding under current climate conditions. By 2070,
however, tidal flooding will be the dominant flooding mechanism with even
nuisance flooding expected to happen daily due to SLR. In 2070, nuisance
flooding is expected to cause a 4.6% total link close time (TLC), which is more
than two times that of a 50-year storm surge (1.8% TLC) in 2020. The coupled
model was compared with a widely used but physically simplistic bathtub method
to assess the difference resulting from the more complex modeling presented.
Results show that the bathtub method overestimated the flooded area near the
shoreline by 9.5% and 3.1% for a 10-year storm surge event in 2020 and 2070,
respectively, but underestimated flooded area in the inland region by 9.0% and
4.0% for the same events. The findings demonstrate the benefit of sophisticated
modeling methods in climate adaptive planning and policy in coastal
communities.
