Assessment of Compound Coastal-Riverine Flooding Risks Under Climate
Change along the U.S. Coasts
Abstract
Coastal cities are exposed to multiple flood drivers such as extreme
coastal high tide, storm surge, and extreme river discharge. The
interaction among these flood drivers may cause compound flooding
events, which could exacerbate social and economic consequences. Climate
change can put greater pressure on these areas by increasing the
frequency and intensity of coastal and riverine flooding. In this study,
a bivariate compound flooding risk assessment method is developed to
incorporate sea level rise (SLR) and nonstationary river discharge
conditions. Extreme sea water level (SWL) and river stage are identified
using the peak-over-threshold method, and subsequently, pairs of
extremes are selected when both SWL and river stage exceed their defined
thresholds within ±1 day from each other. A copula-based approach is
then used to estimate the joint distribution and return period of
compound coastal riverine flooding by incorporating nonstationarity into
the marginal distributions of extreme SWL and river stage. The future
flood risk is assessed using the notation of failure probability, which
here refers to (1) the probability of occurrence of at least one major
coastal or riverine flooding for a given design life (i.e., total flood
risk); and (2) the probability of occurrence of at least one compound
major coastal riverine flooding for a given design life (i.e., compound
flood risk). Compound flood risk assessment is conducted at 26 paired
NOAA-USGS stations along the Contiguous United States coast with
long‐term observed data and defined flood thresholds. The results
indicate that in some regions the joint return period of
coastal/riverine flooding are substantially lower when considering the
projected future hydroclimate conditions and SLR. The importance impact
of future SLR and hydroclimate conditions is discussed regionally in
terms of changes in the frequency of compound major coastal riverine
flooding events.