Joint projections of US East Coast sea level and storm surge using a novel flood index

Future coastal flood risk will be strongly influenced by: 1) sea level rise (SLR) and 2) changes in the frequency and intensity of tropical cyclones (TCs). These two factors are generally considered independently. Here, we assess 21st century changes in the United States East Coast hazard using a flood index (FI) that accounts for changes in flood duration and magni- tude driven by SLR and changes in Power Dissipation Index (PDI, an integrated measure of TC intensity, frequency, and duration). SLR and PDI are derived from representative con- centration pathway (RCP) simulations of 15 atmosphere-ocean general circulation models (AOGCMs). By 2080-2099, changes in the FI relative to 1986-2005 are substantial and posi- tively skewed: a 10th-90th percentile range of 4-75× higher in RCP 2.6 and 35-350× higher for RCP 8.5. High-end FI projections are driven by three AOGCMs that project the largest increases in SLR, PDI, and upper ocean temperatures. Changes in PDI are particularly in- fluential if their intra-model correlation with SLR is included, increasing the RCP 8.5 90th percentile FI by an additional 25%. SLR arising from other, possibly correlated, climate processes (e.g. ice sheet and glacier mass changes) will further increase coastal flood risk and should be accounted for in comprehensive assessments.Peer reviewe