Storm surge is among the most severe hazards of landfalling tropical cyclones (TCs), causing almost half of fatalities associated with TCs in the United States. Due to global warming, sea level rise (SLR) is expected to exacerbate storm surges and coastal flooding. Furthermore, TC intensity, which is one of the main drivers of storm surges, is also projected to increase in a warmer future climate. We therefore investigated the combined impact of projected SLR and increased TC intensity on the storm surge generated by 10 historically impactful TC events in the last decade. We performed storm surge simulations with the ADvanced CIRCulation (ADCIRC) model. The historical control simulations were forced by the meteorological boundary conditions of the TC events and the present-day sea level. To represent the TC events in the future, we enhanced the intensity of the TCs by 10% at the time of landfall, in line with future projections. Additionally, we investigated two future SLR scenarios (0.44m and 0.74m). We conducted storm surge experiments to investigate the effects of SLR and stronger TCs individually and in combination using the (i) historical meteorological conditions and the future SLR scenarios, (ii) future meteorological conditions and present sea-level conditions, and (iii) future meteorological conditions and SLR scenarios.

We found that increasing TC intensity has minimal influence on the inundated area compared to SLR. When TC intensity is increased by 10% only, the mean change in the inundated area across all TC events is about 5% relative to the historical control. On the other hand, the mean change when considering SLR only is 90% and 165% for SLR levels of 0.44m and 0.74m respectively. The combined impact of both SLR and TC intensity increase results in a mean change of 91% and 166% for a 10% increase in TC intensity with SLR levels of 0.44m and 0.74m respectively. However, increasing TC intensity has a considerable impact on the inundation volume, as a 10% increase in intensity leads to about 12% greater inundation volume on average relative to the historical control. SLR only also increases the inundation volume by about 11% for a 0.44m SLR and 24% for 0.74m SLR. The impact of combined SLR and TC intensity increase on inundation volume is much larger. The increased volume of inundation is dominant along the path of the TC and around the location of landfall when only TC intensity is increased, whereas SLR causes the water to spread out to other locations, which implies an increase in flooding extent. In the experiments with SLR, we also found that the duration of surge inundation decreases regardless of whether the TC intensity increases or remains unchanged.