“The flood risk for New York City due to tropical cyclones and their resultant storm surges has increased significantly during the last millennium. Mean flood heights increased by >1.2 m from ∼A.D. 850 to A.D. 2005 due to rising relative sea levels. Additionally, there were increases in the types of tropical cyclones that produce the greatest surges for the region. Subsequently, the 500-y flood height return periods have fallen to ∼24.4 y throughout the millennium.”
Andra J. Reed, Michael E. Mann, Kerry A. Emanuel, Ning Lin, Benjamin P. Horton, Andrew C. Kemp, and Jeffrey P. Donnelly, Increased threat of tropical cyclones and coastal flooding to New York City during the anthropogenic era, PNAS 2015 ; published ahead of print September 28, 2015, doi:10.1073/pnas.1513127112
Figure: Distributions of flood heights for the pre-anthropogenic era (blue) and the anthropogenic era (red) for (A) the MPI model, (B) the CCSM4 model, and (C) the IPSL model. Each distribution is normalized by the number of events it contains. The 99% confidence interval, found by running 100,000 bootstraps of the mean of each set, is shown in light blue for pre-anthropogenic era flood events, and in light red for anthropogenic era flood events.
In a changing climate, future inundation of the United States’ Atlantic coast will depend on both storm surges during tropical cyclones and the rising relative sea levels on which those surges occur. However, the observational record of tropical cyclones in the North Atlantic basin is too short (A.D. 1851 to present) to accurately assess long-term trends in storm activity. To overcome this limitation, we use proxy sea level records, and downscale three CMIP5 models to generate large synthetic tropical cyclone data sets for the North Atlantic basin; driving climate conditions span from A.D. 850 to A.D. 2005. We compare pre-anthropogenic era (A.D. 850–1800) and anthropogenic era (A.D.1970–2005) storm surge model results for New York City, exposing links between increased rates of sea level rise and storm flood heights. We find that mean flood heights increased by ∼1.24 m (due mainly to sea level rise) from ∼A.D. 850 to the anthropogenic era, a result that is significant at the 99% confidence level. Additionally, changes in tropical cyclone characteristics have led to increases in the extremes of the types of storms that create the largest storm surges for New York City. As a result, flood risk has greatly increased for the region; for example, the 500-y return period for a ∼2.25-m flood height during the pre-anthropogenic era has decreased to ∼24.4 y in the anthropogenic era. Our results indicate the impacts of climate change on coastal inundation, and call for advanced risk management strategies.