Coastal Vulnerability in Long Island Sound: The Spatial Structure of Extreme Sea Level Statistics

The magnitude of the change of coastal sea level during storms is a crucial parameter in planning cost-effective coastal construction projects and wise environmental management strategies. We summarize the frequency of occurrence of meteorologically forced high water level anomalies in Long Island Sound using archived sea level records. We then explain the spatial variation of the return interval for anomalies resulting from extra-tropical (nor'easters) and tropical (hurricanes) cyclones. Extra-tropical cyclones generate much larger sea level anomalies in the western Sound because the locally generated setup augments the shelf response. As a result, 2m anomalies due to nor'easters have a return period of approximately a decade in the western Sound and a century in the eastern Sound. Hurricanes are infrequent and affect New England in the late summer. The direction of the winds they induce and their rapid translation speeds do not lead to the same superposition of effects; therefore, statistics of sea level extremes in the summer are similar throughout the Sound. The return period for a 2m surge due to a hurricane is approximately a century. Since larger anomalies occur much more frequently in the western Sound than the east, it is likely that the coastal communities in the east are more vulnerable to hurricane induced surges. Further, since sea level rise will have a greater impact on the return periods of large surges in the eastern Sound the vulnerability will increase.