On Sandy’s return period

I’m making it a bit of a mission to recruit younger colleagues, especially postdocs and graduate students, to try writing for nonscientist audiences. In this piece, new PhD Madeleine Lopeman (Columbia Civil Engineering, just defended her thesis, advisor Prof. George Deodatis), explains how her innovative extreme value analysis of tide gauge data at the Battery yields a lower return period for Sandy than all previous ones – meaning maybe it wasn’t all that rare an event after all.

An interesting question is what relationship there is, if any, between return periods defined for different characteristics, either of the storm itself or its impacts. Tim Hall and I published a paper in 2013, for example, that estimated a 700-year return period (95% confidence interval 400-1400 years) for the track of Sandy – strictly, for a storm with at least category 1 intensity intersecting the New Jersey coast at an angle at least as steep as Sandy’s track did. Despite the different numbers, our estimate could be consistent with Madeleine’s, because the numbers describe two different things. It’s reasonable to expect the return period for the flood at the Battery to be shorter than that for the track, because one could get the same flood from tracks coming in at shallower angles if the storm had stronger winds, or made landfall closer to NYC.

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