I was interviewed the other day on WNYC regarding flood events of the past few months — there is a concern that the three events that flooded some low-lying neighborhoods with roughly a foot of water signify a “new normal”, but what I’m seeing from the science and data is that we just had an unlucky few months where wind events coincided with the largest tides (spring tides).

Some think that the landscape was altered by Sandy and is leading to higher floods — I am skeptical that this has had any measurable effect.  Much like one recent study, we are evaluating whether the tide channels have changed by comparing pre-Sandy sea level data to post-Sandy data, but initial qualitative looks at the data suggest nothing abruptly changed in Jamaica Bay (or places to the east, where people are also concerned that there is “a new normal”).

In the longer-term, of course, Jamaica Bay’s inlet and channels are massively overdredged, and the recent flood was subtly AMPLIFIED (contrasting Sandy Hook and Jamaica Bay Inwood tide gauge peaks) going into the bay, whereas the shallower system of prior decades-to-centuries did not amplify flood levels. One recent research paper of ours addresses this in a very qualitative sense, but we are working on publishing some more detailed analyses comparing the 1880s landscape to the present-day, and how the present-day shipping channel amplifies flooding in the bay.

I also had a recent email exchange with NYC City Planning about whether we can measure compaction of land areas over 5-10 year periods using recent LIDAR data, but this withered and went silent recently.  It is possible that the heavy water from Sandy caused abrupt compaction in some landfilled neighborhoods, perhaps lowering land areas by many inches in one day.  That would lend credence to the claim that things have gotten worse for some locations.

Sea level rise has been about 4 inches in 25 years (10 cm), so is just a gradual change.  Actually the past few years had lower mean sea levels than the few years prior … there is year-to-year variability.  So there isn’t really a “new normal” for sea level rise, just a gradual drowning by a million drops.

Also, tides this year and in recent years and the near future are larger than normal by about an inch … there is a 19-year cycle set by the planes of the earth-moon orbit and earth-sun orbit that is at its peak right now.  So this is a minor factor, but one more …