Thursday, November 1, 2012

Understanding Sandy's storm surge


The impact of the storm surge from Sandy on New York City and New Jersey is now becoming clear: it was tremendous. The surge at the Battery reached more than 13 feet above mean low tide, and water flooded streets and subways stations and tunnels. The screenshot is from Climate Central's sea level change forecast map, showing what a 10-foot rise in sea level will look like in lower Manhattan.

Three different but related actions contribute to a storm surge:
  • Wind - which piles water up high
  • Waves - which push the water ahead faster than the water can drain back
  • Pressure - low pressure of a hurricane means that water typically is higher near the eye
You can find a very clear explanation of a storm surge, by Jeffrey Masters of Weather Underground, here.

Why is a storm surge so damaging? All that water is heavy, and carries a lot of force. As Masters explains it,
A cubic yard of sea water weighs 1,728 pounds--almost a ton. A one-foot deep storm surge can sweep your car off the road, and it is difficult to stand in a six-inch surge. Compounding the destructive power of the rushing water is the large amount of floating debris that typically accompanies the surge.
Here's a photograph of some of the local debris deposited by the storm surge:


And yes, while no particular event is due to global warming, it's clear that global warming made Sandy worse: warmer seas meant that the storm was stronger and generated a bigger surge, and higher seas meant there was no place for the water to go but inland. Here's a good explanation.

Update: The Center for Climate and Energy Solutions has produced a useful fact sheet.

And in case you don't believe that Mitt Romney really said that the federal government should get out of the post-disaster aid business, here's a link to the transcript.


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