Haiyan Surge: Wrong Place, Wrong Time

Steve's picture

2013 was a quiet season for hurricanes in the Atlantic.  In the Pacific however, one hurricane (called typhoons there) drew lots of attention --  Typhoon Haiyan.

I’ve blogged about hurricanes several times here…

http://www.openhazards.com/content/sandy-surge

http://www.openhazards.com/content/galveston-oh-galveston

http://www.openhazards.com/blogs/steve/hurricane-storm-surge-double-dose-trouble

If you have read any of these, you know that hurricanes are double-barrel disasters.  If the wind don’t get you, the storm surge will.  While hurricane winds vary fairly smoothly place to place, hurricane storm surge is far more fickle.  One coast may get 50 cm of surge, where another coast ten km away might suffer an 8 meter flood.

It is a bit more scientific than ‘luck-of-the-draw’,  but being in the wrong place at the wrong time is the kernel of the story when it comes to storm surge. In Haiyan, Tacloban City was wrong and wrong.

 

Storm surge has three elements: low pressure, waves and wind.  The storm’s low pressure draws up the sea, but the effect is small -- one meter tops.  Waves ride on the surge, but they too add perhaps a meter to the total.  The main culprit in surge is wind.  If it blows onshore long and hard enough, water ‘banks up’ and floods the land. Herein lies the fickleness. What exactly defines “onshore”, “long” and “hard enough”?   Sadly, the definition is most often revealed only after the fact in the pattern of destruction.

Look at a map of the Philippine Islands.  Coasts scatter helter-skelter.  They face every direction of the compass with a full range of exposure to the sea.  When a Typhoon passes, it stands to reason that at least one shore will be at the wrong place at the wrong time. If that location is sparsely settled, then a bullet may be dodged. If population centers there, a less happy ending ensues.

Tacloban City sits at the north end of Leyte Gulf. In Haiyan’s crossing, the Gulf acted like a funnel.  Southeast winds forced water to the funnel’s narrow end where it had no place to go save for city streets. If the storm tracked just 100 km further north, such conditions would not have developed, and Tacloban mostly spared, although perhaps at the expense of some other City this time missed.

I’ve made several surge simulations of Haiyan.  There is no narration, but I think that they effectively illustrate fickle surge.

Steven N. Ward   Santa Cruz

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