The Why Files The Why Files --

Hurricanes: The heat is ON

Bye-bye Big Easy
Katrina was a shock, but not a surprise. Everybody worried that a hurricane might someday drown the birthplace of the blues. After Katrina, the Big Easy and the neighboring Gulf Coast have a bucketful of blues.

Family in terror waits on top of vehicle as men wade in shoulder high water to rescue them.
Volunteers rescue the Taylor family from the roof of their SUV, which was trapped on U.S. 90 due to flooding during Hurricane Katrina on Monday, Aug. 29, 2005, in Bay St. Louis, Miss. Photo : Ben Sklar/AP Photo

Thousands may be dead. Hundreds of thousands who fled the city and its low-lying environs face economic ruin and months or years of displacement, even now that the levee breaks have been fixed and the big pump-out has begun. Only a final body count will tell if Katrina will surpass the 1900 hurricane that obliterated nearby Galveston, Texas, as the deadliest natural disaster in American history.

Back in 1900, nobody was tracking hurricanes with airplanes or satellites. But satellite photos showed Katrina bearing down on the Gulf Coast, and most residents left New Orleans -- if they owned a car, that is.

The human hand?
That little discrepancy is one of several signs that, before we label Katrina a "natural disaster," we need to consider the human role. Take the whole issue of land level -- critical in New Orleans, the only major American city built below sea level.

 Seen from space, the Gulf Coast meets an azure sea.
The coasts of Louisiana, Mississippi, Alabama and part of Florida, seen from space on October 15, 2001. Original photo from NASA

Before the 1800s, the ever-sinking land of the Mississippi Delta was regularly replenished when floods brought sediment from the Mississippi River. No longer. The vast network of dams on the Mississippi River system holds most of that sediment in the north. And the levees that protect New Orleans, ironically, channel the sediment that does reach the South directly to the depths of the Gulf of Mexico.

Those same levees also route sediment away from the many low-lying barrier islands between New Orleans and the Gulf of Mexico. These islands temper hurricane winds and storm surges -- the ruinous mounds of hurricane-driven water that can boost sea level by 20 feet or more. The sediment shortage, compounded by development, channeling and oil pipelines, is annually destroying about 30 square miles of the barrier islands. In 50 to 80 years, New Orleans could stand naked before the Gulf.

But there's more. Following the earliest predictions of global warming, sea level is rising as glaciers melt and warming ocean water expands. If, as projected, sea level rises another 50 to 100 centimeters over the next century, storm surges will be yet more dangerous, and levees yet less effective.

So even if we ignore population growth along the coast and allegations that the federal government was lackadaisical in repairing levees, building up the barrier islands or responding to the flood, it's not clear that Katrina is entirely a "natural disaster."

Spirals of Katrina are just offshore, south of the Gulf Coast.
A gigantic, dangerous storm, Hurricane Katrina takes aim at New Orleans and the Mississippi coast. Photo: NASA

Global warming is warming the oceans. Hurricanes are powered by warm seas.

Could global warming make hurricanes more frequent or more intense?


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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