28 August 2005

Of hurricanes and tsunami

There's an interesting WaPo article up about the potential impact of Hurricane Katrina. There's another available on CNN's website, titled, "Katrina may be 'our asian tsunami'". After reading the first, I found the title of the second to be somewhat ironic.

In the CNN "our tsunami" article, the potential for hurricane-caused toxic chemical releases is outlined:
Some 25 feet of standing water is expected in many parts of the city -- almost twice the height of the average home -- and computer models suggest that more than 80 percent of buildings would be badly damaged or destroyed, he said. (Watch a report on the worst-case scenario)

Floodwaters from the east will carry toxic waste from the "Industrial Canal" area, nicknamed after the chemical plants there. From the west, floodwaters would flow through the Norco Destrehan Industrial Complex, which includes refineries and chemical plants, said van Heerden, who has studied computer models about the impact of a strong hurricane for four years.

"These chemical plants are going to start flying apart, just as the other buildings do," he predicted. "So, we have the potential for release of benzene, hydrochloric acid, chlorine and so on."

In the Washington Post article, Ken Ringle concludes with a discussion of the possibility that the loss of wetlands may be increasing the risk of damages from the hurricane:
For more than 2½ centuries, that precise scenario [the overflow of lake Pontchartrain -TQA] has never quite happened, though hurricanes rake the Louisiana/Mississippi Gulf Coast regularly and sideswipe the Big Easy more often than not. One reason it hasn't is that the city was long protected by scores of miles of surrounding saltwater marshes capable of sponging up even massive storm surges like a swampy dishrag.

But for the last half of the 20th century and into the present day, those wetlands have been disappearing -- hundreds of acres of them every year -- starved by levees from the Mississippi River overflows that once fed them with silt from Minnesota and Iowa and Missouri, and eroded by canals dug for oil exploration and suburban subdivisions. To compare a 1930 aerial portrait of Louisiana with a contemporary satellite picture is to realize with stunning force how hundreds of miles of the state's beautiful if mosquito-laden southern wetlands now resemble moth-eaten lace.

With a far smaller marshland buffer zone to suck up Katrina's ferocious storm surge, New Orleans is very definitely in harm's way. Never mind the roof-ripping winds. Water fed New Orleans with commerce most of her life. If she dies today, it will be water -- born of Katrina's catastrophic power -- that's the death of her.

The irony in the title of the CNN article is this: it appears that one of the factors that may have increased the damages caused by the December 26 tsunami was a loss of coastal mangrove forests, coral reefs, and other forms of natural barriers. From a December 31, 2004 Wall Street Journal article:
Mangroves -- trees and shrubs that live in tropical tidal zones -- line one-quarter of the world's tropical coastlines. But Asia is hurriedly uprooting them as its economies take off. In less than 20 years between 1975 and 1993, Thailand's mangrove area was almost halved, says Edward Barbier, a professor of economics at Wyoming University and editor of a recent book on Asia's disappearing mangrove ecosystems. India laid waste to as much as 50% of its mangroves between 1963 and 1977. Belatedly, some countries have made efforts at replanting.

Mangroves offer a double layer of protection against the pounding surf: Low red mangroves anchor themselves in mud flats along tidal estuaries, their flexible branches and tangled roots absorbing the sea's power. Behind them stand black mangroves as tall as trees.

Environmentalists point out that coastal communities around the world are vulnerable to natural calamities: Florida took four direct hits this year from hurricanes. But whereas the cleanup in Florida takes just a few months, it could be years before life returns to normal in poor parts of Asia.

To be sure, not even mangroves could have parried the blow from Sunday's tsunamis, and the waves inflicted severe damage on relatively undeveloped sections of coastline, too.

But ecological damage "has left coastlines vulnerable," says Mr. Barbier, and if natural defenses had been left standing, they "would have reduced some of the losses" by reducing how far and fast the waves surged inland.

I truly, truly hope that New Orleans will once again escape the worst case scenario. But no matter what happens, we should take this as a warning that wetlands - no matter how mosquito infested - are important barriers that help protect the land from the ocean's fury. We may not need them to do this very often, but when we do, we really need them to be there.
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