'Walls of water' threat to big US cities

Stronger hurricanes forecast for the next few decades could flood major United States cities, including Miami and New Orleans, environmental scientists said yesterday.

Storm surges - walls of water up to 9m high pushed ashore by hurricanes - could pose a higher risk to coastal areas than the threat of rising seas tied to global warming, scientists from the group Environmental Defence said.

More intense hurricanes - some as strong as 2005's devastating Katrina - are likely in the future, the scientists said, because global climate change could mean warmer sea surface temperatures, which fuel hurricanes' development.

"There's been a lot of talk about the threat to coastal areas of sea level rise, and that is a very, very real issue ... but one that is going to unfold over a period of decades, if not a century," said Bill Chameides, Environmental Defence's chief scientist.

"What we think will actually be a more immediate risk to coastal areas ... is the threat of storm surge, which is actually exacerbated by sea level rise due to these growing-intensity storms," Dr Chameides said.

Using US Government data, the scientists created maps showing flood risk areas in Wilmington, North Carolina; Charleston, South Carolina, and Miami, based on projections of storm surges from hurricanes ranked as Category Three, Category Four and Category Five.

A Category Three storm, with a typical surge of 2.7m to 3.7m above normal, would pose a flood risk to all of Miami Beach and much of downtown Miami.

By contrast, a Category Five storm, with surges of 5.5m or higher, would threaten a larger area, extending further inland.

For New Orleans, the scientists did not project possible risk of flooding; instead, they used data from the US Geological Survey showing how far the flood waters went after Hurricane Katrina.

"As Hurricanes Katrina and Rita showed, the 24,720sq km of land close to sea level [in Louisiana] are especially vulnerable to storm surges - highly destructive moving crests of water that often cause the bulk of the damage in a high-category storm," the scientists wrote online.

Dr Chameides agrees with many climate scientists who believe human-caused global warming is responsible for raising sea surface temperatures, making stronger hurricanes more likely; but other scientists maintain hurricane intensity goes in natural cycles, and say the record-breaking 2005 Atlantic and Caribbean season was part of a high-category hurricane cycle.

This week US Government forecasters revised their hurricane predictions for 2006, saying the Atlantic hurricane season would be slightly less intense than last year - and less active than they predicted in May - with 12 to 15 named storms and seven to nine hurricanes, of which three or four could be classified as "major" hurricanes.

Last year there were 28 tropical storms, of which 15 became hurricanes, including four major hurricanes, notably Katrina, which devastated New Orleans, killed 1300 people and caused US$80 billion ($129.4 billion) in damage.

- REUTERS