When the levee system that protected New Orleans broke in August 2005, it was on a grand scale. According to the Met Office, 80 per cent of New Orleans was flooded with up to six metres of water.
The other impacts were as severe: Crops flattened, three million people left without electricity for over a week, and oil refining capacity for the US reduced.
Statistics and facts aside, Hurricane Katrina is also remembered for images of New Orleans under martial law, as the National Guard sought to control civil disorder – real, or perhaps imagined. This was the world’s most powerful country – yet to be humbled by recession – seemingly unable to handle a major humanitarian crisis with competence or compassion.
As for the storm itself, Katrina was not so unusual. ‘The thing to remember with Katrina is that at landfall it was a category three hurricane. It was weakening. It was not one of the strongest,’ says Julian Heming, a tropical storm scientist with the Met Office.
What made Katrina so deadly, according to Heming, was the storm’s track and weaknesses in the Louisiana levee system combined with the geography of the Mississippi delta.
A hurricane’s destructive capacity is more connected to where it strikes than the storm’s strength.
‘We have had storms stronger make landfall before and after Katrina,’ says Heming. ‘In terms of US landfalls one of the things that is increasingly raising concerns is that the US has had such a long period of not really experiencing a major hurricane event,’ he adds. A major hurricane is one classed at category 3 or higher.
As for prediction, there have been improvements in tracking capability thanks to developments in computer and models and increased observational data, according to Heming.
‘For the National Hurricane Center in the US, errors in building a hurricane track have reduced in the last five years so that their four-day error is now the same as their five-day error in the previous decades,’ he says. ‘The hurricane track forecast has seen between a 20 to 25 per cent drop in errors. That was due to a huge package of changes, a culmination of ten years of work. We still need to improve prediction of intensity.’
Meanwhile, New Orleans has made major investments in preparing for floods. ‘The US Army Corps of Engineers was directed to complete a flood risk reduction system capable of protecting the community from a ‘100-year’ event. The resulting system of protection spans three parishes (counties) and is interconnected,’ says Stephen Estopinal, President, Southeast Louisiana Flood Protection Authority East. These measures include storm surge prediction with the latest analysis programs – the Katrina storm surge was a major factor in the hurricane’s destructiveness. Additional storm surge protection has been anchored at the south shore of Lake Pontchartrain. Levees have been strengthened, and redesigned.
But there’s a risk to all this investment. ‘There is concern that people who have seen the massive protection structures, particularly elected officials, will over-estimate the protection provided,’ says Estopinal.
Authorities have changed their approach from ‘protection’ to ‘risk reduction’, according to Estopinal, in recognition that absolute flood protection is not possible.
That doesn’t mean New Orleans is finished with preparations. ‘A 100-year return frequency design (one per cent risk) is much too high for one of the world’s great cities. We are working to increase the protection to a 500-year (0.2 per cent risk) by armouring, foreshore protection and revising building codes,’ says Estopinal.
Levee and regional subsidence is also an unaddressed problem. ‘As levees sink and the land outside of the levees disappear, the conversion of land to open water increases the height of the storm surge wave combination increasing overtopping rates,’ he adds.
Funding is a problem, with requirements to maintain the system expected to increase beyond local government resources. Future flood protection measures could include artificial islands outside the levee system to reduce wave height.
There’s also a risk that people will forget Katrina. Estopnial’s recommendation is simple. ‘Propagandise the true risk factors and fight the growing public complacently brought on by the drought of hurricanes and the fading collective memory of Katrina.’