Parts of New Orleans had been sinking much faster than previously thought before Hurricane Katrina hit last August, new research suggests.
The city's flood protection is now being upgraded
Subsidence may explain why some levees were easily breached by floodwaters, the study in the Nature journal says.
It argues some very low-lying areas of the US city should not be rebuilt, describing them as "death traps".
US engineers say the city is prepared for the start of the hurricane season, which "officially" begins on Thursday.
However, some storm experts think the work of rebuilding the levees is incomplete.
US meteorologists say there could be up to five major storms during 2006, but the season will not be as devastating as 2005.
Last August saw Hurricane Katrina sweep across five US states, killing more than 1,300 people.
The study published on Thursday in the international scientific journal was produced by a University of Miami team.
It is based on new satellite radar data taken from 2002 to 2005, which shows that New Orleans sank by an average of 0.22 inches (0.5cm) a year during that period.
But the study says some low-lying areas are subsiding by more than one inch (2.54cm) a year - raising concerns about the city's future.
The scientists name overdevelopment, drainage and natural seismic shifts as the main causes.
"My concern is the very low-lying areas," said lead author Tim Dixon, geophysicist at the University of Miami.
"I think those areas are death traps. I don't think those areas should be rebuilt," he said.
The study says the areas of the city most at risk are Lakeview, Kenner and St Bernard Parish.
According to the report, one of the city's levees has sunk by more than 3 ft (0.91m) since its construction three decades ago.
"The people in St Bernard got wiped out because the levee was too low. It's as simple as that," said co-author Roy Dokka from the Louisiana State University.
The study says the new evidence should be taken into account when rebuilding the city's defences.