RMS said at least 50 percent of economic loss is expected to come from flooding in New Orleans, hurricane losses from wind and coastal surge, infrastructure damage and indirect economic impacts.

The estimate is separate from estimates of insured losses. RMS has projected up to 25 billion dollars in losses covered by insurance, and other estimates have varied.

RMS, a consultant for insurers, reinsurers and other financial institutions, said the New Orleans flood "has developed into the most damaging flood in US history."

It said at least 150,000 properties have been flooded, topping the previous US record from flooding and levee failures on the lower Mississippi River in 1927, which affected 137,000 properties.

"The economic and insurance consequences of the 2005 Great New Orleans Flood will depend highly on how quickly authorities can respond to the event," said Laurie Johnson, vice president of technical marketing at RMS.

"The speed at which existing pumps are reactivated and additional pumping capacity is added will determine how rapidly the floodwaters are removed. But this is only the first step in restoring services to flooded areas of the city," Johnson said.

RMS said the value of physical property in the flooded areas is approximately 100 billion dollars. It said that while the majority of property damage occurs once floodwaters enter a structure, the longer the property remains inundated, the greater the damage.

RMS also estimated that the costs of interrupted economic activity exceed 100 million dollars per day.

It said the closest parallel to the 2005 disaster is the 1953 flood in the Netherlands, which led to more than 1,800 deaths and the inundation of 47,000 properties. In that case, it took six months to pump out all the water from the flood bowl.

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