Christopher Cooper and Robert Block’s book Disaster: Hurricane Katrina and the Failure of Homeland Security is essential:

If, after four years and billions of dollars spent on preparedness, Homeland Security can’t handle a hurricane, it is likely to struggle when faced with any manner of other disasters. The preparation for and response to Hurricane Katrina should disturb all Americans. If New Orleans is vulnerable, so are we all.

….

From the very start, FEMA’s bureaucratic brass had trouble integrating all of these subdepartments, with their starkly different cultures, into one cohesive federal agency. President Carter did his best to work out the problem by appointing John Macy as FEMA’s first director. A career bureaucrat with a knack for organization, Macy attempted to unite the various fiefs behind a common philosophy that all disasters – by they unseen or expected, extraordinary or run-of-the-mill – demanded the same response from Washington. He developed what he called the “Integrated Emergency Management System,” which people now refer to as the “all-hazards approach” to disaster preparedness. It is a simple concept, rooted in the assumption that many response tools such as warnings, evacuations, and damage assessments are equally applicable across the universe of disasters.

More from Cooper and Block in the near future.

See also: FEMA (Wikipedia)