On August 30, Secretary of Homeland Security Michael Chertoff labeled Katrina "an incident of national significance." In doing so, he set into action the National Response Plan (NRP). Secrecy News, published by the Federation of American Scientists, points out that in a little-noticed maneuver, Chertoff did not designate the hurricane as a "catastrophic event," a special sub-category of emergency situation that entails the expedited deployment of emergency response capabilities. On September 8, Chris Strohm of Government Executive Daily Briefing asked if Chertoff had exercised his catastrophic-incident authority in response to Hurricane Katrina. DHS spokesman Russ Knocke told the reporter that "it was too early to make a determination." FEMA officials continued to dodge the question last week. After repeated phone calls, one FEMA official, who refused to give her name, told the Voice that on August 31 the Department of Homeland Security declared Katrina "an incident of national significance." Asked if the storm ever had been declared a catastrophic event, the woman replied, "Homeland Security did not." In another conversation, Barbara Ellis of FEMA public affairs said, "Katrina rose to the level of 'incident of national significance.' " Asked if it was ever declared a catastrophic event, she repeated that the storm was an "incident of national significance."
In short, the government made sure it would not invoke laws setting into motion an expensive federal response. Instead, the feds blamed Blanco for the slipshod handling of the affair, explaining that they were prohibited by law from acting as a first responder.
Someone needs to explain the exact difference between the two designations and give examples of how they impacted the response. And, there's the possibility that under some new rule or other they're the same or can be made to be the same.