FIVE YEARS AGO today, hell was unleashed on New Orleans. The storm surge created by the winds and rains of Hurricane Katrina overwhelmed the city's levee system, which the Army Corps of Engineers had poorly designed and poorly maintained. For days, with much of the city flooded, people pleaded for help from rooftops, the Superdome and the convention center. Scenes of depravation, desperation and death shocked the nation and the world. Of course, New Orleans wasn't the only site of devastation. Regions of Mississippi, Alabama, Texas and other parts of Louisiana were caught in Katrina's cross hairs. The initial response was inexcusably slow, exposing holes in the nation's disaster preparedness plans. Recovery throughout the Gulf Coast region, particularly in Louisiana, was hobbled by a toxic combination of red tape, turf battles and mistrust between state and federal officials. Still, when Air Force One touches down Sunday, President Obama will alight on a New Orleans that is recovering -- from Hurricane Katrina, the recession and this year's oil spill in the Gulf of Mexico as well. There remain concerns about housing, coastal restoration and crime, but New Orleans is undergoing a fragile yet positive transformation that once seemed impossible. The economy is beginning to diversify. A once-inept education system is rebounding. And civic engagement is way up, promising to hold the new mayor, Mitch Landrieu, accountable like none before him. People who fled are coming home. According to a report marking the fifth anniversary of Hurricane Katrina from the Brookings Metropolitan Policy Program and the Greater New Orleans Program Community Data Center, the population of the metropolitan area is 90 percent of what it was pre-Katrina. With 100,000 fewer residents, the population of the city itself is 78 percent of what it was on Aug. 29, 2005. African Americans make up a majority of the displaced who have not returned.