Hurricane Katrina was the eleventh named storm and fifth hurricane of the 2005 Atlantic hurricane season. It was the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. The storm is currently ranked as the third most intense United States landfalling tropical cyclone, behind only the 1935 Labor Day hurricane and Hurricane Camille in 1969. Overall, at least 1,245 people died in the hurricane and subsequent floods, making it the deadliest United States hurricane since the 1928 Okeechobee hurricane. Total property damage was estimated at $108 billion (2005 USD), roughly four times the damage wrought by Hurricane Andrew in 1992. Later, Hurricane Ike in 2008 and Hurricane Sandy in 2012 caused more damage than Hurricane Andrew, but both were far less destructive than Katrina.
Katrina originated over the Bahamas on August 23 from the interaction between a tropical wave and the remnants of Tropical Depression Ten. Early the following day, the new depression intensified into Tropical Storm Katrina. The cyclone headed generally westward toward Florida and strengthened into a hurricane only two hours before making landfall Hallandale Beach and Aventura on August 25. After very briefly weakening to a tropical storm, Katrina emerged into the Gulf of Mexico on August 26 and began to rapidly deepen. The storm strengthened to a Category 5 hurricane over the warm waters of the Gulf of Mexico, but weakened before making its second landfall as a Category 3 hurricane on August 29 in southeast Louisiana.
Katrina caused severe destruction along the Gulf coast from central Florida to Texas, much of it due to the storm surge. The most significant number of deaths occurred in New Orleans, Louisiana, which flooded as its levee system failed, in many cases hours after the storm had moved inland. Eventually 80% of the city and large tracts of neighboring parishes became flooded, and the floodwaters lingered for weeks. However, the worst property damage occurred in coastal areas, such as Mississippi beachfront towns; over 90 percent of these were flooded. Boats and casino barges rammed buildings, pushing cars and houses inland; water reached 6–12 miles (10–19 km) from the beach.
The hurricane surge protection failures in New Orleans are considered the worst civil engineering disaster in U.S. history, and prompted a lawsuit against the U.S. Army Corps of Engineers (USACE), the designers and builders of the levee system as mandated by the Flood Control Act of 1965. Responsibility for the failures and flooding was laid squarely on the Army Corps in January 2008 by Judge Stanwood Duval, U.S. District Court, but the federal agency could not be held financially liable because of sovereign immunity in the Flood Control Act of 1928. There was also an investigation of the responses from federal, state and local governments, resulting in the resignation of Federal Emergency Management Agency (FEMA) director Michael D. Brown, and of New Orleans Police Department (NOPD) Superintendent Eddie Compass. Many other government officials were criticized for their responses, especially New Orleans Mayor Ray Nagin, Louisiana Governor Kathleen Blanco, and President George W. Bush.
On August 29, Katrina's storm surge caused 53 different breaches to various flood protection structures in and around the greater New Orleans area, submerging eighty percent of the city. A June 2007 report by the American Society of Civil Engineers indicated that two-thirds of the flooding were caused by the multiple failures of the city's floodwalls. The storm surge also devastated the coasts of Mississippi and Alabama, making Katrina the most destructive and costliest natural disaster in the history of the United States, and the deadliest hurricane since the 1928 Okeechobee Hurricane. The total damage from Katrina is estimated at $108 billion (2005 U.S. dollars).
The death toll from Katrina is uncertain, with reports differing by hundreds. According to the National Hurricane Center, 1,836 fatalities can be attributed to the storm: 1 in Kentucky, 2 each in Alabama, Georgia, and Ohio, 14 in Florida, 238 in Mississippi, and 1,577 in Louisiana. However, 135 people remain categorized as missing in Louisiana, and many of the deaths are indirect, but it is almost impossible to determine the exact cause of some of the fatalities. A 2008 report by the Disaster Medicine and Public Health Preparedness journal indicates that 966 deaths can be directly attributed to the storm in Louisiana, including out of state evacuees, and another 20 indirectly (such as firearm related deaths and gas poisoning). Due to uncertain causes of death with 454 evacuees, an upper-bound of 1,440 is noted in the paper. A followup study by the Louisiana Department of Health & Hospitals determined that the storm was directly responsible for 1,170 fatalities in Louisiana.
Federal disaster declarations covered 90,000 square miles (230,000 km2) of the United States, an area almost as large as the United Kingdom. The hurricane left an estimated three million people without electricity. On September 3, 2005, Homeland Security Secretary Michael Chertoff described the aftermath of Hurricane Katrina as "probably the worst catastrophe, or set of catastrophes," in the country's history, referring to the hurricane itself plus the flooding of New Orleans. Even in 2010, debris remained in some coastal communities.
The economic effects of the storm were far-reaching. The Bush Administration sought $105 billion for repairs and reconstruction in the region, which did not account for damage to the economy caused by potential interruption of the oil supply, destruction of the Gulf Coast's highway infrastructure, and exports of commodities such as grain. Katrina damaged or destroyed 30 oil platforms and caused the closure of nine refineries; the total shut-in oil production from the Gulf of Mexico in the six-month period following Katrina was approximately 24% of the annual production and the shut-in gas production for the same period was about 18%.
The forestry industry in Mississippi was also affected, as 1.3 million acres (5,300 km2) of forest lands were destroyed. The total loss to the forestry industry from Katrina is calculated to rise to about $5 billion. Furthermore, hundreds of thousands of local residents were left unemployed. Before the hurricane, the region supported approximately one million non-farm jobs, with 600,000 of them in New Orleans. It is estimated that the total economic impact in Louisiana and Mississippi may eventually exceed $150 billion. Forensic accountants such as Esther A. Young of MDD Forensic Accountants were involved in the assessment of economic damages resulting from this catastrophe.
Katrina displaced over one million people from the central Gulf coast to elsewhere across the United States, becoming the largest diaspora in the history of the United States. Houston, Texas, had an increase of 35,000 people; Mobile, Alabama, gained over 24,000; Baton Rouge, Louisiana, over 15,000; and Hammond, Louisiana, received over 10,000, nearly doubling its size. Chicago received over 6,000 people, the most of any non-southern city. By late January 2006, about 200,000 people were once again living in New Orleans, less than half of the pre-storm population. By July 1, 2006, when new population estimates were calculated by the U.S. Census Bureau, the state of Louisiana showed a population decline of 219,563, or 4.87%. Additionally, some insurance companies have stopped insuring homeowners in the area because of the high costs from Hurricanes Katrina and Rita, or have raised homeowners' insurance premiums to cover their risk.