Hurricane Katrina, explained

Hurricane Katrina made landfall off the coast of Louisiana on August 29, 2005. It hit land as a Category 3 storm with winds reaching speeds as high as 120 miles per hour. Because of the ensuing destruction and loss of life, the storm is often considered one of the worst in U.S. history. An estimated 1,200 people died as a direct result of the storm, which also cost an estimated $108 billion in property damage, making it the costliest storm on record.

The devastating aftermath of Hurricane Katrina exposed a series of deep-rooted problems, including controversies over the federal government's response, difficulties in search-and-rescue efforts, and lack of preparedness for the storm, particularly with regard to the city's aging series of levees—50 of which failed during the storm, significantly flooding the low-lying city and causing much of the damage. Katrina's victims tended to be low income and African American in disproportionate numbers, and many of those who lost their homes faced years of hardship.

Ten years after the disaster, then-President Barack Obama said of Katrina, "What started out as a natural disaster became a man-made disaster—a failure of government to look out for its own citizens."

(What are hurricanes, cyclones, and typhoons?)

The city of New Orleans and other coastal communities in Katrina's path remain significantly altered more than a decade after the storm, both physically and culturally. The damage was so extensive that some pundits had argued, controversially, that New Orleans should be permanently abandoned, even as the city vowed to rebuild.

The population of New Orleans fell by more than half in the year after Katrina, according to Data Center Research. As of this writing, the population had grown back to nearly 80 percent of where it was before the hurricane.

Timeline of a Storm

Katrina first formed as a tropical depression in Caribbean waters near the Bahamas on August 23, 2005. It officially reached hurricane status two days later, when it passed over southeastern Miami as a Category 1 storm. The tempest blew through Miami at 80 miles per hour, where it uprooted trees and killed two people. Katrina then weakened to a tropical storm, since hurricanes require warm ocean water to sustain speed and strength and begin to weaken over land. However, the storm then crossed back into the Gulf of Mexico, where it quickly regained strength and hurricane status. (Read a detailed timeline of how the storm developed.)

On August 27, the storm grew to a Category 3 hurricane. At its largest, Katrina was so wide its diameter stretched across the Gulf of Mexico.

Before the storm hit land, a mandatory evacuation was issued for the city of New Orleans, which had a population of more than 480,000 at the time. Tens of thousands of residents fled. But many stayed, particularly among the city's poorest residents and those who were elderly or lacked access to transportation. Many sheltered in their homes or made their way to the Superdome, the city's large sports arena, where conditions would soon deteriorate into hardship and chaos.

Katrina passed over the Gulf Coast early on the morning of August 29. Officials initially believed New Orleans was spared as most of the storm's worst initial impacts battered the coast toward the east, near Biloxi, Mississippi, where winds were the strongest and damage was extensive. But later that morning, a levee broke in New Orleans, and a surge of floodwater began pouring into the low-lying city. The waters would soon overwhelm additional levees.

The following day, Katrina weakened to a tropical storm, but severe flooding inhibited relief efforts in much of New Orleans. An estimated 80 percent of the city was soon underwater. By September 2, four days later, the city and surrounding areas were in full-on crisis mode, with many people and companion animals still stranded, and infrastructure and services collapsing. Congress issued $10 billion for disaster relief aid while much of the world began criticizing the U.S. government's response.

Geography of New Orleans

The city of New Orleans was at a disadvantage even before Hurricane Katrina hit, something experts had warned about for years, but it had limited success in changing policy. The region sits in a natural basin, and some of the city is below sea level so is particularly prone to flooding. Low-income communities tend to be in the lowest-lying areas.

Just south of the city, the powerful Mississippi River flows into the Gulf of Mexico. During intense hurricanes, oncoming storms can push seawater onto land, creating what is known as a storm surge. Those forces typically cause the most hurricane-related fatalities. As Hurricane Katrina hit, New Orleans and surrounding parishes saw record storm surges as high as 19 feet.

Levees

Levees can be natural or manufactured. They are essentially walls that prevent waterways from overflowing and flooding nearby areas. New Orleans has been protected by levees since the French began inhabiting the region in the 17th century, but modern levees were authorized for construction in 1965 after Hurricane Betsy flooded much of the city. The U.S. Army Corps of Engineers then built a complex system of 350 miles of levees. Yet a report by the

Corps released in 2006 concluded that insufficient funding, information, and poor construction had left the flood system vulnerable to failure.

Even before Katrina made landfall off the Gulf, the incoming storm surge had started to overwhelm the levees, spilling into residential areas. More than 50 levees would eventually fail before the storm subsided. While the winds of the storm itself caused major damage in the city of New Orleans, such as downed trees and buildings, studies conducted in the years since concluded that failed levees accounted for the worst impacts and most deaths.

The aftermath

An assessment from the state of Louisiana confirmed that just under half of the 1,200 deaths resulted from chronic disease exacerbated by the storm, and a third of the deaths were from drowning. Hurricane death tolls are debated, and for Katrina, counts can vary by as much as 600. Collected bodies must be examined for cause of death, and some argue that indirect hurricane deaths, like being unable to access medical care, should be counted in official numbers.

Hurricane Katrina was the costliest in U.S. history and left widespread economic impacts. Oil and gas industry operations were crippled after the storm and coastal communities that rely on tourism suffered from both loss of infrastructure and business and coastal erosion.

An estimated 400,000 people were permanently displaced by the storm. Demographic shifts followed in the wake of the hurricane. The lowest-income residents often found it more difficult to return. Some neighborhoods now have fewer residents under 18 as some families chose to permanently resettle in cities like Houston, Dallas, and Atlanta. The city is also now more racially diverse, with higher numbers of Latino and Asian residents, while a disproportionate number of African-Americans found it too difficult to return.

Rebuilding part of New Orleans's hurricane defenses cost $14.6 billion and was completed in 2018. More flood systems are pending construction, meaning the city is still at risk from another large storm. A series of flood walls, levees, and flood gates buttress the coast and banks of the Mississippi River.

Simulations modeled in the years after Katrina suggest that the storm may have been made worse by rising sea levels and warming temperatures. Scientists are concerned that hurricanes the size of Katrina will become more likely as the climate warms. Studies are increasingly showing that climate change makes hurricanes capable of carrying more moisture. At the same time, hurricanes are moving more slowly, spending more time deluging areas unprepared for major flooding.