Hurricane Katrina

Hurricane Katrina hit the south-eastern part of the USA in late August 2005. The damage caused, at $300 billion, was the most costly disaster ever to strike the USA. It was one of the strongest storms to hit the USA in the last 100 years, and had winds of 127 miles per hour (200 kilometres per hour). It is believed to have killed about 1,500 people.

Fig 1: Satellite Image of Hurricane Katrina, 28 August 2005 at 2045 GMT. Image courtesy of NOAA. Click on image to view a larger version.

Movie loop of Katrina making landfall on 29 August 2005 (large file - 5 Mb)
Image Courtesy NOAA/CIMSS/SSEC

Fig 2: South-eastern USA.		Fig 3: Location of New Orleans.

Fig 4: Evacuation. Source unknown (please contact us if you own the copyright of this image)		Fig 5: Evacuation.		Fig 6: Damage to property. Image courtesy of NOAA

Storm surges leading to flooding

In a hurricane, sea level can rise far more than in normal conditions, called a storm surge. This is often a hurricane’s most dangerous part in low-lying coastal regions. It is often responsible for most hurricane-related deaths. On the northern gulf coast near New Orleans, most of which is below sea level, waves of about 8 metres on the Gulf coast were generated when Hurricane Katrina passed over. Levees, protective embankments which had helped New Orleans escape previous damage, were broken by the storm surge moving inland through rivers raising the level of Lake Pontchartrain and straining the levees by the pressure on them. Hurricane Katrina was responsible for flooding 80% of New Orleans city to depths of up to 6 metres.

Fig 7: Broken levee. Image courtesy of NOAA

Fig 8: heights of normal high tides compared to storm surge heights. Image courtesy of NOAA

On the northern gulf coast near New Orleans, most of which is below sea level, waves of about 8 metres on the Gulf coast were generated when Hurricane Katrina passed over.

Levees, protective embankments which had helped New Orleans escape previous damage, were broken by the storm surge moving inland through rivers raising the level of Lake Pontchartrain and straining the levees by the pressure on them.

Hurricane Katrina was responsible for flooding 80% of New Orleans city to depths of up to 6 metres.

Rainfall leading to flooding

Fig 11: Flooding in New Orleans. Image courtesy of NOAA

Hurricane Katrina also produced a lot of rainfall, the animation below shows the rainfall rate measured by a radar over New Orleans on 29 August. The different colours represent the rate of the rainfall. The brighter colours (yellow, orange, reds) show where the heaviest rain is falling.

Strong winds

The strongest winds during 25-30 August were over the coastal areas of Louisiana and Florida. A map of the maximum wind speeds which were recorded during the Hurricane Katrina episode is shown. Although the winds did not directly kill many people, it did produce a storm surge over the ocean which led to flooding in coastal areas and was responsible for many deaths.

Fig 13: Strong winds. Image courtesy of NOAA		Fig 14: Map of maximum wind speeds (miles per hour) recorded during 25-30 August. Image courtesy of NOAA

Tornadoes

Hurricanes can create tornadoes. Thirty-three tornadoes were produced by Hurricane Katrina over a five-day period, although only one person died due to a tornado which affected Georgia. More information Tornadoes Impact on humans - issues 1,500 deaths occurred in the states of Louisiana, Mississippi and Florida The impacts of Katrina is thought to have cost about $300 billion Thousands of homes and businesses were destroyed Thousands of jobs have been lost and millions of dollars in lost tax incomes to the affected states and USA federal government. Agricultural production was damaged by tornadoes and flooding. Cotton and sugar-cane crops were flattened. Three million people were left without electricity for over a week after the Hurricane struck. Tourism centres were badly affected, probably reducing income for several years. There have been adverse impacts on the oil and gas industry. A significant part of the USA oil refining capacity was disrupted after the storm due to flooded refineries and broken pipelines, and several oil rigs in the Gulf were damaged. Evacuees have not returned to the affected areas, producing a shortage of workers for businesses that reopened months after the hurricane struck. Major highways were disrupted and some major road bridges were destroyed. Many people have moved to live in other parts of the USA and many may never return to their original homes.
	Fig 15: A tornado. Image courtesy of NOAA

Fig 16: Destroyed boats washed ashore.

What is a hurricane?

It is a very powerful area of low pressure that has very strong winds (over 74 miles per hour). Hurricanes, typhoons and cyclones are all kinds of tropical storm. A Hurricane is the term given to tropical cyclones which forms in the Atlantic Ocean. Each hurricane is given a name, Hurricane Katrina was the 11th named tropical cyclone of 2005.

Why do they form?

They form when there are disturbances in the upper atmosphere over a very warm sea (over 26 °C), where they obtain most energy and moisture.

The air over several hundred square kilometres then starts to rotate anti-clockwise very quickly and can move over hundreds of kilometres. They usually die out when they travel over the land after a while because they are then removed from the source of their heat and moisture.

Hurricanes usually form in the tropical Atlantic Ocean and then affect the Caribbean and the south-eastern part of the USA.

When do they occur?

Hurricanes usually occur from July to November, and can lasts for a few days or even up to a week.

Fig 21: Rising flood waters.

Responses discussion

There were several responses to the Hurricane, both short and long term, in the south-east USA. For example, there was the immediate evacuation of hundreds of thousands of people. Some migration has become permanent as people have settled in other parts of the USA, for instance when peoples’ houses and businesses were permanently destroyed.

Around 20,000 people in New Orleans sheltered in the Superdome football stadium when warned the hurricane was about to strike. However, the living conditions in the Superdome soon deteriorated. It became hot and stuffy, toilets were broken and there were no washing facilities. Eventually a convoy of 475 buses transported many of these people to the Astrodome stadium in nearby Houston, Texas.

Lawlessness broke out and emergency services could not operate properly. Criminal gangs roamed the streets, looting homes and businesses and committing other crimes. Army and police had to try with difficulty to maintain order when living conditions became intolerable and there was competition for food and drink. Some looters were shot on sight, home and business owners took the law into their own hands and defended their properties.

Unfortunately, bodies of people who died in the August 2005 were still being discovered late into 2005.

Repairing the levees

The broken levees were repaired by engineers and the flood water in the streets of New Orleans took several months to drain away. The broken levees and consequent flooding were largely responsible for most of the deaths in New Orleans. One of the first challenges in the aftermath of the flooding was to repair the broken levees. Vast quantities of materials, such as sandbags, were airlifted in by the army and air force and the levees were eventually repaired and strengthened. Although the USA is one of the wealthiest developed countries in the world, it highlighted that when a disaster is large enough, even very developed countries struggle to cope with natural disasters, particularly the poorest people
		Fig 24: Repairing the levees