At least 1,500 people were killed and around $300 billion worth of damage was caused when Hurricane Katrina hit the south-eastern part of the USA. Arriving in late August 2005 with winds of up to 127 mph, the storm caused widespread flooding.
Hurricanes can cause the sea level around them to rise, this effect is called a storm surge. This is often the most dangerous characteristic of a hurricane, and causes the most hurricane-related deaths. It is especially dangerous in low-lying areas close to the coast.
There is more about hurricanes in the weather section of the Met Office website:
Hurricane Katrina tracked over the Gulf of Mexico and hit New Orleans, a coastal city with huge areas below sea-level which were protected by defence walls, called levees. The hurricane's storm surge, combined with huge waves generated by the wind, pushed up water levels around the city.
The levees were overwhelmed by the extra water, with many collapsing completely. This allowed water to flood into New Orleans, and up to 80% of the city was flooded to depths of up to six metres.
Hurricane Katrina also produced a lot of rainfall, which also contributed to the flooding.
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.
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.
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.
Last updated: 23 May 2014
Fig 3. Map of America showing highest wind speeds. Image courtesy of NOAA