Hurricane theory, fieldwork and Katrina

1) Hurricane Theory

(i) What is a hurricane?

They are low pressure weather systems which have very strong sustained winds over 120km/h are bring torrential rainfall. Cyclones, typhoons and hurricanes are all names for the same weather event.

(ii) How do hurricanes form?

Firstly, for hurricane to develop certain conditions are needed e.g. sea temperatures over 27°, wind speeds need to be constant at ground level and at 12km above ground level and it needs to be in the trade wind belt between latitudes of 5° and 20°.

In low pressure conditions, the air draws in the water vapour from sea. As the air rises, it spirals up. By the time the hurricane gets to land there is air still spiralling upwards. However, the air which has already reached the top has cooled and condensed and this is what causes the torrential rainfall.

Further, for hurricanes to occur wind speed is already relatively medium to high and the upward spirally of unstable warm air causes the wind speed to increase.

(iii) Why do hurricanes form

They form because during spring and summer there is an imbalance between atmospheric heat and the Earth’s heat energy. They form because the sun heats the upper portion of the ocean and a lot of heat energy builds up as a result of it. To remove this amount of heat energy, condensation takes place in the atmosphere.

(iv) Where are hurricanes usually found?

They occur around equatorial countries and are created in oceans in the equatorial region for example; the Gulf of Mexico, the Bay of Bengal and the Indian Ocean.

2. Hurricane fieldwork

(i) How can we measure the magnitude of a hurricane?

They are measured through a Saffir-Simpson scale where the rating of a hurricanes is based on wind speed, storm surge (rise in sea level because of low pressure and strong winds) and damage. See table above.

(ii) How can we predict hurricanes?

Wind speed and temperature across hurrricane forming regions are measured with satellites.On these satellites we can even see the cloud formation and swirling winds. From these meterologists can predict hurricanes. Hurricane Katrina was predicted accurately 6 days before. The official huricane forecasting organisation is the ‘National Hurricane Centre’. (Link: )

3. Hurricane Katrina

(i) What is the location, date and any crucial facts of the hurricane?

Location: New Orleans
Date: 29th August 2005
Rating: Category 5
Wind speed: 175 mph
Rainfall: up to 16 inches in some areas

(ii) What were the causes?

(a)Hurricanes have always occurred and are a way of nature balancing heat.
(b)The city of New Orleans is below sea level; it survives by having levees and flood walls at each side of the city.

(a) Well global warming is causing sea levels to rise which makes it easier for hurricanes to form and reach high intensities is one theoretical cause.
(b) Due to the construction of levees wetlands which were one form of natural defence against hurricanes are disappearing at 25 square miles per year!

Something to think about: should the New Orleans have grown to the size it did in such a perilous location.  Added to that the fact that the levees have not been maintained properly.

(iii)What were the impacts?


(a) 1464 people died.
(b) 80% of the people managed to evacuate but 20% who remained were frightened and traumatised (this 20% consisted of particularly poor people)
(c)Every aspect of life was disrupted; people lost jobs, financial securities, families and health.
(d)Many residents moved to other parts of of the U.S.A – in particular Housten (Texas)
(e) There were many health concerns due to lack of clean water, food and toilet facilities.
(f) 600,000 pets were either killed or stranded in the disaster.


(a)Everyone became unemployed; people lost so much of  their financial stability that the government wasn’t able to collect taxes.
(b)In 2006, it was calculated that the cost of repair and reconstruction was $10.5bn.
(c)Total economic impact was over $150bn.
(d) Oil and gas production was affected hence prices of these resources and joint goods e.g. petrol rose in price too.


(a)There was a significant damage to forestry.
(b) The city incurred severe flooding; it was so bad that by the 31st August 80% of the city was underwater.
(c)Almost all infrastructure was destroyed.
(d)Levees and flood-walls protecting the New Orleans breached.

(iv) How was the hurricane managed: what were the responses?

(a) People were instructed to evacuate.
(b) Within a year levees were repaired.
(c) Temporary floodgates and pumps were put around four main canal entrances to prevent further flooding and damage.
(d) Weirs (low-head dams) were put in place to regulate the flow of the Mississippi River Gulf Outlet (which is a river which comes from the Gulf of Mexico).
(e)Wetlands are being restored as a natural form of protection from future hurricanes.
(f) Improvements are continually being made to preparation plans e.g. more education is given in schools, awareness weeks happen once a year etc.

The lack of a decent local and national government response to evacuating people who could not get out themselves in personal transport which made it seem more like an LEDC disaster

Coast 2050 is a $14bn , 30-year scheme to help protect the area. It includes flood controls, water diversion and coastal restoration. Through this the government will create more marsh land and set up many other defence systems.

(v) Who were the key players involved?

(a) the National Hurricane Centre
(b) Local authority
(c) Central government
(d) Local residents
(e) Emergency services
(f) Engineers

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