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Hurricanes

The GCSE geography syllabus requires that you study natural hazards and hurricanes are one of these. A hurricane is also known as a cyclone or a typhoon, depending on which part of the world you are in. You need to know in detail the sequence of events leading to their formation plus the structure and characteristics of a hurricane. As with many other aspects of your studies, you will need to be able to compare the social, economic and environmental effects and short-term and long-term responses (monitoring, prediction, protection and preparation) for both MEDCs and LEDCs.

A hurricane is defined as a tropical revolving storm with violent winds. They are classed as force 12 on the Beaufort scale which means the wind speeds are greater than 75 mph (120 km/h). Winds of these speeds can uproot trees and destroy buildings so hurricanes endanger both the natural and built environments.

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In general and for a variety of reasons, there are more deaths caused by the effects of hurricanes in LEDCs than MEDCs.

In MEDCs, the population has access to storm warnings via traditional media such as the radio and TV plus the internet and mobile phones. This enables them to evacuate the area or take shelter in places that can withstand the battering from the hurricane. In LEDCs, the population are usually a lot poorer and the country's communications infrastructure is less well-developed so storm warnings may not reach large numbers of people. For many, the first they know is when they see it on the horizon. They don't have as much time to evacuate to safer areas and nor do they have much access to storm-proof shelters.

Hurricanes are huge intense low pressure systems - they can be up to about 800 km across. The intense storm at the centre of the system is usually 300 km (the distance from Leeds to London) or less. Outside of the central storm, the winds and rain are less intense. They form from low pressure areas at sea and gain their enormous energy from warm water. The water needs to be at 26°C or more at the surface and between about 5 and 20 degrees either north or south of the equator. Shallow seas like the Caribbean and the Bay of Bengal are therefore ideal places for hurricanes to develop.

Warm moist air rises from just above the surface of the sea. As it does, it condenses to form large clouds that precipitate heavy rainfall. As the air rises, the coriolis force causes it to spin (clockwise in the northern hemisphere and anticlockwise in the southern hemisphere) so images from space show its spiral structure. The airflow high in the hurricane is diverging and cold air is thrown back in at the very centre, forming the eye of the storm. Since cold air sinks, no clouds are formed in the eye. The eye can be up to 30 miles (45 km) across. Once a hurricane makes landfall, it starts to lose its strength as its energy comes from rising warm moist air from the sea.

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  1. In 2005, hurricane Katrina devastated New Orleans in the south of the USA. Much of the city was flooded but what was the main cause of the flooding?
    The strong winds of a hurricane create a bulge of water which is called a storm surge. In the case of New Orleans, the surge was about 6m. The flood defences were poorly constructed and failed to stop the surge from entering the city
  2. Where do hurricanes form?
    Further away from the equator, the seas never become warm enough to start a hurricane. The rising air must be rotating, any closer to the equator than 5 degrees and the coriolis force is too weak to cause rotation
  3. Where do hurricanes usually form?
    Hurricanes require rising air that contains a lot of moisture, warm air rises and can hold more moisture than cold air. Warm air over a warm sea can hold the greatest amount of moisture
  4. Which of the following is not a hazard to human settlements caused by hurricanes?
    There is no link between earthquakes and hurricanes
  5. Which of the following is not a name for a tropical revolving storm?
    A tornado is much smaller and is also called a whirlwind
  6. Why does a hurricane lose strength when it is over a land mass?
    There is not as much warm moist air over land as there is at sea so there is a lot less energy to power the hurricane
  7. To be called a hurricane, the wind speed in a storm must be ...
    If you are caught outside in a hurricane, it would be difficult to walk, lighter people may not even be able to stand upright. The biggest problem would be avoiding being hit by flying debris - imagine even just a small object hitting you at a similar speed to a car driving along a motorway in the fast lane ...
  8. What temperature must the sea be for a hurricane to form?
    Where the sea surface temperature is 26°C or more, it is possible for a hurricane to form. Once a hurricane forms, it can travel long distances
  9. The centre of a hurricane is called the ...
    It is an area that is clear of clouds because it is where cold air is sinking downwards. Clouds only form from rising warm air that cools down at higher altitudes
  10. Which of the following is not a reason why there is a larger loss of life in LEDCs than MEDCs during a hurricane?
    There are other reasons too such as higher literacy rates so populations understand the dangers and what they should do to stay safer during a hurricane, better hurricane survival education programmes and more sturdily-constructed buildings

Author: Kev Woodward

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