Hazard Prone: London

Tornadoes in the capital

There are over 70 tornadoes a year in the UK but they are very minor
In December 2006, North London was hit by a tornadoes that was so localized that it affected just a few streets in Kensal Rise
Roofs were ripped from house, trees were blownn down and cars were damaged or crushed
Amazingly no one was killed and there were few minor injuries

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Storms are brought by depressions or low pressure areas, formed by circulating air around an area of low pressure
These draw together cold winds from polar regions to the north and tropical winds from the south
Tornadoes in the UK are most likely to form when cold air moves rapidly south over warmer land or sea
As the warm air rises to the surface it becomes lighter making it unstable
This sets up small convection currents whci hrise through the atmosphere, like gusts of wind
The Earth's rotation causes the rising air to spin
The faster the spin, the more the air is likely to touch down on the Earth's surface, this forms the tornado

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The worst-affected areas are close to the Thames, it has 4 main causes
Prolonged rainfall, when surface run-off flows over impermeable tarmac and concrete surfaces into drains, which lead to the sewers and then to the river
Sudden storms. London's summer temperatures are the highest in the UK. Evapouration from the Thames causes huge amounts of mositure to be transported to the upper atmosphere - where it condenses and falls as rain, often in thunderstorms, this causes blockages in drains causeing flooding
Storm Surges. These occur when tides are highest, bringing incoming tides up the River Thames to the point where they meet out-going river flow
Exceptionally low pressure, reducing the weight on the seaand causing it to rise above its normal level
The Thames barrier attempts to stop these storm surges

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