The Boscastle Floods

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The Boscastle Floods

Heavy seasonal rainfall is a common feature of the climate of South

West England and has been documented many times, sometimes it has

little affect on the landscape and just drains away but very

occasionally it has far more destructive effects. On the 16th of

August this year, massive amounts of rainfall over the North Cornish

coast caused a disaster on a scale that has not been seen since 1952.

A flash flood devastated the small coastal town of Boscastle, this

investigation will highlight the causes, effects and responses seen in

the event.

Heavy Rainfall

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The root cause of the flood is heavy rainfall; to understand all the

effects of this we must examine the cause of the heavy rainfall.

Thunderstorms are common in Britain, they are usually small and short

and while they may generate a lot of rainfall in a short time it is

not normally a problem. The thunderstorm over Boscastle was slightly

different, it is a phenomenon only seen roughly once a decade and very

rarely with such devastating results.

Thunderstorms are caused by huge masses of warm, wet air rising high

into the atmosphere to form cumulonimbus clouds. The updraft that is

generated by the air being heated near the ground causes the air to

rise taking the moisture with it, it then cools and condenses causing

a downdraft that carries a lot of precipitation. Boscastle is an

exceptional example of this however; the amount of precipitation

involved is an indicator of how rare an event it was.

The first of the unique conditions was the wind direction, onshore

winds from both the north and the south were bringing air into the low

pressure zone that was located over Cornwall, this low pressure zone

was due to the air over the land being heated and rising higher into

the atmosphere throughout the day.

[IMAGE]

Here you can see the direction of the wind during the day.

As the day went on the evaporation rate in the areas of sea increased

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