Friday, 15 January 2010

Increasing the risk of extreme weather...

How are people and places increasingly at risk from and vulnerable to extreme weather?

We are increasing our risk to these events by both human and natural causes.

  1. Global warming - all over the globe scientists are saying that global warming is creating more and more disastrous events like heat waves, droughts, floods etc.
  2. Demographics - Our population is increasingly on such are large scale that now it is hard to split resources evenly. This is also means that more people are living within one area of land so when there is a extreme weather event like a hurricane more people than before are being affected.
  3. Land management - As we become more technologically advance and progress; more and more land become urbanised. This means that we have to exploit nature i.e. deforestation, dig land for precise resources. This leads to increased risk of flooding, more people in extreme weather prone area and more risk of destruction.
  1. Sunspots - Variations in levels of solar radiation levels can have effects on the Earth’s climate. Increased solar activity can have short-term warming effects on Earth.
  2. Volcanoes - Volcanic eruptions such as Mount Tembora in 1815 can have major effects on the Earth’s climate because of the huge excretion of volcanic dust and various gases.
  3. Milankovitch cycles - extreme weather is affected by changes in climate and according to one theory the Earth’s orbit varies every 100,000 years which means its distance from the sun and glaciation cycles vary. 

Increasing the risk 2004 Boscastle Flash Floods 

Lets first remind ourselves of the location of Boscastle....

View Boscastle in a larger map

Meteorological reasons why the flood risk was increased:
  1. Localised rain; There was a trough passing straight through Boscastle which meant that rainfall in boscastle was 184mm and in surrounding areas only 1.5mm.
  2. The trough was part of a depression which had develop over the eastern atlantic ocean. In this the air had even sucked in remains on Hurricane Alex in the USA.
Physical characteristics of the place that increased the risk.
  1. The village is based at the bottom of a steep hill.
  2. The upper part of the village has been urbanising recently which means deforestation increased there.
  3. The overall land use of the area has been changing - it is becoming more and more built up. The consequence of this that there are more impermeable surfaces and surface runoff is increased.
So how was the flood managed?

4 long-term hard engineering defence systems were put into place to reduce the risk of such a destructive flood happening again. It cost £4.6 million.
  1. The environmental agency laid a large relief culvert that would carry excess rainwater (a bit like a drain). It was made twice the size of the old one.
  2. The river shape is being altered. The River Valency is being widened and lowered from the lower bridge to the car park, so that it has a bigger capacity to carry water.
  3. As the so many cars swept; the car park is now being raised with stone from the river bed and barriers are being added to it so next time less cars are swept away.
  4. There are plans to demolish the lower bridge near the harbour and replace it with a higher bridge downstream. This will give the river more capacity and help reduce the impacts of flooding.

For more information on the Boscastle Flash Flood in 2004 please see my post on Boscastle 2004 flood.

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