geo

• Global circulation system


  The global circulation of air masses creates pressure belts and causes different weather conditions in different global locations
• Air masses movement


  1. Move in cells

  2. Determine weather conditions
• Air cells


  • Hadley Cells
  • Ferrel cells
  • Polar Cells
• Hadley Cells


  • Hot air rises at the equator creating low pressure
  • The air descends at 23°N+S creating low pressure
• Ferrel cells


  • Air descends at 23°N+S creating high pressure
  • Air rises at 60°N+S creating low pressure
• Polar Cells


  • Air rises at 60°N+S
  • Air descends at the Poles
• High pressure


  Dry, calm conditions
• Belts of high pressure at 23°N + S of the equator


  Create hot + dry landscapes= perfect conditions for a desert
• Low pressure


  Wet, stormy conditions
• Belts of low pressure along the equator and 60°N/S

  Create rainy conditions
• Temperature is higher at the equator


  Hot + wet =perfect conditions for tropical rainforests
• It is milder at 60°N

  Cool + wet= deciduous forest
• Droughts


  Prolonged periods of no rain (high pressure)
• Regions at risk of droughts

  • Saharan Africa
  • Middle East
• Tropical storms

  Strong spinning storms, also known as typhoons or hurricanes
• How droughts will change

  More droughts in the future as climate change changes amount and predictability of rainfall
• How tropical storms will change


  More storms (higher frequency) as sea temp will be higher, severity may increase but distribution of where they are found does not change
• There was a Flash Flood in Boscastle in August 2004
• Flash flood


  When lots of water suddenly flows into a river, causing it to overflow its banks
• They're often caused by a short period of heavy rainfall
• The village of Boscastle on the north coast of Cornwall was devastated by a flash flood on 16th August 2004
• Causes of the Boscastle Flash Flood


  1. 75 mm of rain (the amount that would normally fall in a month) fell in just two hours

  2. A low pressure system brought warm, moist air from the Atlantic Ocean. This air mass cooled as it rose above the land, causing thunderstorms with intense rainfall

  3. Lots of rain over the previous weeks meant that the ground was wetter than normal, and could not absorb the water. So much of the rainfall simply ran off the land surface

  4. Boscastle is in a steep-sided valley close to the confluence of three rivers. The steep valley sides meant that surface water ran into the river channels very quickly, and the confluences meant that about two billion litres of water were funnelled down the river valleys into Boscastle

  5. The old bridge in the village had a low arch over a very narrow river channel. The flooding was made worse because trees and vehicles in the flood water became trapped under the bridge, forming a dam
• Boscastle


  • Steep-sided valley
  • Close to the confluence of three rivers
• Boscastle Flash Flood


  • 58 properties, 4 businesses, roads and bridges were destroyed or damaged
  • The flood was so sudden that people couldn't evacuate or move belongings to safer places
  • About 50 cars were washed out into sea, causing some environmental pollution
  • After the floods, the number of tourists dropped significantly, as the village is a popular tourist destination and 90% of the local economy relies on tourism
  • One person was seriously injured, and some residents suffered mental health problems after the flood due to stress relating to the floods and insurance claims
• Response to the Boscastle Flash Flood


  1. Emergency services quickly responded to save people

  2. Around 100 people had to be airlifted to safety by seven helicopters

  3. Residents and tourists that were flooded out of their accommodation were looked after in local accommodation and the village hall

  4. Homes, businesses and roads were eventually rebuilt

  5. The bridge was rebuilt with a higher arch, so that debris is less likely to dam the river

  6. A £10 million new flood defence scheme was opened in 2008, which included widening and deepening the river to improve its flow