Weather Hazards

Global Atmospheric Circulation (GAC)
1. Definition
  1. The movement of air by which heat is distributed on the surface of the earth.
  2. Global Atomspheric Circulation involves a number of circular air movements called cells, which join together to form the overall circulation of the earth's atmosphere.
    1. These cells are: the Hadley Cell, the Ferrel Cell and the Polar Cell
  3. Atmospheric Circulation is also a response to differences in insolation (heat) between high and low latitudes.
    1. A global pattern of surface winds and pressure belts results from this circulation.
      1. The patterns of pressure belts and winds are affected by seasonal changes, which cause them to move north during our summer and then south during our winter.
2. Diagram
3. How does GAC work?
  1. Air that is sinking towards the ground surface forms areas of high pressure. Winds on the ground move outwards from these areas.
    1. An example is at the North Pole.
  2. Air that is rising from the ground surface forms areas of low pressure on the ground. Winds on the ground move towards these areas of low pressure.
    1. An example is at the Equator.
  3. The Wind direction is distorted and deflected due to the Earth's rotation- known as the Coriolis Effect.
  4. GAC is what drives the world's weather.
    1. For example, the trade winds in the tropics drive tropical storms.
Tropical Storms
1. What are Tropical Storms?
  1. There are several different names for tropical storms; used in different regions of the world.
    1. In the USA and Carribean, they are called Hurricanes.
    2. In South-East Asia and Australia, they are called Cyclones.
    3. In Japan and the Philippines, they are called Typhoons.
  2. A Tropical Storm ia a large storm that forms over Tropical Oceans.
    1. They are very powerful and can cause much devastation to small islands and coastal regions.
2. Where do Tropical Storms Form?
  1. Tropical Storms form over warm oceans (above 27 degrees).
  2. Tropical Storms form in the Summer and in the Autumn, when sea temperatures are at their highest.
  3. Most Tropical Storms form about 5-15 degrees North or South of the Equator.
    1. This is because, at the Equator, there is not enough 'spin' from the rotation of the Earth, and a Tropical Storm is a spinning mass of clouds.
  4. In Tropical Regions, the intense heat makes the air unstable, causing it to rise rapidly. These unstable conditions are important for the formation of hurricanes.
3. How do Tropical Storms Form?
  1. 1) A strong upward movement of air draws water vapour up from the warm ocean surface.
    1. 2) This evaporated air cools as it rises and condenses to form thunderstorm clouds.
      1. 3) As the air condenses, it releases heat, which powers the storm and draws up more water vapour from the ocean.
        4) Several small thunderstorms join together to form a gaint spinning storm.
        When Surface winds reach 120 km per hour, the storm becomes a tropical storm.
        5) The storm develops an eye at the centre, where air descends rapidly. The outer edge of the eye is the eyewall, where there are the most extreme weather conditions.
        6) The storm is carried across the ocean by prevailing winds and continues to gather strength.
        7) When the strom reaches land, it's energy supply (evaporated water) is cut off. Friction with the land slows it down and it begins to weaken.
4. What is the structure of a Tropical Storm?
  1. At the direct centre of the storm there is an eye, which is a small area where relatively cold air sinks and warms up.
    1. At the eye of the storm, there are no clouds and conditions are calm.
  2. On either side of the eye is a tall bank of cloud called the eye wall. Here, there are strong winds (excess of 120 km/h), heavy rain, thunder and lightning.
Case Study: Typhoon Haiyan | 2013
1. Facts about the Hurricane
  1. Category 5 on the Saffir- Simpson Scale
  2. Occurred in November 2013
  3. The hurricane hit the Philippines
  4. Large areas of coastline and several towns devastated by winds of up to 275 km/h and waves up to 15m.
    1. One of the strongest storms ever recorded.
2. Effects
  1. City of Tacloban one of the worst affected places- with most of the 220,000 inhabitants left homeless.
    1. Destruction caused by a 5m high storm surge.
    2. 90% of Tacloban city destroyed.
      1. Tacloban Airport terminal was badly damaged
  2. Primary Effects- impacts of strong winds, heavy rain and storm surge.
    1. 6300 people killed (mostly drowned by the storm surge)
    2. Over 600,000 people displaced and 40,000 homes damaged or flattened.
    3. 30,000 fishing boats destroyed
    4. Over 400mm of rain caused widespread flooding.
    5. Strong winds damaged buildings and power lines and destroyed crops.
    6. Airport terminal badly damaged.
  3. Secondary Effects- longer-term impacts resulting from primary effects.
    1. 14 million people affected - with many people left homeless and 6 million lost their source of income.
    2. Flooding caused landslides and blocked roads, which cut off remote communities.
    3. Power supplies cut off for a month in some areas.
    4. Shortages of food, water and shelter- led to outbreaks of disease.
    5. Looting and violence
    6. Many jobs were lost as hospitals, shops and schools were damaged- affecting people's livelihoods and education.
3. Responses
  1. Immediate Responses
    1. International governments and aid agencies responded with food, water and temporary shelters.
    2. Over 1200 evacuation shelters set up to help the homeless.
    3. Field hospitals set up to help the injured.
    4. The UK government sent shelter kits to provide emergency shelter for families.
  2. Long-Term responses
    1. Many countries donated financial aid, supplies and medical support.
    2. Roads, bridges and airports rebuilt.
    3. 'Cash for Work' programmes- people paid to clear debris and rebuild the city.
    4. Oxfam supported the replacement of fishing boats- a vital source of income.
    5. Thousands of homes rebuilt away from areas at risk from flooding.
Weather Hazards in the UK
1. Case Study: The Somerset Levels Floods | 2014
  1. What caused the floods in 2014?
    1. It was the wettest January since records began in 1910- about 350mm of rain fell in January and February (100mm above average).
    2. Rivers had not been dredged for at least 20 years, and so were clogged with sediment.
    3. High tides and storm surges swept water up the Bristol Channel, which spilled over the riverbanks.
  2. What were the impacts of the flood?
    1. Social
      1. Over 600 houses flooded
      2. 16 farms evacuated
      3. Villages cut off
      4. Power supplies cut off
      5. Residents evacuated to temporary accommodation for months
    2. Economic
      1. Cost of flood damage estimated to be more than £10 million
      2. Railway line closed
      3. Over 1000 livestock evacuated
      4. Local roads cut off by floods
    3. Environmental
      1. Stagnant water had to be reoxygenated before being pumped back into rivers
      2. Debris had to be cleared
      3. Floodwater heavily contaminated with sewage etc.
  3. Immediate Responses
    1. Local community groups and volunteers gave support
    2. Boats used to go to school etc
  4. Long-Term Responses
    1. Somerset County Council- £20 million flood action plan
    2. March 2014- rivers Tone and Parrett dredged
    3. Road levels raised
    4. River banks raised and strenghened
    5. More pumping stations built
2. Extreme Weather in the UK
3. What are the UK's weather hazards?
  1. Weather is driven towards the UK by south-westerly prevailing winds.
  2. Thunderstorms
  3. Prolonged Rainfall (can lead to flooding)
  4. Drought and extreme heat
  5. Strong Winds
  6. Heavy snow and extreme cold
Reducing the effects of Tropical Storms
1. Monitoring and Prediction
  1. Hurricane Watch: This warns that hurricane conditions are possible.
  2. Hurricane Warning: This advises that hurricane conditions are expected and that people should take immediate action.
2. Protection
  1. Reinforcement of windows, doors and roofs to strengthen buildings.
  2. Construction of storm drains in urban areas to help against flooding.
  3. Sea walls built to protect important properties from storm surges.
    1. Houses in coastal areas constructed on stilts to protect them from storm surges.
  4. In Bangladesh, almost 2000 cyclone shelters have been built.
3. Planning
  1. Planning involves raising individual and community awareness, as people need to understand potential dangers and be able to respond.
    1. USA- Hurricane Preparedness Week.

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	Created by Louise Elmslie over 6 years ago