Weather Hazards

Weather Hazards

1. Global Atmospheric Circulation (GAC)

   • Definition
     • The movement of air by which heat is distributed on the surface of the earth.
     • 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.
       • These cells are: the Hadley Cell, the Ferrel Cell and the Polar Cell
     • Atmospheric Circulation is also a response to differences in insolation (heat) between high and low latitudes.
       • A global pattern of surface winds and pressure belts results from this circulation.
         • 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.
   • Diagram
   • How does GAC work?
     • Air that is sinking towards the ground surface forms areas of high pressure. Winds on the ground move outwards from these areas.
       • An example is at the North Pole.
     • 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.
       • An example is at the Equator.
     • The Wind direction is distorted and deflected due to the Earth's rotation- known as the Coriolis Effect.
     • GAC is what drives the world's weather.
       • For example, the trade winds in the tropics drive tropical storms.

2. Tropical Storms

   • What are Tropical Storms?
     • There are several different names for tropical storms; used in different regions of the world.
       • In the USA and Carribean, they are called Hurricanes.
       • In South-East Asia and Australia, they are called Cyclones.
       • In Japan and the Philippines, they are called Typhoons.
     • A Tropical Storm ia a large storm that forms over Tropical Oceans.
       • They are very powerful and can cause much devastation to small islands and coastal regions.
   • Where do Tropical Storms Form?
     • Tropical Storms form over warm oceans (above 27 degrees).
     • Tropical Storms form in the Summer and in the Autumn, when sea temperatures are at their highest.
     • Most Tropical Storms form about 5-15 degrees North or South of the Equator.
       • 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.
     • 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.
   • How do Tropical Storms Form?
     • 1) A strong upward movement of air draws water vapour up from the warm ocean surface.
       • 2) This evaporated air cools as it rises and condenses to form thunderstorm clouds.
         • 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.
   • What is the structure of a Tropical Storm?
     • At the direct centre of the storm there is an eye, which is a small area where relatively cold air sinks and warms up.
       • At the eye of the storm, there are no clouds and conditions are calm.
     • 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.

3. Case Study: Typhoon Haiyan | 2013

   • Facts about the Hurricane
     • Category 5 on the Saffir- Simpson Scale
     • Occurred in November 2013
     • The hurricane hit the Philippines
     • Large areas of coastline and several towns devastated by winds of up to 275 km/h and waves up to 15m.
       • One of the strongest storms ever recorded.
   • Effects
     • City of Tacloban one of the worst affected places- with most of the 220,000 inhabitants left homeless.
       • Destruction caused by a 5m high storm surge.
       • 90% of Tacloban city destroyed.
         • Tacloban Airport terminal was badly damaged
     • Primary Effects- impacts of strong winds, heavy rain and storm surge.
       • 6300 people killed (mostly drowned by the storm surge)
       • Over 600,000 people displaced and 40,000 homes damaged or flattened.
       • 30,000 fishing boats destroyed
       • Over 400mm of rain caused widespread flooding.
       • Strong winds damaged buildings and power lines and destroyed crops.
       • Airport terminal badly damaged.
     • Secondary Effects- longer-term impacts resulting from primary effects.
       • 14 million people affected - with many people left homeless and 6 million lost their source of income.
       • Flooding caused landslides and blocked roads, which cut off remote communities.
       • Power supplies cut off for a month in some areas.
       • Shortages of food, water and shelter- led to outbreaks of disease.
       • Looting and violence
       • Many jobs were lost as hospitals, shops and schools were damaged- affecting people's livelihoods and education.
   • Responses
     • Immediate Responses
       • International governments and aid agencies responded with food, water and temporary shelters.
       • Over 1200 evacuation shelters set up to help the homeless.
       • Field hospitals set up to help the injured.
       • The UK government sent shelter kits to provide emergency shelter for families.
     • Long-Term responses
       • Many countries donated financial aid, supplies and medical support.
       • Roads, bridges and airports rebuilt.
       • 'Cash for Work' programmes- people paid to clear debris and rebuild the city.
       • Oxfam supported the replacement of fishing boats- a vital source of income.
       • Thousands of homes rebuilt away from areas at risk from flooding.

4. Weather Hazards in the UK

   • Case Study: The Somerset Levels Floods | 2014
     • What caused the floods in 2014?
       • It was the wettest January since records began in 1910- about 350mm of rain fell in January and February (100mm above average).
       • Rivers had not been dredged for at least 20 years, and so were clogged with sediment.
       • High tides and storm surges swept water up the Bristol Channel, which spilled over the riverbanks.
     • What were the impacts of the flood?
       • Social
         • Over 600 houses flooded
         • 16 farms evacuated
         • Villages cut off
         • Power supplies cut off
         • Residents evacuated to temporary accommodation for months
       • Economic
         • Cost of flood damage estimated to be more than £10 million
         • Railway line closed
         • Over 1000 livestock evacuated
         • Local roads cut off by floods
       • Environmental
         • Stagnant water had to be reoxygenated before being pumped back into rivers
         • Debris had to be cleared
         • Floodwater heavily contaminated with sewage etc.
     • Immediate Responses
       • Local community groups and volunteers gave support
       • Boats used to go to school etc
     • Long-Term Responses
       • Somerset County Council- £20 million flood action plan
       • March 2014- rivers Tone and Parrett dredged
       • Road levels raised
       • River banks raised and strenghened
       • More pumping stations built
   • Extreme Weather in the UK
   • What are the UK's weather hazards?
     • Weather is driven towards the UK by south-westerly prevailing winds.
     • Thunderstorms
     • Prolonged Rainfall (can lead to flooding)
     • Drought and extreme heat
     • Strong Winds
     • Heavy snow and extreme cold

5. Reducing the effects of Tropical Storms

   • Monitoring and Prediction
     • Hurricane Watch: This warns that hurricane conditions are possible.
     • Hurricane Warning: This advises that hurricane conditions are expected and that people should take immediate action.
   • Protection
     • Reinforcement of windows, doors and roofs to strengthen buildings.
     • Construction of storm drains in urban areas to help against flooding.
     • Sea walls built to protect important properties from storm surges.
       • Houses in coastal areas constructed on stilts to protect them from storm surges.
     • In Bangladesh, almost 2000 cyclone shelters have been built.
   • Planning
     • Planning involves raising individual and community awareness, as people need to understand potential dangers and be able to respond.
       • USA- Hurricane Preparedness Week.

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