Typhoon Haiyan - Case Study

At any one time there are multiple weather systems active around the globe with variable winds. When these winds are averaged over many years a well-defined global circulation pattern appears.

The global circulation

• Over the major parts of the Earth's surface there are large-scale wind circulations present. The global circulation can be described as the world-wide system of winds by which the necessary transport of heat from tropical to polar latitudes is accomplished.

• In each hemisphere there are three cells (Hadley cell, Ferrel cell and Polar cell) in which air circulates through the entire depth of the troposphere. The troposphere is the name given to the vertical extent of the atmosphere from the surface, right up to between 10 and 15 km high. It is the part of the atmosphere where most of the weather takes place.

Types Of Cells

• Hadley cell

• The largest cells extend from the equator to between 30 and 40 degrees north and south, and are named Hadley cells, after English meteorologist George Hadley.

• Within the Hadley cells, the trade winds blow towards the equator, then ascend near the equator as a broken line of thunderstorms, which forms the Inter-Tropical-Convergence Zone (ITCZ). From the tops of these storms, the air flows towards higher latitudes, where it sinks to produce high-pressure regions over the subtropical oceans and the world's hot deserts, such as the Sahara desert in North Africa.

• Ferrel cell

• In the middle cells, which are known as the Ferrel cells, air converges at low altitudes to ascend along the boundaries between cool polar air and the warm subtropical air that generally occurs between 60 and 70 degrees north and south. This often occurs around the latitude of the UK which gives us our unsettled weather. The circulation within the Ferrel cell is complicated by a return flow of air at high altitudes towards the tropics, where it joins sinking air from the Hadley cell.

• The Ferrel cell moves in the opposite direction to the two other cells (Hadley cell and Polar cell) and acts rather like a gear. In this cell the surface wind would flow from a southerly direction in the northern hemisphere. However, the spin of the Earth induces an apparent motion to the right in the northern hemisphere and left in the southern hemisphere. This deflection is caused by the Coriolis effect and leads to the prevailing westerly and southwesterly winds often experienced over the UK.

• Polar cell

• The smallest and weakest cells are the Polar cells, which extend from between 60 and 70 degrees north and south, to the poles. Air in these cells sinks over the highest latitudes and flows out towards the lower latitudes at the surface.

Tropical Storms

• A tropical storm is a hazard that brings heavy rainfall, strong winds and other related hazards such as mudslides and floods.

• Tropical storms usually form between approximately 5° and 15° latitude and move westward due to easterly winds. The Coriolis force sends them spinning towards the poles.

• It is hard to predict the path of a tropical storm, and therefore difficult to manage an adequate evacuation of an area if needed.

• Tropic storms form during the summer and autumn when the sea temperatures are at their highest.They form when oceans are above 27°C  which explains why they are found in the tropic.

• In tropical regions the intense heat makes the air unstable causing it to rise rapidly. These unstable condition are important in the formation of hurricanes

Formation of a Tropical Storm

1. The sun is close to the equator, providing energy to heat the ocean.

2. The warm ocean heats the air above it causing it to rise rapidly.

3. Water evaporates quickly from the hot surface of the ocean, so the rising air contains great amounts of water vapour.

4. The rising air starts to spin (clockwise in the northern hemisphere)

5. The centre of the storm - the eye - is calm.

6. As the air rises it cools, condenses and forms towering cumulonimbus clouds.

7. The rapidly rising air creates an area of intense low pressure. The low pressure sucks in air, causing very strong winds.

8. Once the storm moves over land it starts to lose energy and fades.

Typhoon Haiyan - Case Study

Primary Effects -

• About 6300 people was killed - most drowned by the storm surge.

• Over 600000 people displaced and 40000 homes damaged or flattened - 90% of tacloban city destroyed.

• Tacloban airport terminal badly damaged.

• The typhoon destroyed 30000 fishing boats.

• Strong winds damaged buildings and power lines and destroyed drops

• Over 400mm of rain caused widespread flooding

Secondary Effects -

• 14 million people affected, many left homeless and 6 million people lost their source of income.

• Flooding caused landslides and blocked roads, cutting off aid to remote communities.

• Power supplies in some areas cut off for a month.

• Ferry services and airline flights disrupted for weeks, slowing down aid efforts.

• Shortages of water, food and shelter affected many people, leading to outbreaks in disease.

• Many jobs lost, hospitals were damages, shops and schools were destroyed, affecting people's livelihoods and education.

• Looting and violence broke out in tacloban

Immediate Responses -

• International government and aid agencies responded quickly with food aid, water and temporary shelters.

• US aircrafts carrier George Washington and helicopters assisted with search and rescue and delivery of aid.

• Over 1200 evacuation centres were set up to help the homeless.

• UK government sent shelter kits, each one able to provide emergency shelter for a family.

• French, Belgian and Israeli field hospitals set up to help the injured.

• The philippines Red Cross delivered basic food aid, which included rice, canned food, sugar, salt and cooking oil.

Long-term Responses -

• The UN and countries including the UK, Australia, Japan and the US donated financial aid, supplies and medical support.

• Rebuilding of roads, bridges and airport facilities.

• ‘Cash for work’ programmes - people paid to help clear debris and rebuild the city.

• Foreign donors, including the US, Australia and the EU, supported new, livelihood opportunities.

• Rice farming and fishing quickly re-established. Coconut production - where's the trees may take five years to bear fruit - will take longer.

• Aid agencies such as Oxfam supported the replacement of fishing boats - a vital source of income.

• Thousands of homes have been built away from areas at risk of flooding.

• More cyclone shelter built to accommodate people evacuated from coastal areas.

Management:

• Monitoring - Spotting hurricanes in imagery. Satellite information is very important for tracking and determining intensity trends of hurricanes and other tropical storms. When a hurricane is well offshore and out of effective radar range, forecasters use satellite imagery to continuously track the storm's movement and development.

• Predicting - Scientists can predict the number of named storms and their breakdown by intensity (i.e. the number of hurricanes, tropical storms, intense hurricanes, etc.). They can also predict approximate wind speeds and intensity for sustained winds. These can be easily calculated using elementary statistics.

• Protection -  Disaster Plan (Safe meeting points, escape routes, contacts, pet plans, insurance, emergency kit/supplies)

- Disaster Supply Kit (Water, Food, Blankets, Pillows, First aid, Torch etc.)

- Building Design (Deep Foundations, Stilts, Stormproof doors and roofs, window shutters.)

- Evacuation (Signed exits, warning system)

- Cyclone Shelters (Storm proof buildings with supplies)

- Mangrove Trees (Natural Barrier against the wind and rain.)

- Cyclone Walls (Protection from the storm surge, and a safe evacuation route.)

- Levees and Concrete Sea walls (Designed to hold back flood waters and storm surges.)