HAZARD #2: TROPICAL CYCLONES (HURRICANES, TYPHOONS, CYCLONES)

Category 5 tropical cyclone “Isabel” (2003), North of the Caribbean islands, seen from space, with peak winds of 265 km/h (only ~ 50 victims)

Tropical cyclone: storm system characterized by a large low-pressure center (depression) and numerous thunderstorms that produce very strong winds (100-300 km/h) and heavy rain (500mm in 24hrs) and ocean surges (1-10 meters)

TROPICAL CYCLONE CHARACTERISTICS: ATMOSPHERIC CIRCULATION

The atmospheric circulation is the result of the Coriolis force due to the rotation of the planetNote: ICTZ = Inter-Tropical Convergence Zone

1. Explain three factors required to lead to formation of cumulonimbus clouds2. Name two regions of the globe which combine these three factors

TROPICAL CYCLONES CHARACTERISTICS: FORMATION OF A TROPICAL CYCLONE (DEPRESSION)

1. Explain why tropical cyclones form in the ITCZ2. State the direction taken by upward spiraling

winds in the Northern hemisphere, due to the Coriolis force

3. Describe the difference between cumulo-nimbus and cirrus clouds

4. Explain why tropical cyclones lose strength when passing over land

Cirrus clouds

Cumulo-nimbusclouds

TROPICAL CYCLONES CHARACTERISTICS: EYE VS RAINBANDS

• Pressure surge is usually about 10mm for every millibar of pressure drop (normal is 1015 mb• Strong tropical depression can drop to ~900 mb (= 1 m pressure surge + wind-effect)

TROPICAL CYCLONES CHARACTERISTICS: PRESSURE + WIND-DRIVEN WATER SURGE

Katrina surge (2005)Explain what causes huge surges during tropical cyclones

TROPICAL CYCLONES: SPATIAL DISTRIBUTION

1. Circle regions which combine high hazard + high vulnerability

2. Suggest factors which explain the extensive damages caused by a tropical cyclone

TROPICAL CYCLONE: DAMAGE FACTORS

• Strength of tropical cyclone: not a factor in itself however, if the storm doesn’t make landfall or doesn’t hit a densely populated area (eg: almost not casualties during category 5 hurricane Frances, 2004)

• Distribution of population: populations living in windward low-lying coastal areas are very vulnerable (e.g.: Cancun, Miami, New Orleans, some Caribbean Islands

• Development level: planning laws, emergency planning, evacuation measures, relief operations, housing types, etc. MEDCs tend to have better preparedness and response to tropical cyclones than some very poor LEDCs

Case-studies in textbook (p.206-207):• Hurricane Katrina (US Gulf Coast, 2005): 1,800 casualties + 800,000 homeless, winds

up to 225 km/h, surge up to 9m

• Cyclone Nargis (Burma, 2008): 134,000 casualties + millions homeless

1. Research why Katrina caused extensive damages2. Explain why Nargis was more destructive than Katrina