Tropical cyclones, also known as hurricanes or typhoons, are large storm systems characterized by strong winds, heavy rain, and storm surges. They form over warm tropical waters and require certain atmospheric and oceanic conditions. When they make landfall, their damage depends on factors like wind speed, storm surge size, population distribution, and a region's development level and emergency preparedness. Hurricane Katrina (2005) caused extensive damage in the US due to its large storm surge and impact on the densely populated Gulf Coast, while Cyclone Nargis (2008) was especially deadly in Burma due to that country's lower development level and emergency response capacity.

1. 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)

2. TROPICAL CYCLONE CHARACTERISTICS: ATMOSPHERIC CIRCULATION
The atmospheric circulation is the result of the Coriolis force due to the rotation of the planet
Note: ICTZ = Inter-Tropical Convergence Zone
1. Explain three factors required to lead to formation of cumulonimbus clouds
2. Name two regions of the globe which combine these three factors

3. TROPICAL CYCLONES CHARACTERISTICS: FORMATION OF A TROPICAL CYCLONE (DEPRESSION)
1. Explain why tropical cyclones form in the ITCZ
2. 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-nimbus
clouds

4. TROPICAL CYCLONES CHARACTERISTICS: EYE VS RAINBANDS

5. TROPICAL CYCLONES CHARACTERISTICS: PRESSURE + WIND-DRIVEN WATER SURGE
• 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)
Explain what causes huge surges during tropical cyclones
Katrina surge (2005)

6. 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

7. 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 damages
2. Explain why Nargis was more destructive than Katrina