Weather Hazards and Tropical Storms

GCSE Geography · The Challenge of Natural Hazards

Global Atmospheric Circulation

The atmosphere redistributes heat energy from the equator towards the poles through a system of circulation cells:

Hadley Cell (0°–30°): Warm air rises at the equator (creating low pressure and heavy rainfall — the ITCZ), moves poleward at high altitude, cools, and sinks at ~30° (creating high pressure and deserts like the Sahara). Surface winds blow back towards the equator as the trade winds.
Ferrel Cell (30°–60°): Surface winds blow poleward as the westerlies. Air rises at ~60° where it meets cold polar air (creating low pressure and the UK's changeable weather).
Polar Cell (60°–90°): Cold, dense air sinks at the poles (high pressure), flows towards 60° as polar easterlies, and rises where it meets warmer air.

This system explains the global distribution of high and low pressure belts, which control weather patterns and the location of the world's deserts and rainforests.

Tropical Storms

Tropical storms are known as hurricanes (Atlantic/East Pacific), typhoons (Northwest Pacific), or cyclones (Indian Ocean/South Pacific). They are intense low-pressure weather systems with sustained winds exceeding 119 km/h (74 mph).

Formation Conditions

Sea surface temperature of at least 27°C to a depth of 60–70 metres
Located at least 5° north or south of the equator (Coriolis effect needed to spin the storm)
Low wind shear (consistent wind speed and direction at different altitudes)
Existing areas of low pressure or disturbances

Structure

Eye — calm, clear centre, typically 30–65 km across, with sinking air and light winds
Eyewall — ring of the most intense thunderstorms, heaviest rainfall, and strongest winds
Spiral rainbands — bands of thunderstorms extending outward hundreds of kilometres
Storms can be 500–1,000 km in diameter and release energy equivalent to 10,000 nuclear bombs per day

Hazards

Strong winds — up to 300 km/h, destroying buildings, uprooting trees, downing power lines
Storm surge — a dome of seawater pushed ashore, causing coastal flooding (often the deadliest hazard)
Intense rainfall — can exceed 500 mm in 24 hours, causing flash flooding and landslides
Tornadoes — sometimes spawned within the outer rainbands

Case Study: Typhoon Haiyan (Yolanda) — November 2013

Location: Philippines (LIC/NEE) | Category 5 | Wind speeds: up to 315 km/h | Storm surge: up to 5 metres in Tacloban

Primary Effects

6,300 people killed, over 28,000 injured
14 million people affected, 6 million displaced
1 million homes destroyed or severely damaged, particularly in Tacloban city
90% of the city of Tacloban devastated
Infrastructure destroyed — roads, bridges, airport, power lines, water systems

Secondary Effects

Outbreaks of disease — contaminated water led to gastroenteritis and leptospirosis
Shortages of food, clean water, and medicine for weeks
Estimated $12 billion in damage
Psychological trauma — widespread PTSD among survivors
Looting of shops and warehouses due to desperation

Responses

Immediate: Philippine government declared a state of national calamity; US aircraft carrier USS George Washington deployed; international aid totalling $1.5 billion pledged; NGOs provided emergency shelter, water purification, and medical teams
Long-term: "Build Back Better" programme — stronger typhoon-resistant buildings; mangrove replanting along coasts for natural storm surge defence; improved early warning systems; relocation of communities from the most vulnerable coastal areas

Climate Change and Tropical Storms

There is scientific evidence that climate change may increase the intensity of tropical storms (warmer oceans provide more energy), though the frequency may not increase. Storm surge risk increases as sea levels rise. The distribution of tropical storms may shift as ocean temperatures change.