Weather hazards and tropical storms · GCSE Geography

Global atmospheric circulation

The Sun heats the Equator most. Hot air rises there, creating low pressure and heavy rain. It moves towards the poles, cools, and sinks at about 30° north and south, creating high pressure and dry conditions, where the hot deserts are.
This makes three cells in each hemisphere: the Hadley cell (0–30°), the Ferrel cell (30–60°) and the Polar cell (60–90°). Rising air at about 60° gives the UK its wet, changeable weather.
Surface winds blow from high to low pressure: the trade winds blow towards the Equator, and the westerlies blow towards 60°. The Earth's rotation bends the winds (the Coriolis effect), which is why the UK's prevailing wind is from the south-west.

Tropical storms are called hurricanes in the Atlantic, typhoons in the north-west Pacific and cyclones in the Indian Ocean. They form over oceans of at least 27 °C, between about 5° and 30° north and south of the Equator, mostly in late summer and autumn.
Warm, moist air rises quickly, cools and condenses, releasing heat that powers the storm. The Coriolis effect makes the storm spin. It weakens over land or cooler water, because its supply of warm, moist air is cut off.
The eye in the centre is calm, with sinking air and clear skies. Around it, the eyewall has the strongest winds and heaviest rain. Bands of rain spiral outwards.

Typhoon Haiyan hit the Philippines on 8 November 2013, with winds of over 300 km/h and a storm surge of up to 5 m.
Primary effects: more than 6,000 people died, over a million homes were damaged or destroyed, and the city of Tacloban was devastated, including its airport.
Secondary effects: around 4 million people were displaced, there were shortages of food, water and shelter, and many people lost their jobs, fishing boats and crops.
Immediate responses: about 800,000 people were evacuated before the storm, and international aid sent food, water, shelter and medical teams. Aid was slow to reach some remote areas.
Long-term responses: homes and infrastructure were rebuilt with stronger designs, 'no-build zones' were set up along parts of the coast, and mangroves were replanted to protect against storm surges.

Monitoring and prediction (satellites and aircraft), warnings and evacuation plans, storm shelters, stronger building designs, sea walls and planning where to build all reduce the effects.
Climate change may make tropical storms more intense, change where they occur, and raise sea levels, which makes storm surges worse.

The UK's weather hazards include heavy rain and flooding, strong winds, snow and ice, drought and heatwaves. In July 2022, the UK recorded 40 °C for the first time.
Example: the Somerset Levels floods of 2014. After record rainfall in December 2013 and January 2014, about 600 homes and large areas of farmland were flooded, and villages such as Muchelney were cut off for weeks. Afterwards, the rivers Parrett and Tone were dredged, and a £100 million, 20-year Flood Action Plan was set up.

Global atmospheric circulation: The worldwide system of winds that moves heat from the Equator towards the poles.
Hadley cell: The circulation cell between the Equator and about 30° north and south.
Tropical storm: A large, spinning, low-pressure storm with very strong winds and heavy rain.
Eye: The calm centre of a tropical storm, with sinking air.
Storm surge: A rise in sea level caused by the strong winds and low pressure of a storm.
Coriolis effect: The bending of winds caused by the Earth's rotation.
Evacuation: Moving people away from danger.
Extreme weather: Weather that is much more severe than usual, such as a record heatwave.