Edexcel GCSE Geography A (1GA0) — The Physical Environment
Every time a severe storm hits, it can deliver over of rain within 24 hours. A tropical cyclone is an intense, rotating low-pressure weather system. Because they threaten human life, property, and the environment, they are classified as a natural hazard. The actual realization of this threat when it impacts a populated area is called a natural disaster.
The physical characteristics of these storms create primary hazards. They are intense low-pressure systems (often below ) with maximum sustained winds that can exceed . These winds directly cause structural damage and create lethal flying debris.
Primary forces trigger secondary hazards, creating severe socio-economic impact. Intense rainfall saturates steep slopes, causing rapid landslides in vulnerable areas.
Furthermore, extreme low pressure creates a "suction" effect on the ocean, while high winds push this water inland. This creates a storm surge, a temporary rise in sea level that causes catastrophic coastal flooding and drowning.
How do meteorologists know if a storm requires a mass evacuation? They measure its magnitude using the Saffir-Simpson Scale, a 1 to 5 rating system. Crucially, this scale is based solely on sustained wind speed (averaged over a 1-minute interval at a 10-metre height).
Since 2012, central pressure and storm surge are specifically NOT used to determine a storm's category on this scale. Any storm reaching Category 3 or higher is classified as a major hurricane.
Worked Example: Calculating Cyclone Category
A tropical cyclone reaches a maximum sustained wind speed of . Determine its category.
Step 1: Identify the recorded wind speed.
Step 2: Compare the speed against the Saffir-Simpson thresholds.
Step 3: State the category.
Global storm frequency remains surprisingly steady at around 80 to 90 storms per year. However, evidence shows a increase in storm intensity over the last 30 years.
Tropical cyclones often originate near the ITCZ (Intertropical Convergence Zone), a low-pressure belt where trade winds meet. They only form where Sea Surface Temperatures (SST) reach at least and where the Coriolis Effect (deflection force from Earth's rotation) causes them to spin. Because this rotational force is too weak at the equator ( to latitude), storms do NOT form there.
In exams, you must interpret line graphs showing the relationship between rising SST and the Power Dissipation Index (PDI), which measures total storm energy. These graphs generally display a clear positive correlation.
As ocean temperatures rise above the threshold, the PDI increases, meaning warmer oceans provide more energy to power stronger Category 4 and 5 storms. You may also be asked to read an anomaly graph, which shows how current temperatures or storm intensities deviate from a long-term average.
Predicting exactly where a storm will make landfall saves thousands of lives. A GIS (Geographic Information System) is a digital framework used to gather, map, and analyse spatial data.
To track a cyclone, meteorologists collect georeferenced data (data tied to specific latitude and longitude coordinates) from satellites and radar. This information is time-stamped, making it temporal data. By plotting these points at regular intervals (e.g., every 6 hours), GIS creates a visual storm track.
GIS allows analysts to "layer" different attributes over a map. For example, wind speed can be shown by varying the size or colour of dots along the track. Using buffer analysis, emergency planners can create a zone (e.g., ) around the predicted track to identify exactly which schools or hospitals need evacuating.
Students often state that the Saffir-Simpson scale uses central pressure and storm surge to categorize hurricanes; remember that since 2012, it is based solely on sustained wind speed.
For 4-mark 'explain' questions about hazards, examiners expect a clear causal chain: link a physical characteristic (e.g., low pressure) to a specific threat (e.g., storm surge) and finally to a human impact (e.g., drowning).
When describing climate change graphs, always quote specific data points from the axes (e.g., reading exact temperatures or PDI values) to support your statement of a positive correlation.
Always double-check the units provided in the exam data; ensure wind speeds are in km/h before categorising a storm on the Saffir-Simpson scale provided in these notes.
Tropical cyclone
A rotating, organized system of clouds and thunderstorms originating over tropical waters with a closed, low-level circulation.
Natural hazard
A natural event with the potential to cause harm to people, property, or the environment.
Natural disaster
The actual realization of a hazard threat when it impacts a populated area.
Socio-economic impact
The effect of a hazard on people (social) and the economy (economic), such as homelessness or rebuilding costs.
Storm surge
A temporary rise in local sea level caused by low atmospheric pressure and strong winds pushing water onto land.
Saffir-Simpson Scale
A 1 to 5 rating system used to measure the intensity of tropical cyclones based on sustained wind speeds.
Sustained wind speed
The maximum wind speed of a storm averaged over a specific time period, usually 1 minute.
Major hurricane
Any tropical cyclone reaching Category 3 or higher on the Saffir-Simpson Scale.
ITCZ (Intertropical Convergence Zone)
A low-pressure belt near the equator where trade winds meet, acting as a source area for tropical storms.
Coriolis Effect
The force resulting from Earth's rotation causing winds to deflect, allowing cyclones to spin.
Power Dissipation Index (PDI)
An aggregate measure of tropical cyclone intensity that combines storm frequency, intensity, and duration.
Anomaly graph
A type of graph showing how data, such as sea surface temperatures, deviates from a long-term average.
GIS (Geographic Information System)
A digital framework for gathering, managing, and analyzing spatial and geographic data.
Georeferenced data
Information that is tied to specific geographic coordinates, such as latitude and longitude.
Temporal data
Data that is time-stamped, allowing analysts to track changes over time.
Storm track
The visual path of a storm mapped over time using recorded coordinates.
Put your knowledge into practice — try past paper questions for Geography A
Tropical cyclone
A rotating, organized system of clouds and thunderstorms originating over tropical waters with a closed, low-level circulation.
Natural hazard
A natural event with the potential to cause harm to people, property, or the environment.
Natural disaster
The actual realization of a hazard threat when it impacts a populated area.
Socio-economic impact
The effect of a hazard on people (social) and the economy (economic), such as homelessness or rebuilding costs.
Storm surge
A temporary rise in local sea level caused by low atmospheric pressure and strong winds pushing water onto land.
Saffir-Simpson Scale
A 1 to 5 rating system used to measure the intensity of tropical cyclones based on sustained wind speeds.
Sustained wind speed
The maximum wind speed of a storm averaged over a specific time period, usually 1 minute.
Major hurricane
Any tropical cyclone reaching Category 3 or higher on the Saffir-Simpson Scale.
ITCZ (Intertropical Convergence Zone)
A low-pressure belt near the equator where trade winds meet, acting as a source area for tropical storms.
Coriolis Effect
The force resulting from Earth's rotation causing winds to deflect, allowing cyclones to spin.
Power Dissipation Index (PDI)
An aggregate measure of tropical cyclone intensity that combines storm frequency, intensity, and duration.
Anomaly graph
A type of graph showing how data, such as sea surface temperatures, deviates from a long-term average.
GIS (Geographic Information System)
A digital framework for gathering, managing, and analyzing spatial and geographic data.
Georeferenced data
Information that is tied to specific geographic coordinates, such as latitude and longitude.
Temporal data
Data that is time-stamped, allowing analysts to track changes over time.
Storm track
The visual path of a storm mapped over time using recorded coordinates.
