Hazardous Earth: Weather Hazards

What you'll learn

This revision guide covers the testable content on weather hazards from the Pearson Edexcel International IGCSE Geography specification. You'll examine the formation, distribution and impacts of tropical storms and droughts, explore how human and natural factors influence their severity, and analyse responses and management strategies. Case study knowledge is essential for achieving top marks.

Key terms and definitions

Tropical storm — an intense low-pressure weather system with heavy rainfall and winds exceeding 119 km/h, known as hurricanes (Atlantic/Caribbean), typhoons (Pacific) or cyclones (Indian Ocean)

Storm surge — a raised dome of seawater up to several metres high caused by low atmospheric pressure and strong winds, leading to coastal flooding

Drought — a prolonged period of abnormally low rainfall leading to water shortage, typically defined as 15 consecutive days with less than 0.2mm of rain

Meteorological drought — below-average precipitation over a period of months or years

Hydrological drought — depletion of water sources such as rivers, lakes, reservoirs and groundwater following meteorological drought

Aridity — a permanent feature of climate in regions with consistently low rainfall, distinct from drought which is temporary

Coriolis effect — the deflection of moving air caused by Earth's rotation, responsible for the spin of tropical storms

Eye of the storm — the calm, cloudless centre of a tropical storm with low pressure, light winds and no precipitation, typically 30-50 km in diameter

Core concepts

Global atmospheric circulation and tropical storms

The Earth's atmospheric circulation creates three cells in each hemisphere: Hadley, Ferrel and Polar. The Hadley cell is crucial for tropical storm formation. Warm air rises at the equator, creating low pressure, then moves towards the tropics where it descends at approximately 30°N and 30°S, creating high pressure zones.

Tropical storms form between 5° and 30° latitude in both hemispheres, requiring specific conditions:

• Sea surface temperature exceeding 27°C to at least 50m depth
• Location at least 5° from the equator (to allow Coriolis effect to initiate rotation)
• Low wind shear to prevent disruption of the developing storm structure
• Depth of warm ocean water to provide continuous energy through evaporation
• Unstable atmospheric conditions with rising air

Formation sequence:

1. Intense solar heating causes rapid evaporation over warm oceans
2. Warm, moist air rises rapidly, creating an area of very low pressure
3. Air spirals inward due to the Coriolis effect, rotating anticlockwise in the Northern Hemisphere
4. Rising air cools, water vapour condenses, releasing latent heat energy
5. This heat causes further rising and intensifies the low pressure
6. Dense clouds form and torrential rain occurs
7. Cool air descends in the centre, creating the calm eye
8. The whole system moves westward, powered by trade winds

Tropical storms dissipate when they:

• Move over land (cut off from warm ocean energy source)
• Travel over cooler ocean water (below 27°C)
• Encounter strong wind shear in upper atmosphere

Distribution and frequency of tropical storms

Tropical storms occur in distinct ocean basins:

Atlantic/Caribbean basin: Hurricane season runs June to November, with peak activity August-October. Major storms affecting the Caribbean include Hurricane Maria (2017, Dominica) and Hurricane Irma (2017).

Western Pacific: Typhoon season peaks July-November, affecting the Philippines, Taiwan, Japan and Southeast Asia.

Indian Ocean: Cyclones occur May-June and October-November in the Bay of Bengal and Arabian Sea.

South Pacific and Southern Indian Ocean: November-April cyclone season affects countries including Madagascar, Mozambique, Fiji and Vanuatu.

Key distribution factors:

• All occur over warm tropical oceans (27°C+)
• None form within 5° of equator (insufficient Coriolis force)
• Most move westward initially, then curve poleward
• Greatest frequency in late summer/autumn when ocean temperatures peak

Climate change evidence suggests:

• Intensity of strongest storms is increasing
• Overall frequency may be decreasing slightly
• Geographic range potentially expanding as ocean temperatures rise
• More rapid intensification events occurring

Primary and secondary impacts of tropical storms

Primary impacts result directly from the storm hazards:

Strong winds (119-250+ km/h):

• Destruction of buildings, especially poorly-constructed structures
• Uprooting trees and damage to crops
• Flying debris causing injuries and deaths
• Damage to power lines and infrastructure

Storm surge:

• Coastal flooding up to several kilometres inland
• Destruction of coastal settlements and infrastructure
• Contamination of freshwater supplies with salt water
• Drowning — the single biggest cause of death in many tropical storms

Intense rainfall (200-500mm in 24 hours):

• River flooding as drainage systems overwhelmed
• Landslides on steep, saturated slopes
• Destruction of property and agricultural land

Secondary impacts occur in the days, weeks and months following:

Economic:

• Business closure and job losses
• Destruction of fishing boats and tourist facilities
• Long-term reduction in GDP
• Increased government debt from reconstruction costs

Social:

• Spread of waterborne diseases (cholera, typhoid) from contaminated water
• Homelessness and displacement
• Food shortages as crops destroyed and distribution disrupted
• Psychological trauma

Environmental:

• Ecosystem damage (coral reefs, mangroves)
• Soil erosion and salinisation
• Pollution from sewage overflow and damaged industrial facilities

Impacts are typically more severe in lower-income countries due to:

• Lower quality building construction
• Limited early warning systems
• Inadequate emergency services
• Fewer resources for preparation and response
• Higher population density in vulnerable coastal areas
• Greater dependence on primary sector activities (agriculture, fishing)

Formation, distribution and impacts of droughts

Droughts develop when an area experiences significantly below-average rainfall over an extended period. The progression follows stages:

1. Meteorological drought: Below-average precipitation for weeks/months
2. Agricultural drought: Soil moisture depletion affecting crop growth
3. Hydrological drought: Reduced streamflow, reservoir and groundwater levels
4. Socio-economic drought: Water shortage affects human activities and economic sectors

Causes of drought include:

Natural factors:

• Blocking anticyclones preventing rain-bearing depressions
• El Niño events disrupting normal rainfall patterns
• Natural climate variability

Human factors:

• Climate change altering precipitation patterns and increasing evaporation
• Deforestation reducing rainfall through decreased evapotranspiration
• Over-extraction of groundwater

Droughts affect multiple regions:

Sub-Saharan Africa (Sahel): Recurring droughts linked to rainfall variability and desertification. The 2011 East Africa drought affected 13 million people across Somalia, Ethiopia and Kenya.

Australia: The Millennium Drought (1997-2009) severely impacted agriculture in southeast Australia.

California, USA: Multi-year droughts (2012-2016) affected agriculture and urban water supplies.

Impacts vary by development level:

Lower-income countries:

• Crop failure leading to famine and malnutrition
• Livestock death reducing farmer income and food supply
• Migration as people seek water and food
• Conflict over diminishing water resources
• Child mortality from malnutrition and disease

Higher-income countries:

• Agricultural losses and increased food prices
• Water restrictions for domestic and industrial use
• Hydroelectric power generation reduced
• Increased wildfire risk
• Economic cost of importing water or food

Prediction, preparation and response strategies

For tropical storms:

Prediction and monitoring:

• Satellite imagery tracking storm development and movement
• Computer models forecasting track and intensity
• Hurricane hunter aircraft measuring conditions within storms
• Early warning systems issuing alerts 48-72 hours in advance

Preparation (short-term):

• Evacuation of vulnerable coastal areas
• Boarding up windows and securing loose objects
• Stocking emergency supplies (water, food, batteries)
• Moving to hurricane shelters

Preparation (long-term):

• Building codes requiring hurricane-resistant construction
• Sea defences and coastal management
• Education programmes and evacuation drills
• Land-use planning restricting development in high-risk areas

Responses:

• Search and rescue operations
• Emergency supplies (water, food, medical aid)
• Temporary shelter provision
• Infrastructure repair and rebuilding
• International aid for lower-income countries

For droughts:

Prediction:

• Rainfall monitoring and climate forecasting
• Soil moisture and reservoir level tracking
• Drought indices (e.g. Palmer Drought Severity Index)

Preparation:

• Water conservation education
• Drought-resistant crop varieties
• Improved irrigation efficiency (drip irrigation)
• Water storage infrastructure (reservoirs, tanks)
• Diversification of water sources

Responses:

• Water rationing and hosepipe bans
• Food aid distribution
• Financial support for affected farmers
• Cloud seeding attempts to increase rainfall
• Desalination plants in coastal areas

Case study requirements

You must prepare detailed case studies demonstrating:

A tropical storm in a lower-income country — focus on impacts and responses. Hurricane Maria (2017) in Dominica is ideal:

• Category 5 hurricane with 260 km/h winds
• 31 deaths, 90% buildings damaged
• Agricultural sector destroyed (banana crops)
• Response: international aid, slow reconstruction

A tropical storm in a higher-income country — compare impacts and responses. Hurricane Katrina (2005, USA) or recent Caribbean/Atlantic storms work well:

• Better prediction and evacuation
• Still significant impacts due to storm intensity
• More effective emergency response but still challenges
• Faster reconstruction with insurance and government funds

A drought event — causes, impacts and responses. Options include:

• California drought 2012-2016
• East Africa drought 2011
• Australia's Millennium Drought

Include: location, causes (natural and human), primary and secondary impacts, immediate and long-term responses, effectiveness of strategies.

Worked examples

Example 1: Explain how the Coriolis effect contributes to tropical storm formation. (4 marks)

Mark scheme answer: The Coriolis effect is the deflection of moving air caused by the Earth's rotation (1 mark). As air moves towards the low-pressure centre of a developing tropical storm, it is deflected sideways (1 mark). This creates a spinning motion — anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere (1 mark). This rotation is essential for the characteristic spiral structure and intensification of the storm system (1 mark).

Example 2: Assess the reasons why tropical storms have greater impacts in lower-income countries compared to higher-income countries. (8 marks)

Mark scheme approach:

• Buildings in lower-income countries are often poorly constructed from weak materials, leading to greater destruction (2 marks for explanation)
• Limited early warning systems mean fewer people evacuate, increasing casualties (2 marks)
• Inadequate emergency services struggle to respond effectively in the immediate aftermath (2 marks)
• Lower levels of insurance mean individuals and governments cannot afford rapid reconstruction (2 marks)
• Economic dependence on agriculture and fishing means livelihoods are destroyed, creating long-term poverty (2 marks)
• Limited healthcare infrastructure leads to disease outbreaks after contamination of water supplies (2 marks)

Select and develop 4 points thoroughly for full marks. Include named examples where possible.

Example 3: Using a named example, evaluate the effectiveness of responses to a drought event. (9 marks + 3 SPaG)

Mark scheme guidance: Introduction: Name the drought, location, dates, basic context (1 mark)

Short-term responses: Water rationing, emergency food aid, describe and explain effectiveness with specific detail (3 marks)

Long-term responses: Infrastructure investment, policy changes, explain success and limitations (3 marks)

Evaluation: Balance positive outcomes against continuing problems, consider if different approaches could be more effective (2 marks)

Ensure continuous prose, accurate spelling of geographical terms, proper paragraph structure for SPaG marks.

Common mistakes and how to avoid them

• Confusing drought with aridity: Drought is temporary and abnormal for a region; aridity is a permanent climate characteristic. The Sahara Desert experiences aridity, not drought.

• Stating tropical storms need the Coriolis effect to form: They actually need the Coriolis effect to be strong enough, which is why they don't form within 5° of the equator where the effect is minimal.

• Vague case study answers: Always include specific facts, figures and place names. "Many people died" scores zero marks; "31 people died in Dominica during Hurricane Maria" demonstrates case study knowledge.

• Listing impacts without explanation: Don't just write "flooding occurred." Explain: "Storm surge raised sea levels by 3 metres, flooding coastal settlements up to 2km inland and contaminating freshwater supplies with saltwater."

• Ignoring the command word: "Assess" requires judgement of relative importance; "describe" needs factual detail; "explain" demands reasons and processes. Match your answer style to the command word.

• Assuming all responses are successful: In evaluation questions, discuss limitations. Hurricane Katrina had good prediction but evacuation failed for many poor residents without transport.

Exam technique for "Hazardous Earth: Weather Hazards"

• Command words matter: "Assess" and "evaluate" require weighing up different factors and reaching a judgement. "Explain" needs causes, processes or reasons with because/therefore/this leads to language. "Describe" wants factual characteristics without explanation.

• Case study questions reward specificity: For 6+ mark questions on a named example, include at least 5 specific facts (dates, locations, statistics, names). Generic answers cannot access top levels.

• Use appropriate terminology: Show command of geographical vocabulary — "storm surge" not "big wave," "latent heat" not "energy from condensation," "meteorological drought" not "no rain."

• Extended writing structure: For 9-mark questions, write a brief introduction naming your case study, develop 3-4 paragraphs exploring different aspects, and conclude with an overall judgement. Allow 12-15 minutes for these responses.

Quick revision summary

Tropical storms form over warm oceans (27°C+) between 5-30° latitude when warm, moist air rises, creating intense low pressure with rotating winds due to the Coriolis effect. Impacts include wind damage, storm surge flooding and intense rainfall, with worse effects in lower-income countries due to weaker infrastructure and limited resources. Droughts occur after prolonged below-average rainfall, progressing from meteorological to agricultural to hydrological drought. Prediction, preparation and response strategies reduce impacts, with technology and wealth enabling more effective management in higher-income nations.