Geography (9635) | Storm hazards

Study Notes: Storm Hazards (Tropical Cyclones)

Welcome to the "Storm Hazards" chapter! This topic is vital for understanding how the powerful atmosphere interacts with human society, often leading to large-scale disasters. Don's worry if some of the atmospheric science seems tricky at first—we'll break down these giant storms into manageable pieces.

We are focusing on tropical storms (also known as Hurricanes, Typhoons, or Cyclones), looking at how they form, the dangers they pose, and how different communities around the world prepare for and respond to these catastrophic events. This fits directly into our study of Living with Hazards.

1. The Nature and Underlying Causes of Tropical Storms

1.1 What is a Tropical Storm?

Tropical storms are intense, low-pressure weather systems that develop over warm tropical oceans. They rotate rapidly (anti-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere) and are characterised by strong winds and torrential rainfall.

Did you know? These storms are called different names depending on where they form:

• Hurricane: North Atlantic and Northeast Pacific Oceans.
• Typhoon: Northwest Pacific Ocean (Asia).
• Cyclone: Indian Ocean and South Pacific.

Memory Aid: If it starts in the Atlantic, it's an H-word (Hurricane)!

1.2 Conditions Required for Formation (The Underlying Causes)

Tropical storms need a very specific set of ingredients to develop. Think of it like baking a massive, destructive cake!

1. Sea Surface Temperature (SST): Water must be at least 26.5°C (or warmer) and needs to be this warm down to a depth of 50 meters. This provides the massive amount of latent heat energy needed to power the storm.
2. Low Wind Shear: Wind shear is the difference in wind speed and direction between the low and high atmosphere. It needs to be low so that the storm cloud structure isn't ripped apart as it tries to rise.
3. Latitude: They must form 5 to 15 degrees North or South of the Equator. They cannot form right on the Equator because they need the Coriolis Effect to make them spin (the Coriolis force is too weak at 0° latitude).
4. Pre-existing Weather Disturbance: A starting mechanism, such as a cluster of thunderstorms (a 'tropical wave').
5. High Humidity: Abundant moist air in the atmosphere helps fuel the massive rain clouds.

1.3 The Formation Process: A Step-by-Step Guide

This is the process of warm, moist air rising and spinning:

1. Warm, moist air rises rapidly from the ocean surface (convection). This causes a low-pressure area to form at the surface.
2. As the air rises, it cools and condenses, forming towering cumulonimbus clouds and releasing huge amounts of latent heat (stored energy).
3. This released heat warms the surrounding air, causing it to rise even faster, drawing more air and moisture from below. This creates a positive feedback loop, intensifying the storm.
4. The Coriolis Effect deflects the rising air, causing the system to begin rotating around a central point—the Eye (a central area of calm, sinking air).
5. Once sustained winds reach 119 km/h (74 mph), it is officially classified as a tropical storm (or Hurricane/Typhoon/Cyclone).

Key Takeaway: Tropical storms are powered by heat (26.5°C+ water) and rotation (Coriolis effect) and require low wind shear to keep their structure intact.

2. Forms and Characteristics of Storm Hazards

2.1 Spatial Distribution and Characteristics

The distribution of tropical storms is clustered around the major tropical ocean basins (Western Pacific, North Atlantic, Indian Ocean).

• Spatial Distribution: Restricted to tropical and sub-tropical regions, generally within the 5° to 30° latitude bands, where sea temperatures are highest. They dissipate (die out) when they hit cooler water or move over land (losing their energy source).
• Magnitude: Measured using the Saffir-Simpson Hurricane Wind Scale (Categories 1-5). Category 5 storms have the highest magnitude, capable of catastrophic damage.
• Frequency and Regularity: They are seasonal. In the North Atlantic, the season is June to November. Frequency can vary year-to-year, often linked to climate cycles like El Niño, but they are generally regular within their specific seasons.
• Predictability: Improved satellite tracking and computer modelling mean that the general path of a storm can be predicted days in advance. However, the exact track and intensity changes can still be unpredictable, leading to uncertainty in hazard preparation.

2.2 Forms of Storm Hazard (The Dangers)

Tropical storms unleash multiple hazards simultaneously, making them particularly dangerous.

1. High Winds: The most immediate danger, causing structural damage (blowing roofs off, collapsing walls) and turning debris into dangerous projectiles.
2. Storm Surges: This is the most deadly hazard. It is an abnormal rise of water generated by the storm, over and above the predicted astronomical tide. It's caused primarily by the low atmospheric pressure at the eye (which sucks the water level up) and the strong winds pushing water towards the coast.
3. Coastal Flooding: Caused by the storm surge inundating low-lying coastal areas.
4. River Flooding: Caused by the intense, prolonged rainfall overloading river systems, particularly dangerous inland where high winds may not be the primary threat.
5. Landslides: Heavy rainfall saturates slopes, particularly in mountainous or hilly areas, causing ground instability and triggering mass movement.

Quick Review: The primary atmospheric hazard is high wind, but the primary hydrological hazards (flooding and surge) often cause the most fatalities.

3. Impacts of Tropical Storms

We must categorise impacts to fully understand a storm’s effect. We look at primary/secondary effects and then classify them into social, economic, environmental, and political (ESEP).

3.1 Primary vs. Secondary Impacts

• Primary Impacts: Occur immediately during the storm. (Examples: Buildings destroyed by high winds, coastal areas inundated by storm surge, people drowned.)
• Secondary Impacts: Occur later, resulting from the primary effects. (Examples: Water supplies contaminated leading to disease outbreaks, unemployment due to factory destruction, food shortages due to damaged crops.)

3.2 Environmental, Social, Economic, and Political (ESEP) Impacts

E – Environmental Impacts:

Example: Saltwater contamination of freshwater ecosystems and agricultural land (from storm surge). Trees are defoliated or uprooted, leading to soil erosion.

S – Social Impacts:

Example: Loss of life, injury, homelessness, disruption to education, and psychological trauma. Damage to essential services like hospitals and water treatment plants.

E – Economic Impacts:

Example: Destruction of infrastructure (roads, bridges, power lines), loss of income from tourism and agriculture, and massive costs associated with insurance payouts and clean-up/rebuilding.

P – Political Impacts:

Example: Governments face international pressure for aid and internal pressure from displaced populations. Political tensions can arise over the allocation of reconstruction funds, especially if relief efforts are slow or uneven.

Key Takeaway: Always think beyond the immediate destruction. Secondary and long-term ESEP impacts often define the severity of a disaster in the years following the event.

4. Human Responses and Risk Management

4.1 The Goal: Risk Management

Risk management involves actions designed to reduce the impacts of the hazard. The syllabus requires us to look at four key strategies: Preparedness, Mitigation, Prevention, and Adaptation.

Risk Management Strategies:

• Preparedness: Planning how to respond when a storm is forecast. (Example: Setting up early warning systems, creating evacuation routes, stocking emergency supplies.)
• Mitigation: Actions taken before the storm to reduce potential loss of life and property damage. (Example: Building flood defenses, strengthening building codes, land-use zoning to prevent building in high-risk coastal zones.)
• Prevention: While we cannot prevent tropical storms from forming, this term refers to preventing the effects. (Example: Dams/reservoirs upstream to prevent river flooding; artificial barriers against storm surge.)
• Adaptation: Adjusting behaviour or structures to cope with the hazard in the long term, recognising that storms are a permanent reality. (Example: Elevating homes on stilts, developing salt-resistant crop varieties.)

4.2 Short-Term vs. Long-Term Responses

• Short-Term Responses: Immediate relief efforts carried out in the hours and days following the event. Focus is on saving lives and providing basic necessities. (Example: Search and rescue operations, providing emergency food, water, and shelter, issuing immediate international appeals for aid.)
• Long-Term Responses: Recovery efforts taking months or years. Focus is on rebuilding infrastructure, restoring the economy, and implementing risk management strategies to reduce future vulnerability. (Example: Long-term loans for rebuilding homes, infrastructure investment (e.g., repairing power grids), establishing new early warning systems.)

5. Case Studies: Tropical Storms in Contrasting Areas

To achieve high marks, you must use evidence from two recent tropical storms in contrasting areas of the world. This allows you to compare the differences in impacts and responses based on the level of development and geographical location.

5.1 What Makes Areas "Contrasting"?

A good contrast might be:

• A storm hitting a HIC (High-Income Country) vs. a LIC (Low-Income Country).
• A storm in the Atlantic vs. a storm in the Pacific.
• A storm where the primary hazard was wind vs. a storm where the primary hazard was storm surge/flooding.

5.2 Comparing Impacts and Responses

When studying your two case studies, ensure you can compare:

1. Vulnerability: Why was one place more vulnerable? (e.g., lower quality housing, lack of warning systems, higher poverty).
2. Scale of Impact: Compare the ESEP impacts (e.g., economic damage as a percentage of GDP in a LIC will be much higher than in a HIC, even if the absolute dollar cost is lower).
3. Effectiveness of Responses: How well did the HIC implement preparedness and mitigation compared to the LIC? Were the long-term adaptation efforts in the LIC sustainable?

Crucial Tip: The contrast usually shows that while the physical hazard (wind speed, rainfall) might be similar, the human impact and ability to recover are profoundly different, often based on wealth and development levels.