Weather Hazards: Typhoons and Droughts
Hello everyone! Welcome to your study notes on two powerful and very different weather hazards: typhoons and droughts. One brings too much water, and the other, not enough! Understanding these hazards is super important, especially for us in Hong Kong and the wider China region, as we experience them firsthand. In these notes, we'll break down how they form, the problems they cause, and what we can do about them. Let's get started!
Part 1: Typhoons - The Spiralling Giants
You've definitely experienced a T8 signal, with schools closed and winds howling outside. But what exactly is a typhoon? Let's dive in.
What is a Typhoon?
A typhoon is a powerful, rotating storm system with strong winds and heavy rain. It's a type of tropical cyclone that forms over warm ocean waters in the Northwest Pacific Ocean.
Did you know? These storms have different names around the world, but they are the same weather phenomenon!
- In the Atlantic and Northeast Pacific, they're called hurricanes.
- In the Indian Ocean and South Pacific, they're called cyclones.
- Here in the Northwest Pacific, we call them typhoons.
How Do Typhoons Form? - The Perfect Storm Recipe
Don't worry if this seems tricky at first. Think of it like baking a cake – you need the right ingredients and the right steps. Here are the essential conditions for a typhoon to form:
Warm Ocean Water: The sea surface temperature must be at least 26.5°C to a depth of about 50 metres. This warm water is the fuel for the storm, providing the heat and moisture needed.
Location (The Coriolis Effect): Typhoons form between 5° and 20° north or south of the Equator. They can't form right at the Equator because they need the Coriolis effect – a force from the Earth's rotation that makes winds spin. Analogy: Imagine trying to draw a straight line on a spinning basketball; the line will curve. The Coriolis effect does the same to wind!
Low Wind Shear: The winds at different altitudes must be blowing in the same direction and at a similar speed. This allows the storm to grow vertically into a tall, organized structure without being "blown apart".
The Step-by-Step Formation Process
Lift-off: Warm, moist air over the ocean rises quickly, creating an area of lower pressure near the surface.
Power Up: As the air rises, it cools and condenses to form clouds. This process releases a huge amount of energy called latent heat. This heat warms the surrounding air, causing it to rise even faster and making the low pressure at the centre even lower.
Start Spinning: Air from surrounding areas with higher pressure pushes into the low-pressure centre. The Coriolis effect makes this air bend and begin to rotate around the centre.
Full Power: As long as the storm stays over warm water, it acts like a giant engine, sucking up heat and moisture to become a massive, spinning typhoon.
The Structure of a Typhoon
A mature typhoon has three main parts:
The Eye: The calm, clear centre of the typhoon. It has light winds and often no rain because cool, dry air is sinking here.
The Eyewall: This is the most dangerous part! It's a ring of towering thunderstorms right around the eye, with the strongest winds and heaviest rain.
Spiral Rainbands: These are the long "arms" of clouds and rain that stretch out from the centre.
Quick Review Box
Typhoon Formation Needs:
Fuel (Warm water > 26.5°C)
Outside the Equator (5°-20° N/S for Coriolis effect)
Rising Air (Low pressure)
Minimal Wind Shear (To grow vertically)
What are the Impacts of Typhoons?
Typhoons are destructive. Their impacts can be direct (primary) or knock-on effects (secondary).
Primary Impacts (The direct hits)
Strong Winds: Can exceed 200 km/h. They damage buildings, uproot trees, and turn loose objects into dangerous projectiles.
Heavy Rainfall: Can cause severe flooding, especially in low-lying areas.
Storm Surge: This is an abnormal rise in sea level caused by the typhoon's strong winds and low pressure pushing water towards the coast. It's often the deadliest impact, causing massive coastal flooding.
Secondary Impacts (The aftermath)
Flooding: Widespread flooding from a combination of heavy rain and storm surge.
Landslides: Heavy rain saturates hillsides, causing soil and rock to slide down. This is a major risk in a hilly place like Hong Kong.
Disruption to Services: Power cuts, loss of fresh water supply, and complete shutdown of transport (airports, MTR, ferries).
Economic Loss: Damage to property and infrastructure costs billions to repair. Businesses are forced to close, leading to lost income.
How Do We Respond to Typhoons?
Since we can't stop typhoons, we have to learn to live with them. Our response involves actions before, during, and after the storm.
Prediction and Warning Systems: The Hong Kong Observatory (HKO) tracks typhoons and issues warnings, like the familiar T1, T3, T8, T9, and T10 signals, to give everyone time to prepare.
Mitigation and Preparation (Before the storm): This includes building stronger infrastructure (e.g. sea walls), enforcing strict building codes, stabilising slopes to prevent landslides, and educating the public on what to do.
Emergency Response (During and after the storm): This involves rescue operations, opening temporary shelters, clearing fallen trees and debris, and working to restore power and transport as quickly as possible.
Key Takeaway for Typhoons
Typhoons are powerful tropical cyclones fuelled by warm ocean water and the Earth's rotation. They cause immense damage through strong winds, heavy rain, and storm surges. Effective management relies on prediction, public warnings, strong infrastructure, and well-rehearsed emergency plans.
Part 2: Droughts - The Silent Hazard
Now, let's switch gears from too much water to too little. A drought is a less dramatic but equally devastating hazard, especially for agriculture.
What is a Drought?
A drought is a long period with abnormally low rainfall, which leads to a serious shortage of water. It's important to remember that 'low rainfall' is relative. A drought in a rainforest is very different from a drought in a desert!
Causes and Impacts of Drought in North China
The syllabus specifically wants us to focus on North China, which is a vital agricultural region but is very prone to drought.
Why does North China suffer from droughts?
The causes are a mix of natural and human factors.
Natural Causes (Climate and Geography)
Unreliable Monsoons: North China relies on the summer monsoon for its rain. If the monsoon is weak or arrives late, the region gets much less rain than it needs.
High Evaporation: Strong winds and dry air, especially in spring, can cause a lot of water to evaporate from the soil and rivers before it can be used.
Human Causes (What people do)
Over-abstraction of water: The population and industries in North China have grown rapidly. They are taking too much water from rivers and groundwater supplies, causing them to dry up.
Deforestation: Removing trees reduces the amount of moisture recycled into the atmosphere and increases water runoff, meaning less water soaks into the ground to replenish groundwater.
Water Pollution: Industrial and agricultural pollution can make the available water sources too dirty to use, creating a water shortage even if the water is physically there.
What are the impacts of drought in North China?
Economic Impacts: Massive crop failures, as North China is the country's main wheat-growing area. This leads to food shortages and huge financial losses. Industries may have to cut production due to a lack of water.
Environmental Impacts: Rivers and reservoirs dry up, the ground cracks, and soil can turn to dust. This can lead to desertification, where fertile land becomes desert. Sandstorms can become more frequent.
Social Impacts: People may not have enough water for drinking and sanitation, leading to health problems. Farmers can lose their livelihoods, forcing them to migrate to cities.
How is China Combating Drought? (Management Strategies)
China has adopted several large-scale strategies to fight drought.
Water Transfer Projects: The most famous example is the South-to-North Water Diversion Project. This massive engineering project uses canals and pipelines to move water from the water-rich Yangtze River in the south to dry northern cities like Beijing.
- Evaluation: It successfully provides water to the north, but it is incredibly expensive and has caused environmental problems and displacement of people in the south.Improved Farming Methods: Encouraging farmers to use water-saving techniques like drip irrigation (which delivers water directly to plant roots) and to plant crop types that are more resistant to drought.
Water Conservation and Management: Running public awareness campaigns to encourage people to save water, increasing the price of water to discourage waste, and improving infrastructure to fix leaky pipes.
Common Mistakes to Avoid
A common mistake is thinking droughts are only a natural problem. Remember to always discuss the human factors that make droughts much worse, like over-use and pollution of water!
Key Takeaway for Droughts
Drought in North China is caused by a combination of unreliable rainfall (natural) and intense demand for water from farms, cities, and industries (human). The impacts are severe, affecting the economy, environment, and society. China's main strategies involve massive water transfer schemes, improving agricultural efficiency, and promoting water conservation.