Introduction to Drought

Welcome! In this chapter, we are exploring drought. While a tropical cyclone is a sudden, violent event, a drought is often called a "creeping hazard." It develops slowly over time, sometimes taking months or even years to become a serious problem. Understanding why they happen and how different countries cope is a key part of your Paper 1 exam.

What is a drought? In simple terms, it is a prolonged period of abnormally low rainfall that leads to a shortage of water. But as geographers, we look deeper into the different types and causes.


1. The Three Main Causes of Drought

Droughts aren't just about "no rain." They are caused by a mix of weather patterns, water cycles, and human actions. The syllabus identifies three specific categories:

A. Meteorological Causes (Weather)

This refers to a change in the normal pattern of precipitation (rain, snow, etc.).

  • High Pressure (Anticyclones): Usually, rain happens when air rises and cools. In a high-pressure system, air sinks. This prevents clouds from forming, leading to long periods of dry, clear weather.
  • Changing Wind Patterns: Sometimes, the winds that usually bring moist air from the ocean change direction, bringing dry air from over land instead.
  • Climate Change: Global shifts in temperature can alter where rain falls, making some areas much drier than they used to be.

B. Hydrological Causes (Water Stores)

This happens when the actual "stores" of water—like rivers, lakes, and groundwater (water stored in rocks underground)—run low.

  • If there is low snowfall in winter, there is less meltwater to fill rivers in the spring.
  • If the ground is very dry, any rain that does fall might evaporate before it can soak into the ground to refill the aquifers (underground water stores).

C. Human Causes (Our Impact)

Humans can make a natural dry spell much worse through how we manage land and water:

  • Deforestation: Trees release moisture into the atmosphere (transpiration). When we cut them down, the air becomes drier, and the soil loses its ability to hold water.
  • Agriculture: Using too much water for irrigation (watering crops) can drain rivers and lakes faster than they can refill.
  • Dam Building: Building a dam to provide water for one area can stop water from flowing downstream to another area, creating a "man-made" drought for people living there.

Quick Review: Think of a drought like a bank account. Meteorological causes are like getting a lower salary (less rain coming in), and Human/Hydrological causes are like spending too much money (using up the water we already have).


2. Why are some locations more vulnerable?

Some places are hit much harder by drought than others. This is called vulnerability. There are two main reasons for this:

Physical Vulnerability

  • Location: Places near the 30° North and South of the equator (where sinking air creates deserts) are naturally drier.
  • Climate: Areas that rely on a single "rainy season" (like the Monsoon in India) are very vulnerable if that rain fails to arrive.

Human/Social Vulnerability

  • Population Growth: More people means more demand for drinking water and food.
  • Poverty: Wealthier countries can afford expensive technology like desalination (turning seawater into drinking water). Developing or emerging countries may not have the money for these "back-up" plans.
  • Over-farming: In some regions, farmers graze too many animals on the land, which destroys the vegetation and makes the soil turn to dust.

3. Impacts of Drought: People and Ecosystems

Droughts are hazardous because they affect everything from the food we eat to the health of the planet.

Impacts on People (Social and Economic)

  • Subsistence Farmers: In developing countries, many people grow their own food. If the crops fail, it leads to famine and malnutrition.
  • Water Conflicts: As water becomes scarce, people (or even countries) may fight over who gets to use the remaining supply.
  • Economic Loss: Industries that use a lot of water (like beverage companies or paper mills) may have to shut down, leading to job losses.

Impacts on Ecosystems (Environmental)

  • Loss of Biodiversity: Wetlands and ponds may dry up, killing fish, plants, and the animals that rely on them.
  • Wildfires: Dry vegetation acts as fuel. A single spark can lead to massive fires that destroy habitats.
  • Soil Erosion: Without plants to hold the soil together, the wind can blow the fertile top layer away, making it impossible for plants to grow back even when it does rain.

4. Responses to Drought: A Comparison

For your exam, you need to know how responses differ between a Developed country (VHHD - Very High Human Development) and an Emerging/Developing country (LHD/HMHD). Check your class notes for your specific named examples!

Responses in Developed Countries (e.g., USA or Australia)

These responses often involve high-cost technology and strict government laws:

  • Water Restrictions: Fining people for washing cars or watering lawns.
  • Engineering: Building massive pipelines to move water from wet areas to dry ones.
  • Desalination: Building plants to remove salt from seawater (very expensive).
  • Education: National campaigns teaching people how to save water at home.

Responses in Emerging/Developing Countries (e.g., Ethiopia or Namibia)

Responses here often focus on survival and lower-cost, community-led projects:

  • International Aid: Relying on charities (NGOs) for food parcels and emergency water tankers.
  • Intermediate Technology: Building simple tools like "sand dams" or hand pumps that are cheap to maintain.
  • Zai Pits: A traditional farming method where small pits are dug to catch and hold every drop of rainwater for crops.
  • Migration: Often, the only response for people is to leave their homes and move to cities or refugee camps to find water.

Key Takeaways for Revision

  • Meteorological = No rain; Hydrological = Low water stores; Human = Overusing water or cutting down trees.
  • Vulnerability is higher in poor countries with fast-growing populations.
  • Impacts are categorized into Social (people), Economic (money), and Environmental (nature).
  • Developed countries use "High-Tech" and expensive responses; Developing countries often use "Low-Tech" or rely on international help.

Exam Tip: If a question asks you to Calculate the percentage change in rainfall during a drought, use this formula:

\( \text{Percentage Change} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100 \)

Make sure to show your working! Even if the final answer is wrong, you can get marks for the method.