Edexcel IGCSE Geography 复习笔记 1.3.1 Water Uses, Demand & Supply

• Only 2.5% of the water on Earth is freshwater
• 68.7% of freshwater is stored in glaciers and ice sheets and 30% is groundwater
• The remaining 1.3% of freshwater is in rivers, soil moisture, lakes and the atmosphere

Sources of water

• Global water use by sector is:
  • 70% agriculture - irrigation of crops and water for livestock
  • 20% industry - producing goods and generating energy
  • 10% domestic - toilets, cooking, cleaning, washing
• The use by sector varies across countries depending on whether they are developed, emerging or developing

Water Use 

• In developing and emerging countries most water is used for agriculture
• The use of water in leisure and tourism is increasing, particularly in developed countries
• In developed countries most water is used for industry

• Demand is the amount of water requested by users to meet their needs
• Supply is the amount of water available
• Water balance is the difference between supply and demand
• Countries may have a deficit (greater demand than supply) or surplus (more supply than demand)

Water Demand

• The global demand for water is increasing
• Between 1934 and 2014 demand increased from 1 trillion m³ to 4 trillion m³

Water Supply

• The supply of water comes from three main sources:
  • Lakes and rivers
  • Aquifers
  • Reservoir
• The reasons for increased demand include:
  • Improving living standards - people have more appliances/sanitation which use water
  • Increased use of water in leisure and tourism - water parks, golf courses
  • Increased urbanisation
  • Population growth - the more people there are, the more water is needed
  • Increasing industry - water is needed for production of goods and energy production
  • Increasing use in agriculture - more water is needed for livestock

Water Shortages (Deficit)

• Many areas of the world have water shortages (deficits)
• Water deficit can be due to:
  • Low supply - lack of precipitation, high levels of evaporation, poor water management
  • High demand - increasing population, industry and agriculture
  • A combination of low supply and high demand
• Areas with the greatest water deficit include:
  • Australia
  • North, East and South Africa
  • Middle East
  • West USA
  • Parts of South America
  • India

Water surplus and deficit

• Many of these areas have a deficit due to low precipitation throughout the year
• In some areas demand is greater than supply due to increasing population, industry and agriculture
• There are different levels of water shortage - these are water stress and water scarcity:
  • Water stress occurs when the supply of water is below 1700m³ a year per person
  • Water scarcity is when the supply is below 1000m³ a year per person

Water Surplus

• Some areas of the world have a water surplus
• Water surplus can be due to:
  • High supply - high precipitation, low evaporation rates, effective water management
  • Low demand - low population, effective water management, low temperatures
  • A combination of high supply and low demand
• Areas with a surplus include:
  • North-east Brazil in the Amazon rainforest
  • Canada and parts of north USA
  • Russia