6.1.1 Global Water Distribution (Cambridge International AS Environmental Management)

Global Water Distribution

Spec point — 6.1.1

• Water is one of the most essential resources on Earth, crucial for supporting biodiversity, ecosystems, and human activities

• Understanding the distribution of Earth's water across different reservoirs is essential for managing water resources sustainably and addressing global water challenges

• The Earth's water can be roughly divided up into the following categories:

  • Salt water in oceans:

    • Approximately 97.5% of the Earth's water is found in oceans and seas
    • Oceans cover about 71% of the Earth's surface and contain vast quantities of saltwater

  • Surface freshwater:

    • Ice sheets and glaciers:

      • Ice sheets and glaciers store around 68.7% of the Earth's freshwater
      • Most of this freshwater is contained within ice caps covering Antarctica and Greenland

    • Lakes, rivers, swamps and marshes:

      • Lakes, rivers, swamps and marshes collectively hold around 0.3% of the Earth's freshwater
      • These surface water bodies are crucial habitats for diverse aquatic ecosystems and serve as sources of drinking water and irrigation

  • Sub-surface freshwater:

    • Soil Moisture:

      • Soil moisture accounts for approximately 0.05% of the Earth's freshwater.
      • This water is found within the soil profile and is vital for supporting plant growth and agricultural activities

    • Groundwater:

      • Groundwater constitutes around 30.1% of Earth's freshwater resources
      • It is stored in underground aquifers and is accessed through wells for drinking, industrial and agricultural purposes

    • Permafrost:

      • Permafrost, which contains permanently frozen ground, holds a small fraction of the Earth's freshwater
      • While difficult to quantify, permafrost regions contribute to the planet's water cycle and influence surface water availability

  • Atmospheric water:

    • Atmospheric water comprises a tiny fraction of the Earth's total water supply, estimated to be around 0.001%
    • It includes water vapour, clouds and precipitation, which play crucial roles in the global water cycle by transporting water from one location to another

Sources of water on Earth

Comparison of the world's freshwater stores

Exam Hint Don't worry - you don't need to learn the exact percentages here. You just need to be able to describe how Earth's water is divided into different storages, so you need to be able to name these storages and understand how they relate to each other.