LESSON 9.4 Why is water supply variable?
LEARNING INTENTION By the end of this lesson, you should be able to: • describe the distribution of water across the world and explain the impact of climate change on water distribution • explain how Australia’s climate affects water availability • explain the impact of climate change on water availability in Australia.
Tune in Most of the water that Australians use is found in surface water such as the drainage basin shown in FIGURE1 . 1. What direction is this river flowing towards? What evidence supports this response? 2. What do you notice about changes to the shape of the river and to the way it moves as it makes its way to the sea? 3. Brainstorm four ways humans could capture water in this drainage basin for future use.
FIGURE1 How drainage basins work
9.4.1 The world’s water Even though the Earth looks blue from space, most of the water is salt water and not usable. The small amount of fresh water available is not evenly spread around the world. Water covers about 75 per cent of Earth’s surface. But FIGURE2 shows 97.5 per cent is salt water, and only 2.5 per cent is fresh. Most fresh water (69.5 per cent) is locked in glaciers, ice, snow and permafrost. The rest is mostly groundwater, and only 0.4 per cent is in rivers, lakes, wetlands, and in plants and animals.
SkillBuilder discussion Communicating 1. Which water body stores the most water? 2. What percentage of fresh water is stored in glaciers? 3. Which water body stores the most water that is not saline?
FIGURE2 The distribution of water on Earth
Total water
Surface and atmospheric water 0.4%
Oceans
Fresh water 2.5%
Oceans 97.5%
Freshwater lakes 67.4%
Glaciers 68.7%
Soil moisture 12.2%
Other wetlands 8.5%
Groundwater 30.1%
Rivers 1.6% Atmosphere 9.5% Plants and animals 0.8%
Permafrost 0.8%
TOPIC9 Water in the world 259
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