Year 7 Science · Unit 2 · Lesson 12
Challenge Worksheet
Learning Goals
Read the graph
Study the bar chart showing how Earth's water is distributed, then answer the three questions below.
Data: USGS Water Science School; UNESCO World Water Assessment Programme, 2023.
(a) Using the graph, calculate approximately what percentage of Earth's water is accessible freshwater (rivers, lakes, and atmosphere combined). Show your working.
(b) The oceans contain 97.5% of all water. Why can't we simply use ocean water for drinking and irrigation without any treatment?
(c) Why does it matter so much to protect groundwater aquifers, even though they contain less than 1% of Earth's water?
What if…?
Scenario
The Paris Agreement (2015) set a target to limit global average temperature rise to 1.5–2°C above pre-industrial levels. Scientists predict that if temperatures rise by 2°C, the water cycle will intensify, meaning evaporation rates increase, rainfall events become more intense but less frequent, and periods between rain events lengthen. Australia's Bureau of Meteorology projects that southern Australia, including the Murray-Darling Basin, will experience reduced rainfall and more frequent extreme droughts. At the same time, tropical northern Australia may experience more intense cyclones and flooding events.
(a) Predict how a 2°C temperature rise would change evaporation rates in the Murray-Darling Basin, and explain what effect this would have on river flows and drought frequency. Use water cycle terminology.
(b) The scenario describes more intense but less frequent rainfall. Explain why this could actually make flooding AND drought worse at the same time. How does the water cycle explain this apparent contradiction?
(c) If freshwater flow in the Murray-Darling is significantly reduced, which water security strategy from the lesson would be most useful for South Australia? Justify your choice with reference to how it works.
Wrap Up
In one sentence, what was the main idea of this lesson?