Liz Bonnin introduces a clip explaining the water cycle.
Video
LIZ BONNIN: Hi, Liz Bonnin here. I'm a science, wildlife and natural history presenter and I'm passionate about conservation and the natural world, and today, we're here on the south coast by the stunning Seven Sisters cliffs, to talk to you about physical geography.
Now physical might make you think that the subject only covers solid things, like rocks and landscapes, but actually it also requires an understanding of the things that have an impact on our surroundings, and that is why we're now going to look at water.
Water is everywhere around us, as vapour, rain or clouds in the air, or in rivers and seas, and it's essential for all life, both plants and animals, to survive.
And it's constantly moving around in a process called the water cycle.
Now that's got nothing to do with floating bicycles, which is a shame, but in this clip Professor Ian Stewart does get to go on very impressive ride in a para-glider.
PROFESSOR STEWART: The fresh water that we depend on begins its life in the oceans. As the sun's rays beat down on the surface of the sea they heat the water molecules until some evaporate. It's the start of an extraordinary journey.
You know, when water evaporates it feels like it vanishes into thin air, but although we barely notice it, water molecules are suspended around us all the time. Just that we're only aware of it when they clump together as cloud.
At any one time, less than a thousandth of the world's fresh water is up here in the atmosphere. It may not seem much, but this is what spreads water from the seas to the land.
A water molecule doesn't hang around up here for very long. In fact it spends less time up here in the atmosphere than in any other time in its journey. A mere nine days until a typical water molecule crashes to earth as rain.
For most of us, rain is perhaps the most familiar stage of the water cycle. But, notoriously, the least reliable.
When the water falls as rain, it joins a bigger system cascading and carving its way across the land surface as streams and rivers. Look at that! Water absolutely everywhere!
Rivers and rain are the part of the water cycle that we depend on. Whoa! And yet they're only a tiny proportion of the world's fresh water. A measly 2% of all fresh water on the planet.
The rest of the Earth's fresh water is locked away down there, on the ground. (As the para-glider lands) Wahey! Oh, what a landing. The vast majority of it is stored as ice.
Most of the rest seeps deep into the earth, where it's known as ground water. Hidden away down here is the planet's second largest store of fresh water. But in the end, all water arrives back in the oceans, and the cycle begins again.
LIZ BONNIN: So there you go. Most of the Earth's fresh water supplies, over 65%, are frozen in the ice caps and glaciers. There's a huge amount, over 30%, trickling around in the ground and rocks beneath us, and rivers and streams only account for tiny amount. A drop in the ocean!
Download/print a transcript of the video.
Liz Bonnin introduces the water cycle - part of Hydrology at KS3 and Rivers and water at KS4 - and explains that water is constantly moving around Earth.
Professor Iain Stewart examines the constant process of evaporation, condensation and precipitation. Water evaporates and forms clouds in the atmosphere; it condenses and returns to the Earth as rain or snow; it forms rivers that eventually lead to the sea or lakes; the water evaporates and the cycle begins again.
Professor Stewart explains that only 2% of the world’s freshwater is held in rivers and rain: most is locked away as ice or stored deep in the earth as groundwater.
Teacher notes
Download/print the Teacher Notes for this episode (pdf).
Before watching the video
Ask students to draw their understanding of the water cycle on a mini whiteboard or a piece of paper. Can they label their diagram with the different parts of the water cycle?
Introduce key terms such as:
Water vapour: The gaseous state of water.
Water cycle: The continuous movement of water on, above and below the Earth’s surface.
During the video
You may wish to stop at relevant points during this short film to pose questions and check understanding or wait until the end. Useful questions might include:
- What is the beginning stage of our cycle?
- What is evaporation?
- What happens to this water vapour when it rises?
- How long does it take for water to come back to Earth as rain?
- Why is 2% an important number?
- What is groundwater?
- How much water is frozen in the ice caps and glaciers?
After watching
Ask students to return to their diagram of the water cycle, what terminology did they include in comparison to what they saw in the clip. Show students a full diagram of the water cycle and ask students to draw this into their notes alongside the labels for each stage of the diagram. Students could also match the key terminology with the definitions. An empty diagram could also be provided for students to add labels to.
Ask students what could affect the water cycle, for example what might prevent water from being intercepted or infiltrated. This gives an opportunity to explore the impacts of deforestation and urbanisation and how this might lead to flooding.
Look at each stage of the cycle and categorise these into stores and flows. For example, an ocean is a store and groundwater flow is a flow.
Where next?
A practical way to explore this is through half filling a sealed plastic sandwich bag with coloured water and adding labels such as evaporation, condensation and precipitation to the bag. Attach the bag to a window and watch the processes happen. The heat through the window will cause some water to evaporate and condense.
An example of how to do this can be found at the Royal Meteorological Society.
Curriculum notes
This topic appears in Geography at KS3 (Hydrology) and KS4 / GCSE (Rivers and water) in England, Wales and Northern Ireland and National 4/5 in Scotland.
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