The
Water Cycle Written by Alison Milford
Contents Exploring the water cycle
2
Drinking water
26
Precipitation
4
How we use water
30
Surface run-off
6
Water underground
8
Human effects on the water cycle
32
Evaporation
12
Climate change
36
Transpiration
14
Extreme weather
38
Condensation
16
The water footprint
40
Clouds
18
Don’t waste water!
42
Where does it rain?
20
Glossary
44
Forecasting rain
22
Index
45
Water world
46
How nature needs water 24
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Exploring the water cycle What should we drink to keep healthy? What do plants need to help them grow? The answer is water. You may think that drops of water are newly made but, in fact, water is being renewed over and over again in a natural recycling process called the water cycle. There are parts of the water cycle that we can see, such as clouds, rain and sun, but there are also other important parts that we can’t see. This book explores how the water cycle works and how water affects our lives and the future of our planet.
Did you know? Millions of years ars ago, ank the same dinosaurs drank e today y! water we use today!
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The water cycle sun clouds
precipitation
condensation
transpiration
run-off evaporation
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Precipitation Rainfall The water cycle is like a cycle wheel, with no exact start or end. Perhaps the best place to start is when water rains down from the sky. This is called precipitation. Precipitation happens when water droplets in the clouds become too heavy to carry and have to fall to the ground.
Did you know? Rain drops fall in flat oval shapes and can be different sizes.
1 mm
2 mm
3 mm >4.5 mm
rain drop shapes
Some larger raindrops form shapes like this.
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Snowfall When the air is very cold, the water droplets freeze and fall as snow instead of rain. Snow can fall during winter and all year round in places with cold climates such as the Arctic and Antarctica.
Sleet is a mix of rain and melting snow.
Hailstones are hard balls of frozen water droplets.
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Surface run-off Water run-off When you tip a bucket of water down a slope, the water flows down to the bottom. Water always flows downhill. As a result, water flows downhill in streams and rivers or collects at the bottom of hills in lakes. This part of the water cycle is called the run-off. The water runs off the land into lakes, or streams and rivers, which flow into an ocean or sea.
Surface water run-off
rainfall
run-off water
lake
stream river ocean
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Snow run-off During springtime, warm air melts the snow that’s fallen in cold places such as mountain tops. The melted water, called meltwater, flows quickly down streams and rivers to join other run-off water.
Did you know? Lots of meltwater and run-off water can cause major floods.
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Water underground Ground water Water is everywhere – even under our feet! As rainwater runs off across the land some of it seeps through the soil into the ground below.
Collecting ground water experiment This experiment shows how groundwater collects. • Put a kitchen towel over a cup. • Slowly pour water over the towel.
kitchen towel water
• Some water stays on the towel. • Some water seeps into the cup.
cup water
Rivers and lakes can also be found underground.
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Some ground water joins underground channels flowing into rivers and oceans above ground.
Aquifers Most of the world’s fresh water is stored underground. This happens when ground water finds its way into small open areas between rocks. These storage areas are This well has been dug to get fresh water from an aquifer.
called aquifers.
Aquifers top surface
soil
clay
well
aquifer bedrock
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Surface water drains In a rainstorm, water can fall on to the roads. However, thanks to square holes at the side of the road, they rarely flood. These holes are called surface water drains.
The grating stops rubbish getting into the drain.
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The rainwater runs towards the kerb and through the drain into an underground pipe. The rainwater then flows along the underground pipe until it comes out into a large water outlet such as a river, canal or sea.
These people are exploring underground drain-water pipes. It would be dangerous to go down there just after a rainfall as the pipes would be filled with rushing water.
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