Earth & climate
The water cycle
Evaporation, clouds, rain, river: how the same water has been travelling around the Earth for billions of years.
What you need first
Where was the raindrop that just landed on your nose last week? Maybe in the sea off Portugal, maybe in a puddle on your street. Water never disappears, it is constantly on the move. This journey is called the water cycle.
From the puddle to the cloud
The sun powers the whole cycle. It warms seas, lakes and puddles, and water evaporates: it turns into invisible water vapour and rises with the warm air. The higher the vapour gets, the colder it becomes around it. Cold air can hold less water vapour, so the vapour gathers into tiny droplets. This is called condensation, and billions of such droplets together are nothing other than a cloud.
The sun warms the sea, water turns into invisible vapor.
Back to the sea
When the droplets in the cloud become too heavy, they fall to the ground as : as rain, snow or hail. How much has fallen is given in millimetres: 1 millimetre of precipitation means that exactly 1 litre of water has landed on every square metre. Some of the precipitation seeps into the ground, some collects in streams and rivers. The rivers flow downhill, join together and carry the water back to the sea. There the sun is already waiting, and the next round begins.
An endless cycle
The most astonishing thing about the water cycle: no new water is added, and none is lost. The same water have been circling the Earth for billions of years. The water in your glass was once ice, seawater and cloud, and maybe a dinosaur even drank from it.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What powers the water cycle?
What happens during condensation?
About 2 litres of water evaporate from a garden pond on a hot day. How many litres is that after 5 such days?
Put the stages of the water cycle into the right order.
- 1Precipitation falls from the clouds
- 2Water evaporates and rises
- 3The water flows back to the sea
- 4The vapour cools and forms clouds
In a rainy week 3 mm of precipitation fall every day. How many millimetres add up over 7 days?
Complete the sentence: when water vapour cools and turns liquid again, this is called ….
Where this leads