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Water Cycle

Water exists at the surface of the earth in many different forms, such as in rivers, oceans and glaciers, but it also exists in the atmosphere as water vapour, which we can’t see.

In the atmosphere, we can see liquid water droplets in clouds and we can also see ice crystals as clouds too, but these are usually much higher up.

What is the water cycle?

The water cycle is the process by which water is continuously transferred between the surface of the earth and the atmosphere.

How does the water cycle work?

The water cycle works by using the energy of the sun to exchange water from the surface of the earth to the atmosphere and back again in a continuous cycle, whether liquid, solid or gas. It’s always happening, all around us, all the time.

What are the processes of the water cycle?

Evaporation, transpiration and sublimation: Water at the surface of the earth, in rivers, streams, oceans or whatever, is heated by the sun. It then evaporates - turns from liquid to gas - and becomes water vapour, rising into the atmosphere. Plants and trees also release water vapour into the atmosphere through their leaves by transpiration.

Water normally change between solid, liquid and gas in single stages, but sometimes a stage can be skipped. Ice, for example, can change straight into water vapour by a process known as sublimation.

Condensation

All this water vapour in the atmosphere will then eventually be forced to condense from a gas into a liquid water droplet. In the atmosphere this is done as air rises and cools, often forming clouds in the process.

Precipitation

Within a cloud, the liquid water droplets are likely to merge together over time, forming larger droplets. At some point these droplets may get large enough that they fall from the sky, and depending on the conditions we may see hail, rain, sleet or snow falling from the clouds.

When this rain, sleet or snow reaches the surface, many things can happen. The water may flow into rivers, oceans and streams. It may soak into the soil, where it will still move towards a river, but it will do so very slowly over a long time as it filters through the ground. It may also collect on ice caps
or glaciers. It may even soak into the roots of a plant or tree and be used to help it grow.

No matter what happens to the water, it is now ready to be evaporated, sublimated or transpired again which completes the water cycle.

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