The Water Cycle

What happens with the 300 cubic kilometres of rainfall on land  we get every day, where does the water go 1? The amount of water on Earth is constant; none of it is ever lost. Instead it forms part of a never-ending cycle, the Water Cycle. This is what people mean when they say that we drink the same water the dinosaurs drank 65 million years ago.

Water cycle

The sun heats up the oceans, lakes and other bodies of water. Heating turns the liquid water into a vapour, or gas, which goes into the atmosphere. This process is called evaporation. When water contained in plants turns into vapour, we call this transpiration.

Water vapour cools as it rises through the atmosphere. Cooling makes the vapour return to a liquid state, forming clouds. This is called condensation.

The next step in the cycle is precipitation: when enough water has condensed, a cloud grows heavy and water starts falling back to Earth. That water may fall as rain, hail, sleet or snow.

Water that precipitates back to Earth may fall directly into oceans and lakes, or onto land. There, the water will soak into the ground (infiltration) and become part of the groundwater or an aquifer. Or, it may flow along the land surface and collect in oceans, lakes or rivers.

From there, the cycle starts again.


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