What is the water cycle?

Science for Youth November 02, 2011 Print Friendly and PDF

Earth has its own water recycling system. It is called the water cycle (also known as the hydrologic cycle). The actual amount of water on our planet does not change. In fact, there is the same amount of water on earth today as there was in the time of dinosaurs! In the water cycle, water simply changes its form and location. It is a never-ending cycle! In this cycle, water travels from the ground into the atmosphere and then back down to the ground again. This is why water is known as a recyclable resource.

The water cycle is important because it ensures the availability of water for all living things. In the water cycle, water continually changes between all three of its forms gas, liquid and solid. Water on the ground changes to a gas as it warms from the sun's heat. This process is called evaporation. When water evaporates, it becomes water vapor. It rises with warm air, expands, and cools.

As water cools it changes back to liquid droplets. This process is called condensation. The water droplets form clouds. When enough vapor condenses, these heavy droplets will cause the clouds to release them as rain or snow. The name of moisture in the atmosphere falling to the ground is precipitation. The precipitation will fall down onto the ground. The ground can absorb the water. Plants use the water in the soil. If precipitation did not occur, all the water would evaporate into the air and it would not rain. There would be no water in any of the streams or lakes!

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.