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The water cycle

Review your understanding of the water cycle in this free article aligned to NGSS standards.

Key points:

  • The water cycle describes how water continuously moves between Earth’s surface and the atmosphere.
  • This movement occurs by different physical processes.
    • Water moves into the atmosphere from oceans, lakes, and streams by evaporation. During evaporation, water changes from liquid water to water vapor (a gas).
    • Water also moves into the atmosphere by transpiration, or the evaporation of water from plants. Both evaporation and transpiration are driven by the sun’s energy.
    • Water forms clouds in the atmosphere by condensation. During condensation, water changes from water vapor to liquid water.
    • Water falls down to Earth’s surface by precipitation. This process is driven by gravity. Of the water that reaches land, some flows downhill as runoff and some soaks into the ground to become groundwater.
A diagram shows mountains sloping down to land and a body of water. Trees are at the base of the mountains and clouds are in the sky. Different parts of the water cycle are labeled on the diagram as follows: 1. Evaporation from oceans, lakes, and streams. Arrows point from the body of water to a cloud in the sky. 2. Transpiration from plants. An arrow points from trees at the base of a mountain to a cloud in the sky. 3. Condensation. A cloud is shown in the sky. 4. Precipitation. An arrow in the rain points from a rain cloud to the top of a mountain. 5. Surface runoff. An arrow points from the middle of a mountain to the bottom. 6. Groundwater. Water is shown seeping into the ground.
The water cycle. Image credit: “Water cycle” by NASA, CC BY 2.0

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