EARTH 530
The Critical Zone

Water cycle

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The term "water cycle" does not refer to water craft you can peddle across water—instead the water cycle describes the transit of water through all of the components or "spheres" of the Critical Zone (atmosphere, hydrosphere, lithosphere, biosphere, and soil) and the processes involved in that transit.

Reading assignment

  1. An excellent discussion of the water cycle is available at the U.S. Geological Survey Web site. Please go to that page and thoroughly read and study the information presented there. I suggest that you read the entire summary page, then return to the Quick Summary and read it, visiting and studying each blue hot-button link for more detail.
  2. The USGS water cycle summary includes discussions of the general distribution of water on Earth and how precipitation rates vary geographically. However, I would like you to further study the geographic distribution of precipitation. To do so you must first understand the manner in which precipitation occurs—go to the Wikipedia entry for "Precipitation (meteorology)" and read the section on types of precipitation.
  3. Next please visit and read the Wikipedia entry for "Atmospheric Circulation."
  4. Visit and read "Why are Deserts Dry?" Pay close attention to the figure: Do you notice any relationship between the distributions of descending and ascending air masses and deserts?
  5. Other processes influence the distribution of precipitation on Earth. Perhaps most prominent among these are the so-called monsoons, seasonal episodes of intense rainfall followed by periods of relative drought. Read the Wikipedia entry for "Monsoon" to learn more.
  6. Much of the reading to this point in this section has focused on liquid forms of precipitation. To provide you with some insight into the presence of solid water and its role in the hydrosphere, water cycle, and Critical Zone (and more knowledge to support what you learned about glaciers in our lesson on paleoclimatology) please read the Wikipedia entry for "Cryosphere."

Want to learn more?

  • To learn more about the water cycle and specifically the role of NASA satellite research in understanding the water cycle, see NASA's "The Water Cycle."
  • A very simple interactive video called "Thirstin's Water Cycle" is also available on the EPA's Web site.
  • The EPA site also has a collection of water-related K–12 resources!
  • Teacher's Domain provides a lesson plan and multimedia resources that may be useful for your classroom. Though it is rated for grades 3–5, Cycling Water through the Environment has some interesting products including: "Observe precipitation," "Water cycle animation," and "The hydrologic cycle."
  • The National Science Foundation provides a lot of information regarding water resources and humanity's dependence on and use of water, but this one in particular may be of interest.
  • Several simple on-line model tools for understanding the water cycle and human influences on it are available from the Stroud Water Research Center, a co-host of the Christina River Basin CZO.