Unit 2: The Hydrologic Cycle and Freshwater Resources

Unit 2 activities support the overall module goals by guiding students through the basic structure, components and interactions of the hydrologic cycle as they relate to the use and conservation of water resources. Upon completion of this unit students should be able to:

• Describe the distribution of Earth's water among the major water sources.
   
• Outline and reproduce components of the water cycle.
• Predict ways in which human activities are most likely to affect water availability and quality as it passes through the water cycle.

This unit may be used as a general introduction to the hydrologic cycle. It can be used as part of the environmental justice module or as an individual lesson in an introductory Earth science classroom. It provides students with vocabulary terms and hands-on activities embedded into the lesson notes and as handout materials in the lesson plan.

Lesson Plan

This lesson is designed to be completed within a 50-minute class period. Sections of the lesson plan can be expanded through in-class discussions and supplemental activities to accommodate longer class times. Note: students who have previously taken an introductory geology course may find the exercise elementary. In such cases, we recommend that the instructor skip the hydrologic cycle exploration activity and move right to the water cycle sustainability role-play.

Pre-Class Activity: Water Footprint

Give students the handout Water Footprint (word) (Microsoft Word 2007 (.docx) 20kB Jun11 15) (also available as a PDF (Acrobat (PDF) 62kB Jun11 15)) prior to starting this lesson to complete and bring to class. Have students predict which activities will use the most water. Advise students that they will be expected in class to compare answers in groups and then share their conclusions with the class as a whole. Expect that the instructor will need to guide the discussion with the questions below.

Activity 2.1: In-Class Discussion of Pre-Class Activity (15 min)

In-class discussion should facilitate the learning objective that students be enabled to predict ways that human activities affect water availability and quality as it moves through the water cycle. As a result of in-class discussion, students will be able to quantify ways in which human beings utilize water resources and they will compare personal, national, and world use statistics to predict the effects of such utilization across the globe. Students should be asked to ponder ways that they could optimize the use of water resources to facilitate environmental justice.

To achieve these goals:

• Review, compare and share student answers to the pre-class activity.
• Consider aloud how water consumption is linked to the water cycle.
• Have class as a whole use a water use average and multiply that by the population of their city.
• Discuss with the class how such water usage might compare to other cities or other countries around the world.
• Ask students to consider with a classmate changes they would be willing to make to their water use to accommodate a decline in water supply.

Activity 2.2: Hydrologic Cycle Exploration Activity (20 min)

• Ask students to think of ways in which water is present on Earth. 
   
• As students recall various examples of where water is found, make a list and begin to illustrate with a basic diagram of the hydrologic cycle in mind. Key components that may be identified in the diagram are oceans, rivers, lakes, wetlands, ice caps, groundwater, soils, clouds, plants and animals. It is likely that some classes may miss a few of these water reservoirs and may need to be directed to these items in the next step.
   
• Next, ask students to identify how water moves between these reservoirs (and changes state) to create a complete diagram of the hydrologic cycle. Key mechanisms would be evaporation and condensation (lakes, ocean to atmosphere and clouds), precipitation (clouds to land, oceans, ice caps), run-off (rivers), infiltration (from surface to groundwater), evapotranspiration (plants to atmosphere), melting/freezing (glaciers to streams and oceans, ocean water to sea ice) and sublimation (ice to atmosphere). Students will not get some of these, and some may be to obscure to include.
   
• Explain to students that the diagram is a simplified version of how water travels and that water movement is based on several factors such as solar energy from the sun and gravity.
  

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• Before detailing the distribution of water among the different components of the cycle, ask students to:
   
  • Predict whether the atmosphere or land contains more water.
  • Rank the components of the land (ice caps, streams and lakes, soil, plants and animals, groundwater) in order on the basis of which stores the most freshwater. Use this opportunity to note that there is much more water in groundwater than in surface water.
  • Explain why precipitation over the oceans is less than evaporation from the oceans.

Answer sheet: Components of the Hydrologic Cycle -- private instructor-only file

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Answer sheet: Components of the Hydrologic Cycle

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• For a more advanced class, the following exercise can be incorporated to create a conceptual and mathematical model of the hydrological cycle of a basin:
  Basin Mass Balance by Eric Peterson.
   

Activity 2.3: Sustainability Role-Play (15 min)

For longer class periods, instructors may choose to have the students enact a role-play that facilitates understanding of sustainability issues in relation to the water cycle as follows:

• Have students break into groups, representing the major mechanisms of transport (clouds, rain, rivers, groundwater, plants).
   
• The instructor plays the role of a consumer of water whether as a farmer, industrial site manager, park ranger, or town citizen.
   
• As a class, discuss what would happen if changes occurred in the cycle.
   
• Possible different scenarios to use include consideration of:
   
  • What would happen to people living downstream if someone diverts or dams the river in your semi-arid region?
  • If global warming increases evaporation, what are the consequences?
  • If a company dumps toxic waste on the ground in an urban area, what are the potential consequences?
  • If your town relies on a well for water supply and it dries out, what are your options?
  • What would happen if any of the variables (input/output/transport) are changed? 
     

See detailed guidance, instructor-only, in

Teaching Notes for Instructors, Unit 2 -- private instructor-only file

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The student responses on the water footprint handout can be turned in for credit (individual answers will differ). Assessment is to be based on completion of the table.

Students' participation in the activities and their ability to answer how the different scenarios may affect and influence their communities will provide an opportunity for assessment. Students will draw water cycle diagrams labeling reservoirs and mechanisms of transport within the cycle. A rubric is provided to enable instructor assessment of achievement of learning goals.

• Unit 2 Assessment Rubric (Word doc) (Microsoft Word 2007 (.docx) 16kB Nov1 14) or as a PDF (Acrobat (PDF) 175kB Nov1 14)

Unit 2 lecture notes (PowerPoint 2007 (.pptx) 1.2MB Jun11 15) with embedded assessments on water distribution and usage. These may be used to summarize the major ideas discussed in the activities at the end of the module.

The US Geological Survey provides a detailed diagram of the hydrologic cycle.