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5E Flow of Matter and Energy #2
The amount of life any environment can support is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the residue of dead organic materials....
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Defining Drought
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Purpose
To examine the hydrologic impacts of drought.
Context
Drought affects humans, animals, and plants. Humans can change the course of the water cycle, to some extent, to meet their needs, but can they do so without imposing risks on the plants and animals? As urban areas continue to grow, policy makers must plan for potential water shortages, taking into account competing interests for water.
In this lesson, students will look at drought from a variety of perspectives. The lesson focuses first on the scientific definition of drought, including weather patterns, water cycles, water requirements by plants and animals, and physiological responses by plants and animals to drought. The lesson also focuses on the current and historic social and economic impacts of drought.
Generally speaking, drought occurs when the atmosphere fails to deliver anticipated water supplies for any given area. Droughts can result in long-term ecosystem changes if there are additional factors (e.g., severe soil loss during prolonged drought) that alter the environment. Increasing drought frequency and severity may be part of long-term climate change. Both droughts and floods are part of the normal continuum of weather patterns. Droughts represent a lower than average precipitation; there are arid climates (i.e., deserts) in which dryness is a normal condition. It also is important to emphasize that weather isn't the only cause of a drought. Human activities that increase demand for water also can contribute to a drought. Moreover, human activities contribute to the effects of a drought. For example, humans didn’t cause the dust bowl drought, but our agricultural practices certainly contributed to the excessive soil loss that resulted from the drought.
Drought also provides an interesting context for understanding social risks and trade-offs. By answering questions like, "What can happen when a drought occurs?" and "What are the odds of a drought occurring?" students can practice gathering information, understanding the accuracy of the information, and using that information to better understand the potential risks of societal and personal decisions. Manipulation of the hydrological cycle (such as building dams, deforestation, irrigation, weather modification, etc.) to meet water demands can alter the relationship between people and ecosystems in often unpredictable ways.
Planning Ahead
Materials:
Teacher Background Knowledge:
Familiarize yourself with the pages used in this lesson, especially the information on drought indices and the PDSI reconstructions on the NOAA Paleoclimatology page. The Understanding and Defining Drought page also may be useful to you in preparing for this lesson.
Motivation
Using the Understanding Droughts student E-Sheet, students will read the following Web articles that introduce the impacts of drought in a historical context:
People's perception of benefits and risks related to drought are often based on past experiences and other information that they have heard or read about drought. After students have explored one or both of the resources listed above, discuss these questions:
- How important is water to society?
- What are some examples of the role that droughts played in American history?
- Do you think drought could affect you? How would you prepare for a drought?
- What do people use water for (besides consumption and agriculture)?
- Where do people get their water from and what happens when something, such as drought, threatens the water supply?
Development
Ask students to discuss any personal experiences they may have had with droughts.
Based on these experiences, how would they define a drought? Write their definitions on a chart and post it on the wall or bulletin board.
Have students use their student E-Sheet to go to What is meant by the term drought?, which discusses various ways that drought can be defined:
- Meteorological—a measure of departure of precipitation from normal. Due to climatic differences, what is considered a drought in one location may not be a drought in another location.
- Agricultural—refers to a situation when the amount of moisture in the soil no longer meets the needs of a particular crop.
- Hydrological—occurs when surface and subsurface water supplies are below normal.
- Socioeconomic—refers to the situation that occurs when physical water shortage begins to affect people.
Students should have little difficulty understanding that less than normal amounts of precipitation can affect soils and plants. However, when below normal precipitation persists for weeks, months, or years, the water levels in lakes, reservoirs, and wells decrease, creating potentially widespread water shortages. You also can give students a copy of the Drought Fact Sheet.
After students have read the selection, ask if they would like to add to or revise the definitions of drought that were listed on the chart. After they have done so, go over the student definitions and categorize them according to one of the four categories above.
Assessment
Refer students to the Understanding What You Learned section of the E-Sheet. This will ask them to go to Understanding Your Risk: A Comparison of Droughts, Floods and Hurricanes in the U.S. This resource will help students understand that drought is a natural hazard, too, even though it moves slowly. Students should use these resources to explore the impacts of drought on humans and wildlife. They should explain how drought compares to other natural hazards such as floods and hurricanes.
Students should understand that a drought is a complex natural and sociological phenomenon that can be looked at from a variety of perspectives.
Extensions
Droughts, Floods and Sprawl –They’re All Connected is a resource on the Delaware River Basin Commission website. Have students write a short essay in which they summarize the article and relate it to what they have learned, particularly stressing the impact of human activities on droughts.
In Hard Lessons from the US Dam-Building Era, students can read about the benefits and drawbacks of dam building in the U.S. After reading the article, students can list some of the trade-offs and explain why, though we did it ourselves, the author feels we should not encourage other countries to engage in large dam-building projects.
Created :06/20/2005
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