3 - Where's The Rain? (What is a Desert?)

Description:
The students will identify the characteristics of a desert and locate the major deserts on a world map.

Educational Objectives:

Vocabulary:
Vocabulary:

• arid
• sporadic
• humidity
• evaporation
• habitat
• heat
• precipitation

Aldine Benchmarks:
7

Materials:

• world globe or map (1 for the class or multiple sets for groups if available)
• blackline world map (for students)1:1
• world map transparency with desert areas shaded in 1:22
• set of crayons or map pencils 1:4
• chart paper 1:22
• optional: books, magazines, and pictures of deserts
• optional: sand and glue for wall mural

Teacher Background:

A desert is most often thought of as being very hot, dry, and lifeless. While deserts are the driest places on earth, not all of them are hot. Deserts (also called arid regions) are grouped into two types by temperature: cold desert (a desert with daytime temperatures below freezing for part of the year) and hot desert (a desert with hot daytime temperatures for most of the year). Approximately one-third of the land surface of the earth is desert. (Figure 2.1) The major deserts of the world are located in Africa, the Middle East, Asia, North America, South America, and Australia. Most deserts are located in the horse latitudes, typically straddling the Tropic of Cancer and the Tropic of Capricorn, between 15 and 30 degrees north and south of the equator. Some deserts, such as the Kalahari in central Africa, are geologically ancient. The Sahara Desert in northern Africa is 65 million years old, while the Sonoran Desert of North America reached its northern limits only within the last 10,000 years.

Deserts lose more water through evaporation than they gain from precipitation. An area is considered a desert if it receives less than 10 inches (25 cm) of precipitation a year. Most have less than 4 inches (10 cm) of precipitation a year. The polar ice caps are examples of cold deserts that often receive less than 2 inches (5 cm) of precipitation per year. Not only is there a shortage of precipitation in a desert, but the precipitation doesn't fall evenly throughout the year. In some deserts, it may not rain the whole year, and then a violent thunderstorm may dump 5 inches (12.5 cm) or more of rain at once. Most of this water runs off or evaporates before plants and animals have a chance to use it. Extremely low humidity results in a high rate of evaporation.

Wind is almost constantly blowing, increasing the rate of evaporation from the surface of both soil and plants and eroding the landscape as bits of blowing sand "scrub" and wear away obstacles in their path. There is little cloud cover in desert skies, resulting in wide swings in daily temperatures. Days are very bright, sunny, and hot. Temperatures can climb to well over 38 degrees Celsius (100 degrees Fahrenheit), evaporating water from land and plants very rapidly. At night, without cloud cover to hold the day's heat, temperatures can fall quickly, sometimes even to freezing. The Gobi Desert in Mongolia and the Great Basin Desert in North America are cold deserts.

Desert plants and animals have adapted shapes, structures, or habits that allow them to survive conditions of high heat and drought. Plant life is sparse, and plants are spaced far from one another. (Figures 2.2 and 2.3) Desert land features vary from mountains and hills, canyons, sand dunes, to salt flats. Desert soils also vary from rocky to sandy. (Figure 2.4) Because they are poised in such harsh extremes of heat and aridity, deserts are among the most fragile ecosystems on the planet.

The focus of this unit will be on the four North American deserts: the Great Basin, Sonoran, Mojave, and the Chihuahuan deserts. All references to flora and fauna in the unit will be based on these deserts.

Advanced Preparation:

1. Make a transparency of the world map from the appendix to show where the deserts are located.
2. Assemble the materials for the activity.
3. Hang the chart paper and title it "What is a Desert?"
3. If you are going to do the wall mural map, decide whether you want the students to draw the map or have it already drawn for them.

Procedures:

1. Explain that the earth is made up of large and small places called habitats. A habitat is the place where a plant or animal gets the things it needs to live. Some examples of large habitats are forests, oceans, and deserts. Small habitats could be gardens, ponds, or even a tree. Tell the students that they will be studying a large habitat called a desert.

2. Discuss with the students the characteristics of a desert. If available, show students pictures of different deserts from books, magazines, the internet, etc. Compare and contrast the different deserts by hypothesizing why the terrain and inhabitants differ. Refer back to the KWL charts the students created and add any information that was not previously included. Guide the students to think about the weather including temperatures, rainfall, and landscape. If you consistently are told that deserts are hot, make sure you point out that there are cold deserts, too. List the characteristics on the chart paper.

3. Display the world outline transparency with the desert areas shaded. Discuss where the deserts are located. Compare the different deserts by asking: "Which desert seems to be the largest?" "Which is the smallest?" "Which desert covers most of a continent?" "Which areas have no desert?" "What part of the world do most of the deserts seem to be located?" Hypothesize why the deserts are located in certain areas.

4. Have the students locate, color, and identify the deserts on the blank world map outlines. The students should use the transparency and a world globe or map to help them. They could also identify the continents and oceans.

5. Optional Activity: Create a similar map on butcher paper to hang as a mural. Instead of coloring in the desert areas, use sand and glue to identify them.

Formative assessment:
The students will create a map of the world identifying the major desert areas and explain the characteristics of a desert area.

Teacher Resources:
Graham, Ada and Frank. The Changing Desert. San Francisco: Sierra Club Books, 1981
Leopold, A. Starker. The Desert. Time-Life Books, 1980.
Pringle, Laurence. The Gentle Desert: Exploring an Ecosystem. New York: Macmillan, 1977.
Young, Donald. The Great American Desert. New York: Julian Messner, 1980.
National Wildlife Federation

Websites:

Desert USA - ( Great source of information on all aspects of the desert. Provides details and pictures of the four deserts located in the U.S.: Chihuahuan Desert, Great Basin Desert, Mojave Desert, and the Sonoran Desert)

http://www.desertusa.com/glossary.html

Local Resource - Cactus Nursery
There is a cactus nursery located on I-45 North at the 7800 block called the Cactus King. It is a wonderful resource for samples of desert plants and a reference for any questions you may have. The owner is Lyn Rathburn and the phone is 281-591-8833.

Student Resources:
Baylor, Byrd, and Peter Parnall. Desert Voices. New York: Charles Scribner's Sons, 1981.
Catchpole, Clive. Deserts: The Living World. New York: Dial Books for Young Readers, 1984.
Dewey, Jennifer Owings. A Night and Day in the Desert. Boston: Little, Brown & Co., 1991.
George, Jean Craighead. One Day in the Desert. New York: Crowell, 1983.
Graham, Ada and Frank. The Changing Desert. New York: Charles Scribner's Sons, 1981.
May, Julian. Deserts, Hot and Cold. Mankato, MN: Creative Educational Society, 1972.
Norden, Carroll R. Deserts. Milwaukee, WI: Raintree Childrens Books, 1988.
Rinard, Judith E. Wonders of the Desert World. Washington, DC: National Geographic Society, 1976.
Sabin, Louis. Wonders of the Desert. Mahwah, NJ: Troll Associates, 1982.
Sayre, April Pulley. Desert. New York: Twenty-First Century Books, 1994.

Extensions: Optional: Extension 1 - Have the students research the four deserts of the United States: the Mojave, the Great Basin, the Sonoran, and the Chihuahuan Desert. The students could write reports, create a poster, or a booklet. Extension 2 - Have students create a booklet about the desert habitat and add pages for each lesson in the unit. Extension 3 - Assign a continent to each student and have them research for themselves what deserts are located on each continent. They could create a poster, a research report, etc. Extension 4 - SongThere is an old song by a group called America entitled "Horse With No Name" that talks about going to a desert. It might be fun to play, learn, or adapt. Appendices: blank world map for students and transparency