Types of Deserts

Deserts cover some one fifth of the Earth’s surface and come in a variety of types. While the definition of "desert" varies somewhat, deserts generally arid regions that receive less than ten inches (50 cm) of precipitation a year or regions where the potential evaporation rate is twice as great as the precipitation. Most deserts, such as the Sahara of North Africa and the deserts of the southwestern U.S., Mexico, and Australia, occur at low latitudes. However, there is another kind of desert--the cold desert--that's found in the basin and range area of Utah and Nevada and in parts of western Asia.

Subtropical Deserts

Locations:
Mojave (Arizona, Colorado, Nevada, Utah, California); Sonoran U.S. (Arizona, California, Mexico); Chihuahuan (Mexico, southwestern U.S.); the Western Desert of Australian including the Gibson (southern part), Great Sandy (northern part), and Great Victoria (southern part); Simpson and Sturt Stony (eastern half of the Australain continent); Sahara and Arabian deserts.

Conditions:
Many mean annual temperatures range from 20-25° C. The extreme maximum ranges from 43.5-49° C. Minimum temperatures sometimes drop to -18° C. Soils in subtropical deserts typically consist of a shallow layer of course rocky or gravely material with good drainage. "Desert pavement" can occur here because strong winds blow away the fine sand particles and leave the heavier particals behind to compact.

Plants:
Plants here are mainly low-lying shrubs and short woody trees. In the cacti, the leaves are much-reduced (to spines) and photosynthetic activity is restricted to the stems. Some plants open their stomata (microscopic openings in the epidermis of leaves that allow for gas exchange) only at night when evaporation rates are lowest. These plants include: yuccas, ocotillo, turpentine bush, prickly pears, false mesquite, sotol, ephedras, agaves and brittlebush.

Semiarid Desert/Cold Winter

Locations:
The major deserts of this type include the sagebrush of Utah, Montana and the Great Basin (Nevada, Oregon, Utah); Colorado Plateau U.S. (Arizona, Colorado, New Mexico, Utah, Wyoming) and the Gobi desert in Mongolia. They also include the Nearctic realm (North America, Newfoundland, Greenland, Russia, Europe and northern Asia), which have little percipitation.

Conditions:
Cold winter deserts are marked by dramatic temperature differences from season to season, ranging from 100° F (38° C) in the summer to 10° F (–12° C) in the winter. Summer temperatures usually average between 21-27° C. It normally does not go above 38° C and evening temperatures are cool, at around 10° C.The average rainfall ranges from 2-4 cm annually. The soil can range from sandy and fine-textured to loose rock fragments, gravel or sand. It has a fairly low salt concentration, compared to rainier deserts. In areas such as mountain slopes, the soil is shallow, rocky or gravely with good drainage. The bajada, low spreading hills of gravel and sand deposited by streams leaving the mountain valleys. These hills extend from the mountain base into the surrounding valley. In the upper bajada (lower slopes) they are coarse-textured, rocky, well-drained. The lower bajada (bottom land) contains sandy and fine-textured soil, often with “caliche hardpan.”

Plants:
Semiarid plants include: Creosote bush, bur sage (Franseria dumosa or F. deltoidea), white thorn, cat claw, mesquite, brittle bushes (Encelia farinosa), lyciums, and jujube.

Other Desert Classifications

Coastal Deserts:
Coastal deserts generally are found on the western edges of continents near the Tropics of Cancer and Capricorn. The average summer temperature ranges from 13-24° C; winter temperatures are 5° C or below. The maximum annual temperature is about 35° C and the minimum is about -4° C. In Chile, the temperature ranges from -2 to 5° C in July and 21-25° C in January. The average rainfall measures 8-13 cm in many areas. The soil is fine-textured with a moderate salt content. The plants living in this type of desert include the salt bush, buckwheat bush, black bush, rice grass, little leaf horsebrush, black sage, and chrysothamnus.

Rain shadow deserts :
Rain shadow deserts are formed because tall mountain ranges prevent moisture-rich clouds from reaching areas on the lee, or protected side, of the range. As air rises over the mountain, water is precipitated and the air loses its moisture content. A desert is formed in the leeside "shadow" of the range. Examples: Deserts east of the Sierra Nevada Mountains, California & Nevada, East of the Cascades of Oregon and Washington, and East of the Andes Mountains in South America.

Monsoon deserts:
"Monsoon," derived from an Arabic word for "season," refers to a wind system with pronounced seasonal reversal. Monsoons develop in response to temperature variations between continents and oceans.

Paleodeserts:
The Nebraska Sand Hills is an inactive 57,000square kilometer dune field in central Nebraska. The largest sand sea in the Western Hemisphere, it is now stabilized by vegetation and receives about 500 millimeters of rain each year. Dunes in the Sand Hills are up to 120 meters high.