Deserts

Climate

Arid climates that fluctuate temperatures throughout the day and the seasons

Rainfall

• Precipitation is the abiotic factor that mostly defines this biome

• Very little rainfall

  • Rainfall tends to come all at once in a short period, causing temporary flooding

• Less than 25 cm/yr

Temperature

• Extreme fluctuations in temperature between months and even day to night

• Desert can occupy average annual extremes: -10° to 30°C 

  • Hot deserts occupying the lower righthand portion of the graph

  • Cold deserts occupy the lower middle portion of the graph

  • Notice that the desert biomes occupies a broad temperature range at the bottom of the Whittaker graph (right)

Types

Hot & dry deserts

• Seasons are generally warm throughout the year and very hot in the summer. The winters usually bring little rainfall.

• Annual average temperatures: 20-25° C

• e.g., Chihuahuan, Sonoran, Mojave, and Great Basin of the United States, as well as the Sahara and Arabian deserts

Semiarid deserts

• Summers are moderately long and dry, and like hot deserts, the winters normally bring low concentrations of rainfall

• Summer temperatures usually average between 21-27° C, and evening temperatures are cool, at around 10° C

• Condensation of dew caused by night cooling may equal or exceed the rainfall received by some deserts

• e.g., Utah, Montana, and the Great Basin

Coastal deserts

• Deserts found along the edge of oceans, but receive little precipitation due to wind patterns

• e.g., Atacama desert in Chile, and the Namibian desert

Cold deserts

• These areas have cold winters with snowfall and large rainfalls widely during the winter and occasionally over the summer

• The mean winter temperature is -2-4° C, and the mean summer temperature is 21-26° C

• Cold deserts and tundras can sometimes be viewed as synonymous, but subtle differences can be noted

  • Tundras are usually covered in small plants and have many small streams and ponds during the melt of summer. 

  • A cold desert will have very few streams or ponds, and very few plants.

  • e.g., Antarctica interior, Greenland, and the Nearctic realm

Soil

• Abundant nutrients, but water is limited for absorption

• The common desert soil types are aridisols (dry and deficient in organic matter

• Most deserts are not sandy, except the Saharan and Arabian deserts

• n.b. "desertification" is a process by which fertile top soils are damaged by over-farming or over-grazing, resulting in increasingly dry and infertile land (e.g. Dust Bowl in the 1930s Midwest; modern impacts on the Sahel of Africa)

Regional Expressions

• southwest North America, Namibia, southern Argentina, north and south Africa, middle east, central Australia, mountains of Asia