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Arid Lands Maps

Desert Facts

• About one-third of the earth's land area is arid and semiarid--in total size, this is roughly equal to the combined areas of North and South America.

• Drylands are found in over 60 of the world's nations. There are 30 nations, many in the Middle East and Africa, that are at least 75% drylands.

• The world's largest area of drylands is the Saharan-Arabian-Iranian-Thar Desert, which stretches some 6,000 miles from North Africa through the Middle East to northwest India.

• Drylands occur in the tropics and the midlatitudes. Tropical drylands occur from 15-35 degrees latitude and extend from west coasts into continental interiors. Midlatitude drylands occur from 35-55 degrees latitude and are concentrated in continental interiors.

• Although vast stretches of desert are devoid of human settlement, the world's drylands have been occupied and utilized by humans for tens of thousands of years.

• North America's Sonoran Desert has the richest diversity of plants and animals of all the world's deserts, with more than 3000 plant species, many thousands of invertebrates (1200 different bee species alone!), and more than 550 vertebrate species (fish, reptiles, amphibians, mammals and birds).

• Some desert rodents, like the "Kangaroo rats" (Dipodomys spp), that live in many North American drylands, never have to drink water--they can metabolize all the water they need from the seeds that they eat.

• Surprisingly, bees are much more abundant in deserts and savannas, both in terms of individuals and of species, than in wetter climates. The desert regions of nothern Sonora (Mexico) and southern Arizona (USA), are thought to have more bee species (between 1,000 and 1,200) than any other region in the world.

• Because deserts are too dry for many wood-decaying fungi to exist, termites play a crucial ecological role by eating, breaking down, and recycling cellulose (wood, grasses, cactus skeletons, and dung). Without termites, the entire desert ecosystem would collapse.

• There are some 2,500 species of cactus in the world. With one possible exception, all are found naturally only in the Americas (North, Central, and South America, and the Caribbean).

• The largest cactus in the world is the Cardon (Pachyserius pringlei), which dominates the deserts of Baja California and coastal Sonora, Mexico; Cardons can be up to 20 meters high and live for 200 years. They are closely related to Saguaro cactus (Carnegeia gigantea).

• Cities now house almost half of the world's population, and megacities with more than 10 million population are increasing. (per AAAS Atlas of Population and Environment, atlas.aaas.org/ ). Roughly 800-900 million people in the world's drylands live in cities. (per Philip Dobie, 2001, UNDP: Poverty and the Drylands).

• Major dryland cities include Beijing (located in a dry subhumid zone of northern China); Mexico City, Mexico; Los Angeles, USA; Santiago, Chile; Madrid, Spain; Cairo, Egypt; Teheran, Iran.

Deserts: geology and resources by A.S. Walker, a USGS online book, 1998.

Deserts in the American Southwest by DesertUSA

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