Where Deserts Are Found

The world's deserts are generally found in four areas: in the subtropics; in continental interior areas at middle latitudes; on the leeward side of mountain ranges; and along coastal areas. Most of the earth's greatest deserts are found in the subtropics. The subtropical deserts center on the tropic of Cancer and the tropic of Capricorn. The aridity of these areas is due primarily to the general circulation of air around the earth. Subtropical areas have consistently high atmospheric pressure because of descending air currents and are swept by hot, dry winds. Such conditions keep moisture-bearing winds from entering the region and prevent the formation of clouds.

The absence of cloud cover is largely responsible for the high temperatures that occur in subtropical deserts. Without the protection of clouds, the land receives nearly the full heating effect of the sun's rays. Although temperatures are relatively high the year round, in summer the heat is extreme. Summer daytime temperatures often exceed 100° F. (38° C.) and sometimes rise to as much as 120° F. (49° C.). The earth's highest recorded temperature, 136.4° F. (58° C.), occurred in the Libyan Desert of northern Africa. At night, however, with no clouds to provide insulation, daytime heat dissipates quickly and temperatures drop abruptly. Nighttime temperatures average around 70° F. (21° C.) in summer and can fall below freezing during winter.

The world's largest desert, the Sahara, is a subtropical desert. It occupies about 3,500,000 square miles (9,000,000 km2) in Africa.

Middle-latitude continental interior deserts include the vast Gobi and Taklimakan deserts of Central Asia. The scant precipitation in middle-latitude deserts is due mainly to their inland location, far from the oceans The air that enters such areas is usually extremely dry; whatever moisture it may have contained was released before reaching the interior. These deserts, too, are cloudless for most of the year. Summer daytime temperatures can rise as high as those of subtropical deserts; winter temperatures, however, are considerably lower. Average daily temperatures below freezing are common during winter.

Deserts found on the leeward sides of mountains include the deserts of the southwestern United States. Mountain ranges act as barriers to moisture-carrying winds. Clouds release precipitation on the windward slopes, leaving the dry air to pass down the leeward sides. This phenomenon is known as the “rain shadow effect.”

The presence of cold coastal water can contribute to the creation of a desert along the adjoining shore. This occurs because cold ocean currents tend to stabilize the air over the coast and inhibit cloud formation. Large coastal deserts include the Atacama Desert in Chile and the Namib Desert in Namibia.