18.2: How Do Deserts Develop?

How Do Deserts Develop?

Deserts are not randomly located on the Earth’s surface, instead many deserts are gathered in distinct belts or regions. For example, sinking, dry air currents occurring at 30° North and South of the equator produce many of the most famous deserts including the Saharan Desert in Africa These areas are commonly referred to as subtropical deserts (Figure 18.2).

Subtropical deserts are the hottest deserts. In the US, the Chihuahuan Links to an external site., Sonoran Links to an external site., and Mojave Links to an external site. are all examples of subtropical deserts (Figure 18.3). These deserts are often very hot and dry in the summer and cooler and dry in the winter. Rainfall does occur, but it short bursts, which may lead to flash flooding Links to an external site..

Dry areas located along a coast are referred to as coastal deserts. Coastal deserts typically occur in cool to warm areas along the west coasts of continents between 20° to 30° latitude and have cool winters and long, warm summers. Coastal winds blow in an easterly pattern (from the interior of the continent) and prevent moisture from moving onto the land. Examples include the Namib Desert in Africa (Figure 18.4) and the Atacama Desert in Chile, the driest place on Earth.

Other deserts can be found in the rain shadow Links to an external site. created from prevailing winds blowing over mountain ranges (Figure 18.5). As the wind drives air up and over mountains, atmospheric moisture is released as snow or rain. Atmospheric pressure is lower at higher elevations, causing the moisture-laden air to cool.  Cool air holds less moisture than hot air, and precipitation occurs as the wind rises up the mountain. After releasing its moisture on the windward side of the mountain, the dry air descends on the leeward or downwind side of the mountains to create an arid region with little precipitation called a rain shadow. Most rain shadow deserts in the western United States, including the Great Basin Desert, are due to the Sierra Nevada and Cascade ranges (Figure 18.3).

Finally, polar deserts Links to an external site., like the vast areas of the Antarctic (Figure 18.6) and the Arctic, are created from sinking air that is too cold to hold much moisture. Although they are covered with ice and snow, these deserts have very low average annual precipitation. Consequently, Antarctica is Earth’s driest continent.