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13.1: Prelude to Deserts

  • Page ID
    8870
  • The dune is made of white sand
    Figure \(\PageIndex{1}\): A playa filled with evaporite minerals (such as gypsum) erodes and forms ripple-covered dunes in White Sands National Monument, New Mexico.
    Koppen_World_Map_BWh.png
    Figure \(\PageIndex{1}\): World hot deserts (Koppen BWh)

    The location of climates on Earth’s surface is not random. Jungles, tundras, and deserts have scientific explanations for their locations. Approximately 30 percent of Earth’s terrestrial surface is desert. Deserts are defined as locations of low precipitation. While temperature extremes are often associated with deserts, they do not define them. The lack of moisture, including the lack of humidity and cloud cover, allow temperature extremes to occur. The sun’s energy is more absorbed by the Earth’s surface without cloud cover, and nighttime cooling is more drastic without cloud cover and humidity to absorb the emitted heat, so temperature extremes are common in deserts.

    Rainshadow.jpg
    Figure \(\PageIndex{1}\): Diagram of rain shadow.

    Deserts tend to occur at latitudes of around 30° and at the poles, both north and south, driven by circulation and prevailing wind patterns in the atmosphere. At approximately 30° north and south of the equator, sinking air produces trade wind deserts like the Sahara and the Outback of Australia [1]. Rainshadow deserts are produced where prevailing winds with moist air dries as it is forced to rise over mountains.

    There are several ranges, some more snowy than others.
    Figure \(\PageIndex{1}\): In this image from the ISS, the Sierra Nevada Mountains are perpendicular to prevailing westerly winds, creating a rain shadow to the east (down in the image). Note the dramatic decrease in snow on the Inyo Mountains.

    The Western Interior Desert of North America and the Atacama Desert of Chile (the driest warm desert on earth) are examples of rain shadow deserts. Finally, polar deserts, such as the vast areas of the Antarctic and Arctic are covered by sinking cold air which is usually too cold to hold much moisture. Though covered with ice and snow, the average annual precipitation is very low, with Antarctica being Earth’s driest continent.