Deserts cover approximately one fifth of the world’s surface and fall in roughly the same latitudes all around the globe: between 15 and 35 degrees. In the Southern Hemisphere, this area falls roughly over the Tropic of Capricorn, while in the Northern Hemisphere it is closer to the Tropic of Cancer. There are three general varieties: the rain shadow desert, the coastal desert, and the remote interior basin desert.
The climate in desert ecosystems is highly varied, but a few common characteristics do emerge when defining a desert. These characteristics are:
There are some deserts that receive more than 10 inches of rain per year, but the evaporation rate greatly exceeds the amount of rainfall in these places. Temperatures vary greatly from season to season in deserts, and they also vary from desert to desert.
The four North American Deserts are (from largest to smallest): Chihuahuan Desert, Great Basin Desert, Sonoran Desert, and Mojave Desert.
Two distinct forces related to global weather patterns form the four deserts found in North America: rain shadow effect and ocean currents. The rain shadow effect occurs when high mountains force moist, warm air upward as it moves in from the oceans. As the air is forced upward, it cools and the moisture held within it condenses. The moisture is then released in the form of rain before it reaches the summit of the mountain. After the air has released its burden of water, it continues its journey on the far, or lee, side of the mountain. The lee side air mass is now much colder and drier than when it began. As a result, the lee side of the mountain receives almost no rain and desert-like conditions are created.
Ocean currents are also responsible for the formation of the deserts in North America. Due to global weather patterns, ocean currents on the west side of any large land mass are colder than their eastern counterparts. The current on the west coast of North America is called the California Current and moves cold water from the Gulf of Alaska. This cold current keeps the air cool as well. Since cold air cannot hold moisture, dry air hits the coast first. It does not warm up until it is further inland, meaning that deserts can be found along many western coastlines, as is the case in North America.
Introduction (current location)
People and Places
The Sonoran Desert Index (multimedia version)
Views of the National Parks Visitor Center