Deserts are classified by their location and weather pattern.
High-pressure deserts occur at the polar regions and between 20 and 30 degrees latitude on both sides of the equator. These deserts are located in areas of high atmospheric pressure where ongoing weather patterns cause dry air to descend. As the dry air descends, it warms up and absorbs much of the moisture in the area.
Rain-shadow deserts occur as a result of a mountain range’s effects on the prevailing winds. As wind travels over a mountain range, it cools and dumps its moisture in the form of rain or snow. As it descends to over elevations on the other side of the mountain range, the wind becomes very dry and warm. Unless moisture is provided in some other form, a rain-shadow desert will form on the protected side of the mountain range as a result.
Continental deserts occur in the centers of large continents. As inland winds travel from the sea over land, they lose moisture in the form of rain, and by the time they reach the center of a large continent, they are very dry.
Cool Coastal Deserts
Cool coastal deserts are the result of the cold ocean currents that parallel the western coastline near the Tropics of Cancer and Capricorn. At these locations, the cold ocean current touches a warm landmass, and as a result almost no moisture is transferred from the ocean’s cold water to the air that flows over the adjoining coastline. The descending air mass, which is already dry, becomes even drier. These deserts are some of the driest in the world.