There are more deserts in the Northern Hemisphere than in the Southern Hemisphere, because there is more land in the former than the latter.
Deserts may be found in regions where atmospheric movement [Figure 1] is conducive to aridity. These are areas of high pressure (Hadley Cells). Examples of atmospherically controlled deserts include: most of the
Sahara, Australian deserts and the Kalahari.
Figure 1: Atmospheric Circulation
[Graphic courtesy of USGS]
Figure 2: Hadley Cells [Courtesy of NOAA]
Rain Shadow Deserts:
form on the lee side of mountains develop due to that which is known as a Rain shadow effect. As air rises, cools and condenses moisture is dropped as it passes over the mountain leaving a far drier region to the leeward side, in the shadow of the mountain. Examples of this type of desert, as the result of orographic uplift, are: Mojave, the Great Basin of North America, Anza-Borrego, and the Taklamakan.
Cold Water Current:
Cold water currents act similarly as does orographic uplift, in that just as rising air cools, water over the current is cooled and looses its ability to hold moisture. As it reaches the coast, much of the moisture is gone [except where fog occurs], thus contributing to the aridity of these types of deserts. Examples of these deserts include Baja California, the Western Sahara, and the Namib of South-western Africa.