There are a number of processes in the world that are all equally responsible in the creation of deserts. First off, there is a low-pressure band along the equator. The low air pressure is hot air. Hot air absorbs the moisture held on land. Absorbing the moisture the hot air rises, moving away from the Earth's surface it cools. This process of cooling creates clouds. Cold air in which the clouds are now in, can't hold any more moisture triggering rain to fall. In the tropics and places near the equator it rains at 3:00pm every day. After this cold air descends it creates high pressure. After this low pressured air has finished descending it begins to warm up because it is coming closer to the Earth's surface. The air becomes warm and high pressure and warm air can hold moisture. So the warm air sucks up moisture like a dry sponge.
The air pressure tries to equalise but is blown back to the equator where there is low pressure via the North East and the South East trades. The whole process now starts again and constantly dries the land where the deserts are located.
Deserts and the Tropics:
Most hot deserts are bisected by the tropics. An example of this is the Australian Deserts. They are bisected by the Tropic of Capricorn. This is basically because winds blow away from the deserts taking away all the moisture they sucked up with them to the Equator.
Deserts and the location of sea currents:
The cold sea currents are located on the Western side of most coastal deserts. An example of this is the Benguela cold current and the Kalahari and Namib Deserts. This cold current absorbs energy received in the tropics cooling the air above. This cool air moves...