Deserts in hot climates owe their origin to lack of water resulting from the capacity of warm air above the desert area to retain most of the available moisture. This, combined with the high evaporation rate, turn the land into desert.
Another factor in the formation of deserts is a high mountain range, such as the Andes. These enormous mountains lie across the path of the rain clouds and moist winds, thus forming a shield. So most of the rain clouds burst over the mountains before they ever reach the plains. Other deserts, such as the Gobi in Central China, are so deep within the continent that the moisture-laden winds hardly ever reach them.