Dry climates are regions that receive very little precipitation throughout the year. These areas typically receive less than 250 millimeters of rainfall annually. Because evaporation rates are often higher than precipitation rates, moisture does not remain in the soil for long.
Dry climates commonly form under persistent high-pressure systems. High pressure causes air to sink, which prevents cloud formation and limits rainfall. Many dry climates are located around 30 degrees north and south of the equator, where global wind patterns create descending dry air.
There are two main types of dry climates: desert climates and semi-arid climates. Desert climates are extremely dry with very sparse vegetation. Semi-arid climates receive slightly more rainfall and can support grasses and small shrubs.
Because of the lack of moisture, dry climates often experience large temperature changes between day and night. During the day, temperatures can become very hot. At night, temperatures may drop quickly because dry air does not retain heat well.