Why do deserts have low rainfall?

Deserts have low rainfall because they are located in areas where dry air descends, preventing cloud formation. Many deserts, such as the Sahara, lie within high-pressure zones around 30° latitude, where air is warmed and dried. Others, like the Atacama, are in rain shadows, where mountains block moisture-laden winds. Coastal deserts can form due to cold ocean currents, which cool the air and reduce its ability to hold moisture. These factors create arid conditions, limiting precipitation and supporting only specialised ecosystems.