Mountain ranges can create deserts by preventing moist air from reaching certain areas. Known as the ‘rain shadow’ effect, this phenomenon has played a part in the formation of many arid landscapes, including the Mojave, Gobi and Atacama deserts.

How do deserts form? © Daniel Bright

1. Evaporation

Warmed by the Sun, water evaporates from oceans and other bodies of water, entering the atmosphere as water vapour and forming clouds. This warm, moist air is swept inland by winds.

2. Upwards winds

If the prevailing wind passes through a mountain range, warm, moist air is forced upwards. As it rises, it expands and cools. As colder air is not able to carry as much moisture, the water condenses out, falling as rain or snow. This is known as orographic precipitation, and typically supports lush vegetation on the upwind side of the mountain.

3. Warm air descends

Stripped of moisture, the cool, dry air passes across to the other side of the mountain range, warming up again as it descends. On this side of the range, the lack of moisture prevents cloud formation, creating a dry area commonly called a ‘rain shadow’.

4. Low humidity

A region is officially classified as a desert when rainfall is under 250mm per year. Without vegetation, any soil or organic matter is swept away by winds, often leaving behind sand and rocks. Low humidity also means it can get extremely hot when the Sun is shining, but very cold at night.

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