As a definition, a desert is a hot area of land that gets very little rain — not more than 200mm a year, where temperatures during the daytime can get as high as 55°C. At night, deserts cool down, sometimes even below 0°C. Most deserts lie between 15° and 35° north and south of the equator. They were created by air that rises over the equator and comes down over the Tropic of Cancer and the Tropic of Capricorn. All over the world, around 20% of the deserts lie in these regions.
How does this happen?
- Land over the equator becomes very hot because the sun’s rays hit the equator at a direct angle between 23°N and 23°S latitude. The hot and wet air rises and it rains a lot in these areas.
- The air cools down and moves north and southwards as it gets drier.
- The cool and dry air, sinks to the ground over the Tropic of Cancer in the north, and the Tropic of Capricorn in the south, causing high pressure (“sunny weather”) .
- And then again, warm air near the surface moves back to the equator causing the air to rise. These moving air masses are called trade winds. As the rising air cools, clouds and rain develop. The resulting bands of cloudy and rainy weather near the equator create tropical conditions.
But… what makes the Atacama Desert in Chile drier than other deserts?
Well, the cold Humboldt Current, flowing northward along the Chilean coast, creates a strong inversion layer. The cold, humid air produced by the sea stays down along the coastline by the effect of the hot air masses of the continent, not just reducing the moisture in the air but also creating nearly 350 days of clear skies inland.
Also, we have to consider that the Atacama Desert is located over high altitudes, above 2,500 metres above sea level. This fact contributes to low dryng temperatures and very low humidity in the air (about 10%).
Inversion Layer Effect, caused by Humboldt cold current
along the coast of Chile-North
Another important reason is that the Andes Range runs along the Atacama Desert, acting as a formidable natural barrier from the moisture of the Amazon;
the rain shadow effect. This is a dry region of land on the side of a mountain range that is protected from the prevailing winds; those that occur most of the time in a particular location on the Earth. These protected sides, are also called the leeward side or the down-wind side.
Prevailing winds carry air toward the mountain range. As the air rises, the air cools, water vapor condenses, and clouds form. On this side of the mountains, called the windward side, precipitation falls in the form of rain or snow. The windward side of a mountain range is moist and lush because of this precipitation. Once the air passes over the mountain range, it moves down the other side, warms, and dries out. This dry air produces a rain shadow. Land in a rain shadow is typically very dry and receives much less precipitation and cloud, creating desert conditions on the leeward side of the range cover.
Nowhere else on Earth do these climatic features come together as they do in Atacama.
Permaculture Design Certificate (PDC) Course
We are pleased to offer a full PDC between 23 November — 7 December, 2013, in this amazing and still pristine corner on earth. The PDC will be held at:
Atacama Loft facilities at San Pedro de Atacama, Second Región of Chile.
The course will be taught in both Spanish and English by PRI accredited teacher, Grifen Hope.
Find out more here:
- atacamapermacultura (at) gmail.com