Latin America

High and dry

Israel-Hervas-Bengochea

The Atacama Desert in northern Chile is the world’s most arid place, where some areas have never seen rain.

In the mid-1990s, NASA set up an automatic environmental station in the most arid part of the Atacama Desert. Over five years, it recorded a miniscule two millimetres of rain that fell close to midnight. It was so slight that nearby weather stations did not even register it.

Welcome to the driest place on earth. The Atacama Desert, located in the north of Chile, is so arid that some adults here might never have seen rain. It covers 965 kilometres (600 miles) from Bolivia’s southern border, west of the Andes Mountains, and down towards central Chile. Some riverbeds have been dry for 120,000 years. The annual rainfall here is about 0,004 inches. That translates as four inches of rain per thousandth year.

Central Atacama is what climatologists call ‘absolute desert’. Here fauna and diversity is extremely low. Only the odd scorpion roams below scavenging vultures. Some plants have carved out life where underground water reaches the surface. Other places have no life at all: no humans, no animals; not even a tiny lizard; no algae or green growth. The aridity prevents decomposition, meaning some vegetation has been dead for thousands of years. So inhospitable is the climate that scientists study it to understand better whether there could be life on Mars.

The desert is not necessarily hot. Temperatures range from 15˚C to 25˚C. As of 2002, the maximum temperature on record was 37˚C. Only lack of rain is the problem.

Nataliya-Hora

Surprisingly, humans do live here. Residents are crammed into coastal cities, fishing villages and oasis towns. Centrally no permanent settlements exist. “There are places all over the desert that they live,” says Laura Evenstar, professor in earth sciences at the University of Bristol. “In the northerly locations there are rivers fed by the high Andes. So people would live in these river valleys. There are quite a lot of cities along the coast where water is brought in.”

Why is the desert so dry? The classic explanation is that the Andes Mountains cut off moisture drifting in from the Amazon Basin. As clouds rise towards the mountains, they cool and extract rain. The opposite happens once they cross. “As they head into the Atacama Desert the clouds must go down in elevation [from 6,000 to 2,000 metres] and they heat up,” explains Evenstar. “Then they start to evaporate which depresses precipitation. So you get less rainfall on the western side.” As such, fog and hazy skies often cover the desert’s northern fringes.

Paulo-Afonso

The climate aids scientific discovery. Over the past decades, several observatories have been built here. The high altitude, the absence of clouds and the pollution-free environment make the skies perfectly clear. In March, the world’s most powerful telescope was installed: the £860million ($1.3billion) Atacama Large Millimeter Array (ALMA), featuring 66 antenna dishes each spanning 12 metres and weighing 100 tonnes. Scientists, of course, packed their bags and moved with them. Presumably leaving their umbrellas at home.

Photos: Israel Hervas Bengochea, Nataliya Hora, Paulo Afonso [all via Shutterstock.com].

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