On the west coast of South America, there’s an unlikely sight to behold: a bone-dry desert bordering the Pacific Ocean called the Atacama Desert. This arid desert extends from the west coast of Chile and spills over the bordering nations of Argentina, Peru, and Bolivia. While it’s not truly the driest place on the whole planet (that distinction goes to certain parts of Antarctica), it’s the driest hot desert on Earth, receiving less than 0.6 inches of rain on average the whole year. Interestingly, some weather stations in the desert have never received rainfall at all! At first, it may seem bizarre that a location right next to the ocean would be so incredibly dry, but upon further inspection it is evident why this desert is here.
The Atacama Desert can attribute its astoundingly low precipitation to a combination of several “drying” factors: the subtropical high, a double rain shadow, and the cold ocean current running up the west coast of South America. These factors work together to make an amazing synthesis of dry conditions that form the unique climate of the Atacama.
The first factor, the subtropical high, is a global wind and pressure belt that can be found around 30 degrees North or South, right around where the Atacama Desert is. This pressure belt stretches around the world at this latitude and suppresses the formation of clouds by making it difficult for air to rise. Naturally, this creates a zone of low precipitation. Many areas around the world under the subtropical high have lower rainfall levels, but none quite as low as the Atacama. That’s because there are other influences at work here.
The second factor is the double rain shadow over the desert. A rain shadow is an area that receives less rainfall as a result of a nearby mountain chain. Oftentimes, a mountain will have a prevailing wind blowing into one side of it, and that receives a lot of rainfall because that wind pushes the moisture in the wind up the mountain, creating clouds and precipitation. Consequently, the other side of the mountain often has less rain because there’s much less moisture in the air. This phenomenon affects the Atacama Desert on two fronts: the Andes Mountains and the Chilean Coast Range. The desert is primarily on the leeward side of each mountain chain, which is where the rain shadow is for mountain ranges, further decreasing the amount of rain the desert gets.
The third major factor that keeps the Atacama Desert so dry is the cold ocean current that runs adjacent to the coast of South America. This cold current decreases the temperature of the surrounding air, making it unable to accumulate a good deal of moisture over the ocean (since cold air can’t “hold” as much moisture as hot air). Of course, this means that the desert doesn’t have much of a chance to receive moisture from the ocean next to it, making it even drier.
Overall, the Atacama Desert is an important desert to study because it encompasses many important aspects of climate. Not only this, but the desert impacts the well-being of the people that live in or around it. Understanding how the climate of the area came to be is important to understand how climate works, how it changes the environment, and how it impacts people in its environment. While the Atacama desert is a statistical oddity, the factors that influence it are in no way foreign and are essential to understand for anyone who wishes to comprehend how the world’s climate works.
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© 2019 Weather Forecaster Cole Bristow