Major Deserts of South America

Though often seen as a continent rich in rainforests and rivers, South America also hosts two major desert regions, each born out of unique climatic and geographical forces.

Atacama Desert — “The Driest Place on Earth”

Welcome to a desert where rain might not fall for decades — the Atacama Desert, also called the Peruvian Desert, stretches across northern Chile and parts of southern Peru.

• It lies between the Andes Mountains and the Chilean Coast Range — creating a two-sided rain shadow.
• This desert isn’t just dry — it’s hypo-arid, meaning it gets less than 1 mm of rain per year in some places.

🔍 Why is Atacama so dry?

Think of a perfect storm — but for dryness. Here are the five factors:

1. Rain Shadow of the Andes – Moist winds from the Amazon basin rise over the Andes, cool, and drop their moisture before reaching Atacama.
2. Offshore Trade Winds – These winds move from land to sea along the west coast, blocking moist sea air from reaching inland.
3. Absence of Westerlies – Westerly winds, which could bring moisture, blow far south of the Tropic of Capricorn, missing Atacama.
4. Subsidence from South Pacific High – This high-pressure system pushes air downward, warming it and preventing cloud formation.
5. Cold Humboldt Current & Upwelling – The Humboldt (Peru) Current chills the air, reducing its moisture-carrying capacity, and further suppresses rainfall via Walker Circulation-induced upwelling.

📍 Result:

• The most arid zone lies between the Andes and the Coastal Range — a textbook case of a double rain shadow.
• The landscape includes salt pans, alluvial fans, and rocky terrains, with little to no vegetation.

When creating a diagram in exam in your answer writing for mains exam, you should ensure that it should be neatly enclosed in a box and accompanied by a well-labeled caption to enhance its readability. Effective illustration strengthens answer writing, making your explanation more impactful. Here is a diagram showing the rain-shadow effect in the Atacama desert:

Patagonian Desert — “The Cold Desert of the South”

Now move to southern Argentina, where the Patagonian Desert (also known as the Patagonian Steppe) unfolds across vast open spaces.

• It is South America’s largest desert and ranks among the largest cold deserts in the world.
• Located between the Andes (west) and the Atlantic Ocean (east), this desert forms part of Patagonia, a region we earlier met in agricultural zones.

🌦 Why is it dry here?

• Moist winds from the Pacific hit the Andes and release their rain on the western slopes.
• When the winds descend the eastern side (Patagonia), they become dry and warm — classic rain shadow effect again.
• Despite proximity to the Atlantic, cool ocean currents and stable air masses limit moisture transport inland.

🌾 Vegetation and Landforms:

• The terrain alternates between flat-topped plateaus (mesas) and river-carved valleys and canyons.
• Central zones are dominated by shrubs and herbs, while western areas, which get slightly more rain, support grasses.

Here is a diagram illustrating rain-shadow effect in Patagonian Desert:

Comparison of the Two Deserts

Feature	Atacama Desert	Patagonian Desert
Location	Northern Chile & Southern Peru	Southern Argentina (Patagonia region)
Climate Type	Hyper-arid, warm desert	Cold desert / steppe
Main Cause of Aridity	Cold currents, rain shadow, high pressure	Rain shadow from Andes
Vegetation	Almost barren, salt pans	Shrubs and grasses
Unique Feature	Driest desert on Earth	Largest desert in Argentina

Conclusion

South America’s deserts are not just barren lands — they are like climate laboratories, showing how ocean currents, wind patterns, and topography interact to shape landscapes.
While Atacama sets a global benchmark for dryness, Patagonia presents a classic example of a cold rain shadow desert.

Understanding them reveals the power of physical geography in sculpting both ecosystems and human activity in the region.