The global distribution of mid and low latitude deserts and their margins…

The idea

Deserts cover approximately a third of the Earth's land surface, primarily distributed in distinct latitudinal bands. Low latitude deserts, such as the Sahara and Kalahari, are typically found between 15° and 30° North and South of the equator, driven by descending dry air from the Hadley cells. Mid latitude deserts, like the Gobi and Patagonian deserts, occur between 30° and 50° North and South, often located deep within continental interiors or in rain shadows of major mountain ranges. The margins of these deserts transition into semi-arid zones, such as the Sahel, receiving slightly more rainfall (250 to 500 mm annually) than the true arid cores (under 250 mm annually), making them highly vulnerable to desertification.

What earns the marks

• Identify the location of low latitude deserts (15° to 30° North and South) and link them to high-pressure belts caused by Hadley cell subsidence.
• Explain the distribution of mid latitude deserts (30° to 50° North and South) using continentality and rain shadow effects.
• Distinguish between arid desert cores (receiving less than 250 mm annual precipitation) and semi-arid margins (receiving 250 to 500 mm annually).
• Locate specific examples of both mid latitude (e.g., Gobi, Patagonian) and low latitude (e.g., Atacama, Sahara) deserts on a global map.

Common mistakes and how to put them right

• Confusing the locations of mid and low latitude deserts.

  Put it right: Low latitude deserts are near the tropics (15° to 30°), while mid latitude deserts are further poleward (30° to 50°).

• Assuming all deserts are hot environments.

  Put it right: Mid latitude deserts like the Gobi experience extreme cold winters, unlike low latitude hot deserts.

• Defining deserts solely by high temperatures.

  Put it right: Deserts are defined by a moisture deficit (aridity), where potential evapotranspiration exceeds precipitation.

Exam tips

• Use specific named examples of both mid and low latitude deserts when discussing global distribution patterns to secure higher marks.
• Always link the location of a desert to its primary atmospheric or geographical cause, such as descending Hadley cell air or rain shadow effects.
• When describing desert margins, emphasise their transitional nature and their specific vulnerability to climatic shifts and human pressures.