Where Deserts Form: Latitude, Rain Shadows, and Continental Interiors

Deserts—areas receiving <250 mm (10 in) annual precipitation—cluster in predictable geographic settings driven by atmospheric circulation and topography.

1. Subtropical High-Pressure Belts (15°–30° N/S)

Descending air in the Hadley cell warms adiabatically, suppressing clouds. Major deserts:

• Sahara (N Africa) – 9.2M km², largest hot desert.
• Arabian (Middle East) – 2.3M km².
• Sonoran/Mojave (SW North America).
• Kalahari (S Africa), Australian deserts.

2. Rain Shadows (Leeward of Major Ranges)

Moist winds rise, cool, precipitate on windward slopes; descend warm and dry on lee side.

• Atacama (Chile) – Andes block Pacific moisture; driest non-polar desert (<1 mm/yr).
• Patagonian (Argentina) – Andes block westerlies.
• Great Basin (USA) – Sierra Nevada/Cascades block Pacific storms.
• Gobi (Mongolia/China) – Himalayas block Indian monsoon.

3. Continental Interiors (Far from Moisture Sources)

Air masses lose moisture traversing continents.

• Central Asian deserts (Karakum, Kyzylkum) – far from oceans.
• Interior Australian deserts.

4. Cold Deserts (Polar & High Elevation)

• Antarctic (14M km²) – largest desert overall; precipitation <50 mm/yr.
• Arctic polar desert (Greenland, Canadian Archipelago, Svalbard).
• High-altitude: Tibetan Plateau, Altiplano, Andean puna.

Desert Adaptations (Brief)

• Plants: Succulence (cacti, euphorbias), deep taproots, ephemeral life cycles, CAM photosynthesis.
• Animals: Nocturnality, estivation, concentrated urine, metabolic water, burrowing.

Deserts are not "empty"—they are precisely structured by global climate dynamics and host highly specialized biotas.