Are Deserts the Driest Places on Earth? No—Polar Deserts Are Drier

Deserts are dry, but not the driest. The McMurdo Dry Valleys in Antarctica hold the record:

• Precipitation: Near zero (some stations: 0 mm/year for decades).
• Humidity: Extremely low; air is among the driest on Earth.
• Cause: Katabatic winds (gravity-driven, heated by compression) evaporate all moisture; Transantarctic Mountains block ice sheet flow.
• Analogs: Mars-like conditions—used for astrobiology research.

Other hyper-arid zones: Atacama Desert (Chile/Peru) — some weather stations never recorded rain; Sahara (e.g., Aoulef, Algeria — 0.5 mm/yr). But the Dry Valleys are consistently the most extreme.

Deserts are defined by aridity (≤250 mm/yr); the Dry Valleys represent the absolute floor of that scale.