Salar de Uyuni, perched at 3,656 meters (12,000 feet) on the Andean Altiplano, is defined by an extreme, high-altitude desert climate. Its weather is characterized by a binary cycle: a bone-dry winter and a wet summer. Because of the vast, open geography and reflective surface, the region experiences some of the most dramatic diurnal temperature shifts and solar radiation levels on the planet.
Typical Weather Patterns
The climate is classified as a cold semi-arid or desert climate (BWk under Köppen). The air is exceptionally thin and dry for most of the year, which allows solar energy to penetrate with intense heat during the day, only for that heat to escape immediately into the atmosphere once the sun sets.
Seasonal Trends
The Rainy Season (December to March)
Known as the "Mirror Season," this period sees the Altiplano receive the bulk of its 120-200mm annual rainfall.
- The Mirror Effect: When a thin layer of water (just 1–3 cm) accumulates on the impermeable salt crust, it creates a perfectly flat, reflective surface. This occurs most reliably in January and February.
- Temperatures: Highs reach 18°C to 21°C (64°F–70°F), while lows hover around 3°C to 5°C (37°F–41°F). The humidity makes the air feel slightly heavier and less biting than in winter.
- Risks: Heavy rains can lead to flooded access points, occasionally making interior landmarks like Incahuasi Island inaccessible to vehicles.
The Dry Season (May to October/November)
This is the Bolivian winter, a time of stark, cloudless skies and endless white horizons.
- Hexagonal Formations: As the water evaporates, the salt recrystallizes into the iconic raised hexagonal patterns that stretch for miles.
- Extreme Cold: This is the season of deepest freezes. While daytimes remain a crisp 12°C to 15°C (54°F–59°F), night temperatures frequently plummet to -15°C (5°F) or even lower between June and August.
- Atmospheric Clarity: Humidity levels drop to near zero, providing some of the clearest stargazing conditions on Earth.
The Daily Climate Cycle
A single day in the Salar often feels like experiencing two or three seasons.
- Morning: The air is piercingly cold and still. Frost may coat the salt until the sun gains height.
- Midday: The sun’s intensity is fierce. Due to the high altitude and the white surface reflecting nearly 80% of UV rays (the albedo effect), the "feel-like" temperature can be significantly higher than the actual air temperature.
- Afternoon: Winds often pick up in the late afternoon (reaching 50–90 km/h), creating a "wind chill" that makes the transition toward evening feel much faster.
- Night: The drop is sudden. Within an hour of sunset, the temperature can fall by 20 degrees Celsius.
Weather Phenomena and Microclimates
- The Albedo Effect: The white salt acts as a giant mirror for UV radiation. Even on cold days, the solar burn is a major factor of the climate experience.
- Katabatic Winds: Cold, dense air often rolls down from the surrounding Andes at night, creating localized windstorms that scour the flat surface.
- Optical Illusions: The heat rising from the salt in the dry season creates Fata Morgana mirages, where distant mountains appear to float or stretch vertically.
- La Niña Impacts: In La Niña years, the rainy season is significantly wetter and can start earlier, leading to deeper flooding that lasts well into May.
Historical and Cultural Context
Historically, the Salar is the residue of prehistoric lakes (Minchin and Tauca) that evaporated over 30,000 years ago. Locals, primarily from Aymara and Quechua communities, have adapted to this harshness for millennia. Architecture emphasizes thermal mass—traditionally using thick adobe and, more recently, blocks of salt, which acts as a natural insulator against the extreme day-night temperature swings. In the town of Uyuni, the "weather-beaten" look of buildings and infrastructure reflects a century of defending against abrasive salt-laden winds and the unrelenting Andean sun.