Lima, Peru’s capital city with over 10 million residents, lies uniquely between towering Andes mountains and the vast Pacific Ocean. Known for its rare tropical desert climate, Lima surprises with mild temperatures, persistent fog, and almost no rain. Discover why Lima’s climate is unlike any other city in the world.

 

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Lima’s Origins and Tropical Location

Founded in 1535 during the Spanish conquest, Lima is Peru’s capital and sits at just 12°S latitude, placing it deep within the tropics. It spans the Pacific coast, enclosing a population exceeding 10 million in its metropolitan area. Despite its tropical position, the city receives virtually no rain, a stark contrast to other tropical metropolises. Lima instead experiences persistent high humidity, frequent low clouds and fog, and extremely dry weather overall.

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Why Tropical Deserts Are Rare—and Why Lima Is One

Most deserts around the world belong to one of two categories: hot subtropical deserts, found just outside the tropics (beyond 23° latitude), and cold deserts, found inland or in mountain rain shadows. Tropical deserts—especially major urban ones—are nearly unheard of. Lima defies these norms thanks to two key factors: the Andes mountains and the Humboldt Current.

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The Andes: Blocking the Rainy Season

To the city’s east, the Andes soar above 6,300 m (20,000 ft), acting as a natural barrier to moist trade winds arriving from the equatorial Pacific during the summer. Without them, Lima would experience a classic tropical savannah pattern: a defined wet season followed by a dry one. Instead, the Andes block that moisture entirely, leaving the city dry year-round.

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The Humboldt Current: Cooling the Tropics

Parallel to the coast flows the cold Humboldt (or Peru) Current, which brings frigid waters from the mid-latitudes toward the equator. Near Ecuadorian borders, water temperatures hover around 16 °C, roughly 10 °C cooler than expected for a tropical latitude. This dramatically cools the air above the ocean, which shapes Lima’s unusual climate.

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Mild Temperatures and Persistent Fog

Thanks to the cool current, Lima’s coastal climate stays mild. Winters see lows around 14 °C, not the typical low twenties of the tropics, while summers average 26 °C, rather than surpassing 30 °C. With relative humidity often above 80%, moist air and fog blanket the city—especially in winter. Lima is, in fact, one of the cloudiest cities globally, logging just 1,230 sunshine hours annually—which is half what cities like Bangkok enjoy.

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Why Lima’s Humidity Doesn’t Rain

To understand why humidity doesn’t translate into rain here, recall that warm air holds more moisture than cool air. Rain requires air to rise, cool, and condense—either via storm systems or by being lifted over mountains. However, Lima’s daytime land temperatures, heated by tropical suns, remain warmer than the cool ocean. Any fog or moisture that drifts inland quickly evaporates. Without uplift, Lima’s clouds remain shallow, turning to fog rather than rainfall.

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Result: A Never-Raining Tropical Desert

The combination of the rain-blocking Andes and cold Pacific waters creates exceptionally stable atmospheric conditions. The water droplets in Lima’s sky simply don’t collide and grow large enough to become rain. As a result, Lima sits firmly in the BWh (Hot Desert) category of Köppen’s classification: “B” for dry, “W” for desert, and “h” indicating a mean annual temperature above 18 °C. Though some sources have playfully suggested an unofficial “BWn” label for “mild desert,” this is not recognized in peer-reviewed climate studies.

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Desert Cities and Water Solutions

Lima isn’t the only city built in a desert, but being in the tropics makes it unique. Despite its arid conditions, the city has managed to grow steadily, thanks to water sourced from Andean springs and rivers, pumped down into the basin. Meanwhile, more remote coastal communities have turned to innovative methods: they install fog nets, which condense moisture from coastal fog into drinkable water—an ingenious workaround to the city’s lack of rainfall.

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Conclusion: A Climate Shaped by Nature and Geography

Lima defies expectations—a sprawling tropical metropolis in a near-rainless desert climate. The towering Andes shut out rain-bearing winds, while the cold Humboldt Current chills the coast. The result is a city cloaked in fog, bathed in mild air, and rich in water ingenuity despite its desert classification. Lima’s climate is a masterclass in geography, meteorology, and human adaptation.