Lima, the capital of Peru, is classified as a desert city, a fact that surprises many visitors due to its frequently overcast skies and high humidity. Situated on the Pacific coast, Lima sits within the vast Peruvian Coastal Desert region. Its climate is highly unusual because it combines the extreme dryness of a desert with the cool, damp feeling of a coastal environment. This unique combination of aridity and moisture results from powerful global and regional weather mechanisms governing the western coast of South America.
Technical Desert Status: Low Rainfall Definition
The technical classification of a desert is based almost entirely on aridity, defined by the amount of annual precipitation, not by temperature. Under the Köppen-Geiger system, Lima is categorized as having a desert climate (BWh) because it receives extremely little rainfall. The average annual precipitation is often cited as being less than 25 millimeters (1 inch), making it one of the driest capital cities in the world.
This minimal amount of rainfall means there is virtually no rain for most of the year. This lack of measurable precipitation is the sole metric that scientifically confirms Lima’s desert status, despite its mild temperatures. The precipitation that does occur is often only a fine mist or drizzle, rather than a significant downpour.
The Coastal Climate Paradox
Lima’s reputation for being gray and damp, despite its desert status, results from a delicate atmospheric paradox created by geography and ocean currents. The primary mechanism is the cold Humboldt Current (or Peru Current), which flows northward along the South American coast. This cold water dramatically cools the air above the Pacific Ocean surface, creating an atmospheric inversion where cooler air is trapped beneath a layer of warmer air.
As moist air from the Pacific moves inland, this inversion layer prevents the air from rising high enough to cool, condense, and form rain-producing clouds. Instead, the moisture condenses into a persistent, low-lying blanket of thick stratus clouds and fog, known locally as garúa. This dense sea mist often blankets the city, especially during the Southern Hemisphere winter months from June to October, making the city feel continuously overcast and damp.
The garúa does not produce rain, as the water droplets are typically too fine to fall as precipitation, but it delivers moisture to the environment. This moisture sustains certain vegetation, particularly in the unique hillside ecosystems known as lomas, which act as fog oases in the otherwise barren desert.
The towering Andes Mountains to the east act as a formidable barrier, blocking any incoming moisture from the Amazon basin. Consequently, Lima experiences high humidity, often averaging around 84 percent, but receives practically no rainfall, resolving the apparent contradiction of a desert that feels perpetually wet.