Peru, located on the central western coast of South America, exhibits one of the world’s most complex and varied climate profiles despite being entirely within the tropics. This extraordinary diversity is a direct result of the country’s unique geography, which features the Pacific Ocean to the west, the towering Andes mountain range running down its spine, and the vast Amazon Basin to the east. These three distinct geographical features create three primary, yet highly contrasting, climate regions. The environment ranges from some of the driest deserts to high-altitude polar conditions and humid equatorial rainforests within a relatively short distance.
The Arid Pacific Coast
The narrow strip of land along the Pacific Ocean, known as the Costa, experiences a predominantly arid, desert, or semi-arid climate, defying its tropical latitude. This climate is defined by the powerful cooling influence of the Humboldt Current, a cold, low-salinity ocean current flowing north along the South American coast. The cold surface water cools the air mass above it, which suppresses the formation of rain-producing clouds. This leads to extremely low annual precipitation, often less than 30 millimeters in central and southern areas.
Despite the desert-like dryness, the central and southern coast, including the capital city of Lima, experiences high humidity and frequent cloud cover, particularly during the winter months from May to November. This moisture often manifests as a dense, persistent coastal fog or mist known locally as garúa. While the garúa does not produce substantial rainfall, it provides enough condensation to support unique coastal ecosystems. Temperatures remain relatively mild, with Lima seeing daytime highs between 15°C and 19°C in winter and 25°C to 30°C in the summer.
The Diverse Andean Highlands
Moving eastward, the climate transitions dramatically with the ascent into the Andes mountain range, or the Sierra, where altitude becomes the primary determinant of weather conditions. This region is characterized by a dry, temperate climate in the lower valleys that rapidly becomes colder with increasing elevation, creating distinct vertical climate zones. The daily temperature range is often significant, with warm, sunny days contrasting sharply with frigid nights.
The lower to mid-elevations (2,300 and 3,500 meters) typically have a temperate climate (Quechua zone) suitable for agriculture. Above this, from about 4,100 to 4,800 meters, lies the cold, high-altitude grassland known as the Puna, which features a cold climate with high atmospheric dryness. Seasonal variation is defined by precipitation, with a marked wet season occurring during the austral summer (December to March), and a dry season (April to October) that brings clear skies and much colder nighttime temperatures.
The Humid Amazonian Jungle
Beyond the eastern slopes of the Andes lies the Amazonian lowlands, or Selva, which experiences a tropical wet or equatorial climate. This region covers over 60% of Peruvian territory and is characterized by consistently high temperatures, heavy annual rainfall, and intense humidity throughout the year. Average temperatures hover around 28°C, with high relative humidity often exceeding 75%.
The Amazonian climate is further divided into two sub-regions based on altitude: the Selva Alta (high jungle) and the Selva Baja (low jungle). The Selva Alta, or cloud forest, lies on the mountainous eastern slopes of the Andes (400 to 1,000 meters above sea level), and is characterized by high rainfall, sometimes exceeding 4,000 millimeters annually, and slightly cooler temperatures. The Selva Baja is the true Amazonian plain, below 800 meters, which has the warmest and most humid conditions, with abundant rainfall occurring primarily between November and April.
Key Modifying Factors Affecting Climate
While the three primary geographical regions establish the baseline climates, two large-scale forces introduce significant variability: the Humboldt Current and the El Niño-Southern Oscillation (ENSO). The Humboldt Current is the persistent cold water flow that maintains the arid desert conditions along the coast by inhibiting convection necessary for rainfall. This upwelling produces the characteristic high humidity and fog.
However, this stable system is periodically disrupted by the El Niño-Southern Oscillation. During an El Niño event, the sea surface temperatures off the Peruvian coast become anomalously warm, suppressing the cold upwelling of the Humboldt Current. This leads to a dramatic shift in weather patterns: the usually arid northern coast can experience excessive, heavy summer rainfall and flooding, while the highlands may see less rain and higher temperatures than normal. This oscillation is a major source of inter-annual climate variability across all three regions.