Peru’s climate is a mosaic of weather patterns shaped by its location near the equator and immense topographical relief. While its latitudinal position suggests a uniformly tropical climate, the towering Andes Mountains dramatically segment the country into three distinct climatic regions. This geographic diversity, combined with oceanic influences, creates a unique scenario where arid deserts, frigid highlands, and humid jungles exist within a short distance. These regions are the coast, the mountains, and the Amazon, each with specific characteristics and seasonal cycles.
The Climate of the Arid Coast
The Peruvian coast, known as La Costa, stretches as a narrow desert strip along the Pacific Ocean. Its climate is temperate, mild, and profoundly arid, with rainfall being scarce or entirely absent in cities like Lima. Average temperatures along the central and southern coast remain stable, generally ranging from around 66°F (19°C) in winter to 72°F (22°C) in summer.
The lack of extreme temperature swings is due to the moderating influence of the Pacific Ocean. However, the lack of precipitation results from the cold, northward-flowing Humboldt Current, which cools the air and prevents the formation of rain-producing clouds. Instead of rain, the winter months (typically June to September) bring a persistent, thick cloud cover and mist known locally as garúa.
This garúa provides enough moisture through condensation to support small patches of vegetation, creating lomas ecosystems, even as the surrounding desert remains barren. The coastal desert is part of the Atacama Desert, one of the driest places on Earth.
The Climate of the Andean Highlands
The Andean Highlands, or La Sierra, are defined by altitude and a pronounced division into two seasons. Temperatures vary significantly, moving from temperate conditions in the lower valleys to perpetually frigid zones, or puna, at higher altitudes. While lower valleys can experience average annual temperatures around 64°F (18°C), elevations above 13,000 feet (4,000 meters) often drop below freezing.
The highlands experience a wet season from October or November through April, characterized by daily, often intense, downpours. The heaviest precipitation typically occurs between January and March, influencing travel and agricultural cycles. This wet period contrasts sharply with the dry season, which lasts from May to September.
During the dry season, days are typically sunny and relatively warm, but nights are intensely cold, often dropping below freezing in the higher elevations. This drastic temperature difference between day and night, known as a high diurnal range, can frequently exceed 40°F (22°C) due to the clear skies and thin air. At the highest peaks, above 15,700 feet (4,800 meters), the climate is glacial, with permanent snow cover.
The Climate of the Amazon Basin
The Amazon Basin, or La Selva, covers the eastern portion of Peru and is characterized by a tropical equatorial climate. This climate features high temperatures, high humidity, and copious rainfall throughout the year. The average annual temperature is approximately 81°F (27°C), with daytime highs often reaching the mid-90s Fahrenheit (mid-30s Celsius). Humidity levels consistently range between 80% and 90%.
This region lacks the distinct wet and dry seasons found in the highlands, though rainfall is somewhat heavier from December to March. Annual precipitation is substantial, exceeding 90 inches (2,200 mm) in many areas. Despite the constant tropical conditions, the Amazon basin is subject to friajes or surazos, which are occasional, short-lived cold fronts.
These friajes are caused by cold air masses originating from the South Atlantic and Antarctic regions that penetrate north, typically between May and August. During a friaje, temperatures can drop suddenly, sometimes falling to as low as 50°F (10°C) for a few days. This temporary cold snap contrasts sharply with the region’s otherwise hot and humid conditions.
The Major Drivers of Climatic Variation
The climatic diversity of Peru is a consequence of two geographical and oceanic forces: the Andes Mountains and the cold Humboldt Current. The Andes Mountains act as a continental climate barrier, effectively dividing the country into its three zones. The range blocks moisture-laden air masses from the Amazon basin, preventing them from reaching the coast.
This barrier creates a dramatic rain shadow effect, which is the reason the Pacific coast remains a hyper-arid desert. The mountains also dictate the climate of the highlands, where temperatures are stratified by elevation and subject to the diurnal extremes common in high-altitude environments.
The second major driver is the Humboldt Current, also known as the Peru Current. This flow of cold water moves northward along the coast from the Antarctic. The cold surface water cools the overlaying air, leading to atmospheric stability and suppressing the formation of convection and rainfall. This current causes the coastal aridity and the formation of the characteristic garúa fog.
Periodically, these normal climatic patterns are interrupted by the El Niño-Southern Oscillation (ENSO) phenomenon. During an El Niño event, the Pacific Ocean warms significantly, suppressing the cold upwelling of the Humboldt Current. This warming leads to increased evaporation and atmospheric convection, resulting in torrential rainfall and flooding along the usually arid coast, temporarily reversing the region’s climate.