Peru, which varies greatly in climate and topography, falls into three main geographical regions—a narrow strip of desert along the coast, a region of high mountains in the center, and a large area of forested mountains and lowlands in the east. The desert region stretches the entire length (1,410 mi/2,269 km) of Peru's Pacific coastline and owes its aridity to the cold Humboldt, or Peru, Current, which acts as a barrier to the moist air over the Pacific. A persistent warm current (El Niño; see El Niño–Southern Oscillation) appears off the coast every two to seven years, bringing torrential and damaging rainstorms. The coastal and mountainous regions also are frequently shaken by severe earthquakes.
Within the desert are about 40 oases where most of Peru's commercial farming takes place; the principal oases are near Lima, Chiclayo, and Trujillo. Callao (near Lima) and Matarani, Peru's leading ports, are also in the desert region. Near Pisco and Ica are large vineyards. Off the coast are small islands, notably the Lobos and Chincha islands, where guano (used as fertilizer) is harvested.
The central region (c.200 mi/320 km wide) is made up mostly of three ranges of the Andes Mts., the Cordillera Occidental in the west and the Cordillera Central and its continuation, the Cordillera Real, in the east. The Cordillera Occidental includes the loftiest peaks, notably Huascarán (22,205 ft/6,768 m, Peru's highest point) and El Misti (19,150 ft/5,837 m). The rugged eastern ranges receive considerable rainfall and are drained by numerous rivers, which have cut deep canyons. Subsistence agriculture is practiced in the upper parts of the valleys. Between the eastern and western ranges of the Andes in the south, and extending into Bolivia, is the Altiplano Plateau, which includes small, scattered basins of arable land and pastureland and also part of Lake Titicaca. The central region includes about 60% of Peru's population; its main cities are Arequipa, Huancayo, Ayacucho, and Cuzco, an old Inca center.
The eastern region includes more than half of the country's land area. It is made up of the highly forested Cordillera Oriental of the Andes and low-lying tropical plains, covered by rain forests and drained by the Amazon River and its tributaries. The region is generally inaccessible and sparsely inhabited in the north; it is used for the illegal cultivation of coca. Iquitos is the chief city of the eastern region.