A desert climate, which is surprising at these latitudes, occupies the whole Pacific border of the central Andes zone. This situation originates from a very particular climatic phenomenon: under the influence of trade winds that continually blow from the southeast, superficial ocean masses (warm) are pushed from the south to the north, but due to the Coriolis force, are deviated to the west at the level of the Peru-Ecuador border. This drifting of waters to the open sea is known as the Humboldt Current. Along the coast, this movement is compensated by the rising of deep waters with temperatures 5° to 8° lower than those usually measured on the surface at these latitudes. Upon contact with these cold waters, the air coming from the ocean cools down and its humidity is condensed. A sea of clouds is formed, covering the coastline with a very dense fog during much of the year. Rainfall is nonetheless very rare, occurring only episodically when the warm equatorial current, called El Nifio because its effects are generally felt around Christmas, approaches the continent and brings warm water to the coast. Torrential showers can then result. More generally, the absence of rainfall explains the aridity of the ground, though the humidity of the air allows the growth of numerous epiphytes on the sand, and in some sectors, the formation of ‘fog oases’, or lomas, which live on ‘thin air’. To the south, on the borders of Peru and Chile, this aridity increases and attains higher altitudes. Extending from the coast until nearly 3000 m, the Atacama Desert is the most arid in the world.
Following the coastal desert plain and the dry mountainous foothills of the western piedmont of the Cordillera, the highlands correspond to the ensemble of territories located above 3000 m and constitute a geoclimatic unit in which the altitude plays an essential role. Between the more or less parallel, N-S oriented chains, vast, high plateaus extend at altitudes between 3800 and 4800 m, reaching their maximum amplitude in Peru and Bolivia. Called p<aramo in Colombia and Ecuador, and altiplano or puna in Peru to the south, this undulating high steppe, cut by deep valleys and bordered by bald mountain peaks and ice-covered summits, constitutes the archetypal Andean landscape. The vegetation is sparse and not very variable: clusters of graminae grouped under the generic name Ichu, low, thorny bushes, and in the sheltered depressions a few thin coppices of quinuales (Polylepis). Below the puna level, a shrubby steppe carpets the slopes and basins located between 2300 and 3800 m altitude. In Peru, this is the ‘quechua’ level, which is well watered, wooded, and green. It is the most habitable, and perhaps earliest occupied level of the Andean region.
Finally, the climate of the eastern Andes piedmont, with its uneven relief, is permanently hot and humid. Between 1800 and 3000 m, this ‘cloud forest’ (selva nublada) level is carpeted with an almost impenetrable maze of bamboos, ferns, and vines, dominated by a few large trees. Rainfall occurs almost daily and is often violent.
Due to their extension, multiple levels and variable relief, expositions and rainfall amounts, the central Andes present a great diversity of landscapes and climates, resulting in a mosaic of ecological contexts that are both very different and close to each other. But was this true in the past, when humans first began to occupy the region?
World History
