Arid climate of South America

Warm and cold deserts and certain coastal and interior regions are classified as arid climates. Patagonia and northwestern Argentina constitute the largest of the interior arid regions. Rainfall is low, only about four inches in San Juan in the north and about seven inches farther south in Neuquén. The annual range in average monthly temperatures in Patagonia—the greatest in South America—is more than 36° F (20° C), the result of warm summers and cold winters. The Atacama Desert, a narrow strip along the Pacific coast between latitudes 5° and 31° S, is a coastal desert. The cold seas associated with the Peru Current and the proximity of the high Andes produce an inversion of normal atmospheric temperatures, as air in contact with the water cools more rapidly than the upper strata of air. The result is a nearly continuous layer of stratus clouds about 1,200 feet thick, lying at altitudes varying between about 1,000 and 3,000 feet, that prevents air near the ground from being warmed. Temperatures, consequently, are relatively low: Lima has an average annual temperature of 64° F (18° C), ranging from about 72° F (22° C) in February to about 59° F (15° C) in August.

The coast of Peru thus is the cloudiest—and one of the driest—deserts in the world, with no sunshine for at least six months of the year. It almost never rains, except under abnormal circumstances, but condensation of fog (called garúa by the Peruvians) provides a limited amount of moisture. A warm coastal desert extends from northeastern Colombia to Venezuela, covering a zone where rainfall is scarce and droughts are prolonged. Finally, the belt that forms in northeastern Brazil, between the Parnaíba and São Francisco rivers, is classified as an interior warm arid zone. The interior highlands act as a wedge separating the sea winds from the northeast and those from the southeast, which carry their moisture beyond the region. Average annual rainfall is less than four inches, and the dry season may last as long as seven months. The worst feature of the area’s climate is the irregularity of the rainfall, as a result of which severe droughts plague the region. Britannica