upright=2.5, Map showing Köppens climate classification for South America. The arid diagonal can be seen in the form of the almost contiguous zone of BWh and BWk climate running from Ecuador to Southern Patagonia. The Arid Diagonal ( es, link=no, diagonal árida/arreica) is a contiguous zone of arid and semi-arid climate that traverses

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

from coastal

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

in the Northwest to

Argentine Argentines (mistakenly translated Argentineans in the past; in Spanish (masculine) or (feminine)) are people identified with the country of Argentina. This connection may be residential, legal, historical or cultural. For most Argentines, ...

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

in Southeast including large swathes of

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

and

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

. The Arid Diagonal encompasses a number of deserts, for example: Sechura, Atacama, Monte and the Patagonian Desert. The Arid Diagonal acts to isolate the temperate and subtropical forests of Chile and southern Argentina from other forests of South America. Together with the

Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describ ...

s in the Southern Andes, the diagonal has controlled the distribution of vegetation throughout Chile and Argentina. The concept of a South American Arid Diagonal was first coined by French geographer Emmanuel de Martonne in his 1935 work ''Problème des régions arides Sud-Américaines''. However, few works dealing with the Arid Diagonal mention this foundational text. The original Arid Diagonal of de Martonne went from

Antofagasta Antofagasta () is a port city in northern Chile, about north of Santiago. It is the capital of Antofagasta Province and Antofagasta Region. According to the 2015 census, the city has a population of 402,669. After the Spanish American wars ...

in northern Chile to the northern coast of Argentine

. however, other authors like Margarita González Loyarte (1995) later extended it to the coast of northern Peru.

Cause and origin

The northern portion of the Arid Diagonal is a result of the blocking of the

trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisp ...

by the barrier formed by the

Central Andes Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...

and the

South Pacific High The South Pacific High is a semi-permanent subtropical anticyclone located in the southeast Pacific Ocean. The area of high atmospheric pressure and the presence of the Humboldt Current in the underlying ocean make the west coast of Peru and n ...

. To the south in the

westerlies The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and tren ...

, the

rain shadow A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds, known as its leeward side. Evaporated moisture from water bodies (such as oceans and large lakes) is ca ...

that the Southern Andes casts over eastern Patagonia similarly blocks moisture. South of Mendoza (32°53' S), the driest parts of the diagonal move away from the Andes as the mountains lose height, causing some humidity to penetrate; thus, at more southern latitudes the driest parts of the diagonal lie on the Atlantic coast of Patagonia. The Arid Diagonal has existed since the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

. The origin of the aridity of northern part of the diagonal is linked to two geologic events: a) the rise of the Andes — an event that led to the permanent block of both the westward flow of moisture along the tropics, and the eastward flow of moisture in Patagonia and b) the permanent intrusion of cold Antarctic waters (the

Humboldt Current The Humboldt Current, also called the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America.Montecino, Vivian, and Carina B. Lange. "The Humboldt Current System: Ecosystem components and pro ...

) along South America's west coast. Together with the

s in the Southern Andes, the diagonal controls the distribution of the vegetation types over Chile and Argentina.

References

{{reflist Deserts of South America Geography of South America Climate of South America