Arid Diagonal

The Arid Diagonal (Spanish: diagonal árida/arreica) is a contiguous zone of arid and semi-arid climate that traverses South America from coastal Peru in the Northwest to Argentine Patagonia in Southeast including large swathes of Bolivia and Chile.[1] The Arid Diagonal encompasses a number of deserts, for example: Sechura, Atacama, Monte and the Patagonian Desert.

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 acts to isolate the temperate and subtropical forests of Chile and southern Argentina from other forests of South America.[2] Together with the Quaternary glaciations in the Southern Andes, the diagonal has controlled the distribution of vegetation throughout Chile and Argentina.[3]

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.[4] However, few works dealing with the Arid Diagonal mention this foundational text.[4] The original Arid Diagonal of de Martonne went from Antofagasta in northern Chile to the northern coast of Argentine Patagonia.[4] however, other authores like Margarita González Loyarte (1995) later extended it to the coast of northern Peru.[4]

Cause and origin

The northern portion of the Arid Diagonal is a result of the blocking of the trade winds by the barrier formed by the Central Andes and the South Pacific High[5] and to the south in the westerlies the rain shadow the Southern Andes casts over eastern Patagonia.[1] 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.[1]

The Arid Diagonal has existed since the Neogene.[3] The origin of the aridity of northern part of the diagonal is linked to two geologic events: a) the rise of 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[6] and b) the permanent intrusion of cold Antarctic waters (the Humboldt Current) along South America's west coast.[5] Together with the Quaternary glaciations in the Southern Andes the diagonal controls the distribution of the vegetation types over Chile and Argentina.[3]

References
  1. Bruniard, Enrique D. (1982). "La diagonal árida Argentina: un límite climático real". Revista Geográfica (in Spanish): 5–20.
  2. Villagrán, Carolina; Hinojosa, Luis Felipe (1997). "Historia de los bosques del sur de Sudamérica, II: Análisis fitogeográfico". Revista Chilena de Historia Natural (in Spanish). 70: 241–267.
  3. Villagrán, Carolina; Hinojosa, Luis Felipe (2005). "Esquema biogeográfico de Chile". In Llorente Bousquests, Jorge; Morrone, Juan J. (eds.). Regionalización Biogeográfica en Iberoámeríca y tópicos afines (in Spanish). Mexico: Ediciones de la Universidad Nacional Autónoma de México, Jiménez Editores.
  4. Abraham, Elena María; Rodríguez, María Daniela; Rubio, María Clara; Guida-Johnson, Bárbara; Gomez, Laura; Rubio, Cecilia (2020-01-08). "Disentangling the concept of "South American Arid Diagonal"". Journal of Arid Environments. 175. doi:10.1016/j.jaridenv.2019.104089.CS1 maint: date and year (link)
  5. Armesto, Juan J.; Arrollo, Mary T.K.; Hinojosa, Luis F. (2007). "The Mediterranean Environment of Central Chile". In Veblen, Thomas T.; Young, Kenneth R.; Orme, Anthony R. (eds.). Physical Geography of South America. Oxford University Press. pp. 184–199.
  6. Folguera, Andrés; Encinas, Alfonso; Echaurren, Andrés; Gianni, Guido; Orts, Darío; Valencia, Víctor; Carrasco, Gabriel (2018). "Constraints on the Neogene growth of the central Patagonian Andes at thelatitude of the Chile triple junction (45–47°S) using U/Pb geochronology insynorogenic strata". Tectonophysics. 744: 134–154. doi:10.1016/j.tecto.2018.06.011. hdl:11336/88399.
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