Arid Diagonal

[2] Together with the Quaternary glaciations in the Southern Andes, the diagonal has controlled the distribution of vegetation throughout Chile and Argentina.

[4] 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] To the south in the westerlies, the rain shadow that the Southern Andes cast over eastern Patagonia similarly blocks moisture.

[3] The origin of the aridity of the 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[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.

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 (red and pink on this map) running from Ecuador to Southern Patagonia.