The Andean Glacier and Water Atlas

A changing climate

Understanding changing rainfall, snow cover and temperature patterns across the Andes is important for managing water resources and ecosystems. Due to its scale, the Andes experiences different climatic conditions between the east and the west, and between the north and south. The high mountains act as a barrier to atmospheric circulation, which means rainfall and temperatures can be very different on either side of the range. In general, the tropical and sub-tropical Andes are relatively cool and dry along the Pacific Coast and into the western slopes, while the eastern slopes experience warm, wet conditions. This is reversed south of 35° (around central Chile and Argentina), where the western slopes are wet, and the eastern side is semi-arid (Garreaud, 2009). The South American Monsoon System is an important control on the climate of the continent. The temperature difference between the Atlantic Ocean and South America is the main driver of this seasonal cycle (de Carvalho & Cavalcanti, 2016). During the austral summer (December, January, February), the easterly monsoon carries moisture from the Atlantic Ocean, some of which is released as rain on the eastern side of the Andes (Garreaud, 2009). There is a strong precipitation gradient with elevation, with most of the rain falling in areas below 3,000 m (Espinoza et al., 2009). The intense rainfall can cause flooding and high levels of erosion (Espinoza et al., 2015). The interaction that occurs between the mountain barrier

and the moisture-laden wind in the Tropical Andes also occurs in the subtropical Central Andes and results in a similar steep rainfall gradient between the humid low-elevation and semi-arid to arid high-elevation regions (Castino, Bookhagen & Strecker, 2017). The high mountains also deflect the monsoonal trade winds into a narrow stream that channels near-surface flow between the tropics and midlatitudes (the low-level-jet). This fast-moving air

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