The Andean Glacier and Water Atlas

Rivers, basins and lakes Most of the large rivers in South America are fed by water from the Andean mountain range. These high mountains often receive more precipitation than lowlands. In general, they also have glaciers and snow-covered areas, which provide a large reservoir of water. This storage capacity and the release of meltwater are especially important in regions with a high degree of seasonality and low levels of precipitation.

The Amazon river basin is the largest drainage basin in the world, covering an area of almost 6 million km 2 . It occupies more than one third of the South American land mass and contributes almost 20 per cent of the freshwater discharge to the ocean (Calléde et al., 2010; FAO 2015). The transboundary basin has five main tributaries: the Negro river, which drains the Brazilian Shield in the northern Amazon; the Solimões river, which drains the Northern and Central Andes and a large part of the Lowlands; the Madeira river, which drains the Southern Andes, the Southern Foreland basins and part of the Brazilian shield; the Tapajós and Xingu rivers, which drain the remaining area of the Brazilian shield (Bouchez et al., 2017). Glaciers in the eastern cordilleras of Bolivia and Peru contribute to the hydrological cycle of the Amazon Basin. However, their influence tends to decrease rapidly downstream due to the high contribution of precipitation along the eastern slopes of the Andes (Bookhagen and Strecker, 2008). It is estimated that the Amazon rainforest generates and recycles as much as 50 per cent of this precipitation (Jones et al., 2017). On the eastern side of the range and south of the Amazon basin, the La Plata basin covers an area of around 3.1 million km 2 . This transboundary basin includes parts of Brazil, Argentina, Paraguay, Bolivia and Uruguay. It is composed of three large sub-basins, principally fed by the Paraná, Paraguay and Uruguay rivers. The Paraná and Uruguay rivers join the La Plata River which discharges into the Atlantic Ocean near Buenos Aires. In addition to rivers, lakes play a vital role in the hydrology of the Andes and provide water and hydroelectric power for many communities. Many of the high-altitude lakes were formed by glacial movement and are fed by cold turbid meltwater from glacial ablation (Barta et al., 2017). In the Northern Andes wetlands, called páramos and cloud forests are important for water storage (Buytaert et al., 2017). Water yield in these generally wet regions is high, as the wetland soils are usually saturated and therefore have high runoff (Mosquera, Lazo, Célleri, Wilcox, & Crespo, 2015).

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