There is growing evidence that glacier retreat in the tropical Andes has accelerated in recent decades due to atmospheric warming134. Ongoing rapid glacier recession was found to have enhanced discharge at the expense of catchments storage138,139. The recent increase in runoff is not likely to last very long140. In the long run, changes in runoff may occur which could severely affect the availability ofwater resources forfuture generations, particularly during dry periods. Short-term increases in stream discharge with critical long-term loss of storage are likely to be widespread over the Cordillera Blanca region. Since glacier melt currently provides a very significant proportion ofdischarge ofthe Rio Santa River, the latter is also likely to diminish with continued glacier loss.
The melting of glaciers may lead to water shortages for millions of people. Among the Andean countries at risk are Bolivia, Ecuador and Peru, where glaciers feed rivers all year round. On the Pacific side of Peru, 80 per cent of the water resources originate from snow and ice melt. During the dry seasons, glacier-fed surface waters often constitute the sole water resource for domestic, agricultural (Figure 6B.17) and industrial uses, not only for rural areas but also for major cities. A reduced glacier runoff will aggravate the problems associated with the water availability, especially if a potential warming leads to earlier snow melt, regional reductions in precipitation and an increase in evaporation1,141.
Figure6B.17: Glaciers and irrigation. Irrigation ditches on the slopes of Huascaran, Cordillera Blanca, Peru, support extensive agriculture during the dry season. Most water comes from nearby glaciers.
Photo: Michael Hambrey, SwissEduc (www.swisseduc.ch)/Glaciers online (www.glaciers-online.net)
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