Abstract
Runoff from intertropical glaciers is highly variable, indicating that they are greatly affected by climatic changes peculiar to tropical climates. The 3 km 2 basin presented in this case study lies in the Cordillera Real of Bolivia and is 77% covered by glacier ice, ranging in elevation from 6000 to 4830 m a.s.l. A comparison of 2 years of study demonstrates the peculiar feature of intertropical glaciers: that accumulation and melting periods coincide during the rainy season. During the first hydrological year (1991–1992), runoff was 1793 mm for an average precipitation on the glacier of approximately 916 mm. During the second year (1992–1993), runoff was 1080 mm for a precipitation of 1060 mm. Solar radiation and daily mean duration with positive temperature on the ablation zone are the parameters best explaining variation in monthly runoff. Gauge readings taken downstream enable discharge from the glacier to be established over a period of nearly 20 years. The most prominent events coincide with significantly negative values of the Southern Oscillation Index, often linked to El Niño-Southern Oscillation (ENSO) phenomena. In conclusion, results show that these intertropical glaciers are receding rapidly, as precipitation does not compensate for loss from melting.
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