Contrasting climate change impact on river flows from high altitude catchments in the Himalayan and Andes Mountains

Ragettli, Silvan, Immerzeel, Walter and Pellicciotti, Francesca (2016) Contrasting climate change impact on river flows from high altitude catchments in the Himalayan and Andes Mountains. Proceedings of the National Academy of Sciences of the United States of America, 113 (33). pp. 9222-9227. ISSN 1091-6490

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Abstract

Mountain ranges are world’s natural water towers and provide water resources for millions of people. Yet, their hydrological balance and possible future changes in river flow remain poorly understood because of high meteorological variability, physical inaccessibility and the complex interplay between climate, cryosphere and hydrological processes. Here we use a state-of-the art glacio-hydrological model informed by data from high altitude observations and CMIP5 climate change scenarios to quantify the climate change impact on water resources of two contrasting catchments vulnerable to changes in the cryosphere. The two study catchments are located in the Central Andes of Chile and in the Nepalese Himalaya in close vicinity of densely populated areas. Although both sites reveal a strong decrease in glacier area, they show a remarkably different hydrological response to projected climate change. In the Juncal catchment in Chile runoff is likely to sharply decrease in the future and the runoff seasonality is sensitive to projected climatic changes. In the Langtang catchment in Nepal, future water availability is on the rise for decades to come with limited shifts between seasons. Owing to the high spatio-temporal resolution of the simulations and process complexity included in the modelling the response times and the mechanisms underlying the variations in glacier area and river flow can be well constrained. The projections indicate that climate change adaptation in Central Chile should focus on dealing with a reduction in water availability, whereas in Nepal preparedness for flood extremes should be the policy priority.

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