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International audience; Mountains represent significant features covering nearly one-quarter of the world’s terrestrial surface. Mountains support a range of socioeconomic sectors (e.g., tourism, forest production, ecosystem resources) that have experienced considerable change in the last two centuries, resulting from pressures on natural resources and traditions imposed by increasingly-industrialized societies. Development trajectories of these highvalue environments vary considerably across the globe, but certain mountain regions have been extensively transformed, converting them from inaccessible and relatively poor hinterlands into attractive destinations forthe wealthy, sometimes excluding longtime inhabitants from economic benefits. In certain cases, outmigration and an aging population have led to economic declines in agro-pastoral and forestry production. Across the world, such transformative processes in mountain socialecologicalsystems have been accompanied by profound social, institutional, and environmental changes. Asa major supplier of resources, mountains collectively represent in particular the source region for more than 60% of surface waters. A significant fraction of world’s population in lowland regions depends on mountain water resources for agriculture, industry, energy, and domesticwater supply.Rapid climate change occurring in mountains carries broad implications, given that such regions have long been a source of valued ecosystem services and natural resources. For example, future shifts in temperature and precipitation patterns, and changes in the behavior of snow and ice in many mountains may ultimately change the quantity, seasonality, and possibly also the quality of water originating in mountains and uplands. Natural processes controlled by hydro-meteorological triggers (e.g. floods, landslides, debris-flows, earthflows and rockfalls, glacier melt, river erosion) will in a future climate add further environmental pressures on both social and natural systems, thereby highlighting the need to promptly conduct proactive adaptation plans The challenge for both mountain societies and those located downstream but dependent on mountain water resources in particular is thus to estimate as accurately as possible future changes in water availability. This will help to prepare the way for appropriate adaptation strategies and improved water governance. Enhanced awareness and appropriate policies aimed at alleviating the more adverse climate impacts would help indigenous populations to better adapt to rapid change, and for water-dependent economic sectors to pursue their activities with lower risks of economic rivalries or conflicts.

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