Rapid decline of snow and ice in the tropical Andes – Impacts, uncertainties and challenges ahead

Abstract Glaciersin the tropical Andes have been retreating for the past several decades, leading to a temporary increase in dry season water supply downstream. Projected future glaciershrinkage, however, will lead to a long-term reduction in dry season river discharge from glacierizedcatchments. This glacierretreat is closely related to the observed increase in high-elevation, surface air temperature in the region. Future projections using a simple freezing levelheight- equilibrium-line altitude scaling approach suggest that glaciersin the inner tropics, such as Antizana in Ecuador, may be most vulnerable to future warming while glaciersin the more arid outer tropics, such as Zongo in Bolivia, may persist, albeit in a smaller size, throughout the 21st century regardless of emission scenario. Nonetheless many uncertainties persist, most notably problems with accurate snowfall measurements in the glacier accumulation zone, uncertainties in establishing accurate thickness measurements on glaciers, unknown future changes associated with local-scale circulation and cloud coveraffecting glacierenergy balance, the role of aerosols and in particular black carbondeposition on Andean glaciers, and the role of groundwater and aquifers interacting with glacier meltwater. The reduction in water supply for export-oriented agriculture, mining, hydropower production and human consumption are the most commonly discussed concerns associated with glacierretreat, but many other aspects including glacial hazards, tourism and recreation, and ecosystem integrity are also affected by glacierretreat. Social and political problems surrounding water allocation for subsistence farming have led to conflicts due to lack of adequate water governance. Local water management practices in many regions reflect cultural belief systems, perceptions and spiritual values and glacierretreat in some places is seen as a threat to these local livelihoods. Comprehensive adaptation strategies, if they are to be successful, therefore need to consider science, policy, culture and practice, and involve local populations. Planning needs to be based not only on future scenarios derived from physically-based numerical models, but must also consider societal needs, economic agendas, political conflicts, socioeconomic inequality and cultural values. This review elaborates on the need for adaptation as well as the challenges and constraints many adaptation projects are faced with, and lays out future directions where opportunities exist to develop successful, culturally acceptable and sustainable adaptation strategies.