Water security in high mountain cities of the Andes under a growing population and climate change: A case study of La Paz and El Alto, Bolivia

Abstract

Water resources in La Paz and El Alto, Bolivia strongly depend on runoff from mountain catchments in the Cordillera Real, Andes. The balance between the water available from the source catchments and the demand of the cities has become precarious during recent years because of an increasing population and the runoff variability caused by climate change. In this study, a first-order estimate of the future water supply and demand for the El Alto system, the most rapidly growing area in La Paz and El Alto, was obtained for the first time based on a demographic analysis and runoff projection, and effective measures for adapting to water shortage were examined. The water demand in 2036 is expected to increase by 15–53% compared to that of 2011, depending on the scenario for the water loss in the supply system and population estimates, while the projected water supply shows frequent reductions because of the climate variability and decreasing glacial meltwater. Thus, the water transfer from a neighboring system (the Achachicala system) will be indispensable to sustain the supply that cannot be covered by releases from Tuni Lake. Nevertheless, the El Alto system will likely face a serious water shortage after the mid-2020s for the most conservative scenario of demand increase, while large uncertainty was found for the balance of supply and demand, depending on the scenarios for population growth, improvement of water loss, and climate variability and trend. For supply side management, the extended diversion of runoff into Tuni Lake, water transfer from the Achachicala system, and transfer of runoff from the Taypichaca catchment will be effective in securing the water supply under various uncertain conditions.