Uncertainty assessment of water resources and long-term hydropower generation using a large ensemble of future climate projections for the Nam Ngum River in the Mekong Basin

[Study region] The Nam Ngum River Basin, the major tributary of the Mekong River, is located in the Laos PDR. [Study focus] This study aims to assess the sensitivity of Nam Ngum 1 reservoir operation to water resource uncertainty driven by a combination of climate change and upstream cascade dam development. [New hydrological insights for the region] Precipitation projections of the basin under a 4° increase scenario vary in the range of −9.6 % to +6.9 %, compared to the historical observed precipitation (present climate). The impact of climate change on hydropower resources was investigated. Based on the combined effect of climate change and upstream cascade dam development, the projected inflow of the Nam Ngum 1 reservoir at the full development stage will change from −16.0 % to +6.5 %, which results in a large range of annual energy production changes from −18.8 % to +2.8 % compared to the current condition (present climate and existing dam stage). Furthermore, water losses from the reservoir due to water discharge from the spillway for extreme floods and evaporation are expected to increase with increasing temperature, which will lead to a loss in energy production. Our study indicates that the operation of hydropower should be adapted to the effects of climate change. This information can be used by stakeholders to propose water resource management strategies