Precipitation and temperature patterns could be very different in the future. Some river basins may receive more water on average, while others may receive less. These changes could increase or reduce power generation at hydroelectric dams. In this study, scientists aimed to quantify these effects and then explore some potential implications for investments in electricity generation technologies resulting from increases or decreases in hydropower. Applying global projections of rainfall and temperature, researchers generated flows for all global rivers. They used the flows to simulate power generation at approximately 1,600 of the world’s major hydropower dams. Researchers ran the Global Change Assessment Model (GCAM) to understand how losses or gains in hydropower might affect the deployment of alternative generating technologies. The study showed that, in certain drying regions such as the Balkans, significant financial outlays could be required to deploy new generating capacity to address shortfalls in hydropower. For instance, under one scenario applied in the model, the additional cumulative investment requirement for the Balkans region totaled $68 billion by 2100. Researchers estimated a global, cumulative investment need—summed across all drying regions—of approximately $1 trillion (±$500 billion) in this century. For regions projected to experience increased precipitation, total investments avoided were of a similar magnitude.