While the impacts of existing dams have been extensively studied, the global implications of future dam construction under changing climatic and socio-economic conditions remain less quantified. This study assesses the role of future dams in flow regulation, flood mitigation (changes in flood magnitude), and water stress alleviation (measured by the Cumulative Abstraction to Demand, CAD) by comparing simulations of the H08 global hydrological model with and without future dams, using ISIMIP3b provided data under Shared Socioeconomic Pathways (SSPs) for the period 2015–2100. Results show that future dam development substantially increases global simulated reservoir storage through enhanced flow regulation, with total storage reaching approximately 6,000–7,000 km³ under SSP1-2.6 and SSP3-7.0 and up to ~9,000–10,000 km³ under SSP5-8.5 Adaptation Scenarios by the late 21st century, compared to ~4,700–5,200 km³ in corresponding No-Future-Dam Simulations. Consistent with this increased regulation capacity, mean annual outlet discharge volumes decrease in several highly regulated basins, with reductions of up to ~4.2% in the Indus and ~1.8% in the Yellow River under SSP5-8.5. Despite modest relative changes, absolute reductions in annual discharge under SSP5-8.5 can reach ~8 km³ yr⁻¹ in high-flow systems such as the Amazon when future dams are incorporated. Similarly, water stress patterns change with future dams, with spatially heterogeneous responses across basins. To our knowledge, this is one of the first global assessments explicitly incorporating future dams in hydrological models at the global scale, providing new insights for evaluating trade-offs between infrastructure-based adaptation, flood control, and water stress alleviation, offering guidance on where future dam development may deliver upstream benefits versus potential downstream risks.