The increasing interconnections of Energy-Water-Land (EWL) systems and rapid socioeconomic and climate change at the global scale, pose challenges for reservoirs to reliably meet water demands and mitigate droughts. Challenges associated with infrastructure investments and misalignment between spatial and temporal water demands and available water resources render water a scarce commodity in some regions. Exploring future pathways for reservoir storage capacity expansion and its storage capacity potential within an integrated multisectoral system can inform both short-term and long-term strategic planning. Additionally, understanding the feedbacks between evolving water infrastructures and the coevolution of the human-Earth systems can elucidate the implications of complex global changes on regional water resources vulnerability. Our newly developed Global Reservoir Yield (GLORY) model, dynamically linked with the Global Change Analysis Model (GCAM), addresses these challenges by improving the representation of both the water supply from reservoir storage capacity and its associated economic value under the changing climate and socioeconomic conditions. Our research aims to identify the drivers of future reservoir expansion and the regions that will benefit significantly from increased storage capacity under a wide range of scenarios, including the climate impacts on runoff, agricultural yield, and energy demand globally, alongside different levels of water demand and constraints on reservoir storage capacity expansion potential. Our preliminary results reveal strong regional heterogeneity in reservoir expansion pathways to meet water demands, providing valuable insights into multisector planning, water resources management, and infrastructure investment. This work is at the forefront of exploring GCAM-centered multi-model coupling and feedbacks, enhancing our ability to capture interactive responses of water storage and its multisector implications under evolving climate and socioeconomic changes.