This presentation was given during the 2022 EWRI Conference, Atlanta GA. Abstract: River basin managers are increasingly relying on modeling and simulation to manage the resources available to them. Water availability modeling efforts in recent decades have produced numerous models that attempt to capture how hydroclimatic and human operations move and consume water. These efforts have generally been divided in two: large-scale modeling prioritizing theoretical soundness and the consistency of hydro-climatological processes across regional and global scales, and basin-scale system modelers placing focus on the environmental, infrastructural, and institutional features that shape water scarcity at the local level. Both rely on dynamics at different scales and have been increasingly converging toward one another. Basin-scale models increasing their efforts to better incorporate climatic processes through the use of synthetic generators and other tools, and global- and regional-scale hydrologic models improving their representation of how human operation and management, by increasing their use of data-driven methods to characterize processes. This study assesses whether the insights drawn from two state-of-the-art models from each of these communities are also converging, specifically with regard to water scarcity vulnerability. We employ MOSART-WM (large-scale hydrological model) and StateMod (basin-scale systems model) and focus on the Upper Colorado Basin within the state of Colorado. Our results suggest that the large-scale model can capture the aggregate effect of all water operations in the basin, in terms of regulated flow, but is limited in representing processes in the sub-basin scale. The basin-scale model suggests a larger variance of scarcity across the basin’s water users, primarily due to its more detailed representation of human elements in the basin, specifically reservoir capacity and operations, and the institutional mechanisms of allocation. These outcomes can be used to inform how the two scales of analysis can be bridged to maintain both large-scale theoretical soundness and regional consistency, as well as relevance to basin-scale decision making.