The Colorado River is the largest river in the southwestern United States, underpinning economic activities worth an estimated $300 billion/year within the state of Colorado alone. The most productive portion of the river within Colorado is the Upper Colorado sub-basin, which supports several thousand diversions, administered to water rights holders through the system of prior appropriation. These right holders form a network of interdependent water users from agricultural, municipal, industrial and energy sectors. Increasing climatic stress and demand for water have these users vying for this limited resource, in a competition intrinsically shaped by the seniority of their rights and their location in the basin. In their planning efforts, state agencies have the task of balancing these competing demands in the face of changing climatic and societal stressors.

Through the use of exploratory modeling approaches, we investigate a large ensemble of potential future changes that could take place in the basin and analyze how they might impact the degree of water shortages experienced by the basin’s multitude of users. We look at how changes in climatic extremes, municipal demands, agricultural demands, and water rights and infrastructure propagate through this integrated water allocation network to affect the magnitude, frequency and duration of water shortage for different users. To do so, we make use of the State’s own water allocation and accounting model, which is able to represent the demand and supply of water to individual diversions in the basin. The exploratory ensemble is then paired with novel diagnostic evaluation methods that employ sensitivity analysis tools to improve our inferences on stakeholder-specific shortage controls. Exploratory work of this type allows us to investigate both cross-sectoral impacts in the basin (e.g., the effects on agricultural users of a hydropower plant controlling a major senior water right changing its operations), as well as how the large heterogeneity in potential impacts to water users, in terms of the timing, magnitude, and frequency of shortages.