Sustainable Water Management in the Lower Colorado Basin: Influence of Climate and Regulatory Context on the Ability to Meet Human and Environmental Water Needs

Meeting human and ecosystem needs via management of river flows has become critical with a changing climate. This is particularly true for the Lower Colorado Basin (LCB), a highly-managed, over-a llocated river system with diversions and transboundary management. In addition, the LCB system has undergone a multi-decadal, severe drought. In this study, we used a multi-objective reservoir operation model to identify trade-offs between human consumptive and non-consumptive water use, as well as ecosystem water needs under different hydroclimatic and regulatory scenarios. The model identified monthly dam releases that would maximize societal and river ecosystem water goals ('designer flows'), contingent on hydroclimatic conditions. The benefits and limitations of the Law of the River were addressed by quantifying constraints on the designer flows using parameters from existing regulations and water rights allocations, and by simulating potential changes in the hierarchy among them (e.g., overriding water rights seniority to prioritize cities over agriculture). The performance of designer flows in fulfilling human and ecosystem water needs was compared to that of natural flow regimes, and this comparison was run across scenarios of increased drought and regulatory change. The proposed modeling framework is transferrable to water management problems in other water systems that are challenged by increasing hydroclimatic variability and the need to balance trade-offs multiple goals.