Water Storage Decisions and Consumptive Use May Constrain Ecosystem Management under Severe Sustained Drought

Abstract Drought has impacted the Colorado River basin for past 20 years and is predicted to continue. In response, decisions about how much water should be stored in large reservoirs can consumptively used will necessary. These have potential limit riverine ecosystem management options through effect water‐supply on reservoir elevations. We projected hydrology river temperatures compare outcome of combinations storage scenarios consumptive use limits metrics associated with Grand Canyon. Ecosystem included ability implement designer flows, temperature suitability fishes, fragmentation. compared current operations prioritizing either Lake Mead or Powell combined three levels use. Projected limited environmental flow delivery increased fragmentation regardless where was if not limited. Warmer low are likely, creating suitable conditions non‐native species concern, such as smallmouth bass. Water provided variability flexibility, but less important when available, highlighting importance keeping system provide flexibility achieving goals.