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

Authors: Lindsey Bruckerhoff, Kevin Wheeler, Kimberly Dibble, Bryce Mihalevich, Bethany Neilson, Jian Wang, Charles Yackulic, Jack Schmidt

Year: 2021

Abstract

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