Modeling Shasta Reservoir Water-Temperature Response to the 2015 Drought and Response under Future Climate Change

Stress on California’s salmon fisheries drives a need for effective temperature management in California’s Sacramento River. Shasta Dam has a temperature control device that enables managers to provide cold discharge temperatures to the river that are required for downstream Chinook salmon spawning and rearing. An added stress to water temperature management is prolonged drought and associated high air temperatures. California experienced its worst drought in a century from 2012 to 2015, and these conditions may provide insight into future reservoir conditions, as climate change predictions suggest that droughts will be more frequent and intense. In this study, a two-dimensional hydrodynamic model of Shasta Reservoir was used to simulate: (1) alternative reservoir operations during 2015 aimed at sustaining the volume of cold water in the reservoir to provide downstream cold water habitat during the critical time for endangered winter-run Chinook salmon egg incubation; and (2) reservoir temperature conditions under potential climate change scenarios. Results suggest that, with climate change, water managers at Shasta Reservoir may have increasing difficulty maintaining adequate cold pool volume in the reservoir through November, and even extreme reductions in reservoir outflows may not be enough to mitigate this result.