Shasta Dam operations and stream temperature sensitivities in response to climate change

Shasta Reservoir maintains critical stream habitat by releasing cold-water on the Sacramento River to almost ~50 miles downstream in support of seasonal spawning runs of endangered fish species. Successful stream temperature management requires sufficient cold water assets in the reservoirs throughout the summer and fall. Climate change has the potential to alter current management operations based on recent indications of seasonal shifts in mountain watershed runoff. This study explores seasonal and multi-year operational sensitivities in the Shasta Reservoir watersheds and the sensitivities those shifts will have on critical stream habitats. Community Climate System Model 3 data developed by the National Center for Atmospheric Research community will be used to generate runoff from 2000 -2099 on the upper watershed of Shasta Reservoir. Four climate change scenarios, namely the A1B, A2, B1, and IPCC scenarios are selected for this study. Runoff patterns were routed through Shasta Reservoir and coupled with the Sacramento River Water Quality Model to quantify sensitivities in stream temperature. In the summer of 2037 and 2038, stream temperatures downstream from the dam were elevated above the suitable temperature threshold of 56oF for all climate change scenarios. Stream temperatures were elevated at most by 2oF. A more persistent six-year dry cycle from 2091 to 2096 also had great implications on stream temperatures. Stream temperatures downstream from the dam were elevated (at most ~10oF) above the suitable temperature threshold of 56oF. All climate change scenarios had stream temperatures elevated above 56 oF in the summers of 2093 through 2095. Shasta Reservoir reached dead pool from November 2094 to February 2095. At dead pool, cold-water in the reservoir is depleted, and accessibility to water becomes an issue. Sustained six-year dry cycle will likely result in lack of water behind the reservoir, and cause elevated steam temperatures, which is rendered as unsuitable for habitats spawning.