Abstract
Sacramento River Winter-run Chinook Salmon (salmon) populations are declining and have been classified as an endangered species since 1994. Populations are sensitive to water temperatures and flow, both of which have changed due to hydraulic operations, and may continue to change in response to climate change. The purpose of this study is to estimate changes in salmon populations in response to a hypothetical climate change scenario using computer models. For two hypothetical climate scenarios, flow data for California's water system have been simulated and made publicly available as part of Department of Water Resource’s 2011 State Water Project Delivery Reliability Report. The climate scenarios are: (1) historical climate conditions, and (2) medium-to-high emissions and air temperature changes (a 2050 level of development, A2 greenhouse gas level of emissions). For this study, DWR’s flow data, based on 80 years of historical hydrology, and the associated temperatures projected by the ECHAM-5 climate model were used to simulate water temperatures, salmon mortality rates, and salmon production in the upper Sacramento River between Keswick Dam and Red Bluff Dam. The models used in this study -- the Sacramento River Water Quality Model (SRWQM) and the Salmonid Population Model (SALMOD) -- are the same models used by the U.S. Department of Interior Bureau of Reclamation (USBR). SRWQM results show that climate change causes a 3°F increase in maximum water temperatures. SALMOD results show water temperature changes affect the salmon population significantly more than flow. In typical years, calculated salmon mortalities were not changed significantly by climate change (CC). In contrast, when conditions were unfavorable, salmon mortalities were substantially higher under the CC scenario and these unfavorable conditions happened with greater frequency.