Effects of projected climate change on flooding and water temperatures of Yolo Bypass: Implications for fishes and ecosystem function

Larry R. Brown, Marissa L. Wulff and Brock M. Huntsman, California Water Science Center, U.S. Geological Survey, Ted Sommer, California Department of Water Resources, Wayne Wagner, University of New Orleans

1) Background/Question/Methods
Yolo Bypass is an ecological feature of the Bay-Delta ecosystem in California that provides floodplain habitat for spawning and rearing of Sacramento Splittail (Pogonichthys macrolepidotus) and rearing of juvenile Chinook Salmon (Oncorhynchus tshawytscha) when inundated. We used outputs from 10 climate change models for two Representative Concentration Pathways (RCPs) for greenhouse gas concentrations to assess the effects of climate change on the frequency, duration, and timing of flood flows in Yolo Bypass. We also considered water temperatures during flood flows. Response was measured as the annual mean of the water temperature projections during flood events for each combination of climate change model and RCP annually from 2010 to 2099. Finally, we assessed a planned notched weir modification to the primary weir that controls inflow from the Sacramento River into Yolo Bypass that has been designed to cause the bypass to be inundated at lower river flows.
2) Results/Conclusions
The notched weir configuration increased the frequency and duration of floods 30 days or greater compared to the existing no-notch configuration. Floods of 30 days or greater occurred about every 3 years for the no-notch configuration and every 2 years for the notched configuration. These differences were maintained through the end of the century under both RCPs. Few strong trends were observed in other projected flood metrics of flood frequency, duration, and timing through the end of the century. Projected spring and winter water temperatures during flooding generally increased through the century for both RCPs (≤2°C). Projected spring water temperatures exhibited little change for the lower RCP and increased slightly for the higher RCP. Winter water temperatures were generally less than 15°C with occasional temperatures greater than 15°C after 2050. Climate change projections suggest that the notched weir configuration would increase the frequency and duration of floodplain access for fishes that use Yolo Bypass for spawning and rearing, and that these habitats will be maintained through the current century. Further, results indicate that adaptation to climate change through management strategies is possible in some situations.