Inter-annual precipitation in California is highly variable, and future projections indicate an increase in the intensity and frequency of hydroclimatic "whiplash." Understanding the implications of these shocks on California's water system and its degree of resiliency is critical from a planning perspective. Therefore, we quantify the resilience of reservoir services provided by water and hydropower systems in four basins in the western Sierra Nevada. Using downscaled runoff from 10 climate model outputs, we generated 200 synthetic hydrologic whiplash sequences of alternating dry and wet years to represent a wide range of extremes and transitional conditions used as inputs to a water system simulation model. Sequences were derived from upper (wet) and lower (dry) quintiles of future streamflow projections (2030-2060). Results show that carryover storage was negatively affected in all basins, particularly in those with lower storage capacity. All basins experienced negative impacts on hydropower generation, with losses ranging from 5% to nearly 90%. Reservoir sizes and inflexible operating rules are a particular challenge for flood control, as in extremely wet years spillage averaged nearly the annual basins' total discharge. The reliability of environmental flows and agricultural deliveries varied depending on the basin, intensity, and duration of whiplash sequences. Overall, wet years temporarily rebound negative drought effects, and greater storage capacity results in higher reliability and resiliency, and lesser volatility in services. We highlight potential policy changes to improve flexibility, increase resilience, and better equip managers to face challenges posed by whiplash while meeting human and environmental needs. Inter-annual precipitation is naturally highly variable in California, and future projections indicate an increase in the intensity and frequency of hydroclimatic "whiplash." This study investigates the potential impacts of these hydroclimatic events to comprehend their implications on California's water system and its level of resilience, which holds critical importance from a planning perspective. We focus on four basins in the western Sierra Nevada, to quantify the resilience of reservoir services provided by the water and hydropower systems in the region. Using downscaled runoff data from 10 climate models, we generated 200 synthetic hydrologic whiplash sequences to represent combinations of extreme wet and dry conditions. Results show that all basins experienced negative effects on carryover storage, with losses ranging from 5% to nearly 90%, consequently decreasing hydropower generation. Flood control is challenged during extremely wet years due to reservoir sizes and operating rules. The reliability of environmental flows and agricultural deliveries varied across basins and whiplash sequences. Wet years tend to mitigate negative drought effects temporarily, and greater storage capacity improved the reliability and resilience of services. We highlight the need for potential policy changes to enhance flexibility and resilience, and equip managers to face challenges posed by whiplash. Wet years can temporarily rebound negative drought effects, although challenging flood control due to reservoir sizes and operating rules. Environmental flows and agricultural deliveries oscillated depending on the basin, intensity, and duration of whiplash sequences. Greater storage capacity generally provided greater reliability and resiliency, and lesser volatility in water and power services.
