The bigger impact will likely be water stored on land -- e.g. snowpack. All of California's major rivers are fed by snowpack/glacial melt from the Sierras, if a

The bigger impact will likely be water stored on land -- e.g. snowpack. All of California's major rivers are fed by snowpack/glacial melt from the Sierras, if all that starts melting more, there will be flooding, and then in later years there will be much less water coming off the mountains (as it'll have already melted).